Rainfall thresholds for the initiation of shallow landslides in the Wiśnicz Foothills region (the Flysch Carpathians Mountain, Poland)

NASA Astrophysics Data System (ADS)

Demczuk, Piotr; Zydroń, Tymoteusz; Siłuch, Marcin

2017-04-01

Determination of the magnitude of the rainfall threshold is a complex task, as it depends on the properties of the engineering-geological formations deposited on slopes and lithological conditions; it is also a resultant of the intensity and duration of precipitation. Meteorological monitoring and knowledge of the geological structure and adequate engineering tools (models of the soil and rock substrate) can greatly contribute to identification of the magnitude of rainfall that can pose a threat to slope stability. Calculation programs, which include the physical description of changes in the stress state in the soil substrate, are widely used tools for assessment of the slope stability conditions. Such programs take into account only the impact of rainfall on slope stability conditions and disregard the role of other meteorological factors. Development of a model that would be able to estimate these values is difficult; hence, this paper presents an attempt to determine the impact of precipitation on slope stability of selected shallow landslide slopes located in the area of the Wiśnicz Foothills (Outer Carpathians, Poland) using physically-based model taking into account meteorological conditions. Firstly, based on the meteorological data from 2004-2013 calculations of slope stability were performed to verify the geotechnical parameters of the soils. The calculations also yielded the range of pore pressure changes in the analysed period of 2004-2013, which simultaneously facilitated determination of extreme slope stability conditions prevailing during the growing seasons in the analysed years. Further investigations were focused on determination of changes in slope stability induced in response to 120-day long rainfalls with increasing, constant, and decreasing intensities characterised by a 1-99% probability of occurrence. For the analysis, three systems of pore pressure distribution in the slope were employed. Two of them corresponded to the maximum and minimum soil wetness values at the beginning of the growing seasons in 2004-2013 (period between late March and late July, which substantially coincides with periods of intensification of mass movements in Polish Flysch Carpathians). The analyses were performed with the calculation modules of the GeoSlope Inc. package: - Vadose/W was used to determine the impact of meteorological conditions (temperature, humidity, wind speed, precipitation) on the pore pressure distribution in the slope, - Slope/W - calculations of slope stability. The stability calculations have confirmed that the rainfall threshold values are a function of many variables, primarily the hydraulic properties of slope covers and rock substratum, temporal distribution of precipitation, and wetness conditions (degree of slope cover saturation). The major mechanism of stability failure by the analysed slopes in the Wiśnicz Foothills is the saturation of slope covers. Given this mechanism, observations of the groundwater table can be an important factor in assessment of the susceptibility of slopes to mass movements, besides meteorological observations. It also seems that slope stability calculations can be an important tool for assessment of landslide hazards. Importantly, the calculations have to take into account not only precipitation data but also other meteorological factors, which have impact on the amount of water accumulated in slope covers.

Use of DFIWG for Improvement of Voltage Stability Condition of a Power System

NASA Astrophysics Data System (ADS)

Hazarika, Durlav; Das, Ranjay

2017-12-01

This paper describes a method for improvement of voltage stability condition of a multi-bus power system by regulating reactive power generation at a Doubly Fed Induction Wind Generator (DFIWG). For this purpose, sensitivity relation between changes in voltage stability index at a bus with respect to change in reactive power generation of the DFIWG is derived. This relation is used to determine the required amount of change in rotor current of the DFIWG to improve the voltage stability index of the bus.

Diffusion of counterfeit drugs in developing countries and stability of galenics stored for months under different conditions of temperature and relative humidity

PubMed Central

Baratta, Francesca; Germano, Antonio; Brusa, Paola

2012-01-01

Aim To investigate the diffusion of counterfeit medicines in developing countries and to verify the stability of galenic dosage forms to determine the stability of galenics prepared and stored in developing countries. Methods We purchased 221 pharmaceutical samples belonging to different therapeutic classes both in authorized and illegal pharmacies and subjected them to European Pharmacopoeia, 7th ed. quality tests. An UV-visible spectrophotometric assay was used to determine the galenics stability under different conditions of temperature (T) and relative humidity (RH). Results A substantial percentage of samples was substandard (52%) and thus had to be considered as counterfeit. Stability tests for galenics showed that the tested dosage forms were stable for 24 months under “standard” (t = 25 ± 2°C, RH = 50 ± 5%) conditions. Under “accelerated” (t = 40 ± 2°C, RH = 50 ± 5%) conditions, samples were stable for 3 months provided that they were stored in glass containers. Stability results of samples stored in “accelerated” conditions were similar to those obtained by on site in tropical countries and could so supply precious information on the expected stability of galenics in tropical countries. Conclusion This study gives useful information about the presence of counterfeit medicinal products in the pharmacies of many developing countries. This should serve as an alarm bell and an input for the production of galenics. We recommend setting up of galenic laboratories in developing countries around the globe. PMID:22522996

Determination of Global Stability of the Slosh Motion in a Spacecraft via Num Erical Experiment

NASA Astrophysics Data System (ADS)

Kang, Ja-Young

2003-12-01

The global stability of the attitude motion of a spin-stabilized space vehicle is investigated by performing numerical experiment. In the previous study, a stationary solution and a particular resonant condition for a given model were found by using analytical method but failed to represent the system stability over parameter values near and off the stationary points. Accordingly, as an extension of the previous work, this study performs numerical experiment to investigate the stability of the system across the parameter space and determines stable and unstable regions of the design parameters of the system.

Cooperative folding near the downhill limit determined with amino acid resolution by hydrogen exchange

PubMed Central

Yu, Wookyung; Baxa, Michael C.; Gagnon, Isabelle; Freed, Karl F.; Sosnick, Tobin R.

2016-01-01

The relationship between folding cooperativity and downhill, or barrier-free, folding of proteins under highly stabilizing conditions remains an unresolved topic, especially for proteins such as λ-repressor that fold on the microsecond timescale. Under aqueous conditions where downhill folding is most likely to occur, we measure the stability of multiple H bonds, using hydrogen exchange (HX) in a λYA variant that is suggested to be an incipient downhill folder having an extrapolated folding rate constant of 2 × 105 s−1 and a stability of 7.4 kcal·mol−1 at 298 K. At least one H bond on each of the three largest helices (α1, α3, and α4) breaks during a common unfolding event that reflects global denaturation. The use of HX enables us to both examine folding under highly stabilizing, native-like conditions and probe the pretransition state region for stable species without the need to initiate the folding reaction. The equivalence of the stability determined at zero and high denaturant indicates that any residual denatured state structure minimally affects the stability even under native conditions. Using our ψ analysis method along with mutational ϕ analysis, we find that the three aforementioned helices are all present in the folding transition state. Hence, the free energy surface has a sufficiently high barrier separating the denatured and native states that folding appears cooperative even under extremely stable and fast folding conditions. PMID:27078098

Comparison of the relative stability of pharmaceutical cocrystals consisting of paracetamol and dicarboxylic acids.

PubMed

Suzuki, Naoto; Kawahata, Masatoshi; Yamaguchi, Kentaro; Suzuki, Toyofumi; Tomono, Kazuo; Fukami, Toshiro

2018-04-01

The aim of this study is to evaluate the relative stability of pharmaceutical cocrystals consisting of paracetamol (APAP) and oxalic acid (OXA) or maleic acid (MLA). These observations of cocrystal stability under various conditions are useful coformer criteria when cocrystals are selected as the active pharmaceutical ingredient in drug development. The relative stability was determined from the preferentially formed cocrystals under various conditions. Cocrystal of APAP-OXA was more stable than that of APAP-MLA in a ternary cogrinding system and possessed thermodynamical stability. On the other hand, when grinding with moisture or maintaining at high temperatures and relative humidity conditions, APAP-MLA was more stable, and OXA converted to OXA dihydrate. In the slurry method, APAP-OXA was more stable in aprotic solvents because the APAP-OXA with low-solubility product precipitated. The relative stability order was affected by preparing conditions of presence of moisture. This order might attribute to the small difference of crystal structure in the extension of the hydrogen bond network.

A heterogenous Cournot duopoly with delay dynamics: Hopf bifurcations and stability switching curves

NASA Astrophysics Data System (ADS)

Pecora, Nicolò; Sodini, Mauro

2018-05-01

This article considers a Cournot duopoly model in a continuous-time framework and analyze its dynamic behavior when the competitors are heterogeneous in determining their output decision. Specifically the model is expressed in the form of differential equations with discrete delays. The stability conditions of the unique Nash equilibrium of the system are determined and the emergence of Hopf bifurcations is shown. Applying some recent mathematical techniques (stability switching curves) and performing numerical simulations, the paper confirms how different time delays affect the stability of the economy.

A multiloop generalization of the circle criterion for stability margin analysis

NASA Technical Reports Server (NTRS)

Safonov, M. G.; Athans, M.

1979-01-01

In order to provide a theoretical tool suited for characterizing the stability margins of multiloop feedback systems, multiloop input-output stability results generalizing the circle stability criterion are considered. Generalized conic sectors with 'centers' and 'radii' determined by linear dynamical operators are employed to specify the stability margins as a frequency dependent convex set of modeling errors (including nonlinearities, gain variations and phase variations) which the system must be able to tolerate in each feedback loop without instability. The resulting stability criterion gives sufficient conditions for closed loop stability in the presence of frequency dependent modeling errors, even when the modeling errors occur simultaneously in all loops. The stability conditions yield an easily interpreted scalar measure of the amount by which a multiloop system exceeds, or falls short of, its stability margin specifications.

[THERMAL STABILITY AS A PROGNOSTIC INDICATOR OF CONSERVATION OF LIVE EMBRYONIC SMALLPOX VACCINE (TEOVAC) DURING STORAGE].

PubMed

Zhukov, V A; Kokorev, S V; Rogozhkina, S V; Melnikov, D G; Terentiev, A I; Kovalchuk, E A; Vakhnov, E Yu; Borisevich, S V

2016-01-01

Determination of values of coefficients of thermal stability of TEOVac for prognosis of conservation of the vaccine (specific biological activity) during the process of warranty period storage. TEOVac (masticatory tablets) in primary packaging was kept at increased temperature (accelerated and stress-tests) and at the conditions established by PAP for the preparation (long-term tests). Biological activity of the vaccine was determined by titration on 12-day chicken embryos. A correlation between the value of coefficients of thermal stability and conservation of the prepared series of the condition preparation at the final date of storage was experimentally established. Coefficients of thermal stability could be used as a prognostic indicator of quality of the produced pelleted formulation of the preparation for evaluation of conservation of the vaccine during warranty period storage.

[Effect of heat transfer in the packages on the stability of thiamine nitrate under uncontrolled temperature conditions].

PubMed

Nakamura, Toru; Yamaji, Takayuki; Takayama, Kozo

2013-01-01

To accurately predict the stability of thiamine nitrate as a model drug in pharmaceutical products under uncontrolled temperature conditions, the average reaction rate constant was determined, taking into account the heat transfer from the atmosphere to the product. The stability tests of thiamine nitrate in the three packages with different heat transfers were performed under non-isothermal conditions. The stability data observed were compared with the predictions based on a newly developed method, showing that the stability was well predicted by the method involving the heat transfer. By contrast, there were some deviations observed from the predicted data, without considering heat transfer in the packages with low heat transfer. The above-mentioned result clearly shows that heat transfer should be considered to ensure accurate prediction of the stability of commercial pharmaceutical products under non-isothermal atmospheres.

[Study on stability of curcumine, demethoxycurcumin and bisdemethoxycurcumin].

PubMed

Han, Gang; Cui, Jing-jing; Bi, Rui; Zhao, Lin-lin; Zhang, Wei-guo

2008-11-01

To investigate the stability of curcumin, demethoxycurcumin and bisdemethoxycurcumin in different buffer solution. To determine concentration of curcumin by HPLC when added curcumin, demethoxycurcumin and bisdemethoxycurcumin into the buffer solution the equation of degradation was established. The sequence of stability are bisdemethoxycurcumin > or = demethoxycurcumin > or =curcumin at the same condition. The demethoxycurcumin can stabilize curcumin more strong than the others. The demethoxycurcumin is a nature stabilizing agent for curcumin.

Accurate Determination of Soluble Axl by Enzyme-Linked Immunosorbent Assay.

PubMed

Dengler, Mirko; Huber, Heidemarie; Müller, Christian J; Zellmer, Angela; Rauch, Peter; Mikulits, Wolfgang

2016-11-01

Levels of soluble Axl (sAxl) are routinely assessed in human sera by sandwich enzyme-linked immunosorbent assay (ELISA). Although sAxl values are suggested to diagnose different types of disorders, no uniform ELISA method is available, allowing the reliable interassay comparison between results. Furthermore, little is known about the stability of sAxl under storage conditions, which is a relevant parameter for biomedical trials. The evaluation of sAxl stability under various stress conditions and the determination of proper conditions to use the sAxl ELISA for routine clinical applications are of great interest. In this study, serum samples were subjected to freeze-thaw cycles and incubation at different temperatures to analyze the stability of sAxl by ELISA. Dilution and spike-in experiments were carried out to examine the impact of serum and diluent components on the ELISA performance. Various diluents and media were employed to resolve masking effects of the serum. The assay components were further optimized for long-term usability by treatment with stabilizers and validation under temperature stress. Indeed, sAxl showed long-term stability in serum during freeze-thaw cycles and incubation under temperature stress conditions. The dilution experiments revealed that unknown components in the serum caused masking effects that can be reduced by proper dilutions. The assay performance was further increased by using a standardized buffer system to dilute serum samples. Stabilization of coated plates and of streptavidin-horseradish peroxidase allowed long-term storage for up to 6 months. In sum, our data demonstrate proper ELISA conditions, allowing the accurate analysis of sAxl levels in human serum.

Physicochemical Properties and Oxidative Storage Stability of Milled Roselle (Hibiscus sabdariffa L.) Seeds.

PubMed

Juhari, Nurul Hanisah; Petersen, Mikael Agerlin

2018-02-11

Milled Roselle ( Hibiscus sabdariffa L.) seeds of the UMKL cultivar were analyzed for proximate composition, water and oil absorption capacity, and the influence of storage conditions on storage stability. The storage stability was determined under four types of conditions: light/oxygen (air) (LO), light/nitrogen (LN), darkness/oxygen (air) (DO), and darkness/nitrogen (DN) while monitoring for seven consecutive months. During the storage period, the formation of volatiles was determined using dynamic headspace sampling and Gas Chromatography-Mass Spectrometry (GC-MS) analysis. In total, 85 volatiles were identified, mainly aldehydes, alcohols, ketones, furans, and acids indicating lipid oxidation. It is recommended that milled Roselle seeds should be flushed with nitrogen and stored in darkness. Under these conditions, the seeds can be stored for at least three months without changes in volatile profile. This is important to ensure the good quality of milled Roselle seeds for further commercialization.

Wind-Tunnel Investigation at Low Speed of the Yawing, Pitching, and Static Stability Characteristics of a 1/10-Scale Model of the Grumman F9F-9 Airplane, TED No. NACA AD 3109

NASA Technical Reports Server (NTRS)

Wolhart, Walter D.; Thomas, David F., Jr.

1955-01-01

An experimental investigation has been made in the Langley stability tunnel to determine the low-speed yawing, pitching, and static stability characteristics of a 1/10-scale model of the Grumman F9F-9 airplane. Tests were made to determine the effects of duct-entrance-fairing plugs on the static lateral and longitudinal stability characteristics of the complete model in the clean condition. The remaining tests were concerned with determining tail contributions as well as the effect of duct-entrance-fairing plugs, slats, flaps, and landing gear on the yawing and pitching stability derivatives. These data are presented without analysis in order to expedite distribution.

Wind-Tunnel Investigation at Low Speed of the Rolling Stability Derivatives of a 1/10-Scale Model of the Grumman F9F-9 Airplane, TED No. NACA AD 3109

NASA Technical Reports Server (NTRS)

Wolhart, Walter D.; Thomas, David F., Jr.

1955-01-01

An experimental investigation has been made in the Langley stability tunnel to determine the low-speed yawing, pitching, and static stability characteristics of a 1/10-scale model of the Grumman F9F-9 airplane. Tests were made to determine the effects of duct-entrance-fairing plugs on the static lateral and longitudinal stability characteristics of the complete model in the clean condition. The remaining tests were concerned with determining tail contributions as well as the effect of duct-entrance-fairing plugs, slats, flaps, and landing gear on the yawing and pitching stability derivatives. These data are presented without analysis in order to expedite distribution.

The Impact of Social-Cognitive Stress on Speech Variability, Determinism, and Stability in Adults Who Do and Do Not Stutter.

PubMed

Jackson, Eric S; Tiede, Mark; Beal, Deryk; Whalen, D H

2016-12-01

This study examined the impact of social-cognitive stress on sentence-level speech variability, determinism, and stability in adults who stutter (AWS) and adults who do not stutter (AWNS). We demonstrated that complementing the spatiotemporal index (STI) with recurrence quantification analysis (RQA) provides a novel approach to both assessing and interpreting speech variability in stuttering. Twenty AWS and 21 AWNS repeated sentences in audience and nonaudience conditions while their lip movements were tracked. Across-sentence variability was assessed via the STI; within-sentence determinism and stability were assessed via RQA. Compared with the AWNS, the AWS produced speech that was more variable across sentences and more deterministic and stable within sentences. Audience presence contributed to greater within-sentence determinism and stability in the AWS. A subset of AWS who were more susceptible to experiencing anxiety exhibited reduced across-sentence variability in the audience condition compared with the nonaudience condition. This study extends the assessment of speech variability in AWS and AWNS into the social-cognitive domain and demonstrates that the characterization of speech within sentences using RQA is complementary to the across-sentence STI measure. AWS seem to adopt a more restrictive, less flexible speaking approach in response to social-cognitive stress, which is presumably a strategy for maintaining observably fluent speech.

The Impact of Social–Cognitive Stress on Speech Variability, Determinism, and Stability in Adults Who Do and Do Not Stutter

PubMed Central

Tiede, Mark; Beal, Deryk; Whalen, D. H.

2016-01-01

Purpose This study examined the impact of social–cognitive stress on sentence-level speech variability, determinism, and stability in adults who stutter (AWS) and adults who do not stutter (AWNS). We demonstrated that complementing the spatiotemporal index (STI) with recurrence quantification analysis (RQA) provides a novel approach to both assessing and interpreting speech variability in stuttering. Method Twenty AWS and 21 AWNS repeated sentences in audience and nonaudience conditions while their lip movements were tracked. Across-sentence variability was assessed via the STI; within-sentence determinism and stability were assessed via RQA. Results Compared with the AWNS, the AWS produced speech that was more variable across sentences and more deterministic and stable within sentences. Audience presence contributed to greater within-sentence determinism and stability in the AWS. A subset of AWS who were more susceptible to experiencing anxiety exhibited reduced across-sentence variability in the audience condition compared with the nonaudience condition. Conclusions This study extends the assessment of speech variability in AWS and AWNS into the social–cognitive domain and demonstrates that the characterization of speech within sentences using RQA is complementary to the across-sentence STI measure. AWS seem to adopt a more restrictive, less flexible speaking approach in response to social–cognitive stress, which is presumably a strategy for maintaining observably fluent speech. PMID:27936276

Trapped particle stability for the kinetic stabilizer

NASA Astrophysics Data System (ADS)

Berk, H. L.; Pratt, J.

2011-08-01

A kinetically stabilized axially symmetric tandem mirror (KSTM) uses the momentum flux of low-energy, unconfined particles that sample only the outer end-regions of the mirror plugs, where large favourable field-line curvature exists. The window of operation is determined for achieving magnetohydrodynamic (MHD) stability with tolerable energy drain from the kinetic stabilizer. Then MHD stable systems are analysed for stability of the trapped particle mode. This mode is characterized by the detachment of the central-cell plasma from the kinetic-stabilizer region without inducing field-line bending. Stability of the trapped particle mode is sensitive to the electron connection between the stabilizer and the end plug. It is found that the stability condition for the trapped particle mode is more constraining than the stability condition for the MHD mode, and it is challenging to satisfy the required power constraint. Furthermore, a severe power drain may arise from the necessary connection of low-energy electrons in the kinetic stabilizer to the central region.

Stability test and analysis of the Space Shuttle Primary Reaction Control Subsystem thruster

NASA Technical Reports Server (NTRS)

Applewhite, John; Hurlbert, Eric; Krohn, Douglas; Arndt, Scott; Clark, Robert

1992-01-01

The results are reported of a test program conducted on the Space Shuttle Primary Reaction Control Subsystem thruster in order to investigate the effects of trapped helium bubbles and saturated propellants on stability, determine if thruster-to-thruster stability variations are significant, and determine stability under STS-representative conditions. It is concluded that the thruster design is highly reliable in flight and that burn-through has not occurred. Significantly unstable thrusters are screened out, and wire wrap is found to protect against chamber burn-throughs and to provide a fail-safe thruster for this situation.

Biological and physical factors controlling aggregate stability under different climatic conditions in Southern Spain.

NASA Astrophysics Data System (ADS)

Ángel Gabarrón-Galeote, Miguel; Damián Ruiz-Sinoga, Jose; Francisco Martinez-Murillo, Juan; Lavee, Hanoch

2013-04-01

Soil aggregation is a key factor determining the soil structure. The presence of stable aggregates is essential to maintain a good soil structure, that in turn plays an important role in sustaining agricultural productivity and preserving environmental quality. A wide range of physical and biological soil components are involved in the aggregate formation and stabilization, namely clay mineral content; the quantity and quality of organic matter, that can be derived from plants, fungal hyphae, microorganism and soil animals; and the soil water content. Climatic conditions, through their effect on soil water content, vegetation cover and organic matter content, are supposed to affect soil aggregation. Thus the main objective of this research is to analyse the effect of organic matter, clay content and soil water content on aggregate stability along a climatic transect in Southern Spain. This study was conducted in four catchments along a pluviometric gradient in the South of Spain (rainfall depth decreases from west to east from more than 1000 mm year-1 to less than 300 mm year-1) and was based on a methodology approximating the climatic gradient in Mediterranean conditions. The selected sites shared similar conditions of geology, topography and soil use, which allowed making comparisons among them and relating the differences to the pluviometric conditions. In February 2007, 250 disturbed and undisturbed samples from the first 5cm of the soil were collected along the transect. We measured the aggregate stability, organic matter, clay content and bulk density of every sample. In the field we measured rainfall, air temperature, relative humidity, wind speed, wind direction, solar radiation, potential evapotranspiration, soil water content, vegetation cover and presence of litter. Our results suggest that aggregate stability is a property determined by a great number of highly variable factors, which can make extremely difficult to predict its behavior taking in account only a few of them. The climate exerted a great influence in aggregate stability and could determine by itself the soil structure along the climate transect. As a result, properties unrelated in a specific point of the climate transect became highly associated if we took it into account completely. Along the climate transect analyzed could be defined two areas, separated by a threshold located between 573.6 mm y-1 and 335.9 mm y-1. In the wettest part soil structure was mainly determined by biotic factors and in the driest part was highly probable that abiotic factors play a key role determining aggregate stability.

Postural Stability Assessment of University Marching Musicians Using Force Platform Measures.

PubMed

Magnotti, Trevor D; McElhiney, Danielle; Russell, Jeffrey A

2016-09-01

Lower extremity injury is prevalent in marching musicians, and poor postural stability is a possible risk factor for this. The external load of an instrument may predispose these performers to injury by decreasing postural stability. The purpose of this study was to determine the relationship between instrument load and static and dynamic postural stability in this population. Fourteen university marching musicians were recruited and completed a balance assessment protocol on a force platform with and without their instrument. Mean center of pressure (CoP) displacement was then calculated for each exercise in the anterior/posterior and medial/lateral planes. Mean anterior/posterior CoP displacement significantly increased in the instrument condition for the static surface, eyes closed, 2 feet condition (p≤0.005; d=0.89). No significant differences were found in the medial/lateral plane between non-instrument and instrument conditions. Significant differences were not found between test stance conditions independent of group. Comparisons between the non-instrument-loaded and instrument-loaded conditions revealed possible significance of instrument load on postural stability in the anterior/posterior plane. Mean differences indicated that an unstable surface created a greater destabilizing effect on postural stability than instrument load.

Poppet valve control of throat stability bypass to increase stable airflow range of a Mach 2.5. inlet with 60 percent internal contraction

NASA Technical Reports Server (NTRS)

Mitchell, G. A.; Sanders, B. W.

1975-01-01

The throat of a Mach 2.5 inlet with a coldpipe termination was fitted with a stability-bypass system. System variations included several stability bypass entrance configurations. Poppet valves controlled the bypass airflow. The inlet stable airflow range achieved with each configuration was determined for both steady state conditions and internal pulse transients. Results are compared with those obtained without a stability bypass system. Transient results were also obtained for the inlet with a choke point at the diffuser exit and for the inlet with large and small stability bypass plenum volumes. Poppet valves at the stability bypass exit provided the inlet with a stable airflow range of 20 percent or greater at all static and transient conditions.

Morphological stability of sapphire crystallization front

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

Baranov, V. V., E-mail: baranov.isc@gmail.com; Nizhankovskyi, S. V.

2016-03-15

The main factors and specificity of growth conditions for sapphire and Ti:sapphire crystals, which affect the morphological stability of the crystal–melt interface, have been investigated with allowance for the concentration and radiative melt supercooling. It is shown that the critical sapphire growth rate is determined to a great extent by the optical transparency of the melt and the mixing conditions near the crystallization front.

Temperature stability of proteins: Analysis of irreversible denaturation using isothermal calorimetry

PubMed Central

Schön, Arne; Clarkson, Benjamin R; Jaime, Maria; Freire, Ernesto

2017-01-01

The structural stability of proteins has been traditionally studied under conditions in which the folding/unfolding reaction is reversible, since thermodynamic parameters can only be determined under these conditions. Achieving reversibility conditions in temperature stability experiments has often required performing the experiments at acidic pH or other nonphysiological solvent conditions. With the rapid development of protein drugs, the fastest growing segment in the pharmaceutical industry, the need to evaluate protein stability under formulation conditions has acquired renewed urgency. Under formulation conditions and the required high protein concentration (~100 mg/mL), protein denaturation is irreversible and frequently coupled to aggregation and precipitation. In this article, we examine the thermal denaturation of hen egg white lysozyme (HEWL) under irreversible conditions and concentrations up to 100 mg/mL using several techniques, especially isothermal calorimetry which has been used to measure the enthalpy and kinetics of the unfolding and aggregation/precipitation at 12°C below the transition temperature measured by DSC. At those temperatures the rate of irreversible protein denaturation and aggregation of HEWL is measured to be on the order of 1 day−1. Isothermal calorimetry appears a suitable technique to identify buffer formulation conditions that maximize the long term stability of protein drugs. PMID:28722205

Temperature stability of proteins: Analysis of irreversible denaturation using isothermal calorimetry.

PubMed

Schön, Arne; Clarkson, Benjamin R; Jaime, Maria; Freire, Ernesto

2017-11-01

The structural stability of proteins has been traditionally studied under conditions in which the folding/unfolding reaction is reversible, since thermodynamic parameters can only be determined under these conditions. Achieving reversibility conditions in temperature stability experiments has often required performing the experiments at acidic pH or other nonphysiological solvent conditions. With the rapid development of protein drugs, the fastest growing segment in the pharmaceutical industry, the need to evaluate protein stability under formulation conditions has acquired renewed urgency. Under formulation conditions and the required high protein concentration (∼100 mg/mL), protein denaturation is irreversible and frequently coupled to aggregation and precipitation. In this article, we examine the thermal denaturation of hen egg white lysozyme (HEWL) under irreversible conditions and concentrations up to 100 mg/mL using several techniques, especially isothermal calorimetry which has been used to measure the enthalpy and kinetics of the unfolding and aggregation/precipitation at 12°C below the transition temperature measured by DSC. At those temperatures the rate of irreversible protein denaturation and aggregation of HEWL is measured to be on the order of 1 day -1 . Isothermal calorimetry appears a suitable technique to identify buffer formulation conditions that maximize the long term stability of protein drugs. © 2017 Wiley Periodicals, Inc.

The algebraic criteria for the stability of control systems

NASA Technical Reports Server (NTRS)

Cremer, H.; Effertz, F. H.

1986-01-01

This paper critically examines the standard algebraic criteria for the stability of linear control systems and their proofs, reveals important previously unnoticed connections, and presents new representations. Algebraic stability criteria have also acquired significance for stability studies of non-linear differential equation systems by the Krylov-Bogoljubov-Magnus Method, and allow realization conditions to be determined for classes of broken rational functions as frequency characteristics of electrical network.

Selective determination of ertapenem in the presence of its degradation product

NASA Astrophysics Data System (ADS)

Hassan, Nagiba Y.; Abdel-Moety, Ezzat M.; Elragehy, Nariman A.; Rezk, Mamdouh R.

2009-06-01

Stability-indicative determination of ertapenem (ERTM) in the presence of its β-lactam open-ring degradation product, which is also the metabolite, is investigated. The degradation product has been isolated, via acid-degradation, characterized and elucidated. Selective quantification of ERTM, singly in bulk form, pharmaceutical formulations and/or in the presence of its major degradant is demonstrated. The indication of stability has been undertaken under conditions likely to be expected at normal storage conditions. Among the spectrophotometric methods adopted for quantification are first derivative ( 1D), first derivative of ratio spectra ( 1DD) and bivariate analysis.

Comparisons of Predictions of the XB-70-1 Longitudinal Stability and Control Derivatives with Flight Results for Six Flight Conditions

NASA Technical Reports Server (NTRS)

Wolowicz, C. H.; Yancey, R. B.

1973-01-01

Preliminary correlations of flight-determined and predicted stability and control characteristics of the XB-70-1 reported in NASA TN D-4578 were subject to uncertainties in several areas which necessitated a review of prediction techniques particularly for the longitudinal characteristics. Reevaluation and updating of the original predictions, including aeroelastic corrections, for six specific flight-test conditions resulted in improved correlations of static pitch stability with flight data. The original predictions for the pitch-damping derivative, on the other hand, showed better correlation with flight data than the updated predictions. It appears that additional study is required in the application of aeroelastic corrections to rigid model wind-tunnel data and the theoretical determination of dynamic derivatives for this class of aircraft.

Case history : use of Tenax and Tensar geogrids for base course stabilization : technical assistance report.

DOT National Transportation Integrated Search

1999-01-01

Geogrids can be used successfully for subgrade stabilization under permanent pavements. To be successful, proper designs incorporating existing soil conditions and anticipated loading need to be performed. subgrade soil strength should be determined ...

Retinoic acid stability in stem cell cultures.

PubMed

Sharow, Kyle A; Temkin, Boris; Asson-Batres, Mary Ann

2012-01-01

It has been reported that retinoids, such as retinoic acid (RA) and retinol (ROL), dissolved in aqueous solutions are susceptible to oxidative damage when exposed to light, air, and relatively high temperatures, conditions that are normal for culturing stem cells. Thus, questions arise regarding the interpretation of results obtained from studies of mouse embryonic stem cells exposed to retinoids because their isomerization state, their stability in culture conditions, and their interactions with other potential differentiation factors in growth media could influence developmental processes under study. Media samples were supplemented with retinoids and exposed to cell culture conditions with and without mouse embryonic stem cells (mESC), and retinoids were extracted and analyzed using HPLC. To determine whether retinoids are stable in media supplemented with fetal bovine serum (FBS) or in chemically-defined, serum-free media, mESC adapted to each type of growth media were investigated. Studies reported here indicate there was little loss or isomerization of at-RA, 9-cis-RA, 13-cis-RA, or ROL in cell cultures grown in serum-supplemented media when cell cultures were maintained in the dark and manipulated and observed under yellow light. In contrast, the stability of both at-RA and ROL were determined to be greatly reduced in serum-free media as compared with serum-supplemented media. Addition of 6 mg/ml bovine serum albumin was found to stabilize retinoids in serum-free media. It was also determined that ROL is less stable than RA in cell culture conditions.

Effect of an Unstable Load on Primary and Stabilizing Muscles During the Bench Press.

PubMed

Ostrowski, Stephanie J; Carlson, Lara A; Lawrence, Michael A

2017-02-01

Ostrowski, SJ, Carlson, LA, and Lawrence, MA. Effect of an unstable load on primary and stabilizing muscles during the bench press. J Strength Cond Res 31(2): 430-434, 2017-Unstable resistance exercises are performed to increase activity of stabilizing muscles. The premise is that this increase in activity will yield greater strength gains than traditional resistance exercises. The purpose of this study was to determine if an unstable load increases muscle activity of stabilizing muscles during a bench press as compared with a standard bench press with a typical load. Fifteen resistance-trained males (age 24.2 ± 2.7 years, mass 84.8 ± 12.0 kg, height 1.77 ± 0.05 m, weight lifting experience 9.9 ± 3.4 years, and bench press 1 repetition maximum [1RM] 107.5 ± 25.9 kg) volunteered for this study. Subjects pressed 2 sets of 5 repetitions in both stable (75% 1RM) and unstable (60% 1RM) conditions using a standard barbell and a flexible Earthquake bar, respectively. Surface electromyography was used to detect muscle activity of primary movers (pectoralis major, anterior deltoid, and triceps) and stabilizing musculature (latissimus dorsi, middle and posterior deltoid, biceps brachii, and upper trapezius). Muscle activity was compared using a multivariate analysis of variance to determine significant (p ≤ 0.05) phase and condition differences. The right and left biceps and the left middle deltoid were significantly more active in the unstable condition. Some of the stabilizing muscles were found to be significantly more active in the unstable condition with 15% less weight. Therefore, bench pressing with an unstable load appears promising in activating stabilizing musculature compared with pressing a typical barbell.

Stability and Interaction of Coherent Structure in Supersonic Reactive Wakes

NASA Technical Reports Server (NTRS)

Menon, Suresh

1983-01-01

A theoretical formulation and analysis is presented for a study of the stability and interaction of coherent structure in reacting free shear layers. The physical problem under investigation is a premixed hydrogen-oxygen reacting shear layer in the wake of a thin flat plate. The coherent structure is modeled as a periodic disturbance and its stability is determined by the application of linearized hydrodynamic stability theory which results in a generalized eigenvalue problem for reactive flows. Detailed stability analysis of the reactive wake for neutral, symmetrical and antisymmetrical disturbance is presented. Reactive stability criteria is shown to be quite different from classical non-reactive stability. The interaction between the mean flow, coherent structure and fine-scale turbulence is theoretically formulated using the von-Kaman integral technique. Both time-averaging and conditional phase averaging are necessary to separate the three types of motion. The resulting integro-differential equations can then be solved subject to initial conditions with appropriate shape functions. In the laminar flow transition region of interest, the spatial interaction between the mean motion and coherent structure is calculated for both non-reactive and reactive conditions and compared with experimental data wherever available. The fine-scale turbulent motion determined by the application of integral analysis to the fluctuation equations. Since at present this turbulence model is still untested, turbulence is modeled in the interaction problem by a simple algebraic eddy viscosity model. The applicability of the integral turbulence model formulated here is studied parametrically by integrating these equations for the simple case of self-similar mean motion with assumed shape functions. The effect of the motion of the coherent structure is studied and very good agreement is obtained with previous experimental and theoretical works for non-reactive flow. For the reactive case, lack of experimental data made direct comparison difficult. It was determined that the growth rate of the disturbance amplitude is lower for reactive case. The results indicate that the reactive flow stability is in qualitative agreement with experimental observation.

A Stability-Indicating HPLC-DAD Method for Determination of Stiripentol: Development, Validation, Kinetics, Structure Elucidation and Application to Commercial Dosage Form

PubMed Central

Darwish, Hany W.; Abdelhameed, Ali S.; Bakheit, Ahmed H.; Khalil, Nasr Y.; Al-Majed, Abdulrahman A.

2014-01-01

A rapid, simple, sensitive, and accurate isocratic reversed-phase stability-indicating high performance liquid chromatography method has been developed and validated for the determination of stiripentol and its degradation product in its bulk form and pharmaceutical dosage form. Chromatographic separation was achieved on a Symmetry C18 column and quantification was achieved using photodiode array detector (DAD). The method was validated in accordance with the ICH requirements showing specificity, linearity (r 2 = 0.9996, range of 1–25 μg/mL), precision (relative standard deviation lower than 2%), accuracy (mean recovery 100.08 ± 1.73), limits of detection and quantitation (LOD = 0.024 and LOQ = 0.081 μg/mL), and robustness. Stiripentol was subjected to various stress conditions and it has shown marked stability under alkaline hydrolytic stress conditions, thermal, oxidative, and photolytic conditions. Stiripentol degraded only under acidic conditions, forming a single degradation product which was well resolved from the pure drug with significantly different retention time values. This degradation product was characterized by 1H-NMR and 13C-NMR spectroscopy as well as ion trap mass spectrometry. The results demonstrated that the method would have a great value when applied in quality control and stability studies for stiripentol. PMID:25371844

Control system design method

DOEpatents

Wilson, David G [Tijeras, NM; Robinett, III, Rush D.

2012-02-21

A control system design method and concomitant control system comprising representing a physical apparatus to be controlled as a Hamiltonian system, determining elements of the Hamiltonian system representation which are power generators, power dissipators, and power storage devices, analyzing stability and performance of the Hamiltonian system based on the results of the determining step and determining necessary and sufficient conditions for stability of the Hamiltonian system, creating a stable control system based on the results of the analyzing step, and employing the resulting control system to control the physical apparatus.

Signal Processing Methods for Liquid Rocket Engine Combustion Stability Assessments

NASA Technical Reports Server (NTRS)

Kenny, R. Jeremy; Lee, Erik; Hulka, James R.; Casiano, Matthew

2011-01-01

The J2X Gas Generator engine design specifications include dynamic, spontaneous, and broadband combustion stability requirements. These requirements are verified empirically based high frequency chamber pressure measurements and analyses. Dynamic stability is determined with the dynamic pressure response due to an artificial perturbation of the combustion chamber pressure (bomb testing), and spontaneous and broadband stability are determined from the dynamic pressure responses during steady operation starting at specified power levels. J2X Workhorse Gas Generator testing included bomb tests with multiple hardware configurations and operating conditions, including a configuration used explicitly for engine verification test series. This work covers signal processing techniques developed at Marshall Space Flight Center (MSFC) to help assess engine design stability requirements. Dynamic stability assessments were performed following both the CPIA 655 guidelines and a MSFC in-house developed statistical-based approach. The statistical approach was developed to better verify when the dynamic pressure amplitudes corresponding to a particular frequency returned back to pre-bomb characteristics. This was accomplished by first determining the statistical characteristics of the pre-bomb dynamic levels. The pre-bomb statistical characterization provided 95% coverage bounds; these bounds were used as a quantitative measure to determine when the post-bomb signal returned to pre-bomb conditions. The time for post-bomb levels to acceptably return to pre-bomb levels was compared to the dominant frequency-dependent time recommended by CPIA 655. Results for multiple test configurations, including stable and unstable configurations, were reviewed. Spontaneous stability was assessed using two processes: 1) characterization of the ratio of the peak response amplitudes to the excited chamber acoustic mode amplitudes and 2) characterization of the variability of the peak response's frequency over the test duration. This characterization process assists in evaluating the discreteness of a signal as well as the stability of the chamber response. Broadband stability was assessed using a running root-mean-square evaluation. These techniques were also employed, in a comparative analysis, on available Fastrac data, and these results are presented here.

Thermal and storage characteristics of tomato seed oil

USDA-ARS?s Scientific Manuscript database

Thermal oxidative stability and effect of different storage conditions on quality characteristics of tomato seed oil have not been studied. The objectives of this research were to determine the changes in quality and oxidative stability of tomato seed oil, including color, antioxidant activity, per...

Design of a robust fuzzy controller for the arc stability of CO(2) welding process using the Taguchi method.

PubMed

Kim, Dongcheol; Rhee, Sehun

2002-01-01

CO(2) welding is a complex process. Weld quality is dependent on arc stability and minimizing the effects of disturbances or changes in the operating condition commonly occurring during the welding process. In order to minimize these effects, a controller can be used. In this study, a fuzzy controller was used in order to stabilize the arc during CO(2) welding. The input variable of the controller was the Mita index. This index estimates quantitatively the arc stability that is influenced by many welding process parameters. Because the welding process is complex, a mathematical model of the Mita index was difficult to derive. Therefore, the parameter settings of the fuzzy controller were determined by performing actual control experiments without using a mathematical model of the controlled process. The solution, the Taguchi method was used to determine the optimal control parameter settings of the fuzzy controller to make the control performance robust and insensitive to the changes in the operating conditions.

Implementation of Particle Swarm Optimization Method for Voltage Stability Analysis in 150 kV Sub System Grati – Paiton East Java

NASA Astrophysics Data System (ADS)

Kusumaningtyas, A. B.; Hidayat, M. N.; Ronilaya, F.

2018-04-01

Based on the data from State Electric Company on 15 January 2013, the undistributed power in the 150 kV sub system Grati-Paiton Region IV, that consist of 26 bus 150 kV and 2 bus generation 500 kV system, was recorded 3.286,00 MW. At the same time, the frequency of the system was down to 49 Hz. This lead to a deficit generation and unstable voltage condition in the system. Fast Voltage Stability Index (FVSI) method is used in this research to analyze the voltage stability of the buses. For buses with unstable voltage condition, reactive power will be injected through capacitor installation. The site where the capacitor will be installed is determined using the Fast Voltage Stability Index (FVSI) method while the size of the capacitor is determined using the Particle Swarm Optimization (PSO) method. The PSO method has been applied in some researches, such as to determine optimal placement and sizing in radial distribution network as well as in transmission network.. In this research, the PSO method is used to find the Qloss of an interconnection transmission system, which in turn, the value of the Qloss is used to determine the capacitance of the capacitor needed by the system.

Activity of Shoulder Stabilizers and Prime Movers During an Unstable Overhead Press.

PubMed

Williams, Martin R; Hendricks, Dustin S; Dannen, Michael J; Arnold, Andrea M; Lawrence, Michael A

2018-06-08

Williams, MR Jr, Hendricks, DS, Dannen, MJ, Arnold, AM, and Lawrence, MA. Activity of shoulder stabilizers and prime movers during an unstable overhead press. J Strength Cond Res XX(X): 000-000, 2018-Overhead reaching is a common movement that relies heavily on muscles for dynamic stability. Stabilizer muscle activation increased during squatting and bench pressing with an unstable load, but the overhead press (OHP) has yet to be examined. The purpose of this study is to compare muscle activity of the shoulder stabilizers and prime movers and excursions of the center of pressure (CoP) during the OHP in 2 unstable and one stable conditions. Twelve men (aged 25.3 ± 2.7 years, mass: 91.5 ± 8.4 kg, height: 1.81 ± 0.06 m) pressed 50% of their 1 repetition maximum for 10 repetitions over 3 conditions: a straight stable barbell (SS), a straight unstable (SU) barbell with kettlebells suspend by elastic bands, and an unstable Earthquake (EU) bar with kettlebells suspended by elastic bands. Activity of the shoulder stabilizers and prime movers were measured via surface and indwelling electromyography. Center of pressure excursion of the right foot was also measured. A multivariate analysis was used to determine significant differences between conditions. Pressing with the EQ increased activation of the biceps brachii, erector spinae, latissimus dorsi, pectoralis major, rectus abdominus, rhomboids, and serratus anterior over the SS condition, whereas only the SU condition increased activation in the erector spinae and latissimus dorsi muscles. The EQ condition produced greater CoP excursion (35.3 ± 7.9% foot length) compared with the SU (28.0 ± 7.2% foot length) and SS (22.2 ± 6.3% foot length) conditions. Therefore, the EU condition may be an effective exercise to activate scapular stabilizers.

Intrarater test-retest reliability of static and dynamic stability indexes measurement using the Biodex Stability System during unilateral stance.

PubMed

Arifin, Nooranida; Abu Osman, Noor Azuan; Wan Abas, Wan Abu Bakar

2014-04-01

The measurements of postural balance often involve measurement error, which affects the analysis and interpretation of the outcomes. In most of the existing clinical rehabilitation research, the ability to produce reliable measures is a prerequisite for an accurate assessment of an intervention after a period of time. Although clinical balance assessment has been performed in previous study, none has determined the intrarater test-retest reliability of static and dynamic stability indexes during dominant single stance. In this study, one rater examined 20 healthy university students (female=12, male=8) in two sessions separated by 7 day intervals. Three stability indexes--the overall stability index (OSI), anterior/posterior stability index (APSI), and medial/ lateral stability index (MLSI) in static and dynamic conditions--were measured during single dominant stance. Intraclass correlation coefficient (ICC), standard error measurement (SEM) and 95% confidence interval (95% CI) were calculated. Test-retest ICCs for OSI, APSI, and MLSI were 0.85, 0.78, and 0.84 during static condition and were 0.77, 0.77, and 0.65 during dynamic condition, respectively. We concluded that the postural stability assessment using Biodex stability system demonstrates good-to-excellent test-retest reliability over a 1 week time interval.

Using high-performance ¹H NMR (HP-qNMR®) for the certification of organic reference materials under accreditation guidelines--describing the overall process with focus on homogeneity and stability assessment.

PubMed

Weber, Michael; Hellriegel, Christine; Rueck, Alexander; Wuethrich, Juerg; Jenks, Peter

2014-05-01

Quantitative NMR spectroscopy (qNMR) is gaining interest across both analytical and industrial research applications and has become an essential tool for the content assignment and quantitative determination of impurities. The key benefits of using qNMR as measurement method for the purity determination of organic molecules are discussed, with emphasis on the ability to establish traceability to "The International System of Units" (SI). The work describes a routine certification procedure from the point of view of a commercial producer of certified reference materials (CRM) under ISO/IEC 17025 and ISO Guide 34 accreditation, that resulted in a set of essential references for (1)H qNMR measurements, and the relevant application data for these substances are given. The overall process includes specific selection criteria, pre-tests, experimental conditions, homogeneity and stability studies. The advantages of an accelerated stability study over the classical stability-test design are shown with respect to shelf-life determination and shipping conditions. Copyright © 2013 The Authors. Published by Elsevier B.V. All rights reserved.

Dynamic stability of spinning pretwisted beams subjected to axial random forces

NASA Astrophysics Data System (ADS)

Young, T. H.; Gau, C. Y.

2003-11-01

This paper studies the dynamic stability of a pretwisted cantilever beam spinning along its longitudinal axis and subjected to an axial random force at the free end. The axial force is assumed as the sum of a constant force and a random process with a zero mean. Due to this axial force, the beam may experience parametric random instability. In this work, the finite element method is first applied to yield discretized system equations. The stochastic averaging method is then adopted to obtain Ito's equations for the response amplitudes of the system. Finally the mean-square stability criterion is utilized to determine the stability condition of the system. Numerical results show that the stability boundary of the system converges as the first three modes are taken into calculation. Before the convergence is reached, the stability condition predicted is not conservative enough.

Applying the methodology of Design of Experiments to stability studies: a Partial Least Squares approach for evaluation of drug stability.

PubMed

Jordan, Nika; Zakrajšek, Jure; Bohanec, Simona; Roškar, Robert; Grabnar, Iztok

2018-05-01

The aim of the present research is to show that the methodology of Design of Experiments can be applied to stability data evaluation, as they can be seen as multi-factor and multi-level experimental designs. Linear regression analysis is usually an approach for analyzing stability data, but multivariate statistical methods could also be used to assess drug stability during the development phase. Data from a stability study for a pharmaceutical product with hydrochlorothiazide (HCTZ) as an unstable drug substance was used as a case example in this paper. The design space of the stability study was modeled using Umetrics MODDE 10.1 software. We showed that a Partial Least Squares model could be used for a multi-dimensional presentation of all data generated in a stability study and for determination of the relationship among factors that influence drug stability. It might also be used for stability predictions and potentially for the optimization of the extent of stability testing needed to determine shelf life and storage conditions, which would be time and cost-effective for the pharmaceutical industry.

IMPROVED TEMPERATURE STABILITY OF SULFUR DIOXIDE SAMPLES COLLECTED BY THE FEDERAL REFERENCE METHOD

EPA Science Inventory

This report describes an examination of the reagents present in the SO2 Federal Reference Method (FRM) to determine if any change in reagent concentration or condition could bring about substantial, if not complete, retardation of the effect of temperature on the stability of col...

Stability study of carboplatin infusion solutions in 0.9% sodium chloride in polyvinyl chloride bags.

PubMed

Myers, Alan L; Zhang, Yang-Ping; Kawedia, Jitesh D; Trinh, Van A; Tran, Huyentran; Smith, Judith A; Kramer, Mark A

2016-02-01

Carboplatin is a platinum-containing compound with efficacy against various malignancies. The physico-chemical stability of carboplatin in dextrose 5% water (D5W) has been thoroughly studied; however, there is a paucity of stability data in clinically relevant 0.9% sodium chloride infusion solutions. The manufacturer's limited stability data in sodium chloride solutions hampers the flexibility of carboplatin usage in oncology patients. Hence, the purpose of this study is to determine the physical and chemical stability of carboplatin-sodium chloride intravenous solutions under different storage conditions. The physico-chemical stability of 0.5 mg/mL, 2.0 mg/mL, and 4.0 mg/mL carboplatin-sodium chloride solutions prepared in polyvinyl chloride bags was determined following storage at room temperature under ambient fluorescent light and under refrigeration in the dark. Concentrations of carboplatin were measured at predetermined time points up to seven days using a stability-indicating high-performance liquid chromatography method. All tested solutions were found physically stable for at least seven days. The greatest chemical stability was observed under refrigerated storage conditions. At 4℃, all tested solutions were found chemically stable for at least seven days, with nominal losses of ≤6%. Following storage at room temperature exposed to normal fluorescent light, the chemical stability of 0.5 mg/mL, 2.0 mg/mL, and 4.0 mg/mL solutions was three days, five days, and seven days, respectively. The extended physico-chemical stability of carboplatin prepared in sodium chloride reported herein permits advance preparation of these admixtures, facilitating pharmacy utility and operations. Since no antibacterial preservative is contained within these carboplatin solutions, we recommend storage, when prepared under specified aseptic conditions, no greater than 24 h at room temperature or three days under refrigeration. © The Author(s) 2014.

The addition of body armor diminishes dynamic postural stability in military soldiers.

PubMed

Sell, Timothy C; Pederson, Jonathan J; Abt, John P; Nagai, Takashi; Deluzio, Jennifer; Wirt, Michael D; McCord, Larry J; Lephart, Scott M

2013-01-01

Poor postural stability has been identified as a risk factor for lower extremity musculoskeletal injury. The additional weight of body armor carried by Soldiers alters static postural stability and may predispose Soldiers to lower extremity musculoskeletal injuries. However, static postural stability tasks poorly replicate the dynamic military environment, which places considerable stress on the postural control system during tactical training and combat. Therefore, the purpose of this study was to examine the effects of body armor on dynamic postural stability during single-leg jump landings. Thirty-six 101st Airborne Division (Air Assault) Soldiers performed single-leg jump landings in the anterior direction with and without wearing body armor. The dynamic postural stability index and the individual stability indices (medial-lateral stability index, anterior-posterior stability index, and vertical stability index) were calculated for each condition. Paired sample t-tests were performed to determine differences between conditions. Significant differences existed for the medial-lateral stability index, anterior-posterior stability index, vertical stability index, and dynamic postural stability index (p < 0.05). The addition of body armor resulted in diminished dynamic postural stability, which may result in increased lower extremity injuries. Training programs should address the altered dynamic postural stability while wearing body armor in attempts to promote adaptations that will result in safer performance during dynamic tasks.

Stability Formulation for Integrated Opto-mechanic Phase Shifters.

PubMed

Ozer, Yigit; Kocaman, Serdar

2018-01-31

Stability of opto-mechanical phase shifters consisting of waveguides and non-signal carrying control beams is investigated thoroughly and a formula determining the physical limitations has been proposed. Suggested formulation is not only beneficial to determine physical strength of the system but also advantageous to guess the response of the output to the fabrication errors. In the iterative analysis of cantilever and double-clamped beam geometrical configurations, the stability condition is revealed under the strong inter-dependence of the system parameters such as input power, device length and waveguide separation. Numerical calculations involving effective index modifications and opto-mechanic movements show that well-known cantilever beams are unstable and inadequate to generate φ = 180° phase difference, while double-clamped beam structures can be utilized to build functional devices. Ideal operation conditions are also presented in terms of both the device durability and the controllability of phase evolution.

Study on the stability and reliability of Clinotron at Y-band

NASA Astrophysics Data System (ADS)

Li, Shuang; Wang, Jianguo; Chen, Zaigao; Wang, Guangqiang; Wang, Dongyang; Teng, Yan

2017-11-01

To improve the stability and reliability of Clinotron at the Y-band, some key issues are researched, such as the synchronous operating mode, the heat accumulation on the slow-wave structure, and the errors in micro-fabrication. By analyzing the dispersion relationship, the working mode is determined as the TM10 mode. The problem of heat dissipation on a comb is researched to make a trade-off on the choice of suitable working conditions, making sure that the safety and efficiency of the device are guaranteed simultaneously. The study on the effect of tolerance on device's performance is also conducted to determine the acceptable error during micro-fabrication. The validity of the device and the cost for fabrication are both taken into consideration. At last, the performance of Clinotron under the optimized conditions demonstrates that it can work steadily at 315.89 GHz and the output power is about 12 W, showing advanced stability and reliability.

Humidity-corrected Arrhenius equation: The reference condition approach.

PubMed

Naveršnik, Klemen; Jurečič, Rok

2016-03-16

Accelerated and stress stability data is often used to predict shelf life of pharmaceuticals. Temperature, combined with humidity accelerates chemical decomposition and the Arrhenius equation is used to extrapolate accelerated stability results to long-term stability. Statistical estimation of the humidity-corrected Arrhenius equation is not straightforward due to its non-linearity. A two stage nonlinear fitting approach is used in practice, followed by a prediction stage. We developed a single-stage statistical procedure, called the reference condition approach, which has better statistical properties (less collinearity, direct estimation of uncertainty, narrower prediction interval) and is significantly easier to use, compared to the existing approaches. Our statistical model was populated with data from a 35-day stress stability study on a laboratory batch of vitamin tablets and required mere 30 laboratory assay determinations. The stability prediction agreed well with the actual 24-month long term stability of the product. The approach has high potential to assist product formulation, specification setting and stability statements. Copyright © 2016 Elsevier B.V. All rights reserved.

Analysis of Chatter Stability in Facing

NASA Astrophysics Data System (ADS)

Kebdani, S.; Sahli, A.; Rahmani, O.; Boutchicha, D.; Belarbi, A.

This study attempts to develop a chatter model for predicting chatter stability conditions in hard turning. A linear model is developed by introducing non-uniform load distribution on a tool tip to account for the flank wear effect. Stability analysis based on the root locus method and the harmonic balance method is conducted to determine a critical stability parameter. To validate the model, a series of experiment is carried out to determine the stability limits as well as certain characteristic parameters for facing and straight turning. Chatter in hard turning has the feature that the critical stability limits increase very rapidly when the cutting speed is higher than 13 rev sec-1 for all feed directions. The main contributions of the study are threefold. First, chatter-free cutting conditions are predicted and can be used as a guideline for designing tools and machines. Second, the characteristics of chatter in hard turning, which is observed for the first time, helps to broaden our physical understanding of the interactions between the tool and the workpiece in hard turning. Third, experimental stability limits for different flank wear can contribute to lead more reasonable ways to consider the flank wear effect in chatter models of hard turning. Based on these contributions, the proposed linear chatter model will support to improve the productivity in many manufacturing processes. In addition, the chatter experimental data will be useful to develop other chatter models in hard turning.

SO 2 concentrations near tall stacks

NASA Astrophysics Data System (ADS)

Lott, Robert A.

A study was conducted to investigate plume dispersion during convective (stability class A) conditions. The purpose of the study was to determine if high concentrations occur near sources (1.2-1.8 km) with tall stacks and to identify the plume behavior during these episodes. The study was conducted at the Tennessee Valley Authority's Paradise Steam Plant. The highest concentrations were measured near the source during wind shear capping conditions, which normally correspond to stability class B or C conditions. The measured data are compared with results obtained using a convective boundary layer model and a steady-state Gaussian model.

A validated stability-indicating UPLC method for desloratadine and its impurities in pharmaceutical dosage forms.

PubMed

Rao, Dantu Durga; Satyanarayana, N V; Malleswara Reddy, A; Sait, Shakil S; Chakole, Dinesh; Mukkanti, K

2010-02-05

A novel stability-indicating gradient reverse phase ultra-performance liquid chromatographic (RP-UPLC) method was developed for the determination of purity of desloratadine in presence of its impurities and forced degradation products. The method was developed using Waters Aquity BEH C18 column with mobile phase containing a gradient mixture of solvents A and B. The eluted compounds were monitored at 280nm. The run time was 8min within which desloratadine and its five impurities were well separated. Desloratadine was subjected to the stress conditions of oxidative, acid, base, hydrolytic, thermal and photolytic degradation. Desloratadine was found to degrade significantly in oxidative and thermal stress conditions and stable in acid, base, hydrolytic and photolytic degradation conditions. The degradation products were well resolved from main peak and its impurities, thus proved the stability-indicating power of the method. The developed method was validated as per ICH guidelines with respect to specificity, linearity, limit of detection, limit of quantification, accuracy, precision and robustness. This method was also suitable for the assay determination of desloratadine in pharmaceutical dosage forms.

Studies in Thermocapillary Convection of the Marangoni-Benard Type

NASA Technical Reports Server (NTRS)

Kelly, Robert E.; Or, Arthur C.

1996-01-01

The effects of imposed nonlinear oscillatory shear upon the onset of Marangoni-Bernard convection, as predicted by linear theory, in a layer of liquid with a deformable free surface were reported upon by Or and Kelly for small amplitude oscillations. Depending on the operating conditions, either stabilization or destabilization might occur. The aim of the current paper is to report the results for finite amplitude imposed oscillations so that the actual amount of stabilization or destabilization can be determined for prescribed operating conditions.

Development and validation of a stability-indicating RP-HPLC method for determination of atomoxetine hydrochloride in tablets.

PubMed

Patel, Sejal K; Patel, Natvarlal J

2010-01-01

This paper describes the development of a stability-indicating RP-HPLC method for the determination of atomoxetine hydrochloride (ATX) in the presence of its degradation products generated from forced decomposition studies. The drug substance was subjected to stress conditions of acid, base, oxidation, wet heat, dry heat, and photodegradation. In stability tests, the drug was susceptible to acid, base, oxidation, and dry and wet heat degradation. It was found to be stable under the photolytic conditions tested. The drug was successfully separated from the degradation products formed under stress conditions on a Phenomenex C18 column (250 x 4.6 mm id, 5 microm particle size) by using acetonitrile-methanol-0.032 M ammonium acetate (55 + 05 + 40, v/v/v) as the mobile phase at 1.0 mL/min and 40 degrees C. Photodiode array detection at 275 nm was used for quantitation after RP-HPLC over the concentration range of 0.5-5 microg/mL with a mean recovery of 100.8 +/- 0.4% for ATX. Statistical analysis demonstrated that the method is repeatable, specific, and accurate for the estimation of ATX. Because the method effectively separates the drug from its degradation products, it can be used as a stability-indicating method.

Influence of stem design on the primary stability of megaprostheses of the proximal femur.

PubMed

Kinkel, Stefan; Graage, Jan Dennis; Kretzer, Jan Philippe; Jakubowitz, Eike; Nadorf, Jan

2013-10-01

Extended bone defects of the proximal femur can be reconstructed by megaprostheses for which aseptic loosening constitutes one of the major failure modes. The basic requirement for long-term success of endoprostheses is primary stability. We therefore assessed whether sufficient primary stability can be achieved by four different megaprostheses in a standardised bone defect of the proximal femur and whether their different design leads to different fixation patterns. Four different designs of proximal femoral replacements were implanted into 16 Sawbones® after preparing segmental bone defects (AAOS type II). Primary rotational stability was analysed by application of a cyclic torque of ±7 Nm and measuring the relative micromotions between bone and implant at different levels. The main fixation zones and differences of fixation patterns of the stem designs were determined by an analysis of variance. All four implants exhibited micromotions below 150 μm, indicating adequate primary stability. Lowest micromotions for all designs were located near the femoral isthmus. The extent of primary stability and the global implant fixation pattern differed considerably and could be related to the different design concepts. All megaprostheses studied provided sufficient primary stability if the fixation conditions of the femoral isthmus were intact. The design characteristics of the different stems largely determined the extent of primary stability and fixation pattern. Understanding these different fixation types could help the surgeon to choose the most suitable implant if the fixation conditions in the isthmus are compromised.

Nicotinamidase/pyrazinamidase of Mycobacterium tuberculosis forms homo-dimers stabilized by disulfide bonds

PubMed Central

Rueda, Daniel; Sheen, Patricia; Gilman, Robert H.; Bueno, Carlos; Santos, Marco; Pando-Robles, Victoria; Batista, Cesar V.; Zimic, Mirko

2014-01-01

Recombinant wild-pyrazinamidase from H37Rv M. tuberculosis was analyzed by gel electrophoresis under differential reducing conditions to evaluate its quaternary structure. PZAse was fractionated by size exclusion chromatography under non-reducing conditions. PZAse activity was measured and mass spectrometry analysis was performed to determine the identity of proteins by de novo sequencing and to determine the presence of disulfide bonds. This study confirmed that M. tuberculosis wild type PZAse was able to form homo-dimers in vitro. Homo-dimers showed a slightly lower specific PZAse activity compared to monomeric PZAse. PZAse dimers were dissociated into monomers in response to reducing conditions. Mass spectrometry analysis confirmed the existence of disulfide bonds (C72-C138 and C138-C138) stabilizing the quaternary structure of the PZAse homo-dimer. PMID:25199451

A proposed new generation of intact stability criteria for assessment of ship stability in longitudinal waves

NASA Astrophysics Data System (ADS)

Andrei, C.

2017-08-01

Intact ship stability assessment to prevent stability failure in heavy weather conditions is of paramount importance on board vessel. The possibility of assessment the causes that can lead to loss of ship’s stability as well as the assessment of intact stability in heavy seas is a important problem and has attracted a huge interest of the national and international regulatory authorities. Despite the regulations in force, referring to intact ship stability, many ships continued to lose the stability and or capsize due to failure modes that presently are not covered by such regulations. Based on this aspect has been identified the necessity of modelling an updated criteria for assessment of ship’s stability taking into consideration actual possible situations for loss of stability in heavy seas as a measure of increasing she safety of ships. In this respect, the goal of this paper is to illustrate a possible criteria for assessment ship’s stability in heavy seas through a method of determination the possible problems in a form of dynamic stability criteria. A new intact stability criteria is proposed and developed based on separate levels for assessment of vulnerability and susceptibility of ships in situations of parametric rolling and pure loss of stability encountered in extreme sea conditions. Mathematical models correlated with ship’s construction particulars and weather conditions were developed for every separate level in order to assess the ship’s stability. The objective of the proposed criteria is to bring to officers on board ships the possibility of assessment the ship’s intact stability, as a measure of prevention and improvement of safety during the voyage.

Reflex-mediated dynamic neuromuscular stabilization in stroke patients: EMG processing and ultrasound imaging.

PubMed

Yoon, Hyun S; You, Joshua Sung H

2017-07-20

Postural core instability is associated with poor dynamic balance and a high risk of serious falls. Both neurodevelopmental treatment (NDT) and dynamic neuromuscular stabilization (DNS) core stabilization exercises have been used to improve core stability, but the outcomes of these treatments remain unclear. This study was undertaken to examine the therapeutic effects of NDT and DNS core stabilization exercises on muscular activity, core stability, and core muscle thickness. Ten participants (5 healthy adults; 5 hemiparetic stroke patients) were recruited. Surface electromyography (EMG) was used to determine core muscle activity of the transversus abdominis/internal oblique (TrA/IO), external oblique (EO), and rectus abdominis (RA) muscles. Ultrasound imaging was used to measure transversus abdominals/internal oblique (TrA/IO) thickness, and a pressure biofeedback unit (PBU) was used to measure core stability during the DNS and NDT core exercise conditions. Data are reported as median and range and were compared using nonparametric Mann - Whitney U test and Wilcoxon signed rank test at p< 0.05. Both healthy and hemiparetic stroke groups showed greater median EMG amplitude in the TrA/IO muscles, core stability, and muscle thickness values during the DNS exercise condition than during the NDT core exercise condition, respectively (p< 0.05). However, the relative changes in the EMG amplitude, core stability, and muscle thickness values were greater during the DNS exercise condition than during the NDT core exercise condition in the hemiparetic stroke patient group (p< 0.05). Our novel results provide the first clinical evidence that DNS is more effective than NDT in both healthy and hemiparetic stroke subjects to provide superior deep core muscle activation, core stabilization, and muscle thickness. Moreover, such advantageous therapeutic benefits of the DNS core stabilization exercise over the NDT exercise were more apparent in the hemiparetis stroke patients than normal controls.

Bi-Stability of Movement Coordination as a Function of Skill Level and Task Difficulty

ERIC Educational Resources Information Center

Liu, Yeou-Teh; Mayer-Kress, Gottfried; Newell, Karl M.

2010-01-01

This study investigated whether the level of practice interacts with the initial conditions (here manipulated as preparatory movements) and task difficulty (ball angular velocity and friction) in determining the stability of movement coordination for a roller ball motor task. Practice level and task difficulty were manipulated as two control…

Wind-Tunnel Investigation of Effects of Unsymmetrical Horizontal-Tail Arrangements on Power-on Static Longitudinal Stability of a Single-Engine Airplane Model

NASA Technical Reports Server (NTRS)

Purser, Paul E.; Spear, Margaret F.

1947-01-01

A wind-tunnel investigation has been made to determine the effects of unsymmetrical horizontal-tail arrangements on the power-on static longitudinal stability of a single-engine single-rotation airplane model. Although the tests and analyses showed that extreme asymmetry in the horizontal tail indicated a reduction in power effects on longitudinal stability for single-engine single-rotation airplanes, the particular "practical" arrangement tested did not show marked improvement. Differences in average downwash between the normal tail arrangement and various other tail arrangements estimated from computed values of propeller-slipstream rotation agreed with values estimated from pitching-moment test data for the flaps-up condition (low thrust and torque) and disagreed for the flaps-down condition (high thrust and torque). This disagreement indicated the necessity for continued research to determine the characteristics of the slip-stream behind various propeller-fuselage-wing combinations. Out-of-trim lateral forces and moments of the unsymmetrical tail arrangements that were best from consideration of longitudinal stability were no greater than those of the normal tail arrangement.

Atmospheric stability determination at different time intervals for determination of aerial application timing

USDA-ARS?s Scientific Manuscript database

Determination of atmospheric conditions for proper timing of spray application is important to prevent off-target movement of crop protection materials. Susceptible crops can be injured downwind if proper application procedure is not followed. In our previous study, hourly data indicated unfavorable...

Some effects of nonlinear variation in the directional-stability and damping-in-yawing derivatives on the lateral stability of an airplane

NASA Technical Reports Server (NTRS)

Sternfield, Leonard

1951-01-01

A theoretical investigation has been made to determine the effect of nonlinear stability derivatives on the lateral stability of an airplane. Motions were calculated on the assumption that the directional-stability and the damping-in-yawing derivatives are functions of the angle of sideslip. The application of the Laplace transform to the calculation of an airplane motion when certain types of nonlinear derivatives are present is described in detail. The types of nonlinearities assumed correspond to the condition in which the values of the directional-stability and damping-in-yawing derivatives are zero for small angle of sideslip.

Ince-Strutt stability charts for ship parametric roll resonance in irregular waves

NASA Astrophysics Data System (ADS)

Zhang, Xiao; Yang, He-zhen; Xiao, Fei; Xu, Pei-ji

2017-08-01

Ince-Strutt stability chart of ship parametric roll resonance in irregular waves is conducted and utilized for the exploration of the parametric roll resonance in irregular waves. Ship parametric roll resonance will lead to large amplitude roll motion and even wreck. Firstly, the equation describing the parametric roll resonance in irregular waves is derived according to Grim's effective theory and the corresponding Ince-Strutt stability charts are obtained. Secondly, the differences of stability charts for the parametric roll resonance in irregular and regular waves are compared. Thirdly, wave phases and peak periods are taken into consideration to obtain a more realistic sea condition. The influence of random wave phases should be taken into consideration when the analyzed points are located near the instability boundary. Stability charts for different wave peak periods are various. Stability charts are helpful for the parameter determination in design stage to better adapt to sailing condition. Last, ship variables are analyzed according to stability charts by a statistical approach. The increase of the metacentric height will help improve ship stability.

Stability-indicating UPLC method for determination of Valsartan and their degradation products in active pharmaceutical ingredient and pharmaceutical dosage forms.

PubMed

Krishnaiah, Ch; Reddy, A Raghupathi; Kumar, Ramesh; Mukkanti, K

2010-11-02

A simple, precise, accurate stability-indicating gradient reverse phase ultra-performance liquid chromatographic (RP-UPLC) method was developed for the quantitative determination of purity of Valsartan drug substance and drug products in bulk samples and pharmaceutical dosage forms in the presence of its impurities and degradation products. The method was developed using Waters Aquity BEH C18 (100 mm x 2.1 mm, 1.7 microm) column with mobile phase containing a gradient mixture of solvents A and B. The eluted compounds were monitored at 225 nm, the run time was within 9.5 min, which Valsartan and its seven impurities were well separated. Valsartan was subjected to the stress conditions of oxidative, acid, base, hydrolytic, thermal and photolytic degradation. Valsartan was found to degrade significantly in acid and oxidative stress conditions and stable in base, hydrolytic and photolytic degradation conditions. The degradation products were well resolved from main peak and its impurities, proving the stability-indicating power of the method. The developed method was validated as per international conference on harmonization (ICH) guidelines with respect to specificity, linearity, limit of detection, limit of quantification, accuracy, precision and robustness. This method was also suitable for the assay determination of Valsartan in pharmaceutical dosage forms.

Long-Term Stage, Stage-Residual, and Width Data for Streams in the Piedmont Physiographic Region, Georgia

USGS Publications Warehouse

Riley, Jeffrey W.; Jacobson, Robert B.

2009-01-01

This report presents the data used to assess geomorphic adjustment of streams over time and to changing land-use conditions. Thirty-seven U.S. Geological Survey streamgages were selected within the Piedmont physiographic region of Georgia. Width, depth, stage, and discharge data from these streams were analyzed to assess channel stability and determine if systematic adjustments of channel morphology could be related to time or land use and land cover. Residual analyses of stage-discharge data were used to infer channel stability, which could then be used as an indicator of habitat stability. Streamgages, representing a gradient of urbanization, were selected to test hypotheses regarding stream stability and adjustment to urban conditions. Results indicate that 14 sites exhibited long-term channel stability, 11 were degrading, 6 were aggrading, and 6 showed variability in response over the study period.

Analysis of protein stability and ligand interactions by thermal shift assay.

PubMed

Huynh, Kathy; Partch, Carrie L

2015-02-02

Purification of recombinant proteins for biochemical assays and structural studies is time-consuming and presents inherent difficulties that depend on the optimization of protein stability. The use of dyes to monitor thermal denaturation of proteins with sensitive fluorescence detection enables rapid and inexpensive determination of protein stability using real-time PCR instruments. By screening a wide range of solution conditions and additives in a 96-well format, the thermal shift assay easily identifies conditions that significantly enhance the stability of recombinant proteins. The same approach can be used as an initial low-cost screen to discover new protein-ligand interactions by capitalizing on increases in protein stability that typically occur upon ligand binding. This unit presents a methodological workflow for small-scale, high-throughput thermal denaturation of recombinant proteins in the presence of SYPRO Orange dye. Copyright © 2015 John Wiley & Sons, Inc.

Determination of pore-scale hydrate phase equilibria in sediments using lab-on-a-chip technology.

PubMed

Almenningen, Stian; Flatlandsmo, Josef; Kovscek, Anthony R; Ersland, Geir; Fernø, Martin A

2017-11-21

We present an experimental protocol for fast determination of hydrate stability in porous media for a range of pressure and temperature (P, T) conditions. Using a lab-on-a-chip approach, we gain direct optical access to dynamic pore-scale hydrate formation and dissociation events to study the hydrate phase equilibria in sediments. Optical pore-scale observations of phase behavior reproduce the theoretical hydrate stability line with methane gas and distilled water, and demonstrate the accuracy of the new method. The procedure is applicable for any kind of hydrate transitions in sediments, and may be used to map gas hydrate stability zones in nature.

Role of anisotropy in determining stability of electrodeposition at solid-solid interfaces

NASA Astrophysics Data System (ADS)

Ahmad, Zeeshan; Viswanathan, Venkatasubramanian

2017-10-01

We investigate the stability of electrodeposition at solid-solid interfaces for materials exhibiting an anisotropic mechanical response. The stability of electrodeposition or resistance to the formation of dendrites is studied within a linear stability analysis. The deformation and stress equations are solved using the Stroh formalism and faithfully recover the boundary conditions at the interface. The stability parameter is used to quantify the stability of different solid-solid interfaces incorporating the full anisotropy of the elastic tensor of the two materials. Results show a high degree of variability in the stability parameter depending on the crystallographic orientation of the solids in contact, and point to opportunities for exploiting this effect in developing Li metal anodes.

[Stability study of oxaliplatin and doxorubicin for intraperitoneal administration with hyperthermia].

PubMed

Escudero-Ortiz, V; Duart-Duart, M J; Pérez-Ruixo, C; Pérez-Ruixo, J J; Valenzuela, B

2014-05-01

To evaluate the in vitro physicochemical stability of oxaliplatin and doxorubicin when the in vivo hyperthermic intraperitoneal conditions are reproduced. Three solutions were prepared, A (oxaliplatin 200 mg/L), B(doxorubicin 15 mg/L) and C (oxaliplatin 200 mg/L with doxorubicin 15mg/L) in glucose 5%. The three solutions were subjected to the maximum temperature reached in vivo (49° C) for two hours. Physical stability was focused on visual control of particles or precipitates in solutions, discharge of gases, odor and color. Samples were taken every 15 minutes and the chemical stability was evaluated by determining the concentration of oxaliplatin and doxorubicin remaining in the samples. Oxaliplatin concentrations were determined by atomic absorption graphite chamber while doxorubicin was determined by high performance liquid chromatography.The chemical stability criteria selected was the one described by the American Pharmacopoeia, which sets a permissible variation range between the 90-110% of the initial concentration. During the assay there was no appearance of particles, precipitates in the samples, discharge of gases, nor colour changes in the solutions. The samples showed a remaining concentration of oxaliplatin and doxorubicin within the 90-110% limit. The stability of the samples that follow to two cycles of freeze-thaw after hyperthermia was also found within the specified limits. A, B and c solutions in 5% glucose, are physically and chemically stable at 49° C for two hours. Under these conditions, these solutions could be used with guarantees of stability in patients with peritoneal carcinomatosis subsidiary of intraperitoneal hyperthermic chemotherapy based in these antineoplastic agents. Copyright AULA MEDICA EDICIONES 2014. Published by AULA MEDICA. All rights reserved.

Control of manganese dioxide particles resulting from in situ chemical oxidation using permanganate.

PubMed

Crimi, Michelle; Ko, Saebom

2009-02-01

In situ chemical oxidation using permanganate is an approach to organic contaminant site remediation. Manganese dioxide particles are products of permanganate reactions. These particles have the potential to deposit in the subsurface and impact the flow-regime in/around permanganate injection, including the well screen, filter pack, and the surrounding subsurface formation. Control of these particles can allow for improved oxidant injection and transport and contact between the oxidant and contaminants of concern. The goals of this research were to determine if MnO(2) can be stabilized/controlled in an aqueous phase, and to determine the dependence of particle stabilization on groundwater characteristics. Bench-scale experiments were conducted to study the ability of four stabilization aids (sodium hexametaphosphate (HMP), Dowfax 8390, xanthan gum, and gum arabic) in maintaining particles suspended in solution under varied reaction conditions and time. Variations included particle and stabilization aid concentrations, ionic content, and pH. HMP demonstrated the most promising results, as compared to xanthan gum, gum arabic, and Dowfax 8390 based on results of spectrophotometric studies of particle behavior, particle filtration, and optical measurements of particle size and zeta potential. HMP inhibited particle settling, provided for greater particle stability, and resulted in particles of a smaller average size over the range of experimental conditions evaluated compared to results for systems that did not include HMP. Additionally, HMP did not react unfavorably with permanganate. These results indicate that the inclusion of HMP in a permanganate oxidation system improves conditions that may facilitate particle transport.

Short-term action potential memory and electrical restitution: A cellular computational study on the stability of cardiac repolarization under dynamic pacing

PubMed Central

2018-01-01

Electrical restitution (ER) is a major determinant of repolarization stability and, under fast pacing rate, it reveals memory properties of the cardiac action potential (AP), whose dynamics have never been fully elucidated, nor their ionic mechanisms. Previous studies have looked at ER mainly in terms of changes in AP duration (APD) when the preceding diastolic interval (DI) changes and described dynamic conditions where this relationship shows hysteresis which, in turn, has been proposed as a marker of short-term AP memory and repolarization stability. By means of numerical simulations of a non-propagated human ventricular AP, we show here that measuring ER as APD versus the preceding cycle length (CL) provides additional information on repolarization dynamics which is not contained in the companion formulation. We focus particularly on fast pacing rate conditions with a beat-to-beat variable CL, where memory properties emerge from APD vs CL and not from APD vs DI and should thus be stored in APD and not in DI. We provide an ion-currents characterization of such conditions under periodic and random CL variability, and show that the memory stored in APD plays a stabilizing role on AP repolarization under pacing rate perturbations. The gating kinetics of L-type calcium current seems to be the main determinant of this safety mechanism. We also show that, at fast pacing rate and under otherwise identical pacing conditions, a periodically beat-to-beat changing CL is more effective than a random one in stabilizing repolarization. In summary, we propose a novel view of short-term AP memory, differentially stored between systole and diastole, which opens a number of methodological and theoretical implications for the understanding of arrhythmia development. PMID:29494628

Watershed Scale Shear Stress From Tethersonde Wind Profile Measurements Under Near Neutral and Unstable Atmospheric Stability

NASA Astrophysics Data System (ADS)

Parlange, M. B.; Katul, G. G.

1995-04-01

Mean wind speed profiles were measured in the atmospheric surface layer, using a tethersonde system, above the Ojai Valley Watershed in southern California. The valley is mainly planted with mature avocado and orange trees. The surface shear stress and latent and sensible heat fluxes were measured above the trees which are up to 9 m in height. Near-neutral wind speed profile measurements allowed the determination of the watershed surface roughness (z0 = 1.4 m) and the momentum displacement height (d0 = 7.0 m). The wind speed measurements obtained under unstable atmospheric stability were analyzed using Monin-Obukhov similarity theory. New stability correction functions proposed based on theory and experiments of Kader-Yaglom as well as the now classic Businger-Dyer type functions were tested. The watershed shear stress values calculated using the surface layer wind speed profiles with the new Monin-Obukhov stability functions were found to be improved in comparison with the values obtained with the Businger-Dyer functions under strongly unstable stability conditions. The Monin-Obukhov model with the Businger-Dyer stability correction function underpredicted the momentum flux by 25% under strongly unstable stability conditions, while the new Kader-Yaglom formulation compared well on average (R2 = 0.77) with the surface eddy correlation measurements for all atmospheric stability conditions. The unstable 100-m drag coefficient was found to be u*2/V1002 = 0.0182.

NETL- Severe Environment Corrosion Erosion Facility

ScienceCinema

None

2018-01-16

NETL's Severe Environment Corrosion Erosion Facility in Albany studies how new and old materials will stand up to new operating conditions. Work done in the lab supports NETL's oxy-fuel combustion oxidation work, refractory materials stability work, and the fuels program, in particular the hydrogen membrane materials stability work, to determine how best to upgrade existing power plants.

Current Protocols in Protein Science

PubMed Central

Huynh, Kathy

2015-01-01

The purification of recombinant proteins for biochemical assays and structural studies is time-consuming and presents inherent difficulties that depend on the optimization of protein stability. The use of dyes to monitor thermal denaturation of proteins with sensitive fluorescence detection enables the rapid and inexpensive determination of protein stability using real-time PCR instruments. By screening a wide range of solution conditions and additives in 96-well format, the thermal shift assay easily identifies conditions that significantly enhance the stability of recombinant proteins. The same approach can be used as a low cost, initial screen to discover new protein:ligand interactions by capitalizing on increases in protein stability that typically occur upon ligand binding. This unit presents a methodological workflow for the small-scale, high-throughout thermal denaturation of recombinant proteins in the presence of SYPRO Orange dye. PMID:25640896

The Effect of Mass Distribution on the Lateral Stability and Control Characteristics of an Airplane as Determined by Tests of a Model in the Free-Flight Tunnel

NASA Technical Reports Server (NTRS)

Seacord, Charles L; Campbell, John P.

1943-01-01

The effects of mass distribution on lateral stability and control characteristics of an airplane have been determined by flight tests of a model in the NACA free-flight tunnel. In the investigation, the rolling and yawing movements of inertia were increased from normal values to values up to five times normal. For each moment-of-inertia condition, combinations of dihedral and vertical-tail area representing a variety of airplane configurations were tested. The results of the flight tests of the model were correlated with calculated stability and control characteristics and, in general, good agreement was obtained. The tests showed the following effects of increased rolling and yawing moments of inertia: no appreciable change in spiral stability; reductions in oscillatory stability that were serious at high values of dihedral; a reduction in the sensitivity of the model to gust disturbances; and a reduction in rolling acceleration provided by the ailerons, which caused a marked increase in time to reach a given angle of bank. The general flight behavior of the model became worse with increasing moments of inertia but, with combinations of small effective dihedral and large vertical-tail area, satisfactory flight characteristics were obtained at all moment-of-inertia conditions.

Role of anisotropy in determining stability of electrodeposition at solid-solid interfaces

DOE PAGES

Ahmad, Zeeshan; Viswanathan, Venkatasubramanian

2017-10-24

Here, we investigate the stability of electrodeposition at solid-solid interfaces for materials exhibiting an anisotropic mechanical response. The stability of electrodeposition or resistance to the formation of dendrites is studied within a linear stability analysis. The deformation and stress equations are solved using the Stroh formalism and faithfully recover the boundary conditions at the interface. The stability parameter is used to quantify the stability of different solid-solid interfaces incorporating the full anisotropy of the elastic tensor of the two materials. Our results show a high degree of variability in the stability parameter depending on the crystallographic orientation of the solidsmore » in contact, and point to opportunities for exploiting this effect in developing Li metal anodes.« less

Effect of Flame Stabilizer Design on Performance and Exhaust Pollutants of a Two-Row Swirl-Can Combustor Operated to Near-Stoichiometric Conditions

NASA Technical Reports Server (NTRS)

Biaglow, James A.; Trout, Arthur M.

1977-01-01

Emissions and performance characteristics were determined for two full annulus modular combustors operated to near stoichiometric fuel air ratios. The tests were conducted to obtain stoichiometric data at inlet air temperatures from 756 to 894 K and to determine the effects of a flat plate circular flame stabilizer with upstream fuel injection and a contraswirl flame stabilizer with downstream fuel injection. Levels of unburned hydrocarbons were below 0.50 gram per kilogram of fuel for both combustors and thus there was no detectable difference in the two methods of fuel injection. The contraswirl flame stabilizer did not produce the level of mixing obtained with a flat plate circular flame stabilizer. It did produce higher levels of oxides of nitrogen, which peaked at a fuel air ratio of 0.037. For the flat plate circular flame stabilizer, oxides of nitrogen emission levels were still increasing with fuel air ratio to the maximum tested value of 0.045.

A general method to determine the stability of compressible flows

NASA Technical Reports Server (NTRS)

Guenther, R. A.; Chang, I. D.

1982-01-01

Several problems were studied using two completely different approaches. The initial method was to use the standard linearized perturbation theory by finding the value of the individual small disturbance quantities based on the equations of motion. These were serially eliminated from the equations of motion to derive a single equation that governs the stability of fluid dynamic system. These equations could not be reduced unless the steady state variable depends only on one coordinate. The stability equation based on one dependent variable was found and was examined to determine the stability of a compressible swirling jet. The second method applied a Lagrangian approach to the problem. Since the equations developed were based on different assumptions, the condition of stability was compared only for the Rayleigh problem of a swirling flow, both examples reduce to the Rayleigh criterion. This technique allows including the viscous shear terms which is not possible in the first method. The same problem was then examined to see what effect shear has on stability.

Stability properties of a general class of nonlinear dynamical systems

NASA Astrophysics Data System (ADS)

Gléria, I. M.; Figueiredo, A.; Rocha Filho, T. M.

2001-05-01

We establish sufficient conditions for the boundedness of the trajectories and the stability of the fixed points in a class of general nonlinear systems, the so-called quasi-polynomial vector fields, with the help of a natural embedding of such systems in a family of generalized Lotka-Volterra (LV) equations. A purely algebraic procedure is developed to determine such conditions. We apply our method to obtain new results for LV systems, by a reparametrization in time variable, and to study general nonlinear vector fields, originally far from the LV format.

Postural stability in the elderly during sensory perturbations and dual tasking: the influence of refractive blur.

PubMed

Anand, Vijay; Buckley, John G; Scally, Andy; Elliott, David B

2003-07-01

To determine the influence of refractive blur on postural stability during somatosensory and vestibular system perturbation and dual tasking. Fifteen healthy, elderly subjects (mean age, 71 +/- 5 years), who had no history of falls and had normal vision, were recruited. Postural stability during standing was assessed using a force platform, and was determined as the root mean square (RMS) of the center of pressure (COP) signal in the anterior-posterior (A-P) and medial-lateral directions collected over a 30-second period. Data were collected under normal standing conditions and with somatosensory and vestibular system perturbations. Measurements were repeated with an additional physical and/or cognitive task. Postural stability was measured under conditions of binocular refractive blur of 0, 1, 2, 4, and 8 D and with eyes closed. The data were analyzed with a population-averaged linear model. The greatest increases in postural instability were due to disruptions of the somatosensory and vestibular systems. Increasing refractive blur caused increasing postural instability, and its effect was greater when the input from the other sensory systems was disrupted. Performing an additional cognitive and physical task increased A-P RMS COP further. All these detrimental effects on postural stability were cumulative. The findings highlight the multifactorial nature of postural stability and indicate why the elderly, many of whom have poor vision and musculoskeletal and central nervous system degeneration, are at greater risk of falling. The findings also highlight that standing instability in both normal and perturbed conditions was significantly increased with refractive blur. Correcting visual impairment caused by uncorrected refractive error could be a useful intervention strategy to help prevent falls and fall-related injuries in the elderly.

A method to determine residue-specific unfolded-state pKa values from analysis of stability changes in single mutant cycles.

PubMed

Shen, Jana K

2010-06-02

It is now widely recognized that the unfolded state of a protein in equilibrium with the native state under folding conditions may contain significant residual structures. However, due to technical difficulties residue-specific interactions in the unfolded state remain elusive. Here we introduce a method derived from the Wyman-Tanford theory to determine residue-specific pK(a)'s in the unfolded state. This method requires equilibrium stability measurements of the wild type and single-point mutants in which titrable residues are replaced with charge-neutral ones under two pH conditions. Application of the proposed approach reveals a highly depressed pK(a) for Asp8 in the unfolded state of the NTL9 protein. Knowledge of unfolded-state pK(a)'s enables quantitative estimation of the unfolded-state electrostatic effects on protein stability. It also provides valuable benchmarks for the improvement of force fields and validation of microscopic information from molecular dynamics simulations.

Force-Test Investigation of the Stability and Control Characteristics of a 1/4-Scale Model of a Tilt-Wing Vertical-Take-Off-and-Landing Aircraft

NASA Technical Reports Server (NTRS)

Newsom, William A., Jr.; Tosti, Louis P.

1959-01-01

A wind-tunnel investigation has been made to determine the aerodynamic characteristics of a 1/4-scale model of a tilt-wing vertical-take-off-and-landing aircraft. The model had two 3-blade single-rotation propellers with hinged (flapping) blades mounted on the wing, which could be tilted from an incidence of 4 deg for forward flight to 86 deg for hovering flight. The investigation included measurements of both the longitudinal and lateral stability and control characteristics in both the normal forward flight and the transition ranges. Tests in the forward-flight condition were made for several values of thrust coefficient, and tests in the transition condition were made at several values of wing incidence with the power varied to cover a range of flight conditions from forward-acceleration (or climb) conditions to deceleration (or descent) conditions The control effectiveness of the all-movable horizontal tail, the ailerons and the differential propeller pitch control was also determined. The data are presented without analysis.

Transient improvements in fixational stability in strabismic amblyopes following bifoveal fixation and reduced interocular suppression.

PubMed

Raveendran, Rajkumar Nallour; Babu, Raiju J; Hess, Robert F; Bobier, William R

2014-03-01

To test the hypothesis that fixational stability of the amblyopic eye in strabismics will improve when viewing provides both bifoveal fixation and reduced inter-ocular suppression by reducing the contrast to the fellow eye. Seven strabismic amblyopes (Age: 29.2 ± 9 years; five esotropes and two exotropes) showing clinical characteristics of central suppression were recruited. Interocular suppression was measured by a global motion task. For each participant, a balance point was determined which defined contrast levels for each eye where binocular combination was optimal (interocular suppression minimal). When the balance point could not be determined, this participant was excluded. Bifoveal fixation was established by ocular alignment using a haploscope. Participants dichoptically viewed similar targets (a cross of 2.3° surrounded by a square of 11.3°) at 40 cm. Target contrasts presented to each eye were either high contrast (100% to both eyes) or balanced contrast (attenuated contrast in the fellow fixing eye). Fixation stability was measured over a 5 min period and quantified using bivariate contour ellipse areas in four different binocular conditions; unaligned/high contrast, unaligned/balance point, aligned/high contrast and aligned/balance point. Fixation stability was also measured in six control subjects (Age: 25.3 ± 4 years). Bifoveal fixation in the strabismics was transient (58.15 ± 15.7 s). Accordingly, fixational stability was analysed over the first 30 s using repeated measures anova. Post hoc analysis revealed that for the amblyopic subjects, the fixational stability of the amblyopic eye was significantly improved in aligned/high contrast (p = 0.01) and aligned/balance point (p < 0.01) conditions. Fixational stability of the fellow fixing eye was not different statistically across conditions. Bivariate contour ellipse areas of the amblyopic and fellow fixing eyes were therefore averaged for each amblyope in the four conditions and compared with normals. This averaged bivariate contour ellipse area was significantly greater (reduced fixational stability, p = 0.04) in amblyopes compared to controls except in the case of aligned and balanced contrast (aligned/balance point, p = 0.19). Fixation stability in the amblyopic eye appears to improve with bifoveal fixation and reduced interocular suppression. However, once initiated, bifoveal fixation is transient with the strabismic eye drifting away from foveal alignment, thereby increasing the angle of strabismus. © 2014 The Authors Ophthalmic & Physiological Optics © 2014 The College of Optometrists.

Dynamic stability and bifurcation analysis in fractional thermodynamics

NASA Astrophysics Data System (ADS)

Béda, Péter B.

2018-02-01

In mechanics, viscoelasticity was the first field of applications in studying geomaterials. Further possibilities arise in spatial non-locality. Non-local materials were already studied in the 1960s by several authors as a part of continuum mechanics and are still in focus of interest because of the rising importance of materials with internal micro- and nano-structure. When material instability gained more interest, non-local behavior appeared in a different aspect. The problem was concerned to numerical analysis, because then instability zones exhibited singular properties for local constitutive equations. In dynamic stability analysis, mathematical aspects of non-locality were studied by using the theory of dynamic systems. There the basic set of equations describing the behavior of continua was transformed to an abstract dynamic system consisting of differential operators acting on the perturbation field variables. Such functions should satisfy homogeneous boundary conditions and act as indicators of stability of a selected state of the body under consideration. Dynamic systems approach results in conditions for cases, when the differential operators have critical eigenvalues of zero real parts (dynamic stability or instability conditions). When the critical eigenvalues have non-trivial eigenspace, the way of loss of stability is classified as a typical (or generic) bifurcation. Our experiences show that material non-locality and the generic nature of bifurcation at instability are connected, and the basic functions of the non-trivial eigenspace can be used to determine internal length quantities of non-local mechanics. Fractional calculus is already successfully used in thermo-elasticity. In the paper, non-locality is introduced via fractional strain into the constitutive relations of various conventional types. Then, by defining dynamic systems, stability and bifurcation are studied for states of thermo-mechanical solids. Stability conditions and genericity conditions are presented for constitutive relations under consideration.

Influence of vibration modes on control system stabilization for space shuttle type vehicles

NASA Technical Reports Server (NTRS)

Greiner, H. G.

1972-01-01

An investigation was made to determine the feasibility of using conventional autopilot techniques to stabilize the vibration modes at the liftoff flight condition for two space shuttle configurations. One configuration is called the dual flyback vehicle in which both the orbiter and booster vehicles have wings and complete flyback capability. The other configuration is called the solid motor vehicle win which the orbiter only has flyback. The results of the linear stability analyses for each of the vehicles are summarized.

DIFFRACTION SYNCHRONIZATION OF LASERS,

DTIC Science & Technology

semiconductor lasers while suppressing parasitic generation in the plane of the mirror. The diffraction coupling coefficient of open resonators is calculated, and the stability conditions of the synchronized system is determined.

Potential phosphorus eutrophication mitigation strategy: Biochar carbon composition, thermal stability and pH influence phosphorus sorption

Treesearch

L.W. Ngatia; Y.P. Hsieh; D. Nemours; R. Fu; R.W. Taylor

2017-01-01

Phosphorus (P) eutrophication is a major pollution problem globally, with unprecedented amount of P emanating from agricultural sources. But little is known about the optimization of soil-biochar P sorption capacity. The study objective was to determine how biochar feedstocks and pyrolysis conditions influences carbon (C) thermal stability, C composition and pH and in...

Hi-alpha forebody design. Part 2: Determination of body shapes for positive directional stability

NASA Technical Reports Server (NTRS)

Ravi, R.; Mason, William H.

1991-01-01

Computational Fluid Dynamics (CFD) has been used to study aircraft forebody flowfields at low speed high angle-of-attack conditions with sideslip. The purpose is to define forebody geometries which provide good directional stability characteristics under these conditions. The flows of the F-5A forebody and Erickson forebody were recomputed with better and refined grids. The results were obtained using a modified version of cfl3d to solve either the Euler equations or the Reynolds equations employing a form of the Baldwin-Lomax turbulence model. Based on those results, we conclude that current CFD methods can be used to investigate the aerodynamic characteristics of forebodies to achieve desirable high angle-of-attack characteristics. An analytically defined generic forebody model is described, and a systematic study of forebody shapes was then conducted to determine which shapes promote a positive contribution to directional stability at high angle-of-attack. A novel way of presenting the results is used to illustrate how the positive contribution arises. Based on the results of this initial parametric study, some guidelines for aerodynamic design to promote positive directional stability are presented.

Wind-Tunnel Investigation of a 1/5-Scale Model of the Ryan XF2R Airplane

NASA Technical Reports Server (NTRS)

Wong, Park Y.

1947-01-01

Wind-tunnel tests on a 1/5-scale model of the Ryan XF2R airplane were conducted to determine the aerodynamic characteristics of the air intake for the front power plant, a General Electric TG-100 gas turbine, and to determine the stability and control characteristics of the airplane. The results indicated low-dynamic-pressure recover3- for the air intake to the TG-100 gas turbine rith the standard propeller in operation. Propeller cuffs were designed and tested for the purpose of impoving the dynamic-pressure recovery. Data obtained with the cuffs installed and the gap between the spinner an& the cuff sealed indicated a substantial gain in dynamic pressure recovery over that obtained with the standard propeller and with the cuffed propeller unsealed. Stability and control tests were conducted with the sealed cuffs installed on the propeller. The data from these tests indicated the following unsatisfactory characteristics for the airplane: 1. Marginal static longitudinal stability. 2. Inadequate directional stability and control. 3. Rudder-pedal-force reversal in the climb condition. 4. Negative dihedral effect in the power-on approach and wave-off conditions.

Application of a Modal Approach in Solving the Static Stability Problem for Electric Power Systems

NASA Astrophysics Data System (ADS)

Sharov, J. V.

2017-12-01

Application of a modal approach in solving the static stability problem for power systems is examined. It is proposed to use the matrix exponent norm as a generalized transition function of the power system disturbed motion. Based on the concept of a stability radius and the pseudospectrum of Jacobian matrix, the necessary and sufficient conditions for existence of the static margins were determined. The capabilities and advantages of the modal approach in designing centralized or distributed control and the prospects for the analysis of nonlinear oscillations and rendering the dynamic stability are demonstrated.

Theoretical limits on the stability of single-phase kesterite-Cu{sub 2}ZnSnS{sub 4}

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

Sarker, Pranab; Huda, Muhammad N., E-mail: huda@uta.edu; Al-Jassim, Mowafak M.

2015-01-21

The single-phase stability of Cu{sub 2}ZnSnS{sub 4} (CZTS), after an intrinsic defect was incorporated in it, has been examined here for the first time based on ab initio calculations. The stability analysis of such a non-stoichiometric-defect incorporated CZTS shows that the single-phase formation is unlikely at thermodynamic equilibrium conditions. In addition, the effective growth condition of CZTS is determined and quantified for all the elements (Cu-poor, Zn-rich, Sn-poor, and S-rich) to extract maximum photovoltaic efficiency from CZTS. These conditions promote (i) spontaneous formation of Cu vacancy (V{sub Cu}), which might benefit p-type conduction, and (ii) the co-existence of ZnS whilemore » suppressing other harmful defects and secondary phases. Further, the results presented here explain the unavailability of single-phase CZTS to date.« less

Stability Study of Algerian Nigella sativa Seeds Stored under Different Conditions

PubMed Central

Ahamad Bustamam, Muhammad Safwan; Hadithon, Kamarul Arifin; Rukayadi, Yaya; Lajis, Nordin

2017-01-01

In a study to determine the stability of the main volatile constituents of Nigella sativa seeds stored under several conditions, eight storage conditions were established, based on the ecological abiotic effects of air, heat, and light. Six replicates each were prepared and analyzed with Headspace-Gas Chromatography-Mass Spectrometry (HS-GC-MS) for three time points at the initial (1st day (0)), 14th (1), and 28th (2) day of storage. A targeted multivariate analysis of Principal Component Analysis revealed that the stability of the main volatile constituents of the whole seeds was better than that of the ground seeds. Exposed seeds, whole or ground, were observed to experience higher decrement of the volatile composition. These ecofactors of air, heat, and light are suggested to be directly responsible for the loss of volatiles in N. sativa seeds, particularly of the ground seeds. PMID:28255502

Wavelet modeling and prediction of the stability of states: the Roman Empire and the European Union

NASA Astrophysics Data System (ADS)

Yaroshenko, Tatyana Y.; Krysko, Dmitri V.; Dobriyan, Vitalii; Zhigalov, Maksim V.; Vos, Hendrik; Vandenabeele, Peter; Krysko, Vadim A.

2015-09-01

How can the stability of a state be quantitatively determined and its future stability predicted? The rise and collapse of empires and states is very complex, and it is exceedingly difficult to understand and predict it. Existing theories are usually formulated as verbal models and, consequently, do not yield sharply defined, quantitative prediction that can be unambiguously validated with data. Here we describe a model that determines whether the state is in a stable or chaotic condition and predicts its future condition. The central model, which we test, is that growth and collapse of states is reflected by the changes of their territories, populations and budgets. The model was simulated within the historical societies of the Roman Empire (400 BC to 400 AD) and the European Union (1957-2007) by using wavelets and analysis of the sign change of the spectrum of Lyapunov exponents. The model matches well with the historical events. During wars and crises, the state becomes unstable; this is reflected in the wavelet analysis by a significant increase in the frequency ω (t) and wavelet coefficients W (ω, t) and the sign of the largest Lyapunov exponent becomes positive, indicating chaos. We successfully reconstructed and forecasted time series in the Roman Empire and the European Union by applying artificial neural network. The proposed model helps to quantitatively determine and forecast the stability of a state.

Full-scale wind-tunnel test of the aeroelastic stability of a bearingless main rotor

NASA Technical Reports Server (NTRS)

Warmbrodt, W.; Mccloud, J., III; Sheffler, M.; Staley, J.

1981-01-01

The rotor studied in the wind tunnel had previously been flight tested on a BO-105 helicopter. The investigation was conducted to determine the rotor's aeroelastic stability characteristics in hover and at airspeeds up to 143 knots. These characteristics are compared with those obtained from whirl-tower and flight tests and predictions from a digital computer simulation. It was found that the rotor was stable for all conditions tested. At constant tip speed, shaft angle, and airspeed, stability increases with blade collective pitch setting. No significant change in system damping occurred that was attributable to frequency coalescence between the rotor inplane regressing mode and the support modes. Stability levels determined in the wind tunnel were of the same magnitude and yielded the same trends as data obtained from whirl-tower and flight tests.

A stability analysis of AVE-4 severe weather soundings

NASA Technical Reports Server (NTRS)

Johnson, D. L.

1982-01-01

The stability and vertical structure of an average severe storm sounding, consisting of both thermodynamic and wind vertical profiles, were investigated to determine if they could be distinguished from an average lag sounding taken 3 to 6 hours prior to severe weather occurrence. The term average is defined here to indicate the arithmetic mean of a parameter, as a function of altitude, determined from a large number of available observations taken either close to severe weather occurrence, or else more than 3 hours before it occurs. The investigative computations were also done to help determine if a severe storm forecast or index could possibly be used or developed. These mean vertical profiles of thermodynamic and wind parameters as a function of severity of the weather, determined from manually digitized radar (MDR) categories are presented. Profile differences and stability index differences are presented along with the development of the Johnson Lag Index (JLI) which is determined entirely upon environmental vertical parameter differences between conditions 3 hours prior to severe weather, and severe weather itself.

Electrolyte-stimulated biphasic dissolution profile and stability enhancement for tablets containing drug-polyelectrolyte complexes.

PubMed

Kindermann, Christoph; Matthée, Karin; Sievert, Frank; Breitkreutz, Jörg

2012-10-01

Recently introduced drug-polyelectrolyte complexes prepared by hot-melt extrusion should be processed to solid dosage forms with tailor-made release properties. Their potential of stability enhancement should be investigated. Milled hot-melt extruded naproxen-EUDRAGIT® E PO polyelectrolyte complexes were subsequently processed to double-layer tablets with varying complex loadings on a rotary-die press. Physicochemical interactions were studied under ICH guideline conditions and using the Gordon-Taylor equation. Sorption and desorption were determined to investigate the influence of moisture and temperature on the complex and related to stability tests under accelerated conditions. Naproxen release from the drug-polyelectrolyte complex is triggered by electrolyte concentration. Depending on the complex loading, phosphate buffer pH 6.8 stimulated a biphasic dissolution profile of the produced double-layer tablets: immediate release from the first layer with 65% loading and prolonged release from the second layer within 24 h (98.5% loading). XRPD patterns proved pseudopolymorphism for tablets containing the pure drug under common storage conditions whereas the drug-complex was stable in the amorphous state. Drug-polyelectrolyte complexes enable tailor-made dissolution profiles of solid dosage forms by electrolyte stimulation and increase stability under common storage conditions.

Curved-flow, rolling-flow, and oscillatory pure-yawing wind-tunnel test methods for determination of dynamic stability derivatives

NASA Technical Reports Server (NTRS)

Chambers, J. R.; Grafton, S. B.; Lutze, F. H.

1981-01-01

The test capabilities of the Stability Wind Tunnel of the Virginia Polytechnic Institute and State University are described, and calibrations for curved and rolling flow techniques are given. Oscillatory snaking tests to determine pure yawing derivatives are considered. Representative aerodynamic data obtained for a current fighter configuration using the curved and rolling flow techniques are presented. The application of dynamic derivatives obtained in such tests to the analysis of airplane motions in general, and to high angle of attack flight conditions in particular, is discussed.

High-Speed Wind-Tunnel Investigation of the Lateral Stability Characteristics of a 0.10-Scale Model of the Grumman XF9F-2 Airplane, TED No. NACA DE 301

NASA Technical Reports Server (NTRS)

Polhamus, Edward C.; King, Thomas J., Jr.

1949-01-01

An investigation was made in the Langley high-speed 7- by 10-foot tunnel to determine the high-speed lateral and directional stability characteristics of a 0.10-scale model of the Grumman XF9F-2 airplane in the Mach number range from 0.40 to 0.85. The results indicate that static lateral and directional stability is present throughout the Mach number range investigated although in the Mach number range from 0.75 to 0.85 there is an appreciable decrease in rolling moment due to sideslip. Calculations of the dynamic stability indicate that according to current flying-quality requirements the damping of the lateral oscillation, although probably satisfactory for the sea-level condition, may not be satisfactory for the majority of the altitude conditions investigated

Quality control of anti-tuberculosis FDC formulations in the global market: part II-accelerated stability studies.

PubMed

Ashokraj, Y; Kohli, G; Kaul, C L; Panchagnula, R

2005-11-01

To determine the quality and performance of rifampicin (RMP) containing fixed-dose combination (FDC) formulations of anti-tuberculosis drugs sourced from the international market with respect to physical, chemical and dissolution properties after storage at accelerated stability conditions (40 degrees C/75% relative humidity) and to identify appropriate storage specifications. Formulations across different companies and combinations were subjected to 6-month accelerated stability testing in packaging conditions recommended by the manufacturer. Various pharmacopeial and nonpharmacopeial tests for tablets were performed for 3- and 6-month samples. All the formulations were found to be stable, where extent of dissolution was within +/- 10% of that of the initial value, and all formulations passed the pharmacopeial limits for assay and content uniformity of 90-110% and +/- 15% of average drug content, respectively. Good quality RMP-containing FDCs that remain stable after 6-month accelerated stability testing are available in the marketplace.

Effect of light, packaging condition and dark storage durations on colour and lipid oxidative stability of cooked ham.

PubMed

Haile, Demewez Moges; De Smet, Stefaan; Claeys, Erik; Vossen, Els

2013-04-01

The colour and lipid oxidative stability of sliced cooked ham stored at 4 °C were studied in relation to dark storage duration, lighting and packaging conditions. Colour stability was monitored by instrumental colour measurement (CIE L*a*b* colour space) whereas lipid stability was measured by the determination of the 2-thiobarbituric acid reactive substances (TBARS). A significantly higher discoloration observed in products wrapped in foil and kept in light than products wrapped in foil and kept in dark. Colour loss was estimated by loss of redness (a*), a*/b*, nitrosomyoglobin, chroma (C); or increase of lightness (L*), MetMb, hue angle (H°). Colour loss was more dependent upon photochemical process than dark storage duration and packaging types. Lipid oxidation was not significantly affected by light exposure. However lipid oxidation was significantly affected by dark storage duration as noticed from better lipid stability of products stored for short duration in dark. Better colour stability was observed on products packed in MAP with less residual oxygen.

Preformulation considerations for controlled release dosage forms. Part II. Selected candidate support.

PubMed

Chrzanowski, Frank

2008-01-01

Practical examples of preformulation support of the form selected for formulation development are provided using several drug substances (DSs). The examples include determination of the solubilities vs. pH particularly for the range pH 1 to 8 because of its relationship to gastrointestinal (GI) conditions and dissolution method development. The advantages of equilibrium solubility and trial solubility methods are described. The equilibrium method is related to detecting polymorphism and the trial solubility method, to simplifying difficult solubility problems. An example of two polymorphs existing in mixtures of DS is presented in which one of the forms is very unstable. Accelerating stability studies are used in conjunction with HPLC and quantitative X-ray powder diffraction (QXRD) to demonstrate the differences in chemical and polymorphic stabilities. The results from two model excipient compatibility methods are compared to determine which has better predictive accuracy for room temperature stability. A DSC (calorimetric) method and an isothermal stress with quantitative analysis (ISQA) method that simulates wet granulation conditions were compared using a 2 year room temperature sample set as reference. An example of a pH stability profile for understanding stability and extrapolating stability to other environments is provided. The pH-stability of omeprazole and lansoprazole, which are extremely unstable in acidic and even mildly acidic conditions, are related to the formulation of delayed release dosage forms and the resolution of the problem associated with free carboxyl groups from the enteric coating polymers reacting with the DSs. Dissolution method requirements for CR dosage forms are discussed. The applicability of a modified disintegration time (DT) apparatus for supporting CR dosage form development of a pH sensitive DS at a specific pH such as duodenal pH 5.6 is related. This method is applicable for DSs such as peptides, proteins, enzymes and natural products where physical observation can be used in place of a difficult to perform analytical method, saving resources and providing rapid preformulation support.

Stochastic stability of parametrically excited random systems

NASA Astrophysics Data System (ADS)

Labou, M.

2004-01-01

Multidegree-of-freedom dynamic systems subjected to parametric excitation are analyzed for stochastic stability. The variation of excitation intensity with time is described by the sum of a harmonic function and a stationary random process. The stability boundaries are determined by the stochastic averaging method. The effect of random parametric excitation on the stability of trivial solutions of systems of differential equations for the moments of phase variables is studied. It is assumed that the frequency of harmonic component falls within the region of combination resonances. Stability conditions for the first and second moments are obtained. It turns out that additional parametric excitation may have a stabilizing or destabilizing effect, depending on the values of certain parameters of random excitation. As an example, the stability of a beam in plane bending is analyzed.

Impact of Storage Conditions on the Stability of Predominant Phenolic Constituents and Antioxidant Activity of Dried Piper betle Extracts.

PubMed

Ali, Ameena; Chong, Chien Hwa; Mah, Siau Hui; Abdullah, Luqman Chuah; Choong, Thomas Shean Yaw; Chua, Bee Lin

2018-02-23

The phenolic constituents in Piper betle are well known for their antioxidant potential; however, current literature has very little information on their stability under the influence of storage factors. Present study evaluated the stability of total phenolic content (TPC) and antioxidant activity together with individual phenolic constituents (hydroxychavicol, eugenol, isoeugenol and allylpyrocatechol 3,4-diacetate) present in dried Piper betle 's extract under different storage temperature of 5 and 25 °C with and without light for a period of six months. Both light and temperature significantly influenced TPC and its corresponding antioxidant activity over time. More than 95% TPC and antioxidant activity was retained at 5 °C in dark condition after 180 days of storage. Hydroxychavicol demonstrated the best stability with no degradation while eugenol and isoeugenol displayed moderate stability in low temperature (5 °C) and dark conditions. 4-allyl-1,2-diacetoxybenzene was the only compound that underwent complete degradation. A new compound, 2,4-di- tert -butylphenol, was detected after five weeks of storage only in the extracts exposed to light. Both zero-order and first-order kinetic models were adopted to describe the degradation kinetics of the extract's antioxidant activity. Zero-order displayed better fit with higher correlation coefficients ( R ² = 0.9046) and the half-life was determined as 62 days for the optimised storage conditions (5 °C in dark conditions).

Validation of a liquid chromatography method for the simultaneous determination of sulfadimethoxine and trimethoprim and application to a stability study.

PubMed

Louati, K; Mistiri, F; Kallel, M; Safta, F

2010-03-01

A liquid chromatography method is described for the simultaneous determination of sulfadimetoxine and trimethoprim from a veterinary formulation at the proportion of 187 mg and 40 mg respectively in presence of some excipient. The solution was subjected to different International Conference On Harmonisation prescribed stress conditions (hydrolysis, oxidation and photolysis). A stability-indicating high-performance liquid chromatography method was developed for the analysis of active substances in presence of their major degradation products. It involved a Knauer Eurospher C18 thermostated column at 25 degrees C, and 9.57 mM phosphate buffer (pH adjusted to 2.0 with orthophosphoric acid)-acetonitrile (70:30 v/v) as mobile phase. The mobile phase flow rate and sample volume injected were 1.2 mL/min and 20 microL, respectively. The selected wavelength for the determination was 248 nm. The method was validated for linearity, precision, accuracy and specificity, and then applied to a stability study of sulfadimetoxine and trimethoprim in the veterinary solution packaged in high density polyethylene plastic bottles of 1 L and 100 mL thermosealed and no thermosealed and corked by a white cap, at both accelerated and long-term conditions required by the International Conference On Harmonisation. The method developed, which separates all of the most degradation products formed under variety of conditions, proved to be simple, accurate, precise and specific. The results of the stress degradation show that the solution is more sensitive to hydrolysis. The stability studies carried out on three batches of each presentation show that the finished product remains stable for six months. Copyright 2010 Elsevier Masson SAS. All rights reserved.

Stability studies of amphetamine and ephedrine derivatives in urine.

PubMed

Jiménez, C; de la Torre, R; Ventura, M; Segura, J; Ventura, R

2006-10-20

Knowledge of the stability of drugs in biological specimens is a critical consideration for the interpretation of analytical results. Identification of proper storage conditions has been a matter of concern for most toxicology laboratories (both clinical and forensic), and the stability of drugs of abuse has been extensively studied. This concern should be extended to other areas of analytical chemistry like antidoping control. In this work, the stability of ephedrine derivatives (ephedrine, norephedrine, methylephedrine, pseudoephedrine, and norpseudoephedrine), and amphetamine derivatives (amphetamine, methamphetamine, 3,4-methylenedioxyamphetamine (MDA), and 3,4-methylenedioxymethamphetamine (MDMA)) in urine has been studied. Spiked urine samples were prepared for stability testing. Urine samples were quantified by GC/NPD or GC/MS. The homogeneity of each batch of sample was verified before starting the stability study. The stability of analytes was evaluated in sterilized and non-sterilized urine samples at different storage conditions. For long-term stability testing, analyte concentration in urine stored at 4 degrees C and -20 degrees C was determined at different time intervals for 24 months for sterile urine samples, and for 6 months for non-sterile samples. For short-term stability testing, analyte concentration was evaluated in liquid urine stored at 37 degrees C for 7 days. The effect of repeated freezing (at -20 degrees C) and thawing (at room temperature) was also studied in sterile urine for up to three cycles. No significant loss of the analytes under study was observed at any of the investigated conditions. These results show the feasibility of preparing reference materials containing ephedrine and amphetamine derivatives to be used for quality control purposes.

Core stability training: applications to sports conditioning programs.

PubMed

Willardson, Jeffrey M

2007-08-01

In recent years, fitness practitioners have increasingly recommended core stability exercises in sports conditioning programs. Greater core stability may benefit sports performance by providing a foundation for greater force production in the upper and lower extremities. Traditional resistance exercises have been modified to emphasize core stability. Such modifications have included performing exercises on unstable rather than stable surfaces, performing exercises while standing rather than seated, performing exercises with free weights rather than machines, and performing exercises unilaterally rather than bilaterally. Despite the popularity of core stability training, relatively little scientific research has been conducted to demonstrate the benefits for healthy athletes. Therefore, the purpose of this review was to critically examine core stability training and other issues related to this topic to determine useful applications for sports conditioning programs. Based on the current literature, prescription of core stability exercises should vary based on the phase of training and the health status of the athlete. During preseason and in-season mesocycles, free weight exercises performed while standing on a stable surface are recommended for increases in core strength and power. Free weight exercises performed in this manner are specific to the core stability requirements of sports-related skills due to moderate levels of instability and high levels of force production. Conversely, during postseason and off-season mesocycles, Swiss ball exercises involving isometric muscle actions, small loads, and long tension times are recommended for increases in core endurance. Furthermore, balance board and stability disc exercises, performed in conjunction with plyometric exercises, are recommended to improve proprioceptive and reactive capabilities, which may reduce the likelihood of lower extremity injuries.

Pyrite Stability Under Venus Surface Conditions

NASA Astrophysics Data System (ADS)

Kohler, E.; Craig, P.; Port, S.; Chevrier, V.; Johnson, N.

2015-12-01

Radar mapping of the surface of Venus shows areas of high reflectivity in the Venusian highlands, increasing to 0.35 ± 0.04 to 0.43 ± 0.05 in the highlands from the planetary average of 0.14 ± 0.03. Iron sulfides, specifically pyrite (FeS2), can explain the observed high reflectivity. However, several studies suggest that pyrite is not stable under Venusian conditions and is destroyed on geologic timescales. To test the stability of pyrite on the Venusian surface, pyrite was heated in the Venus simulation chamber at NASA Goddard Space Flight Center to average Venusian surface conditions, and separately to highland conditions under an atmosphere of pure CO2 and separately under an atmosphere of 96.5% CO2, 3.5% N2 and 150 ppm SO2. After each run, the samples were weighed and analyzed using X-Ray Diffraction (XRD) to identify possible phase changes and determine the stability of pyrite under Venusian surface conditions. Under a pure CO2 atmosphere, the Fe in pyrite oxidizes to form hematite which is more stable at higher temperatures corresponding to the Venusian lowlands. Magnetite is the primary iron oxide that forms at lower temperatures corresponding to the radar-bright highlands. Our experiments also showed that the presence of atmospheric SO2 inhibits the oxidation of pyrite, increasing its stability under Venusian conditions, especially those corresponding to the highlands. This indicates that the relatively high level of SO2 in the Venusian atmosphere is key to the stability of pyrite, making it a possible candidate for the bright radar signal in the Venusian highlands.

Theoretical and experimental research in aeroelastic stability of an advanced bearingless rotor for future helicopters

NASA Technical Reports Server (NTRS)

Wang, James M.

1991-01-01

The aeroelastic stability of a shaft-fixed bearingless rotor is analyzed in wind-tunnel tests for a wide range of operating conditions in order to determine whether such a system could be made aeroelastically stable without incorporating auxiliary dampers. The model rotor and blade properties are determined and used as an input to a bearingless-rotor analysis. Theoretical predictions are compared with experimental results in hover and forward flights. The analysis predicts the lag mode damping satisfactorily for collective pitch between 5 deg and 10 deg; however, the quasi-steady linear aerodynamic modeling overpredicts the damping values for higher collective pitch settings. It is noted that soft blade pitch links improve aeroelastic stability in hover and at low advance ratio.

Modelling and stability analysis of switching impulsive power systems with multiple equilibria

NASA Astrophysics Data System (ADS)

Zhu, Liying; Qiu, Jianbin; Chadli, Mohammed

2017-12-01

This paper tries to model power systems accompanied with a series of faults in the form of switched impulsive Hamiltonian systems (SIHSs) with multiple equilibria (ME) and unstable subsystems (US), and then analyze long-term stability issues of the power systems from the viewpoint of mathematics. According to the complex phenomena of switching actions of stages and generators, impulses of state, and existence of multiple equilibria, this paper first introduces an SIHS with ME and US to formulate a switching impulsive power system composed of an active generator, a standby generator, and an infinite load. Then, based on special system structures, a unique compact region containing all ME is determined, and novel stability concepts of region stability (RS), asymptotic region stability (ARS), and exponential region stability (ERS) are defined for such SIHS with respect to the region. Third, based on the introduced stability concepts, this paper proposes a necessary and sufficient condition of RS and ARS and a sufficient condition of ERS for the power system with respect to the region via the maximum energy function method. Finally, numerical simulations are carried out for a power system to show the effectiveness and practicality of the obained novel results.

Stability-Indicating HPLC Determination of Gemcitabine in Pharmaceutical Formulations

PubMed Central

Singh, Rahul; Shakya, Ashok K.; Naik, Rajashri; Shalan, Naeem

2015-01-01

A simple, sensitive, inexpensive, and rapid stability indicating high performance liquid chromatographic method has been developed for determination of gemcitabine in injectable dosage forms using theophylline as internal standard. Chromatographic separation was achieved on a Phenomenex Luna C-18 column (250 mm × 4.6 mm; 5μ) with a mobile phase consisting of 90% water and 10% acetonitrile (pH 7.00 ± 0.05). The signals of gemcitabine and theophylline were recorded at 275 nm. Calibration curves were linear in the concentration range of 0.5–50 μg/mL. The correlation coefficient was 0.999 or higher. The limit of detection and limit of quantitation were 0.1498 and 0.4541 μg/mL, respectively. The inter- and intraday precision were less than 2%. Accuracy of the method ranged from 100.2% to 100.4%. Stability studies indicate that the drug was stable to sunlight and UV light. The drug gives 6 different hydrolytic products under alkaline stress and 3 in acidic condition. Aqueous and oxidative stress conditions also degrade the drug. Degradation was higher in the alkaline condition compared to other stress conditions. The robustness of the methods was evaluated using design of experiments. Validation reveals that the proposed method is specific, accurate, precise, reliable, robust, reproducible, and suitable for the quantitative analysis. PMID:25838825

Stability of GNSS Monumentation: Analysis of Co-Located Monuments in the UNAVCO Plate Boundary Observatory

NASA Astrophysics Data System (ADS)

Blume, F.; Herring, T.; Mattioli, G. S.; Feaux, K.; Walls, C. P.; Austin, K. E.; Dittmann, S. T.

2017-12-01

Geodetic-quality permanent GNSS stations have used a number of different monument styles for the purpose of ensuring that the motions of the GNSS antenna reflect those of the Earth's crust while minimizing non-tectonic motions near the surface. Monuments range from simple masts mounted on buildings or drilled into bedrock, costing a few hundred dollars to machine-drilled-braced monuments in soil costing tens of thousands. The stability of an individual monument will depend on its design, the construction techniques used to install it, and the local surface geology where it is installed. Previous studies have separately investigated pairs of identical monuments at a single site, monument type performance using global statistical analysis, and multiple monument styles at a single site, yet the stability of different monument types in similar geologic conditions has not been adequately determined. To better characterize the stability of various monument styles in diverse geologic conditions UNAVCO constructed two additional monuments at five existing PBO stations in 2013. Deep drilled-braced, short drilled-braced, and single mast type monuments were installed at sites with bedrock at the surface; deep drilled-braced, short driven-braced and pillar type monuments were installed at sites with alluvium or soil at the surface. The sites include a variety of geographic, hydrologic, and geologic conditions. Data collected from the PBO Multi-Monument Experiment have been analyzed using a variety of methods. Each site is characterized using quality-control parameters such as multipath, signal-to-noise and previously determined seasonal variations. High-precision processing by PBO Analysis Centers with GAMIT and GIPSY use regional and global schemes and yield time-series with millimeter-level that determine noise content, overall site stability relative to other PBO sites and differential motions between the individual monuments. Sub-millimeter results from single-frequency short-baseline processing efforts show further details of monument performance. Results show that while local site characteristics may dominate time-series stability, braced monuments outperform pillars in sediments, and an inexpensive mast installed in bedrock can be as stable as an expensive drilled-braced monument.

Postural stability changes in the elderly with cataract simulation and refractive blur.

PubMed

Anand, Vijay; Buckley, John G; Scally, Andy; Elliott, David B

2003-11-01

To determine the influence of cataractous and refractive blur on postural stability and limb-load asymmetry (LLA) and to establish how postural stability changes with the spatial frequency and contrast of the visual stimulus. Thirteen elderly subjects (mean age, 70.76 +/- 4.14 [SD] years) with no history of falls and normal vision were recruited. Postural stability was determined as the root mean square [RMS] of the center of pressure (COP) signal in the anterior-posterior (A-P) and medial-lateral directions and LLA was determined as the ratio of the average body weight placed on the more-loaded limb to the less-loaded limb, recorded during a 30-second period. Data were collected under normal standing conditions and with somatosensory system input disrupted. Measurements were repeated with four visual targets with high (8 cyc/deg) or low (2 cyc/deg) spatial frequency and high (Weber contrast, approximately 95%) or low (Weber contrast, approximately 25%) contrast. Postural stability was measured under conditions of binocular refractive blur of 0, 1, 2, 4, and 8 D and with cataract simulation. The data were analyzed in a population-averaged linear model. The cataract simulation caused significant increases in postural instability equivalent to that caused by 8-D blur conditions, and its effect was greater when the input from the somatosensory system was disrupted. High spatial frequency targets increased postural instability. Refractive blur, cataract simulation, or eye closure had no effect on LLA. Findings indicate that cataractous and refractive blur increase postural instability, and show why the elderly, many of whom have poor vision along with musculoskeletal and central nervous system degeneration, are at greater risk of falling. Findings also highlight that changes in contrast sensitivity rather than resolution changes are responsible for increasing postural instability. Providing low spatial frequency information in certain environments may be useful in maintaining postural stability. Correcting visual impairment caused by uncorrected refractive error and cataracts could be a useful intervention strategy to help prevent falls and fall-related injuries in the elderly.

Hydroxide based Benzyltrimethylammonium degradation: Quantification of rates and degradation technique development

DOE PAGES

Sturgeon, Matthew R.; Macomber, Clay S.; Engtrakul, Chaiwat; ...

2015-01-21

Anion exchange membranes (AEMs) are of interest as hydroxide conducting polymer electrolytes in electrochemical devices like fuel cells and electrolyzers. AEMs require hydroxide stable covalently tetherable cations to ensure required conductivity. Benzyltrimethylammonium (BTMA) has been the covalently tetherable cation that has been most often employed in anion exchange membranes because it is reasonably basic, compact (limited number of atoms per charge), and easily/cheaply synthesized. Several reports exist that have investigated hydroxide stability of BTMA under specific conditions, but consistency within these reports and comparisons between them have not yet been made. While the hydroxide stability of BTMA has been believedmore » to be a limitation for AEMs, this stability has not been thoroughly reported. In this paper, we have found that several methods reported have inherent flaws in their findings due to the difficulty of performing degradation experiments at high temperature and high pH. In order to address these shortcomings, we have developed a reliable, standardized method of determining cation degradation under conditions similar/relevant to those expected in electrochemical devices. The experimental method has been employed to determine BTMA stabilities at varying cation concentrations and elevated temperatures, and has resulted in improved experimental accuracy and reproducibility. Finally and most notably, these results have shown that BTMA is quite stable at 80°C (half-life of ~4 years), a significant increase in stability over what had been reported previously.« less

On the manifestation of coexisting nontrivial equilibria leading to potential well escapes in an inhomogeneous floating body

NASA Astrophysics Data System (ADS)

Sequeira, Dane; Wang, Xue-She; Mann, B. P.

2018-02-01

This paper examines the bifurcation and stability behavior of inhomogeneous floating bodies, specifically a rectangular prism with asymmetric mass distribution. A nonlinear model is developed to determine the stability of the upright and tilted equilibrium positions as a function of the vertical position of the center of mass within the prism. These equilibria positions are defined by an angle of rotation and a vertical position where rotational motion is restricted to a two dimensional plane. Numerical investigations are conducted using path-following continuation methods to determine equilibria solutions and evaluate stability. Bifurcation diagrams and basins of attraction that illustrate the stability of the equilibrium positions as a function of the vertical position of the center of mass within the prism are generated. These results reveal complex stability behavior with many coexisting solutions. Static experiments are conducted to validate equilibria orientations against numerical predictions with results showing good agreement. Dynamic experiments that examine potential well hopping behavior in a waveflume for various wave conditions are also conducted.

Estimation of Aerodynamic Stability Derivatives for Space Launch System and Impact on Stability Margins

NASA Technical Reports Server (NTRS)

Pei, Jing; Wall, John

2013-01-01

This paper describes the techniques involved in determining the aerodynamic stability derivatives for the frequency domain analysis of the Space Launch System (SLS) vehicle. Generally for launch vehicles, determination of the derivatives is fairly straightforward since the aerodynamic data is usually linear through a moderate range of angle of attack. However, if the wind tunnel data lacks proper corrections then nonlinearities and asymmetric behavior may appear in the aerodynamic database coefficients. In this case, computing the derivatives becomes a non-trivial task. Errors in computing the nominal derivatives could lead to improper interpretation regarding the natural stability of the system and tuning of the controller parameters, which would impact both stability and performance. The aerodynamic derivatives are also provided at off nominal operating conditions used for dispersed frequency domain Monte Carlo analysis. Finally, results are shown to illustrate that the effects of aerodynamic cross axis coupling can be neglected for the SLS configuration studied

Molecular cloning and expression of a gene for a factor which stabilizes formation of inhibitor-mitochondrial ATPase complex from Saccharomyces cerevisiae.

PubMed

Akashi, A; Yoshida, Y; Nakagoshi, H; Kuroki, K; Hashimoto, T; Tagawa, K; Imamoto, F

1988-10-01

Stabilizing factor, a 9 kDa protein, stabilizes and facilitates formation of the complex between mitochondrial ATP synthase and its intrinsic inhibitor protein. A clone containing the gene encoding the 9 kDa protein was selected from a yeast genomic library to determine the structure of its precursor protein. As deduced from the nucleotide sequence, the precursor of the yeast 9 kDa stabilizing factor contains 86 amino acid residues and has a molecular weight of 10,062. From the predicted sequence we infer that the stabilizing factor precursor contains a presequence of 23 amino acid residues at its amino terminus. We also used S1 mapping to determine the initiation site of transcription under glucose-repressed or derepressed conditions. These experiments suggest that transcription of this gene starts at three different sites and that only one of them is not affected by the presence of glucose.

Organic Complexation of Dissolved Copper and Iron from Shipboard Incubations in the Central California Current System: Investigating the Impacts of Light Conditions and Phytoplankton Growth on Iron- and Copper-Binding Ligand Characteristics

NASA Astrophysics Data System (ADS)

Mellett, T.; Parker, C.; Brown, M.; Coale, T.; Duckham, C.; Chappell, D.; Maldonado, M. T.; Bruland, K. W.; Buck, K. N.

2016-02-01

Two shipboard incubation experiments were carried out in July of 2014 to investigate potential sources and sinks of iron- and copper-binding organic ligands in the surface ocean. Seawater for the experiments was collected from the central California Current System (cCCS) and incubated under varying light conditions and in the presence and absence of natural phytoplankton communities. Incubation treatments were sampled over a period of up to 3 days for measurements of total dissolved copper and iron, and for the concentration and conditional stability constants of copper- and iron-binding organic ligands. Dissolved copper and iron were determined by inductively coupled plasma-mass spectrometry (ICP-MS) following preconcentration on a Nobias PA1 resin. Organic ligand characteristics for iron and copper were determined using a method of competitive ligand exchange-absorptive cathodic stripping voltammetry (CLE-ACSV) with the added competing ligand salicylaldoxime. Trends in ligand concentrations and conditional stability constants across the different treatments and over the course of the incubation experiments will be presented.

Study on the influences of reduction temperature on nickel-yttria-stabilized zirconia solid oxide fuel cell anode using nickel oxide-film electrode

NASA Astrophysics Data System (ADS)

Jiao, Zhenjun; Ueno, Ai; Suzuki, Yuji; Shikazono, Naoki

2016-10-01

In this study, the reduction processes of nickel oxide at different temperatures were investigated using nickel-film anode to study the influences of reduction temperature on the initial performances and stability of nickel-yttria-stabilized zirconia anode. Compared to conventional nickel-yttria-stabilized zirconia composite cermet anode, nickel-film anode has the advantage of direct observation at nickel-yttria-stabilized zirconia interface. The microstructural changes were characterized by scanning electron microscopy. The reduction process of nickel oxide is considered to be determined by the competition between the mechanisms of volume reduction in nickel oxide-nickel reaction and nickel sintering. Electrochemical impedance spectroscopy was applied to analyze the time variation of the nickel-film anode electrochemical characteristics. The anode performances and microstructural changes before and after 100 hours discharging and open circuit operations were analyzed. The degradation of nickel-film anode is considered to be determined by the co-effect between the nickel sintering and the change of nickel-yttria-stabilized zirconia interface bonding condition.

A miniaturized technique for assessing protein thermodynamics and function using fast determination of quantitative cysteine reactivity.

PubMed

Isom, Daniel G; Marguet, Philippe R; Oas, Terrence G; Hellinga, Homme W

2011-04-01

Protein thermodynamic stability is a fundamental physical characteristic that determines biological function. Furthermore, alteration of thermodynamic stability by macromolecular interactions or biochemical modifications is a powerful tool for assessing the relationship between protein structure, stability, and biological function. High-throughput approaches for quantifying protein stability are beginning to emerge that enable thermodynamic measurements on small amounts of material, in short periods of time, and using readily accessible instrumentation. Here we present such a method, fast quantitative cysteine reactivity, which exploits the linkage between protein stability, sidechain protection by protein structure, and structural dynamics to characterize the thermodynamic and kinetic properties of proteins. In this approach, the reaction of a protected cysteine and thiol-reactive fluorogenic indicator is monitored over a gradient of temperatures after a short incubation time. These labeling data can be used to determine the midpoint of thermal unfolding, measure the temperature dependence of protein stability, quantify ligand-binding affinity, and, under certain conditions, estimate folding rate constants. Here, we demonstrate the fQCR method by characterizing these thermodynamic and kinetic properties for variants of Staphylococcal nuclease and E. coli ribose-binding protein engineered to contain single, protected cysteines. These straightforward, information-rich experiments are likely to find applications in protein engineering and functional genomics. Copyright © 2010 Wiley-Liss, Inc.

ON THE RELATIVE STABILITY OF ALUMINUM, TITANIUM, VANADIUM, IRON, AND COPPER TARTRATE COMPLEXES IN ALKALI MEDIA (in Russian)

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

Pyatnitskii, I.V.; Kostyshina, A.P.

1959-06-01

The stability of aluminum, copper, iron, titunium, and vanadium tartrate complexes was determined using bond magnitudes as criteria (the ratio between the concentrations of complexed and free ions at a certain standard acid condition). A method is suggested for determining the ratio of the bonds combining the complexes of two metals. The partition constaats of aluminum, copper, iron(III), and vanadium hydroxyquinolinates between the aqueous solution and chloroform were 2.6 x 10/sup -33/, 7.3 x 10/sup -23/, 1.5 x 10/sup -37/, and 4.2 x 10/sup -23/, respectively. The relative stability of copper and iron turtrate complexes in alkali solution (pH 13)more » and aluminum, iron(III), titunium, and vanadium(IV) tartrate complexes in ammonium solution (pH 9.5) was determined. (R.V.J.)« less

Discrete-time bidirectional associative memory neural networks with variable delays

NASA Astrophysics Data System (ADS)

Liang, variable delays [rapid communication] J.; Cao, J.; Ho, D. W. C.

2005-02-01

Based on the linear matrix inequality (LMI), some sufficient conditions are presented in this Letter for the existence, uniqueness and global exponential stability of the equilibrium point of discrete-time bidirectional associative memory (BAM) neural networks with variable delays. Some of the stability criteria obtained in this Letter are delay-dependent, and some of them are delay-independent, they are less conservative than the ones reported so far in the literature. Furthermore, the results provide one more set of easily verified criteria for determining the exponential stability of discrete-time BAM neural networks.

Stability of midazolam hydrochloride injection 1-mg/mL solutions in polyvinyl chloride and polyolefin bags.

PubMed

Karlage, Kelly; Earhart, Zachary; Green-Boesen, Kelly; Myrdal, Paul B

2011-08-15

The stability of midazolam hydrochloride injection 1-mg/mL solutions in polyvinyl chloride (PVC) and polyolefin bags under varying conditions was evaluated. Triplicate solutions of midazolam hydrochloride 1-mg/mL were prepared in polyolefin and PVC i.v. bags by diluting midazolam hydrochloride injection 5 mg/mL with 5% dextrose injection. Bags were then stored under refrigeration (3-4 °C), exposed to light at room temperature (20-25 °C), or protected from light in amber bags at room temperature. Samples were taken immediately after preparation (day 0) and on days 1, 2, 3, 6, 13, 20, and 27 for analysis with a stability-indicating high-performance liquid chromatography assay in order to determine solution concentration. Stability was defined as retention of at least 90% of the initial drug concentration. The pH of each solution was also measured weekly. Sterility of the i.v. bags was determined at the end of the study by microbiological testing with culture in growth media. Differences in concentrations under the various storage conditions and bags used were analyzed using analysis of variance. All solutions retained over 98% of the initial midazolam hydrochloride concentration, with no statistically significant (p ≥ 0.05) change in concentration over the four-week period. Stability was not affected by temperature, exposure to light, or bag type. The pH of all solutions remained between 3.2 and 3.4 throughout the study. Sterility after 28 days was retained. Midazolam hydrochloride 1-mg/mL solutions diluted in 5% dextrose injection remained stable over 27 days in both polyolefin and PVC i.v. bags, regardless of storage condition.

38 CFR 21.6054 - Criteria for determining good employment potential.

Code of Federal Regulations, 2011 CFR

2011-07-01

...) Stabilization of medical conditions or substance abuse problems. (6) Participation in therapeutic work programs... good potential for achieving employment does not exist, a personal interview will be scheduled, and the...

Thermal stability of epitaxial SrRuO3 films as a function of oxygen pressure

NASA Astrophysics Data System (ADS)

Lee, Ho Nyung; Christen, Hans M.; Chisholm, Matthew F.; Rouleau, Christopher M.; Lowndes, Douglas H.

2004-05-01

The thermal stability of electrically conducting SrRuO3 thin films grown by pulsed-laser deposition on (001) SrTiO3 substrates has been investigated by atomic force microscopy and reflection high-energy electron diffraction (RHEED) under reducing conditions (25-800 °C in 10-7-10-2 Torr O2). The as-grown SrRuO3 epitaxial films exhibit atomically flat surfaces with single unit-cell steps, even after exposure to air at room temperature. The films remain stable at temperatures as high as 720 °C in moderate oxygen ambients (>1 mTorr), but higher temperature anneals at lower pressures result in the formation of islands and pits due to the decomposition of SrRuO3. Using in situ RHEED, a temperature and oxygen pressure stability map was determined, consistent with a thermally activated decomposition process having an activation energy of 88 kJ/mol. The results can be used to determine the proper conditions for growth of additional epitaxial oxide layers on high quality electrically conducting SrRuO3.

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

Daniel S. Clark; Nathaniel J. Fisch

A critical issue in the generation of ultra-intense, ultra-short laser pulses by backward Raman scattering in plasma is the stability of the pumping pulse to premature backscatter from thermal fluctuations in the preformed plasma. Malkin et al. [V.M. Malkin, et al., Phys. Rev. Lett. 84 (6):1208-1211, 2000] demonstrated that density gradients may be used to detune the Raman resonance in such a way that backscatter of the pump from thermal noise can be stabilized while useful Raman amplification persists. Here plasma conditions for which the pump is stable to thermal Raman backscatter in a homogeneous plasma and the density gradientsmore » necessary to stabilize the pump for other plasma conditions are quantified. Other ancillary constraints on a Raman amplifier are also considered to determine a specific region in the Te-he plane where Raman amplification is feasible. By determining an operability region, the degree of uncertainty in density or temperature tolerable for an experimental Raman amplifier is thus also identified. The fluid code F3D, which includes the effects of thermal fluctuations, is used to verify these analytic estimates.« less

Effect of various stabilizing agents on Imperata cylindrica grass pollen allergen extract.

PubMed

Bijli, K M; Singh, B P; Sridhara, S; Gaur, S N; Arora, N

2003-01-01

Allergen extracts are unstable, heat labile or susceptible to proteases. Stability of allergen extracts is important for proper diagnosis and therapy of allergic disorders. The present study was undertaken to determine the preservation and stabilization conditions of Imperata cylindrica (Ic) grass pollen extract. The Ic extract was kept with 0.1 mepsilon-aminocaproic acid (EACA), 0.75 m sucrose, 5% glycerol, 0.03% human serum albumin (HSA) or 0.4% phenol for different time periods. The extracts were stored for 3, 6 and 12 months each at 4 degrees C, 4 degrees C with daily exposure to room temperature (RT) for 1 h, and RT. The quality of extracts was analysed by SDS-PAGE, Western blot, ELISA, ELISA inhibition and skin test. Extracts kept with EACA and sucrose retained most of the protein bands followed by glycerol as determined by SDS-PAGE and Western blot during all storage periods and conditions in comparison with standard extracts. The extracts kept with HSA, phenol and without preservative (WP) showed protein degradation below 33 kDa after 3 months storage at all conditions. However, a 67-kDa allergen was stable in these extracts. EACA extract required 75 to 120 ng of protein for 50% inhibition in IgE binding under different conditions, whereas standard extract required 70 ng for the same. ELISA also demonstrated high allergenic reactivity of EACA extract. ID test on allergy patients with EACA extract demonstrated same allergenic potency as that of standard extract. EACA is the best preservative/stabilizing agent of Ic pollen extract, followed by sucrose and glycerol. Ic extract kept with phenol, HSA and without preservative showed degradation within 3 months. EACA preserved extract is equally potent as that of standard extract up to 1 year's storage.

Relationship between pyrite Stability and arsenic mobility during aquifer storage and recovery in southwest central Florida.

PubMed

Jones, Gregg W; Pichler, Thomas

2007-02-01

Elevated arsenic concentrations are common in water recovered from aquifer storage and recovery (ASR) systems in west-central Florida that store surface water. Investigations of the Suwannee Limestone of the Upper Floridan aquifer, the storage zone for ASR systems, have shown that arsenic is highest in pyrite in zones of high moldic porosity. Geochemical modeling was employed to examine pyrite stability in limestone during simulated injections of surface water into wells open only to the Suwannee Limestone with known mineralogy and water chemistry. The goal was to determine if aquifer redox conditions could be altered to the degree of pyrite instability. Increasing amounts of injection water were added to native storage-zone water, and resulting reaction paths were plotted on pyrite stability diagrams. Native storage-zone water plotted within the pyrite stability field, indicating that conditions were sufficiently reducing to allow for pyrite stability. Thus, arsenic is immobilized in pyrite, and its groundwater concentration should be low. This was corroborated by analysis of water samples, none of which had arsenic concentrations above 0.036 microg/L. During simulation, however, as injection/native storage-zone water ratios increased, conditions became less reducing and pyrite became unstable. The result would be release of arsenic from limestone into storage-zone water.

Effect of stabilizer on the maximum degree and extent of supersaturation and oral absorption of tacrolimus made by ultra-rapid freezing.

PubMed

Overhoff, Kirk A; McConville, Jason T; Yang, Wei; Johnston, Keith P; Peters, Jay I; Williams, Robert O

2008-01-01

Solid dispersions containing various stabilizers and tacrolimus (TAC) prepared by an Ultra-rapid Freezing (URF) process were investigated to determine the effect on their ability to form supersaturated solutions in aqueous media and on enhancing transport across biological membranes. The stabilizers included poly(vinyl alcohol; PVA), poloxamer 407 (P407), and sodium dodecyl sulfate (SDS). In vivo absorption enhancement in rats was also investigated. Dissolution studies were conducted at supersaturated conditions in both acidic media for 24 h and at delayed release (enteric) conditions to simulate intestinal transit. The rank order of C/Ceq(max) in the dissolution studies at acidic conditions was URF-P407 > URF-SDS > Prograf (PRO) > URF-PVA:P407. For C/Ceq(max) under enteric conditions, the order was URF-SDS > PRO > URF-PVA:P407 > URF-P407, and for the extent of supersaturation (AUC) in acidic and pH shift conditions it was URF-SDS>PRO>URF-PVA:P407>URF-P407. The pharmacokinetic data suggests URF-P407 had the greatest absorption having higher C (max) with a 1.5-fold increase in AUC compared to PRO. All URF compositions had a shorter T (max) compared to PRO. The nanostructured powders containing various stabilizing polymers formed by the URF process offer enhanced supersaturation characteristics leading to increased oral absorption of TAC.

Rapid and accurate prediction of degradant formation rates in pharmaceutical formulations using high-performance liquid chromatography-mass spectrometry.

PubMed

Darrington, Richard T; Jiao, Jim

2004-04-01

Rapid and accurate stability prediction is essential to pharmaceutical formulation development. Commonly used stability prediction methods include monitoring parent drug loss at intended storage conditions or initial rate determination of degradants under accelerated conditions. Monitoring parent drug loss at the intended storage condition does not provide a rapid and accurate stability assessment because often <0.5% drug loss is all that can be observed in a realistic time frame, while the accelerated initial rate method in conjunction with extrapolation of rate constants using the Arrhenius or Eyring equations often introduces large errors in shelf-life prediction. In this study, the shelf life prediction of a model pharmaceutical preparation utilizing sensitive high-performance liquid chromatography-mass spectrometry (LC/MS) to directly quantitate degradant formation rates at the intended storage condition is proposed. This method was compared to traditional shelf life prediction approaches in terms of time required to predict shelf life and associated error in shelf life estimation. Results demonstrated that the proposed LC/MS method using initial rates analysis provided significantly improved confidence intervals for the predicted shelf life and required less overall time and effort to obtain the stability estimation compared to the other methods evaluated. Copyright 2004 Wiley-Liss, Inc. and the American Pharmacists Association.

Beta activity in the premotor cortex is increased during stabilized as compared to normal walking

PubMed Central

Bruijn, Sjoerd M.; Van Dieën, Jaap H.; Daffertshofer, Andreas

2015-01-01

Walking on two legs is inherently unstable. Still, we humans perform remarkable well at it, mostly without falling. To gain more understanding of the role of the brain in controlling gait stability we measured brain activity using electro-encephalography (EEG) during stabilized and normal walking. Subjects walked on a treadmill in two conditions, each lasting 10 min; normal, and while being laterally stabilized by elastic cords. Kinematics of trunk and feet, electro-myography (EMG) of neck muscles, as well as 64-channel EEG were recorded. To assess gait stability the local divergence exponent, step width, and trunk range of motion were calculated from the kinematic data. We used independent component (IC) analysis to remove movement, EMG, and eyeblink artifacts from the EEG, after which dynamic imaging of coherent sources beamformers were determined to identify cortical sources that showed a significant difference between conditions. Stabilized walking led to a significant increase in gait stability, i.e., lower local divergence exponents. Beamforming analysis of the beta band activity revealed significant sources in bilateral pre-motor cortices. Projection of sensor data on these sources showed a significant difference only in the left premotor area, with higher beta power during stabilized walking, specifically around push-off, although only significant around contralateral push-off. It appears that even during steady gait the cortex is involved in the control of stability. PMID:26578937

Low cost, microcontroller based heating device for multi-wavelength differential scanning fluorimetry.

PubMed

Hoeser, Jo; Gnandt, Emmanuel; Friedrich, Thorsten

2018-01-23

Differential scanning fluorimetry is a popular method to estimate the stability of a protein in distinct buffer conditions by determining its 'melting point'. The method requires a temperature controlled fluorescence spectrometer or a RT-PCR machine. Here, we introduce a low-budget version of a microcontroller based heating device implemented into a 96-well plate reader that is connected to a standard fluorescence spectrometer. We demonstrate its potential to determine the 'melting point' of soluble and membranous proteins at various buffer conditions.

An embedded mesh method using piecewise constant multipliers with stabilization: mathematical and numerical aspects

DOE PAGES

Puso, M. A.; Kokko, E.; Settgast, R.; ...

2014-10-22

An embedded mesh method using piecewise constant multipliers originally proposed by Puso et al. (CMAME, 2012) is analyzed here to determine effects of the pressure stabilization term and small cut cells. The approach is implemented for transient dynamics using the central difference scheme for the time discretization. It is shown that the resulting equations of motion are a stable linear system with a condition number independent of mesh size. Furthermore, we show that the constraints and the stabilization terms can be recast as non-proportional damping such that the time integration of the scheme is provably stable with a critical timemore » step computed from the undamped equations of motion. Effects of small cuts are discussed throughout the presentation. A mesh study is conducted to evaluate the effects of the stabilization on the discretization error and conditioning and is used to recommend an optimal value for stabilization scaling parameter. Several nonlinear problems are also analyzed and compared with comparable conforming mesh results. Finally, we show several demanding problems highlighting the robustness of the proposed approach.« less

Stability of user-friendly blood typing kits stored under typical military field conditions.

PubMed

Bienek, Diane R; Chang, Cheow K; Charlton, David G

2009-10-01

To help preserve in-theater strength within deployed military units, commercially available, rapid, user-friendly ABO-Rh blood typing kits were evaluated to determine their stability in storage conditions commonly encountered by the warfighter. Methods for environmental exposure testing were based on MIL-STD-810F. When Eldon Home Kits 2511 were exposed to various temperature/relative humidity conditions, the results were comparable to those obtained with the control group and those obtained with industry-standard methods. For the ABO-Rh Combination Blood Typing Experiment Kits, 2 of the exposure treatments rendered them unusable. In addition, a third set of exposure treatments adversely affected the kits, resulting in approximately 30% blood type misclassifications. Collectively, this evaluation of commercial blood typing kits revealed that diagnostic performance can vary between products, lots, and environmental storage conditions.

Feasibility and coexistence of large ecological communities.

PubMed

Grilli, Jacopo; Adorisio, Matteo; Suweis, Samir; Barabás, György; Banavar, Jayanth R; Allesina, Stefano; Maritan, Amos

2017-02-24

The role of species interactions in controlling the interplay between the stability of ecosystems and their biodiversity is still not well understood. The ability of ecological communities to recover after small perturbations of the species abundances (local asymptotic stability) has been well studied, whereas the likelihood of a community to persist when the conditions change (structural stability) has received much less attention. Our goal is to understand the effects of diversity, interaction strengths and ecological network structure on the volume of parameter space leading to feasible equilibria. We develop a geometrical framework to study the range of conditions necessary for feasible coexistence. We show that feasibility is determined by few quantities describing the interactions, yielding a nontrivial complexity-feasibility relationship. Analysing more than 100 empirical networks, we show that the range of coexistence conditions in mutualistic systems can be analytically predicted. Finally, we characterize the geometric shape of the feasibility domain, thereby identifying the direction of perturbations that are more likely to cause extinctions.

Feasibility and coexistence of large ecological communities

PubMed Central

Grilli, Jacopo; Adorisio, Matteo; Suweis, Samir; Barabás, György; Banavar, Jayanth R.; Allesina, Stefano; Maritan, Amos

2017-01-01

The role of species interactions in controlling the interplay between the stability of ecosystems and their biodiversity is still not well understood. The ability of ecological communities to recover after small perturbations of the species abundances (local asymptotic stability) has been well studied, whereas the likelihood of a community to persist when the conditions change (structural stability) has received much less attention. Our goal is to understand the effects of diversity, interaction strengths and ecological network structure on the volume of parameter space leading to feasible equilibria. We develop a geometrical framework to study the range of conditions necessary for feasible coexistence. We show that feasibility is determined by few quantities describing the interactions, yielding a nontrivial complexity–feasibility relationship. Analysing more than 100 empirical networks, we show that the range of coexistence conditions in mutualistic systems can be analytically predicted. Finally, we characterize the geometric shape of the feasibility domain, thereby identifying the direction of perturbations that are more likely to cause extinctions. PMID:28233768

Sum-of-squares-based fuzzy controller design using quantum-inspired evolutionary algorithm

NASA Astrophysics Data System (ADS)

Yu, Gwo-Ruey; Huang, Yu-Chia; Cheng, Chih-Yung

2016-07-01

In the field of fuzzy control, control gains are obtained by solving stabilisation conditions in linear-matrix-inequality-based Takagi-Sugeno fuzzy control method and sum-of-squares-based polynomial fuzzy control method. However, the optimal performance requirements are not considered under those stabilisation conditions. In order to handle specific performance problems, this paper proposes a novel design procedure with regard to polynomial fuzzy controllers using quantum-inspired evolutionary algorithms. The first contribution of this paper is a combination of polynomial fuzzy control and quantum-inspired evolutionary algorithms to undertake an optimal performance controller design. The second contribution is the proposed stability condition derived from the polynomial Lyapunov function. The proposed design approach is dissimilar to the traditional approach, in which control gains are obtained by solving the stabilisation conditions. The first step of the controller design uses the quantum-inspired evolutionary algorithms to determine the control gains with the best performance. Then, the stability of the closed-loop system is analysed under the proposed stability conditions. To illustrate effectiveness and validity, the problem of balancing and the up-swing of an inverted pendulum on a cart is used.

Thermodynamics-hydration relationships within loops that affect G-quadruplexes under molecular crowding conditions.

PubMed

Fujimoto, Takeshi; Nakano, Shu-ichi; Sugimoto, Naoki; Miyoshi, Daisuke

2013-01-31

We systematically investigated the effects of loop length on the conformation, thermodynamic stability, and hydration of DNA G-quadruplexes under dilute and molecular crowding conditions in the presence of Na(+). Structural analysis showed that molecular crowding induced conformational switches of oligonucleotides with the longer guanine stretch and the shorter thymine loop. Thermodynamic parameters further demonstrated that the thermodynamic stability of G-quadruplexes increased by increasing the loop length from two to four, whereas it decreased by increasing the loop length from four to six. Interestingly, we found by osmotic pressure analysis that the number of water molecules released from the G-quadruplex decreased with increasing thermodynamic stability. We assumed that base-stacking interactions within the loops not only stabilized the whole G-quadruplex structure but also created hydration sites by accumulating nucleotide functional groups. The molecular crowding effects on the stability of G-quadruplexes composed of abasic sites, which reduce the stacking interactions at the loops, further demonstrated that G-quadruplexes with fewer stacking interactions within the loops released a larger number of water molecules upon folding. These results showed that the stacking interactions within the loops determined the thermodynamic stability and hydration of the whole G-quadruplex.

The use of an atmospheric dispersion model to determine influence regions in the Prince George, B.C. airshed from the burning of open wood waste piles.

PubMed

Ainslie, B; Jackson, P L

2009-06-01

A means of determining air emission source regions adversely influencing the city of Prince George, British Columbia, Canada from potential burning of isolated piles of mountain pine beetle-killed lodge pole pine is presented. The analysis uses the CALPUFF atmospheric dispersion model to identify safe burning regions based on atmospheric stability and wind direction. Model results show that the location and extent of influence regions is sensitive to wind speed, wind direction, atmospheric stability and a threshold used to quantify excessive concentrations. A concentration threshold based on the Canada Wide PM(2.5) Standard is used to delineate the influence regions while Environment Canada's (EC) daily ventilation index (VI) is used to quantify local atmospheric stability. Results from the analysis, to be used by air quality meteorologists in assessing daily requests for burning permits, are presented as a series of maps delineating acceptable burning locations for sources placed at various distances from the city center and under different ventilation conditions. The results show that no burning should be allowed within 10 km of the city center; under poor ventilation conditions, no burning should be allowed within 20 km of the city center; under good ventilation conditions, burning can be allowed within 10-15 km of the city center; under good to fair ventilation conditions, burning can be allowed beyond 15 km of the city center; and if the wind direction can be reliably forecast, burning can be allowed between 5 and 10 km downwind of the city center under good ventilation conditions.

A free boundary problem for steady small plaques in the artery and their stability

NASA Astrophysics Data System (ADS)

Friedman, Avner; Hao, Wenrui; Hu, Bei

2015-08-01

Atherosclerosis is a leading cause of death in the United States and worldwide; it originates from a plaque which builds up in the artery. In this paper, we consider a simplified model of plaque growth involving LDL and HDL cholesterols, macrophages and foam cells, which satisfy a coupled system of PDEs with a free boundary, the interface between the plaque and the blood flow. We prove that there exist small radially symmetric stationary plaques and establish a sharp condition that ensures their stability. We also determine necessary and sufficient conditions under which a small initial plaque will shrink and disappear, or persist for all times.

Validating internal controls for quantitative plant gene expression studies.

PubMed

Brunner, Amy M; Yakovlev, Igor A; Strauss, Steven H

2004-08-18

Real-time reverse transcription PCR (RT-PCR) has greatly improved the ease and sensitivity of quantitative gene expression studies. However, accurate measurement of gene expression with this method relies on the choice of a valid reference for data normalization. Studies rarely verify that gene expression levels for reference genes are adequately consistent among the samples used, nor compare alternative genes to assess which are most reliable for the experimental conditions analyzed. Using real-time RT-PCR to study the expression of 10 poplar (genus Populus) housekeeping genes, we demonstrate a simple method for determining the degree of stability of gene expression over a set of experimental conditions. Based on a traditional method for analyzing the stability of varieties in plant breeding, it defines measures of gene expression stability from analysis of variance (ANOVA) and linear regression. We found that the potential internal control genes differed widely in their expression stability over the different tissues, developmental stages and environmental conditions studied. Our results support that quantitative comparisons of candidate reference genes are an important part of real-time RT-PCR studies that seek to precisely evaluate variation in gene expression. The method we demonstrated facilitates statistical and graphical evaluation of gene expression stability. Selection of the best reference gene for a given set of experimental conditions should enable detection of biologically significant changes in gene expression that are too small to be revealed by less precise methods, or when highly variable reference genes are unknowingly used in real-time RT-PCR experiments.

Colour-Value Based Method for Polydopamine Coating-Stability Characterization on Polyethersulfone Membranes

PubMed Central

Bucher, Thomas; Clodt, Juliana I.; Grabowski, Andrej; Hein, Martin; Filiz, Volkan

2017-01-01

Porous polyethersulfone membranes as used in oenology were investigated in order to evaluate temperature-dependent permeances in a temperature range from 10 to 35 °C. A temperature correction factor was determined for this type of membrane to get accurate and comparable results for further developments. Moreover, the membranes were modified with a bio-inspired polydopamine coating in order to reduce fouling. The performance of the membranes could be increased with respect to permeance and flux recovery under cross-flow conditions. In order to test the applicability and stability of the coating layer, they were treated with basic and acidic cleaning agents as used in industry for fouled membranes. The chemical stability of the coating layer was studied under basic and acidic conditions, by systematic observation of the colour change of the coated membranes over treatment time. PMID:29258193

Colour-Value Based Method for Polydopamine Coating-Stability Characterization on Polyethersulfone Membranes.

PubMed

Bucher, Thomas; Clodt, Juliana I; Grabowski, Andrej; Hein, Martin; Filiz, Volkan

2017-12-16

Porous polyethersulfone membranes as used in oenology were investigated in order to evaluate temperature-dependent permeances in a temperature range from 10 to 35 °C. A temperature correction factor was determined for this type of membrane to get accurate and comparable results for further developments. Moreover, the membranes were modified with a bio-inspired polydopamine coating in order to reduce fouling. The performance of the membranes could be increased with respect to permeance and flux recovery under cross-flow conditions. In order to test the applicability and stability of the coating layer, they were treated with basic and acidic cleaning agents as used in industry for fouled membranes. The chemical stability of the coating layer was studied under basic and acidic conditions, by systematic observation of the colour change of the coated membranes over treatment time.

The stability behavior of sol-emulsion systems

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

Sunkel, J.M.; Berg, J.C.

1996-05-10

Sol-emulsion systems, i.e., colloids consisting of mixed populations of solid particles and emulsion droplets, are encountered in a number of applications, e.g., oil-assisted agglomeration for particle removal (coal fines from water). The stability characteristics of mixed aqueous dispersions of titanium dioxide and mineral oil emulsion droplets are examined as a function of pH and emulsifier type and content. Zeta potentials of both the titanium dioxide and the mineral oil particles are measured under all conditions to identify regions of expected heterocoagulation and to quantify the electrostatic boundary conditions. The latter are used in the numerical solution of the pair interactionmore » potentials based on the recent theory of McCormack et al. The potential functions are used in a modified version of the stability model of Hogg, Healy, and Fuerstenau to calculate early-stage aggregation rates. Photon correlation spectroscopy is used to determine stability ratios for homo- and heterocoagulation, and initial results indicate good agreement between experiments and computations.« less

Stability and UV completion of the Standard Model

NASA Astrophysics Data System (ADS)

Branchina, Vincenzo; Messina, Emanuele

2017-03-01

The knowledge of the electroweak vacuum stability condition is of the greatest importance for our understanding of beyond Standard Model physics. It is widely believed that new physics that lives at very high-energy scales should have no impact on the stability analysis. This expectation has been recently challenged, but the results were controversial as new physics was given in terms of non-renormalizable higher-order operators. Here we consider for the first time new physics at extremely high-energy scales (say close to the Planck scale) in terms of renormalizable operators, in other words we consider a sort of toy UV completion of the Standard Model, and definitely show that its presence can be crucial in determining the vacuum stability condition. This result has important phenomenological consequences, as it provides useful guidance in studying beyond Standard Model theories. Moreover, it suggests that very popular speculations based on the so-called “criticality” of the Standard Model do not appear to be well founded.

Effect of high-pressure processing on quality and stability of green mango blended mayonnaise.

PubMed

Sethi, Swati; Chauhan, O P; Anurag, Rahul K

2017-07-01

The present work was aimed to study and optimize the high pressure treated green mango blended mayonnaise in terms of oxidative and emulsion stability, as a function of technical parameters; pressure intensity, dwell period and level of green mango pulp. Mayonnaise samples were treated at different combinations of pressure (400-600 MPa), holding time (5-10 min) and level of green mango pulp (10-30%) following Box-Behnken design. Mayonnaise quality was evaluated in terms of oxidative stability and emulsion stability using response surface methodology to optimize the best possible combination among all. Analysis of variance showed that the second-order polynomial model fitted well with the experimental results. Pressure and time were the most important factors determining the oxidative stability (free fatty acids, peroxide value and anisidine value) whereas; the emulsion stability (creaming and thermal creaming) was most significantly affected by the level of green mango pulp. The optimized conditions for preparing green mango blended mayonnaise with high oxidative and emulsion stability were: 435 MPa pressure, 5 min of holding time with the addition of green mango pulp at the rate of 28%. The product prepared at optimum conditions showed good correlations between predicted and actual values.

Comparison of jump-landing protocols with Biodex Balance System as measures of dynamic postural stability in athletes.

PubMed

Krkeljas, Zarko

2017-07-21

The objective of the study was to determine whether a relationship exists between the two common methods for assessing postural stability in athletes: the time-to-stabilisation (TTS) via force-plate and the Biodex Balance System (BBS). The conditions under which these measurements assess dynamic postural control may not provide sufficient feedback to practitioners. Fourty-four amateur soccer players with no history of musculoskeletal disorders volunteered for the study. Pearson correlation was used to compare the anterior-posterior (AP), medio-lateral (ML), and the overall stability indexes measured by BBS, with the corresponding parameters of TTS assessed via force plate. There was no significant correlation between any parameters of dynamic stability measured by force-plate and the stability indexes. However, there was a significant correlation between the resulting vectors and the AP component of TTS for each jump protocol. Furthermore, forward drop landing exhibited shortest TTS in AP direction, while lateral drop landing resulted in longer ML TTS relative to both forward jumps (p < 0.001). These results demonstrate that the TTS and BBS stability indexes should be used as distinct measures of dynamic postural stability. TTS protocols may be modified to target a specific training conditions or athletic population.

Heat stabilization of blood spot samples for determination of metabolically unstable drug compounds

PubMed Central

Blessborn, Daniel; Sköld, Karl; Zeeberg, David; Kaewkhao, Karnrawee; Sköld, Olof; Ahnoff, Martin

2014-01-01

Background Sample stability is critical for accurate analysis of drug compounds in biosamples. The use of additives to eradicate the enzymatic activity causing loss of these analytes has its limitations. Results A novel technique for sample stabilization by rapid, high-temperature heating was used. The stability of six commercial drugs in blood and blood spots was investigated under various conditions with or without heat stabilization at 95°C. Oseltamivir, cefotaxime and ribavirin were successfully stabilized by heating whereas significant losses were seen in unheated samples. Amodiaquine was stable with and without heating. Artemether and dihydroartemisinin were found to be very heat sensitive and began to decompose even at 60°C. Conclusion Heat stabilization is a viable technique to maintain analytes in blood spot samples, without the use of chemical additives, by stopping the enzymatic activity that causes sample degradation. PMID:23256470

Effects of heat, pH, antioxidant, agitation and light on betacyanin stability using red-fleshed dragon fruit (Hylocereus polyrhizus) juice and concentrate as models.

PubMed

Wong, Yen-Ming; Siow, Lee-Fong

2015-05-01

Red-fleshed dragon fruit (Hylocereus polyrhizus) is rich in antioxidants. The aim of this study was to determine the effects of heat pasteurization, pH adjustment, ascorbic acid addition as well as storage under agitation and light or dark condition on betacyanin content in red-fleshed dragon fruit (Hylocereus polyrhizus) juice and concentrate. The concentrate was produced by concentrating clarified red-fleshed dragon fruit juice in a rotary evaporator at 40 °C. UV-Visible spectrophotometer was used for analyzing betacyanin content. Addition of 0.25 % ascorbic acid, pH 4.0, and pasteurization at 65 °C for 30 min were selected as the best processing conditions to retain betacyanin content in red-fleshed dragon fruit juice. Storage at the agitation speed of 220 rpm showed that the concentrated samples had higher betacyanin stability compared to juice, while both juice and concentrate had almost similar betacyanin stability when tested for storage in the presence of light. In summary, ascorbic acid stabilized betacyanin in both juice and concentrate at agitated or non-agitated conditions. In contrast, light degraded betacyanin in both juice and concentrate models.

The stability of stratified spatially periodic shear flows at low Péclet number

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

Garaud, Pascale, E-mail: pgaraud@ucsc.edu; Gallet, Basile; Bischoff, Tobias

2015-08-15

This work addresses the question of the stability of stratified, spatially periodic shear flows at low Péclet number but high Reynolds number. This little-studied limit is motivated by astrophysical systems, where the Prandtl number is often very small. Furthermore, it can be studied using a reduced set of “low-Péclet-number equations” proposed by Lignières [“The small-Péclet-number approximation in stellar radiative zones,” Astron. Astrophys. 348, 933–939 (1999)]. Through a linear stability analysis, we first determine the conditions for instability to infinitesimal perturbations. We formally extend Squire’s theorem to the low-Péclet-number equations, which shows that the first unstable mode is always two-dimensional. Wemore » then perform an energy stability analysis of the low-Péclet-number equations and prove that for a given value of the Reynolds number, above a critical strength of the stratification, any smooth periodic shear flow is stable to perturbations of arbitrary amplitude. In that parameter regime, the flow can only be laminar and turbulent mixing does not take place. Finding that the conditions for linear and energy stability are different, we thus identify a region in parameter space where finite-amplitude instabilities could exist. Using direct numerical simulations, we indeed find that the system is subject to such finite-amplitude instabilities. We determine numerically how far into the linearly stable region of parameter space turbulence can be sustained.« less

Assessment of Nutrient Stability in Space Foods

NASA Technical Reports Server (NTRS)

Zwart, S. R.; Perchonok, M.; Braby, L. A.; Kloeris, V. A.; Smith, S. M.

2009-01-01

Maintaining an intact nutrient supply in the food system flown on spacecraft is a critical issue for mission success and crew health and safety. Early polar expeditions and exploration expeditions by sailing vessels have taught us that a deficiency, or excess, of even a single vitamin in the food supply can be catastrophic. Evidence from ground-based research indicates that some vitamins are destroyed and fatty acids are oxidized (and therefore rendered dangerous or useless) by different types of radiation and by conditions of long-term storage. We hypothesize that radiation and long-term storage in the space-flight environment will affect the stability of vitamins, amino acids, and fatty acids in the space food system. The research objectives of our ongoing stability studies are to determine the stability of water- and fat-soluble vitamins, fatty acids, and amino acids in the space food supply before and after space flight on the International Space Station (ISS). Foods were analyzed after 2 weeks (a flight control), 11, 19, and 28 months of flight. Along with the space-flown foods, ground-based controls matched for time, light, and temperature are analyzed. The flight studies complement planned ground-based studies of the effects of radiation on vitamins, amino acids, and fatty acids. Flight studies are needed because a model based on ground-based data cannot predict all of the effects of the space-flight environment. Flight studies provide a more accurate test system to determine the effects on these nutrients of the temperature, and radiation conditions in the space-flight environment. Ground studies are required to evaluate longer missions and higher radiation levels expected outside low-Earth orbit. In addition to providing information about nutrient stability in space, the results of these studies will help NASA determine if a need exists to develop special packaging that can ensure stability of foods and nutrients in space, or if further studies of nutrient metabolism or nutrient requirements are needed.

Ankle Bracing, Fatigue, and Time to Stabilization in Collegiate Volleyball Athletes

PubMed Central

Shaw, Megan Y; Gribble, Phillip A; Frye, Jamie L

2008-01-01

Context: Fatigue has been shown to disrupt dynamic stability in healthy volunteers. It is not known if wearing prophylactic ankle supports can improve dynamic stability in fatigued athletes. Objective: To determine the type of ankle brace that may be more effective at providing dynamic stability after a jump-landing task during normal and fatigued conditions. Design: Two separate repeated-measures analyses of variance with 2 within-subjects factors (condition and time) were performed for each dependent variable. Setting: Research laboratory. Patients or Other Participants: Ten healthy female collegiate volleyball athletes participated (age  =  19.5 ± 1.27 years, height  =  179.07 ± 7.6 cm, mass  =  69.86 ± 5.42 kg). Intervention(s): Athletes participated in 3 separate testing sessions, applying a different bracing condition at each session: no brace (NB), Swede-O Universal lace-up ankle brace (AB), and Active Ankle brace (AA). Three trials of a jump-landing task were performed under each condition before and after induced functional fatigue. The jump-landing task consisted of a single-leg landing onto a force plate from a height equivalent to 50% of each participant's maximal jump height and from a starting position 70 cm from the center of the force plate. Main Outcome Measure(s): Time to stabilization in the anterior-posterior (APTTS) and medial-lateral (MLTTS) directions. Results: For APTTS, a condition-by-time interaction existed (F2,18  =  5.55, P  =  .013). For the AA condition, Tukey post hoc testing revealed faster pretest (2.734 ± 0.331 seconds) APTTS than posttest (3.817 ± 0.263 seconds). Post hoc testing also revealed that the AB condition provided faster APTTS (2.492 ± 0.271 seconds) than AA (3.817 ± 0.263 seconds) and NB (3.341 ± 0.339 seconds) conditions during posttesting. No statistically significant findings were associated with MLTTS. Conclusions: Fatigue increased APTTS for the AA condition. Because the AB condition was more effective than the other 2 conditions during the posttesting, the AB appears to be the best option for providing dynamic stability in the anterior-posterior direction during a landing task. PMID:18345341

Operational frequency stability of rubidium and cesium frequency standards

NASA Technical Reports Server (NTRS)

Lavery, J. E.

1973-01-01

The frequency stabilities under operational conditions of several commercially available rubidium and cesium frequency standards were determined from experimental data for frequency averaging times from 10 to the 7th power s and are presented in table and graph form. For frequency averaging times between 10 to the 5th power and 10 to the 7th power s, the rubidium standards tested have a stability of between 10 to the minus 12th power and 5 x 10 to the minus 12th power, while the cesium standards have a stability of between 2 x 10 to the minus 13th power and 5 x 10 to the minus 13th power.

Lipschitz stability for an inverse hyperbolic problem of determining two coefficients by a finite number of observations

NASA Astrophysics Data System (ADS)

Beilina, L.; Cristofol, M.; Li, S.; Yamamoto, M.

2018-01-01

We consider an inverse problem of reconstructing two spatially varying coefficients in an acoustic equation of hyperbolic type using interior data of solutions with suitable choices of initial condition. Using a Carleman estimate, we prove Lipschitz stability estimates which ensure unique reconstruction of both coefficients. Our theoretical results are justified by numerical studies on the reconstruction of two unknown coefficients using noisy backscattered data.

Identification of Synchronous Machine Stability - Parameters: AN On-Line Time-Domain Approach.

NASA Astrophysics Data System (ADS)

Le, Loc Xuan

1987-09-01

A time-domain modeling approach is described which enables the stability-study parameters of the synchronous machine to be determined directly from input-output data measured at the terminals of the machine operating under normal conditions. The transient responses due to system perturbations are used to identify the parameters of the equivalent circuit models. The described models are verified by comparing their responses with the machine responses generated from the transient stability models of a small three-generator multi-bus power system and of a single -machine infinite-bus power network. The least-squares method is used for the solution of the model parameters. As a precaution against ill-conditioned problems, the singular value decomposition (SVD) is employed for its inherent numerical stability. In order to identify the equivalent-circuit parameters uniquely, the solution of a linear optimization problem with non-linear constraints is required. Here, the SVD appears to offer a simple solution to this otherwise difficult problem. Furthermore, the SVD yields solutions with small bias and, therefore, physically meaningful parameters even in the presence of noise in the data. The question concerning the need for a more advanced model of the synchronous machine which describes subtransient and even sub-subtransient behavior is dealt with sensibly by the concept of condition number. The concept provides a quantitative measure for determining whether such an advanced model is indeed necessary. Finally, the recursive SVD algorithm is described for real-time parameter identification and tracking of slowly time-variant parameters. The algorithm is applied to identify the dynamic equivalent power system model.

Experimental techniques for studying the structure of foams and froths.

PubMed

Pugh, R J

2005-06-30

Several techniques are described in this review to study the structure and the stability of froths and foams. Image analysis proved useful for detecting structure changes in 2-D foams and has enabled the drainage process and the gradients in bubble size distribution to be determined. However, studies on 3-D foams require more complex techniques such as Multiple-Light Scattering Methods, Microphones and Optical Tomography. Under dynamic foaming conditions, the Foam Scan Column enables the water content of foams to be determined by conductivity analysis. It is clear that the same factors, which play a role in foam stability (film thickness, elasticity, etc.) also have a decisive influence on the stability of isolated froth or foam films. Therefore, the experimental thin film balance (developed by the Bulgarian Researchers) to study thinning of microfilms formed by a concave liquid drop suspended in a short vertical capillary tube has proved useful. Direct measurement of the thickness of the aqueous microfilm is determined by a micro-reflectance method and can give fundamental information on drainage and thin film stability. It is also important to consider the influence of the mineral particles on the stability of the froth and it have been shown that particles of well defined size and hydrophobicity can be introduced into the thin film enabling stabilization/destabilization mechanisms to be proposed. It has also been shown that the dynamic and static stability can be increased by a reduction in particle size and an increase in particle concentration.

Structure and stability of pyrophyllite edge surfaces: Effect of temperature and water chemical potential

NASA Astrophysics Data System (ADS)

Kwon, Kideok D.; Newton, Aric G.

2016-10-01

The surfaces of clay minerals, which are abundant in atmospheric mineral dust, serve as an important medium to catalyze ice nucleation. The lateral edge surface of 2:1 clay minerals is postulated to be a potential site for ice nucleation. However, experimental investigations of the edge surface structure itself have been limited compared to the basal planes of clay minerals. Density functional theory (DFT) computational studies have provided insights into the pyrophyllite edge surface. Pyrophyllite is an ideal surrogate mineral for the edge surfaces of 2:1 clay minerals as it possesses no or little structural charge. Of the two most-common hydrated edge surfaces, the AC edge, (1 1 0) surface in the monoclinic polytype notation, is predicted to be more stable than the B edge, (0 1 0) surface. These stabilities, however, were determined based on the total energies calculated at 0 K and did not consider environmental effects such as temperature and humidity. In this study, atomistic thermodynamics based on periodic DFT electronic calculations was applied to examine the effects of environmental variables on the structure and thermodynamic stability of the common edge surfaces in equilibrium with bulk pyrophyllite and water vapor. We demonstrate that the temperature-dependent vibrational energy of sorbed water molecules at the edge surface is a significant component of the surface free energy and cannot be neglected when determining the surface stability of pyrophyllite. The surface free energies were calculated as a function of temperature from 240 to 600 K and water chemical potential corresponding to conditions from ultrahigh vacuum to the saturation vapor pressure of water. We show that at lower water chemical potentials (dry conditions), the AC and B edge surfaces possessed similar stabilities; at higher chemical potentials (humid conditions) the AC edge surface was more stable than the B edge surface. At high temperatures, both surfaces showed similar stabilities regardless of the water chemical potential. The equilibrium morphology of pyrophyllite crystals is also expected to be dependent on these two environmental variables. Surface defects may impact the surface reactivity. We discuss the thermodynamic stability of a possible Si cation vacancy defect which provides additional hydroxyl group on the surface.

Comparison of dental implant stabilities by impact response and resonance frequencies using artificial bone.

PubMed

Kim, Dae-Seung; Lee, Woo-Jin; Choi, Soon-Chul; Lee, Sam-Sun; Heo, Min-Suk; Huh, Kyung-Hoe; Kim, Tae-Il; Yi, Won-Jin

2014-06-01

We compared implant stability as determined by the peak frequency from the impact response with the implant stability quotient (ISQ) by resonance frequency analysis (RFA) in various artificial bone conditions. The clinical bone conditions were simulated using an artificial bone material with different cortical thicknesses and trabecular densities. The artificial bone material was solid, rigid polyurethane. The polyurethane foam of 0.8g/cm(3) density was used for the cortical bone layer, and that of 0.08, 0.16, 0.24, 0.32, and 0.48g/cm(3) densities for the trabecular bone layer. The cortical bone material of 4 different thicknesses (1.4, 1.6, 1.8, and 2.0mm) was attached to the trabecular bone with varying density. Two types of dental implants (10 and 13mm lengths of 4.0mm diameter) were placed into the artificial bone blocks. An inductive sensor was used to measure the vibration caused by tapping the adapter-implant assembly. The peak frequency of the power spectrum of the impact response was used as the criterion for implant stability. The ISQ value was also measured for the same conditions. The stability, as measured by peak frequency (SPF) and ISQ value, increased as the trabecular density and the cortical density increased in linear regression analysis. The SPF and ISQ values were highly correlated with each other when the trabecular bone density and cortical bone thickness changed (Pearson correlation=0.90, p<0.01). The linear regression of the SPF with the cortical bone thickness showed higher goodness of fit (R(2) measure) than the ISQ value with the cortical bone thickness. The SPF could differentiate implantation conditions as many as the ISQ value when the trabecular bone density and the cortical density changed. However, the ISQ value was not consistent with the general stability tendency in some conditions. The SPF showed better consistency and differentiability with implant stability than the ISQ value by resonance frequency analysis in the various implantation conditions. Copyright © 2013 IPEM. Published by Elsevier Ltd. All rights reserved.

Evaluation of non-volatile metabolites in beer stored at high temperature and utility as an accelerated method to predict flavour stability.

PubMed

Heuberger, Adam L; Broeckling, Corey D; Sedin, Dana; Holbrook, Christian; Barr, Lindsay; Kirkpatrick, Kaylyn; Prenni, Jessica E

2016-06-01

Flavour stability is vital to the brewing industry as beer is often stored for an extended time under variable conditions. Developing an accelerated model to evaluate brewing techniques that affect flavour stability is an important area of research. Here, we performed metabolomics on non-volatile compounds in beer stored at 37 °C between 1 and 14 days for two beer types: an amber ale and an India pale ale. The experiment determined high temperature to influence non-volatile metabolites, including the purine 5-methylthioadenosine (5-MTA). In a second experiment, three brewing techniques were evaluated for improved flavour stability: use of antioxidant crowns, chelation of pro-oxidants, and varying plant content in hops. Sensory analysis determined the hop method was associated with improved flavour stability, and this was consistent with reduced 5-MTA at both regular and high temperature storage. Future studies are warranted to understand the influence of 5-MTA on flavour and aging within different beer types. Copyright © 2016 Elsevier Ltd. All rights reserved.

Convective stability of a plasma in a system of coupled adiabatic open cells in the Kruskal-Oberman model

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

Arsenin, V. V.; Terekhin, P. N.

2010-08-15

The Kruskal-Oberman kinetic model is used to determine the conditions for the convective stability of a plasma in a system of coupled axisymmetric adiabatic open cells in which the magnetic field curvature has opposite signs. For a combination of a nonparaxial simple mirror cell and a semicusp, the boundaries of the interval of values of the flux coordinate where the plasma can be stable are determined, as well as the range in which the ratio of the pressures in the component cells should lie. Numerical simulations were carried out for different particle distributions over the pitch angle.

Changes in leukocyte stability in hypodynamia

NASA Technical Reports Server (NTRS)

Federov, I. I.; Federova, Z. P.; Pekus, Y. N.; Sakun, T. L.

1980-01-01

Leukocytolysis was determined under conditions of hypokinesia of 10 days to 1 month duration in healthy persons and in experiments on albino rats of 1 month duration. It was found that prolonged restriction of movement resulted, both in clinical and experimental conditions, in a considerable increase of leukocytolysis (by two-three-fold). Leukocytolysis also continued for several days after cessation of hypokinesia.

A charging model for three-axis stabilized spacecraft

NASA Technical Reports Server (NTRS)

Massaro, M. J.; Green, T.; Ling, D.

1977-01-01

A charging model was developed for geosynchronous, three-axis stabilized spacecraft when under the influence of a geomagnetic substorm. The differential charging potentials between the thermally coated or blanketed outer surfaces and metallic structure of a spacecraft were determined when the spacecraft was immersed in a dense plasma cloud of energetic particles. The spacecraft-to-environment interaction was determined by representing the charged particle environment by equivalent current source forcing functions and by representing the spacecraft by its electrically equivalent circuit with respect to the plasma charging phenomenon. The charging model included a sun/earth/spacecraft orbit model that simulated the sum illumination conditions of the spacecraft outer surfaces throughout the orbital flight on a diurnal as well as a seasonal basis. Transient and steady-state numerical results for a three-axis stabilized spacecraft are presented.

Applications of high pressure differential scanning calorimetry to aviation fuel thermal stability research

NASA Technical Reports Server (NTRS)

Neveu, M. C.; Stocker, D. P.

1985-01-01

High pressure differential scanning calorimetry (DSC) was studied as an alternate method for performing high temperature fuel thermal stability research. The DSC was used to measure the heat of reaction versus temperature of a fuel sample heated at a programmed rate in an oxygen pressurized cell. Pure hydrocarbons and model fuels were studied using typical DSC operating conditions of 600 psig of oxygen and a temperature range from ambient to 500 C. The DSC oxidation onset temperature was determined and was used to rate the fuels on thermal stability. Kinetic rate constants were determined for the global initial oxidation reaction. Fuel deposit formation is measured, and the high temperature volatility of some tetralin deposits is studied by thermogravimetric analysis. Gas chromatography and mass spectrometry are used to study the chemical composition of some DSC stressed fuels.

Motion of negative ion plasma near the boundary with electron−ion plasma

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

Medvedev, Yu. V., E-mail: medve@mail.ru

2017-01-15

Processes occurring near the boundary between three-component plasma with negative ions and two-component electron−ion plasma are considered. The excited waves and instability are described. Stability condition at the boundary is determined.

Primary implant stability in a bone model simulating clinical situations for the posterior maxilla: an in vitro study

PubMed Central

2016-01-01

Purpose The aim of this study was to determine the influence of anatomical conditions on primary stability in the models simulating posterior maxilla. Methods Polyurethane blocks were designed to simulate monocortical (M) and bicortical (B) conditions. Each condition had four subgroups measuring 3 mm (M3, B3), 5 mm (M5, B5), 8 mm (M8, B8), and 12 mm (M12, B12) in residual bone height (RBH). After implant placement, the implant stability quotient (ISQ), Periotest value (PTV), insertion torque (IT), and reverse torque (RT) were measured. Two-factor ANOVA (two cortical conditions×four RBHs) and additional analyses for simple main effects were performed. Results A significant interaction between cortical condition and RBH was demonstrated for all methods measuring stability with two-factor ANOVA. In the analyses for simple main effects, ISQ and PTV were statistically higher in the bicortical groups than the corresponding monocortical groups, respectively. In the monocortical group, ISQ and PTV showed a statistically significant rise with increasing RBH. Measurements of IT and RT showed a similar tendency, measuring highest in the M3 group, followed by the M8, the M5, and the M12 groups. In the bicortical group, all variables showed a similar tendency, with different degrees of rise and decline. The B8 group showed the highest values, followed by the B12, the B5, and the B3 groups. The highest coefficient was demonstrated between ISQ and PTV. Conclusions Primary stability was enhanced by the presence of bicortex and increased RBH, which may be better demonstrated by ISQ and PTV than by IT and RT. PMID:27588215

Determination of internal controls for quantitative gene expression of Isochrysis zhangjiangensis at nitrogen stress condition

NASA Astrophysics Data System (ADS)

Wu, Shuang; Zhou, Jiannan; Cao, Xupeng; Xue, Song

2016-02-01

Isochrysis zhangjiangensis is a potential marine microalga for biodiesel production, which accumulates lipid under nitrogen limitation conditions, but the mechanism on molecular level is veiled. Quantitative real-time polymerase chain reaction (qPCR) provides the possibility to investigate the gene expression levels, and a valid reference for data normalization is an essential prerequisite for firing up the analysis. In this study, five housekeeping genes, actin (ACT), α-tubulin (TUA), ß-tubulin (TUB), ubiquitin (UBI), 18S rRNA (18S) and one target gene, diacylglycerol acyltransferase (DGAT), were used for determining the reference. By analyzing the stabilities based on calculation of the stability index and on operating the two types of software, geNorm and bestkeeper, it showed that the reference genes widely used in higher plant and microalgae, such as UBI, TUA and 18S, were not the most stable ones in nitrogen-stressed I. zhangjiangensis, and thus are not suitable for exploring the mRNA expression levels under these experimental conditions. Our results show that ACT together with TUB is the most feasible internal control for investigating gene expression under nitrogen-stressed conditions. Our findings will contribute not only to future qPCR studies of I. zhangjiangensis, but also to verification of comparative transcriptomics studies of the microalgae under similar conditions.

Evaluation of oxidative stability of lamb burger with Origanum vulgare extract.

PubMed

Fernandes, R P P; Trindade, M A; Tonin, F G; Pugine, S M P; Lima, C G; Lorenzo, J M; de Melo, M P

2017-10-15

The objective was to evaluate replacement of sodium erythorbate with a natural antioxidant (oregano extract) on physicochemical and sensory stability of lamb burgers, and determine the appropriate amount. Five treatments were prepared, including control (without antioxidant), sodium erythorbate, and three concentrations of oregano extract (13.32, 17.79 and 24.01mL/kg), based on antioxidant capacity determined using the Folin-Ciocalteu, 2,2-diphenyl-1-picrylhydrazyl (DPPH) and ferric reducing antioxidant power (FRAP) methods, respectively. Burgers containing oregano extract, at the concentration determined by FRAP method, had higher oxidative stability, evidenced by an 80% reduction (P<0.001) in thiobarbituric acid reactive substances, effective inhibition of protein oxidation (P<0.01) and less colour loss during frozen storage. Oregano extract did not impair (P>0.05) consumers' sensory acceptance of the lamb burgers. Under the conditions tested, addition of 24mL/kg of oregano extract could be recommended as a natural antioxidant in lamb burgers. Copyright © 2017 Elsevier Ltd. All rights reserved.

Balance between apical membrane growth and luminal matrix resistance determines epithelial tubule shape.

PubMed

Dong, Bo; Hannezo, Edouard; Hayashi, Shigeo

2014-05-22

The morphological stability of biological tubes is crucial for the efficient circulation of fluids and gases. Failure of this stability causes irregularly shaped tubes found in multiple pathological conditions. Here, we report that Drosophila mutants of the ESCRT III component Shrub/Vps32 exhibit a strikingly elongated sinusoidal tube phenotype. This is caused by excessive apical membrane synthesis accompanied by the ectopic accumulation and overactivation of Crumbs in swollen endosomes. Furthermore, we demonstrate that the apical extracellular matrix (aECM) of the tracheal tube is a viscoelastic material coupled with the apical membrane. We present a simple mechanical model in which aECM elasticity, apical membrane growth, and their interaction are three vital parameters determining the stability of biological tubes. Our findings demonstrate a mechanical role for the extracellular matrix and suggest that the interaction of the apical membrane and an elastic aECM determines the final morphology of biological tubes independent of cell shape. Copyright © 2014 The Authors. Published by Elsevier Inc. All rights reserved.

Geometric Effects on the Amplification of First Mode Instability Waves

NASA Technical Reports Server (NTRS)

Kirk, Lindsay C.; Candler, Graham V.

2013-01-01

The effects of geometric changes on the amplification of first mode instability waves in an external supersonic boundary layer were investigated using numerical techniques. Boundary layer stability was analyzed at Mach 6 conditions similar to freestream conditions obtained in quiet ground test facilities so that results obtained in this study may be applied to future test article design to measure first mode instability waves. The DAKOTA optimization software package was used to optimize an axisymmetric geometry to maximize the amplification of the waves at first mode frequencies as computed by the 2D STABL hypersonic boundary layer stability analysis tool. First, geometric parameters such as nose radius, cone half angle, vehicle length, and surface curvature were examined separately to determine the individual effects on the first mode amplification. Finally, all geometric parameters were allowed to vary to produce a shape optimized to maximize the amplification of first mode instability waves while minimizing the amplification of second mode instability waves. Since first mode waves are known to be most unstable in the form of oblique wave, the geometries were optimized using a broad range of wave frequencies as well as a wide range of oblique wave angles to determine the geometry that most amplifies the first mode waves. Since first mode waves are seen most often in flows with low Mach numbers at the edge of the boundary layer, the edge Mach number for each geometry was recorded to determine any relationship between edge Mach number and the stability of first mode waves. Results indicate that an axisymmetric cone with a sharp nose and a slight flare at the aft end under the Mach 6 freestream conditions used here will lower the Mach number at the edge of the boundary layer to less than 4, and the corresponding stability analysis showed maximum first mode N factors of 3.

Design considerations of a thermally stabilized continuous flow electrophoresis chamber 2

NASA Technical Reports Server (NTRS)

Jandebeur, T. S.

1982-01-01

The basic adjustable parameters of a Beckman Continouous Particle Electrophoresis (CPE) Apparatus are investigated to determine the optimum conditions for ground based operation for comparison with space experiments. The possible application of electrically insulated copper/aluminum chamber walls is evaluated as a means to thermally stabilize or equilibrate lateral temperature gradients which exist on the walls of conventional plastic chambers and which distort the rectilinear base flow of buffer through the chamber, significantly affecting sample resolution.

Determining drug release rates of hydrophobic compounds from nanocarriers

PubMed Central

D’Addio, Suzanne M.; Bukari, Abdallah A.; Dawoud, Mohammed; Bunjes, Heike; Rinaldi, Carlos; Prud’homme, Robert K.

2016-01-01

Obtaining meaningful drug release profiles for drug formulations is essential prior to in vivo testing and for ensuring consistent quality. The release kinetics of hydrophobic drugs from nanocarriers (NCs) are not well understood because the standard protocols for maintaining sink conditions and sampling are not valid owing to mass transfer and solubility limitations. In this work, a new in vitroassay protocol based on ‘lipid sinks’ and magnetic separation produces release conditions that mimic the concentrations of lipid membranes and lipoproteins in vivo, facilitates separation, and thus allows determination of intrinsic release rates of drugs from NCs. The assay protocol is validated by (i) determining the magnetic separation efficiency, (ii) demonstrating that sink condition requirements are met, and (iii) accounting for drug by completing a mass balance. NCs of itraconazole and cyclosporine A (CsA) were prepared and the drug release profiles were determined. This release protocol has been used to compare the drug release from a polymer stabilized NC of CsA to a solid drug NP of CsA alone. These data have led to the finding that stabilizing block copolymer layers have a retarding effect on drug release from NCs, reducing the rate of CsA release fourfold compared with the nanoparticle without a polymer coating. This article is part of the themed issue ‘Soft interfacial materials: from fundamentals to formulation’. PMID:27298440

Determining drug release rates of hydrophobic compounds from nanocarriers.

PubMed

D'Addio, Suzanne M; Bukari, Abdallah A; Dawoud, Mohammed; Bunjes, Heike; Rinaldi, Carlos; Prud'homme, Robert K

2016-07-28

Obtaining meaningful drug release profiles for drug formulations is essential prior to in vivo testing and for ensuring consistent quality. The release kinetics of hydrophobic drugs from nanocarriers (NCs) are not well understood because the standard protocols for maintaining sink conditions and sampling are not valid owing to mass transfer and solubility limitations. In this work, a new in vitroassay protocol based on 'lipid sinks' and magnetic separation produces release conditions that mimic the concentrations of lipid membranes and lipoproteins in vivo, facilitates separation, and thus allows determination of intrinsic release rates of drugs from NCs. The assay protocol is validated by (i) determining the magnetic separation efficiency, (ii) demonstrating that sink condition requirements are met, and (iii) accounting for drug by completing a mass balance. NCs of itraconazole and cyclosporine A (CsA) were prepared and the drug release profiles were determined. This release protocol has been used to compare the drug release from a polymer stabilized NC of CsA to a solid drug NP of CsA alone. These data have led to the finding that stabilizing block copolymer layers have a retarding effect on drug release from NCs, reducing the rate of CsA release fourfold compared with the nanoparticle without a polymer coating.This article is part of the themed issue 'Soft interfacial materials: from fundamentals to formulation'. © 2016 The Author(s).

High Reynolds Number Thermal Stability Experiments

NASA Technical Reports Server (NTRS)

Emens, Jessica M.; Brown, Sarah P.; Frederick Robert A., Jr.; Wood, A. John

2004-01-01

This work represents preliminary thermal stability results for liquid hydrocarbon fuels. High Reynolds Number Thermal Stability experiments with Jet A and RP-1 resulted in a quantitative measurement of the thermal stability. Each fuel flowed through a heated capillary tube that held the outlet temperature at 290 C. An optical pyrometer measured the surface temperature of the tube at 12 locations as a function of time. The High Reynolds Number Thermal Stability number was then determined using standards published by the American Society for Testing and Materials. The results for Jet A showed lower thermal stability than similar tests conducted at another facility. The RP-1 results are the first reported using this technique. Because the temperature rise on the capillary tube during testing for the RP-1 fuels was not significant, a new standard for the testing conditions should be developed for these types of fuels.

The application of the Accelerated Stability Assessment Program (ASAP) to quality by design (QbD) for drug product stability.

PubMed

Waterman, Kenneth Craig

2011-09-01

An isoconversion paradigm, where times in different temperature and humidity-controlled stability chambers are set to provide a fixed degradant level, is shown to compensate for the complex, non-single order kinetics of solid drug products. A humidity-corrected Arrhenius equation provides reliable estimates for temperature and relative humidity effects on degradation rates. A statistical protocol is employed to determine best fits for chemical stability data, which in turn allows for accurate estimations of shelf life (with appropriate confidence intervals) at any storage condition including inside packaging (based on the moisture vapor transmission rate of the packaging and moisture sorption isotherms of the internal components). These methodologies provide both faster results and far better predictions of chemical stability limited shelf life (expiry) than previously possible. Precise shelf-life estimations are generally determined using a 2-week, product-specific protocol. Once the model for a product is developed, it can play a critical role in providing the product understanding necessary for a quality by design (QbD) filing for product approval and enable rational control strategies to assure product stability. Moreover, this Accelerated Stability Assessment Program (ASAP) enables the coupling of product attributes (e.g., moisture content, packaging options) to allow for flexibility in how control strategies are implemented to provide a balance of cost, speed, and other factors while maintaining adequate stability.

Long-term thermal stability of nanoclusters in ODS-Eurofer steel: An atom probe tomography study

NASA Astrophysics Data System (ADS)

Zilnyk, K. D.; Pradeep, K. G.; Choi, P.; Sandim, H. R. Z.; Raabe, D.

2017-08-01

Oxide-dispersion strengthened materials are important candidates for several high-temperature structural applications in advanced nuclear power plants. Most of the desirable mechanical properties presented by these materials are due to the dispersion of stable nanoparticles in the matrix. Samples of ODS-Eurofer steel were annealed for 4320 h (6 months) at 800 °C. The material was characterized using atom probe tomography in both conditions (prior and after heat treatment). The particles number density, size distribution, and chemical compositions were determined. No significant changes were observed between the two conditions indicating a high thermal stability of the Y-rich nanoparticles at 800 °C.

Optimization of Freeze Drying Conditions for Purified Pectinase from Mango (Mangifera indica cv. Chokanan) Peel

PubMed Central

Mehrnoush, Amid; Mustafa, Shuhaimi; Yazid, Abdul Manap Mohd

2012-01-01

Response surface methodology (RSM) along with central composite design (CCD) was applied to optimize the freeze drying conditions for purified pectinase from mango (Mangifera indica cv. Chokanan) peel. The effect of pectinase content (−2.66, 62.66 mg/mL), Arabic gum (−1.21, 10.21%, w/v), and maltodextrin (0.73, 7.26%, w/v) as independent variables on activity, yield, and storage stability of freeze-dried enzyme was evaluated. Storage stability of pectinase was investigated after one week at 4 °C and yield percentage of the enzyme after encapsulation was also determined. The independent variables had the most significant (p < 0.05) effect on pectinase activity and yield of the enzyme. It was observed that the interaction effect of Arabic gum and maltodextrin improved the enzymatic properties of freeze-dried pectinase. The optimal conditions for freeze-dried pectinase from mango peel were obtained using 30 mg/mL of pectinase content, 4.5 (%, w/v) of Arabic gum, and 4 (%, w/v) of maltodextrin. Under these conditions, the maximum activity (11.12 U/mL), yield (86.4%) and storage stability (84.2%) of encapsulated pectinase were achieved. PMID:22489134

Distributed-Roughness Effects on Stability and Transition In Swept-Wing Boundary Layers

NASA Technical Reports Server (NTRS)

Carrillo, Ruben B., Jr.; Reibert, Mark S.; Saric, William S.

1997-01-01

Boundary-layer stability experiments are conducted in the Arizona State University Unsteady Wind Tunnel on a 45 deg swept airfoil. The pressure distribution and test conditions are designed to suppress Tollmien-Schlichting disturbances and provide crossflow-dominated transition. The surface of the airfoil is finely polished to a near mirror finish. Under these conditions, submicron surface irregularities cause the naturally occurring stationary crossflow waves to grow to nonuniform amplitudes. Spanwise-uniform stationary crossflow disturbances are generated through careful control of the initial conditions with full-span arrays of micron-high roughness elements near the attachment line. Detailed hot-wire measurements are taken to document the stationary crossflow structure and determine growth rates for the total and individual-mode disturbances. Naphthalene flow visualization provides transition location information. Roughness spacing and roughness height are varied to examine the effects on transition location and all amplified wavelengths. The measurements show that roughness spacings that do not contain harmonics equal to the most unstable wavelength as computed by linear stability theory effectively suppress the most unstable mode. Under certain conditions, subcritical roughness spacing delays transition past that of the corresponding smooth surface.

The physical and chemical stability of anti-tuberculosis fixed-dose combination products under accelerated climatic conditions.

PubMed

Bhutani, H; Mariappan, T T; Singh, S

2004-09-01

To determine the physical and chemical stability of anti-tuberculosis fixed-dose combinations (FDC) of rifampicin (RMP), isoniazid (INH), pyrazinamide (PZA) and ethambutol (EMB) sold on the Indian market. The products were stored for 3 months under ICH/WHO accelerated conditions (40 degrees C / 75% RH), with and without the original packaging in the presence and absence of light. The initial RMP, INH and PZA content was found to be within the range of 90-110% of the label claim. However, the products were found to have some chemical instability even initially; one of the tablets also showed physical instability. Under accelerated conditions, the unpackaged products underwent severe changes, whereas both physical and chemical changes were also observed in the packaged formulations. The physical changes were stronger under lighted conditions. A significant finding is that PZA and perhaps EMB may play a catalytic role in the interaction between INH and RMP. This study suggests that, unless they are packed in barrier packaging, anti-tuberculosis FDC formulations should be considered unstable, and due consideration should be given to their development pharmaceutics, packaging and stability testing.

Optimization of freeze drying conditions for purified pectinase from mango (Mangifera indica cv. Chokanan) peel.

PubMed

Mehrnoush, Amid; Mustafa, Shuhaimi; Yazid, Abdul Manap Mohd

2012-01-01

Response surface methodology (RSM) along with central composite design (CCD) was applied to optimize the freeze drying conditions for purified pectinase from mango (Mangifera indica cv. Chokanan) peel. The effect of pectinase content (-2.66, 62.66 mg/mL), Arabic gum (-1.21, 10.21%, w/v), and maltodextrin (0.73, 7.26%, w/v) as independent variables on activity, yield, and storage stability of freeze-dried enzyme was evaluated. Storage stability of pectinase was investigated after one week at 4 °C and yield percentage of the enzyme after encapsulation was also determined. The independent variables had the most significant (p < 0.05) effect on pectinase activity and yield of the enzyme. It was observed that the interaction effect of Arabic gum and maltodextrin improved the enzymatic properties of freeze-dried pectinase. The optimal conditions for freeze-dried pectinase from mango peel were obtained using 30 mg/mL of pectinase content, 4.5 (%, w/v) of Arabic gum, and 4 (%, w/v) of maltodextrin. Under these conditions, the maximum activity (11.12 U/mL), yield (86.4%) and storage stability (84.2%) of encapsulated pectinase were achieved.

Validating internal controls for quantitative plant gene expression studies

PubMed Central

Brunner, Amy M; Yakovlev, Igor A; Strauss, Steven H

2004-01-01

Background Real-time reverse transcription PCR (RT-PCR) has greatly improved the ease and sensitivity of quantitative gene expression studies. However, accurate measurement of gene expression with this method relies on the choice of a valid reference for data normalization. Studies rarely verify that gene expression levels for reference genes are adequately consistent among the samples used, nor compare alternative genes to assess which are most reliable for the experimental conditions analyzed. Results Using real-time RT-PCR to study the expression of 10 poplar (genus Populus) housekeeping genes, we demonstrate a simple method for determining the degree of stability of gene expression over a set of experimental conditions. Based on a traditional method for analyzing the stability of varieties in plant breeding, it defines measures of gene expression stability from analysis of variance (ANOVA) and linear regression. We found that the potential internal control genes differed widely in their expression stability over the different tissues, developmental stages and environmental conditions studied. Conclusion Our results support that quantitative comparisons of candidate reference genes are an important part of real-time RT-PCR studies that seek to precisely evaluate variation in gene expression. The method we demonstrated facilitates statistical and graphical evaluation of gene expression stability. Selection of the best reference gene for a given set of experimental conditions should enable detection of biologically significant changes in gene expression that are too small to be revealed by less precise methods, or when highly variable reference genes are unknowingly used in real-time RT-PCR experiments. PMID:15317655

Improved Stability of a Model IgG3 by DoE-Based Evaluation of Buffer Formulations

DOE PAGES

Chavez, Brittany K.; Agarabi, Cyrus D.; Read, Erik K.; ...

2016-01-01

Formulating appropriate storage conditions for biopharmaceutical proteins is essential for ensuring their stability and thereby their purity, potency, and safety over their shelf-life. Using a model murine IgG3 produced in a bioreactor system, multiple formulation compositions were systematically explored in a DoE design to optimize the stability of a challenging antibody formulation worst case. The stability of the antibody in each buffer formulation was assessed by UV/VIS absorbance at 280 nm and 410 nm and size exclusion high performance liquid chromatography (SEC) to determine overall solubility, opalescence, and aggregate formation, respectively. Upon preliminary testing, acetate was eliminated as a potentialmore » storage buffer due to significant visible precipitate formation. An additional 2 4full factorial DoE was performed that combined the stabilizing effect of arginine with the buffering capacity of histidine. From this final DoE, an optimized formulation of 200 mM arginine, 50 mM histidine, and 100 mM NaCl at a pH of 6.5 was identified to substantially improve stability under long-term storage conditions and after multiple freeze/thaw cycles. Therefore, our data highlights the power of DoE based formulation screening approaches even for challenging monoclonal antibody molecules.« less

Evaluation of the thermal stability of a novel strain of live-attenuated mumps vaccine (RS-12 strain) lyophilized in different stabilizers.

PubMed

Jamil, Razieh Kamali; Taqavian, Mohammad; Sadigh, Zohreh-Azita; Shahkarami, Mohammad-Kazem; Esna-Ashari, Fatemeh; Hamkar, Rasool; Hosseini, Seyedeh-Marzieh; Hatami, Alireza

2014-04-01

The stability of live-attenuated viral vaccines is important for immunization efficacy. Here, the thermostabilities of lyophilized live-attenuated mumps vaccine formulations in two different stabilizers, a trehalose dihydrate-based stabilizer and a stabilizer containing sucrose, human serum albumin and sorbitol were investigated using accelerated stability tests at 4°C, 25°C and 37°C at time points between 4h (every 4h for the first 24h) and 1 week. Even under the harshest storage conditions of 37°C for 1 week, the 50% cell culture infective dose (CCID50) determined from titrations in Vero cells dropped by less than 10-fold using each stabilizer formulation and thus complied with the World Health Organization's requirements for the potency of live-attenuated mumps vaccines. However, as the half-life of the RS-12 strain mumps virus infectivity was lengthened substantially at elevated temperatures using the trehalose dihydrate (TD)-based stabilizer, this stabilizer is recommended for vaccine use. Copyright © 2013 Elsevier B.V. All rights reserved.

Flight test report of the NASA icing research airplane: Performance, stability, and control after flight through natural icing conditions

NASA Technical Reports Server (NTRS)

Jordan, J. L.; Platz, S. J.; Schinstock, W. C.

1986-01-01

Flight test results are presented documenting the effect of airframe icing on performance and stability and control of a NASA DHC-6 icing research aircraft. Kohlman System Research, Inc., provided the data acquisition system and data analysis under contract to NASA. Performance modeling methods and MMLE techniques were used to determine the effects of natural ice on the aircraft. Results showed that ice had a significant effect on the drag coefficient of the aircraft and a modest effect on the MMLE derived longitudinal stability coefficients (code version MMLE). Data is also presented on asymmetric power sign slip maneuvers showing rudder floating characteristics with and without ice on the vertical stabilizer.

Metal Construction

NASA Technical Reports Server (NTRS)

Verduzio, Rodolfo

1922-01-01

The future development of aerial navigation is closely connected with the condition of obtaining airplanes of great stability and sufficient strength. Different construction materials such as wood, aluminum, iron, and alloys are examined to determine which materials or combination of materials provides a greater coefficient of safety.

Preparation, Purification, and Secondary Structure Determination of Bacillus Circulans Xylanase. A Molecular Laboratory Incorporating Aspects of Molecular Biology, Biochemistry, and Biophysical Chemistry

ERIC Educational Resources Information Center

Russo, Sal; Gentile, Lisa

2006-01-01

A project module designed for biochemistry or cellular and molecular biology student which involves determining the secondary structure of Bacillus circulans xylanase (BCX) by circular dichroism (CD) spectroscopy under conditions that compromise its stabilizing intramolecular forces is described. The lab model enhanced students knowledge of the…

Strong stabilization servo controller with optimization of performance criteria.

PubMed

Sarjaš, Andrej; Svečko, Rajko; Chowdhury, Amor

2011-07-01

Synthesis of a simple robust controller with a pole placement technique and a H(∞) metrics is the method used for control of a servo mechanism with BLDC and BDC electric motors. The method includes solving a polynomial equation on the basis of the chosen characteristic polynomial using the Manabe standard polynomial form and parametric solutions. Parametric solutions are introduced directly into the structure of the servo controller. On the basis of the chosen parametric solutions the robustness of a closed-loop system is assessed through uncertainty models and assessment of the norm ‖•‖(∞). The design procedure and the optimization are performed with a genetic algorithm differential evolution - DE. The DE optimization method determines a suboptimal solution throughout the optimization on the basis of a spectrally square polynomial and Šiljak's absolute stability test. The stability of the designed controller during the optimization is being checked with Lipatov's stability condition. Both utilized approaches: Šiljak's test and Lipatov's condition, check the robustness and stability characteristics on the basis of the polynomial's coefficients, and are very convenient for automated design of closed-loop control and for application in optimization algorithms such as DE. Copyright © 2011 ISA. Published by Elsevier Ltd. All rights reserved.

Evaluation of the stability of gas hydrates in Northern Alaska

USGS Publications Warehouse

Kamath, A.; Godbole, S.P.; Ostermann, R.D.; Collett, T.S.

1987-01-01

The factors which control the distribution of in situ gas hydrate deposits in colder regions such as Northern Alaska include; mean annual surface temperatures (MAST), geothermal gradients above and below the base of permafrost, subsurface pressures, gas composition, pore-fluid salinity and the soil condition. Currently existing data on the above parameters for the forty-six wells located in Northern Alaska were critically examined and used in calculations of depths and thicknesses of gas hydrate stability zones. To illustrate the effect of gas hydrate stability zones, calculations were done for a variable gas composition using the thermodynamic model of Holder and John (1982). The hydrostatic pressure gradient of 9.84 kPa/m (0.435 lbf/in2ft), the salinity of 10 parts per thousand (ppt) and the coarse-grained soil conditions were assumed. An error analysis was performed for the above parameters and the effect of these parameters on hydrate stability zone calculations were determined. After projecting the hydrate stability zones for the forty-six wells, well logs were used to identify and to obtain values for the depth and thickness of hydrate zones. Of the forty-six wells, only ten wells showed definite evidence of the presence of gas hydrates. ?? 1987.

Effects of temperature distribution on boundary layer stability for a circular cone at Mach 10

NASA Astrophysics Data System (ADS)

Rigney, Jeffrey M.

A CFD analysis was conducted on a circular cone at 3 degrees angle of attack at Mach 10 using US3D and STABL 3D to determine the effect of wall temperature on the stability characteristics that lead to laminar-to-turbulent transition. Wall temperature distributions were manipulated while all other flow inputs and geometric qualities were held constant. Laminar-to-turbulent transition was analyzed for isothermal and adiabatic wall conditions, a simulated short-duration wind tunnel case, and several hot-nose temperature distributions. For this study, stability characteristics include maximum N-factor growth and the corresponding frequency range, disturbance spatial amplification rate and the corresponding modal frequency, and stability neutral point location. STABL 3D analysis indicates that temperature distributions typical of those in short-duration hypersonic wind tunnels do not result in any significant difference on the stability characteristics, as compared to an isothermal wall boundary condition. Hypothetical distributions of much greater temperatures at and past the nose tip do show a trend of dampening of second-mode disturbances, most notably on the leeward ray. The most pronounced differences existed between the isothermal and adiabatic cases.

Evaluating the effects of buffer conditions and extremolytes on thermostability of granulocyte colony-stimulating factor using high-throughput screening combined with design of experiments.

PubMed

Ablinger, Elisabeth; Hellweger, Monika; Leitgeb, Stefan; Zimmer, Andreas

2012-10-15

In this study, we combined a high-throughput screening method, differential scanning fluorimetry (DSF), with design of experiments (DoE) methodology to evaluate the effects of several formulation components on the thermostability of granulocyte colony stimulating factor (G-CSF). First we performed a primary buffer screening where we tested thermal stability of G-CSF in different buffers, pH values and buffer concentrations. The significance of each factor and the two-way interactions between them were studied by multivariable regression analysis. pH was identified as most critical factor regarding thermal stability. The most stabilizing buffer, sodium glutamate, and sodium acetate were determined for further investigations. Second we tested the effect of 6 naturally occurring extremolytes (trehalose, sucrose, ectoine, hydroxyectoine, sorbitol, mannitol) on the thermal stability of G-CSF, using a central composite circumscribed design. At low pH (3.8) and low buffer concentration (5 mM) all extremolytes led to a significant increase in thermal stability except the addition of ectoine which resulted in a strong destabilization of G-CSF. Increasing pH and buffer concentration led to an increase in thermal stability with all investigated extremolytes. The described systematic approach allowed to create a ranking of stabilizing extremolytes at different buffer conditions. Copyright © 2012. Published by Elsevier B.V.

Determination of fluvoxamine maleate in human urine and human serum using alkaline KMnO4 -rhodamine B chemiluminescence.

PubMed

Yang, Dongqin; He, Yanyan; Chen, Funan

2017-09-01

The flow-injection chemiluminescence (FI-CL) behavior of a gold nanocluster (Au NC)-enhanced rhodamine B-KMnO 4 system was studied under alkaline conditions for the first time. In the present study, the as-prepared bovine serum albumin-stabilized Au NCs showed excellent stability and reproducibility. The addition of trace levels of fluvoxamine maleate (Flu) led to an obvious decline in CL intensity in the rhodamine B-KMnO 4 -Au NCs system, which could be used for quantitative detection of Flu. Under optimized conditions, the proposed CL system exhibited a favorable analytical performance for Flu determination in the range 2 to 100 μg ml -1 . The detection limit for Flu measurement was 0.021 μg ml -1 . Moreover, this newly developed system revealed outstanding selectivity for Flu detection when compared with a multitude of other species, such as the usual ions, uric acid and a section of hydroxy compounds. Additionally, CL spectra, UV-visible spectroscopes and fluorescence spectra were measured in order to determine the possible reaction mechanism. This approach could be used to detect Flu in human urine and human serum samples with the desired recoveries and could have promising application under physiological conditions. Copyright © 2017 John Wiley & Sons, Ltd.

Thermal and photo-stability of the antioxidant potential of Spirulina platensis powder.

PubMed

Colla, L M; Bertol, C D; Ferreira, D J; Bavaresco, J; Costa, J A V; Bertolin, T E

2017-01-01

This work aimed to evaluate the thermal and photo stability of the antioxidant potential (AP) of the Spirulina platensis biomass. Thermal stability was established at 25ºC, 40ºC and 50ºC for 60 days, in the dark, protected from light. Photo stability was evaluated using UV (15 W, λ = 265 nm) and fluorescent (20 W, 0.16 A, power factor FP > 0.5, 50/60 Hz, 60 lm/w, 1200 lm) light for 90 days in capsules, glass and Petri dishes, at room temperature. The AP of the biomass in these conditions was determined at intervals (every 7 and 30 days in the studies of thermal and photo stability, respectively) using the induction of the oxidation of a lipid system by heat and aeration. In this lipid system, the biomass submitted to degradation was used as an antioxidant. The kinetics of the reaction was determined by the Arrhenius method. Thermal degradation was found to follow zero order kinetics, whereas photo degradation followed first order kinetics. The AP decreased 50% after 50 days at 25°C. At 40°C and 50°C, the AP decreased more than 50% after 35 and 21 days of exposition, respectively. The decrease of the AP of Spirulina was more sensible to UV and fluorescence light. After 30 days of exposition, the AP decreased more than 50% in all storage conditions tested. The antioxidant potential of Spirulina platensis is easily degraded when the biomass is exposed to heat and light, indicating the need for care to be taken in its storage.

Norm stability at Alcatraz Island: Effects of time and changing conditions

Treesearch

William Valliere; Robert Manning

2010-01-01

Research suggests that visitors often have norms about the resource and social conditions acceptable in a park and that understanding such norms can be useful for park management. Most studies of norms use data from cross-sectional surveys, and little is known about how norms may change over time. To explore this issue, we conducted a study in 2007 to determine whether...

Postural steadiness and ankle force variability in peripheral neuropathy

PubMed Central

Paxton, Roger J.; Feldman-Kothe, Caitlin; Trabert, Megan K.; Hitchcock, Leah N.; Reiser, Raoul F.; Tracy, Brian L.

2015-01-01

Introduction The purpose was to determine the effect of peripheral neuropathy (PN) on motor output variability for ankle muscles of older adults, and the relation between ankle motor variability and postural stability in PN patients. Methods Older adults with (O-PN) and without PN (O), and young adults (Y) underwent assessment of standing postural stability and ankle muscle force steadiness. Results O-PN displayed impaired ankle muscle force control and postural stability compared with O and Y groups. For O-PN, the amplitude of plantarflexor force fluctuations was moderately correlated with postural stability under no-vision conditions (r = 0.54, P = 0.01). Discussion The correlation of variations in ankle force with postural stability in PN suggests a contribution of ankle muscle dyscontrol to the postural instability that impacts physical function for older adults with PN. PMID:26284897

Spacecraft stability and control

NASA Technical Reports Server (NTRS)

Barret, Chris

1992-01-01

The Earth's first artificial satellite, Sputnik 1, slowly tumbled in orbit. The first U.S. satellite, Explorer 1, also tumbled out of control. Today, satellite stability and control has become a higher priority. For a satellite design that is to have a life expectancy of 14 years, appropriate spacecraft flight control systems will be reviewed, stability requirements investigated, and an appropriate flight control system recommended in order to see the design process. Disturbance torques, including aerodynamic, magnetic, gravity gradient, solar, micrometeorite, debris, collision, and internal torques, will be assessed to quantify the disturbance environment so that the required compensating torques can be determined. The control torques, including passive versus active, momentum control, bias momentum, spin stabilization, dual spin, gravity gradient, magnetic, reaction wheels, control moment gyros, inertia augmentation techniques, three-axis control, and reaction control systems (RCSs), will be considered. Conditions for stability will also be considered.

Controlling the position of a stabilized detonation wave in a supersonic gas mixture flow in a plane channel

NASA Astrophysics Data System (ADS)

Levin, V. A.; Zhuravskaya, T. A.

2017-03-01

Stabilization of a detonation wave in a stoichiometric hydrogen-air mixture flowing at a supersonic velocity into a plane symmetric channel with constriction has been studied in the framework of a detailed kinetic mechanism of the chemical interaction. Conditions ensuring the formation of a thrust-producing f low with a stabilized detonation wave in the channel are determined. The inf luence of the inf low Mach number, dustiness of the combustible gas mixture supplied to the channel, and output cross-section size on the position of a stabilized detonation wave in the f low has been analyzed with a view to increasing the efficiency of detonation combustion of the gas mixture. It is established that thrust-producing flow with a stabilized detonation wave can be formed in the channel without any energy consumption.

Chemical stability of molten 2,4,6-trinitrotoluene at high pressure

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

Dattelbaum, Dana M., E-mail: danadat@lanl.gov; Chellappa, Raja S.; Bowden, Patrick R.

2014-01-13

2,4,6-trinitrotoluene (TNT) is a molecular explosive that exhibits chemical stability in the molten phase at ambient pressure. A combination of visual, spectroscopic, and structural (x-ray diffraction) methods coupled to high pressure, resistively heated diamond anvil cells was used to determine the melt and decomposition boundaries to >15 GPa. The chemical stability of molten TNT was found to be limited, existing in a small domain of pressure-temperature conditions below 2 GPa. Decomposition dominates the phase diagram at high temperatures beyond 6 GPa. From the calculated bulk temperature rise, we conclude that it is unlikely that TNT melts on its principal Hugoniot.

Stability limits and dynamics of nonaxisymmetric liquid bridges

NASA Technical Reports Server (NTRS)

Alexander, J. Iwan D.; Resnik, Andy; Kaukler, William F.

1993-01-01

This program of theoretical and experimental ground-based and low gravity research is focussed on the understanding of the dynamics and stability limits of nonaxisymmetric liquid bridges. There are three basic objectives to the proposed work: (1) to determine the stability limits of nonaxisymmetric liquid bridges held between non-coaxially aligned disks; (2) to examine the dynamics of nonaxisymmetric bridges and nonaxisymmetric oscillations of initially axisymmetric bridges (some of these experiments require a low gravity environment and the ground-based research will culminate in a definitive flight experiment); and (3) to experimentally investigate the vibration sensitivity of liquid bridges under terrestrial and low gravity conditions.

Round and Oval Window Anatomic Variability: Its Implication for the Vibroplasty Technique.

PubMed

Mancheño, Marta; Aristegui, Miguel; Sañudo, Jose Ramon

2017-06-01

The objective of this study is to evaluate the anatomical variability of round and oval window regions and its relationship with their closest structures, to determine its implication on the fitting and stabilization of the middle ear implant Vibrant Soundbridge. Variations of the anatomy of round and oval window regions were assessed in a total of 85 human dissected temporal bones. Afterward, we evaluated the adaptation and subsequent stabilization of the floating mass transducer (FMT) of the Vibrant Soundbridge in 67 cases in round window (RW) and in 22 cases in oval window (OW), and the influence that the variability of the different anatomical features examined had on this stabilization. We also assessed access and surgeon's view of the RW niche through the facial recess approach. Stabilization of the FMT in the RW was achieved in 53 (79%) of the 67 cases; we found that the less favorable anatomical conditions for stabilization were: membrane smaller than 1.5 mm, presence of a high jugular bulb and a narrow or very narrow RW niche. Frequently, two or more of these conditions happened simultaneously. In seven cases (22%) access to the RW through facial recess approach did not allow positioning the FMT in place. OW stabilization succeeded in 18 (82%) of the 22 cases. Round and oval window vibroplasty are difficult surgical techniques. To place the FMT directly on the OW may be easier as we do not have to drill the niche. In both regions there are some anatomical conditions that hinder fitting the FMT and even make it impossible. Once fitted, the main problem is to achieve good stabilization of the device.

Curvilinear Immersed Boundary Method for Simulating Fluid Structure Interaction with Complex 3D Rigid Bodies

PubMed Central

Borazjani, Iman; Ge, Liang; Sotiropoulos, Fotis

2010-01-01

The sharp-interface CURVIB approach of Ge and Sotiropoulos [L. Ge, F. Sotiropoulos, A Numerical Method for Solving the 3D Unsteady Incompressible Navier-Stokes Equations in Curvilinear Domains with Complex Immersed Boundaries, Journal of Computational Physics 225 (2007) 1782–1809] is extended to simulate fluid structure interaction (FSI) problems involving complex 3D rigid bodies undergoing large structural displacements. The FSI solver adopts the partitioned FSI solution approach and both loose and strong coupling strategies are implemented. The interfaces between immersed bodies and the fluid are discretized with a Lagrangian grid and tracked with an explicit front-tracking approach. An efficient ray-tracing algorithm is developed to quickly identify the relationship between the background grid and the moving bodies. Numerical experiments are carried out for two FSI problems: vortex induced vibration of elastically mounted cylinders and flow through a bileaflet mechanical heart valve at physiologic conditions. For both cases the computed results are in excellent agreement with benchmark simulations and experimental measurements. The numerical experiments suggest that both the properties of the structure (mass, geometry) and the local flow conditions can play an important role in determining the stability of the FSI algorithm. Under certain conditions unconditionally unstable iteration schemes result even when strong coupling FSI is employed. For such cases, however, combining the strong-coupling iteration with under-relaxation in conjunction with the Aitken’s acceleration technique is shown to effectively resolve the stability problems. A theoretical analysis is presented to explain the findings of the numerical experiments. It is shown that the ratio of the added mass to the mass of the structure as well as the sign of the local time rate of change of the force or moment imparted on the structure by the fluid determine the stability and convergence of the FSI algorithm. The stabilizing role of under-relaxation is also clarified and an upper bound of the required for stability under-relaxation coefficient is derived. PMID:20981246

Curvilinear immersed boundary method for simulating fluid structure interaction with complex 3D rigid bodies

NASA Astrophysics Data System (ADS)

Borazjani, Iman; Ge, Liang; Sotiropoulos, Fotis

2008-08-01

The sharp-interface CURVIB approach of Ge and Sotiropoulos [L. Ge, F. Sotiropoulos, A numerical method for solving the 3D unsteady incompressible Navier-Stokes equations in curvilinear domains with complex immersed boundaries, Journal of Computational Physics 225 (2007) 1782-1809] is extended to simulate fluid structure interaction (FSI) problems involving complex 3D rigid bodies undergoing large structural displacements. The FSI solver adopts the partitioned FSI solution approach and both loose and strong coupling strategies are implemented. The interfaces between immersed bodies and the fluid are discretized with a Lagrangian grid and tracked with an explicit front-tracking approach. An efficient ray-tracing algorithm is developed to quickly identify the relationship between the background grid and the moving bodies. Numerical experiments are carried out for two FSI problems: vortex induced vibration of elastically mounted cylinders and flow through a bileaflet mechanical heart valve at physiologic conditions. For both cases the computed results are in excellent agreement with benchmark simulations and experimental measurements. The numerical experiments suggest that both the properties of the structure (mass, geometry) and the local flow conditions can play an important role in determining the stability of the FSI algorithm. Under certain conditions the FSI algorithm is unconditionally unstable even when strong coupling FSI is employed. For such cases, however, combining the strong coupling iteration with under-relaxation in conjunction with the Aitken's acceleration technique is shown to effectively resolve the stability problems. A theoretical analysis is presented to explain the findings of the numerical experiments. It is shown that the ratio of the added mass to the mass of the structure as well as the sign of the local time rate of change of the force or moment imparted on the structure by the fluid determine the stability and convergence of the FSI algorithm. The stabilizing role of under-relaxation is also clarified and the upper bound of the under-relaxation coefficient, required for stability, is derived.

Experimental evaluation of a new morphological approximation of the articular surfaces of the ankle joint.

PubMed

Belvedere, Claudio; Siegler, Sorin; Ensini, Andrea; Toy, Jason; Caravaggi, Paolo; Namani, Ramya; Giannini, Giulia; Durante, Stefano; Leardini, Alberto

2017-02-28

The mechanical characteristics of the ankle such as its kinematics and load transfer properties are influenced by the geometry of the articulating surfaces. A recent, image-based study found that these surfaces can be approximated by a saddle-shaped, skewed, truncated cone with its apex oriented laterally. The goal of this study was to establish a reliable experimental technique to study the relationship between the geometry of the articular surfaces of the ankle and its mobility and stability characteristics and to use this technique to determine if morphological approximations of the ankle surfaces based on recent discoveries, produce close to normal behavior. The study was performed on ten cadavers. For each specimen, a process based on medical imaging, modeling and 3D printing was used to produce two subject specific artificial implantable sets of the ankle surfaces. One set was a replica of the natural surfaces. The second approximated the ankle surfaces as an original saddle-shaped truncated cone with apex oriented laterally. Testing under cyclic loading conditions was then performed on each specimen following a previously established technique to determine its mobility and stability characteristics under three different conditions: natural surfaces; artificial surfaces replicating the natural surface morphology; and artificial approximation based on the saddle-shaped truncated cone concept. A repeated measure analysis of variance was then used to compare between the three conditions. The results show that (1): the artificial surfaces replicating natural morphology produce close to natural mobility and stability behavior thus establishing the reliability of the technique; and (2): the approximated surfaces based on saddle-shaped truncated cone concept produce mobility and stability behavior close to the ankle with natural surfaces. Copyright © 2017 Elsevier Ltd. All rights reserved.

Divalent cations and molecular crowding buffers stabilize G-triplex at physiologically relevant temperatures

PubMed Central

Jiang, Hong-Xin; Cui, Yunxi; Zhao, Ting; Fu, Hai-Wei; Koirala, Deepak; Punnoose, Jibin Abraham; Kong, De-Ming; Mao, Hanbin

2015-01-01

G-triplexes are non-canonical DNA structures formed by G-rich sequences with three G-tracts. Putative G-triplex-forming sequences are expected to be more prevalent than putative G-quadruplex-forming sequences. However, the research on G-triplexes is rare. In this work, the effects of molecular crowding and several physiologically important metal ions on the formation and stability of G-triplexes were examined using a combination of circular dichroism, thermodynamics, optical tweezers and calorimetry techniques. We determined that molecular crowding conditions and cations, such as Na+, K+, Mg2+ and Ca2+, promote the formation of G-triplexes and stabilize these structures. Of these four metal cations, Ca2+ has the strongest stabilizing effect, followed by K+, Mg2+, and Na+ in a decreasing order. The binding of K+ to G-triplexes is accompanied by exothermic heats, and the binding of Ca2+ with G-triplexes is characterized by endothermic heats. G-triplexes formed from two G-triad layers are not stable at physiological temperatures; however, G-triplexes formed from three G-triads exhibit melting temperatures higher than 37°C, especially under the molecular crowding conditions and in the presence of K+ or Ca2+. These observations imply that stable G-triplexes may be formed under physiological conditions. PMID:25787838

Stability Switches, Hopf Bifurcations, and Spatio-temporal Patterns in a Delayed Neural Model with Bidirectional Coupling

NASA Astrophysics Data System (ADS)

Song, Yongli; Zhang, Tonghua; Tadé, Moses O.

2009-12-01

The dynamical behavior of a delayed neural network with bi-directional coupling is investigated by taking the delay as the bifurcating parameter. Some parameter regions are given for conditional/absolute stability and Hopf bifurcations by using the theory of functional differential equations. As the propagation time delay in the coupling varies, stability switches for the trivial solution are found. Conditions ensuring the stability and direction of the Hopf bifurcation are determined by applying the normal form theory and the center manifold theorem. We also discuss the spatio-temporal patterns of bifurcating periodic oscillations by using the symmetric bifurcation theory of delay differential equations combined with representation theory of Lie groups. In particular, we obtain that the spatio-temporal patterns of bifurcating periodic oscillations will alternate according to the change of the propagation time delay in the coupling, i.e., different ranges of delays correspond to different patterns of neural activities. Numerical simulations are given to illustrate the obtained results and show the existence of bursts in some interval of the time for large enough delay.

Fingertip touch improves postural stability in patients with peripheral neuropathy.

PubMed

Dickstein, R; Shupert, C L; Horak, F B

2001-12-01

The purpose of this work was to determine whether fingertip touch on a stable surface could improve postural stability during stance in subjects with somatosensory loss in the feet from diabetic peripheral neuropathy. The contribution of fingertip touch to postural stability was determined by comparing postural sway in three touch conditions (light, heavy and none) in eight patients and eight healthy control subjects who stood on two surfaces (firm or foam) with eyes open or closed. In the light touch condition, fingertip touch provided only somatosensory information because subjects exerted less than 1 N of force with their fingertip to a force plate, mounted on a vertical support. In the heavy touch condition, mechanical support was available because subjects transmitted as much force to the force plate as they wished. In the no touch condition, subjects held the right forefinger above the force plate. Antero-posterior (AP) and medio-lateral (ML) root mean square (RMS) of center of pressure (CoP) sway and trunk velocity were larger in subjects with somatosensory loss than in control subjects, especially when standing on the foam surface. The effects of light and heavy touch were similar in the somatosensory loss and control groups. Fingertip somatosensory input through light touch attenuated both AP and ML trunk velocity as much as heavy touch. Light touch also reduced CoP sway compared to no touch, although the decrease in CoP sway was less effective than with heavy touch, particularly on the foam surface. The forces that were applied to the touch plate during light touch preceded movements of the CoP, lending support to the suggestion of a feedforward mechanism in which fingertip inputs trigger the activation of postural muscles for controlling body sway. These results have clinical implications for understanding how patients with peripheral neuropathy may benefit from a cane for postural stability in stance.

Analytical determination of the effect of structural elasticity on landing stability of a version of the Viking Lander

NASA Technical Reports Server (NTRS)

Laurenson, R. M.

1972-01-01

A limited analytical investigation was conducted to assess the effects of structural elasticity on the landing stability of a version of the Viking Lander. Two landing conditions and two lander mass and inertia distributions were considered. The results of this investigation show that the stability-critical surface slopes were lower for an uphill landing than for a downhill landing. In addition, the heavy footpad mass with its corresponding inertia distribution resulted in lower stability-critical ground slopes than were obtained for the light footpad mass and its corresponding inertia distribution. Structural elasticity was observed to have a large effect on the downhill landing stability of the light footpad mass configuration but had a negligible effect on the stability of the other configuration examined. Because of the limited nature of this study, care must be exercised in drawing conclusions from these results relative to the overall stability characteristics of the Viking Lander.

UPLC and LC-MS studies on degradation behavior of irinotecan hydrochloride and development of a validated stability-indicating ultra-performance liquid chromatographic method for determination of irinotecan hydrochloride and its impurities in pharmaceutical dosage forms.

PubMed

Kumar, Navneet; Sangeetha, Dhanaraj; Reddy, Sunil P

2012-10-01

The objective of the current investigation was to study the degradation behavior of irinotecan hydrochloride under different International Conference on Harmonization (ICH) recommended stress conditions using ultra-performance liquid chromatography and liquid chromatography-mass spectrometry and to establish a validated stability-indicating reverse-phase ultra-performance liquid chromatographic method for the quantitative determination of irinotecan hydrochloride and its seven impurities and degradation products in pharmaceutical dosage forms. Irinotecan hydrochloride was subjected to the stress conditions of oxidative, acid, base, hydrolytic, thermal and photolytic degradation. Irinotecan hydrochloride was found to degrade significantly in oxidative and base hydrolysis and photolytic degradation conditions. The degradation products were well resolved from the main peak and its impurities, thus proving the stability-indicating power of the method. Chromatographic separation was achieved on a Waters Acquity BEH C8 (100 × 2.1 mm) 1.7-µm column with a mobile phase containing a gradient mixture of solvent A (0.02M KH(2)PO(4) buffer, pH 3.4) and solvent B (a mixture of acetonitrile and methanol in the ratio of 62:38 v/v). The mobile phase was delivered at a flow rate of 0.3 mL/min with ultraviolet detection at 220 nm. The run time was 8 min, within which irinotecan and its seven impurities and degradation products were satisfactorily separated. The developed method was validated as per ICH guidelines with respect to specificity, linearity, limit of detection, limit of quantification, accuracy, precision and robustness. This method was also suitable for the assay determination of irinotecan hydrochloride in pharmaceutical dosage forms.

Linearized blade row compression component model. Stability and frequency response analysis of a J85-3 compressor

NASA Technical Reports Server (NTRS)

Tesch, W. A.; Moszee, R. H.; Steenken, W. G.

1976-01-01

NASA developed stability and frequency response analysis techniques were applied to a dynamic blade row compression component stability model to provide a more economic approach to surge line and frequency response determination than that provided by time-dependent methods. This blade row model was linearized and the Jacobian matrix was formed. The clean-inlet-flow stability characteristics of the compressors of two J85-13 engines were predicted by applying the alternate Routh-Hurwitz stability criterion to the Jacobian matrix. The predicted surge line agreed with the clean-inlet-flow surge line predicted by the time-dependent method to a high degree except for one engine at 94% corrected speed. No satisfactory explanation of this discrepancy was found. The frequency response of the linearized system was determined by evaluating its Laplace transfer function. The results of the linearized-frequency-response analysis agree with the time-dependent results when the time-dependent inlet total-pressure and exit-flow function amplitude boundary conditions are less than 1 percent and 3 percent, respectively. The stability analysis technique was extended to a two-sector parallel compressor model with and without interstage crossflow and predictions were carried out for total-pressure distortion extents of 180 deg, 90 deg, 60 deg, and 30 deg.

Determinant representation of the domain-wall boundary condition partition function of a Richardson-Gaudin model containing one arbitrary spin

NASA Astrophysics Data System (ADS)

Faribault, Alexandre; Tschirhart, Hugo; Muller, Nicolas

2016-05-01

In this work we present a determinant expression for the domain-wall boundary condition partition function of rational (XXX) Richardson-Gaudin models which, in addition to N-1 spins \\frac{1}{2}, contains one arbitrarily large spin S. The proposed determinant representation is written in terms of a set of variables which, from previous work, are known to define eigenstates of the quantum integrable models belonging to this class as solutions to quadratic Bethe equations. Such a determinant can be useful numerically since systems of quadratic equations are much simpler to solve than the usual highly nonlinear Bethe equations. It can therefore offer significant gains in stability and computation speed.

Application of Classical Land Surveying Measurement Methods for Determining the Vertical Displacement of Railway Bridges

NASA Astrophysics Data System (ADS)

Gawronek, Pelagia; Makuch, Maria

2017-12-01

The classical measurements of stability of railway bridge, in the context of determining the vertical displacements of the object, consisted on precise leveling of girders and trigonometric leveling of controlled points (fixed into girders' surface). The construction elements, which were measured in two ways, in real terms belonged to the same vertical planes. Altitude measurements of construction were carried out during periodic structural stability tests and during static load tests of bridge by train. The specificity of displacement measurements, the type of measured object and the rail land surveying measurement conditions were determinants to define methodology of altitude measurement. The article presents compatibility of vertical displacements of steel railway bridge, which were developed in two measurement methods. In conclusion, the authors proposed the optimum concept of determining the vertical displacements of girders by using precise and trigonometric leveling (in terms of accuracy, safety and economy of measurement).

Stabilization of Pt monolayer catalysts under harsh conditions of fuel cells

DOE PAGES

Zhang, Xiaoming; Liu, Ping; Yu, Shansheng; ...

2015-05-21

We employed density functional theory (DFT) to explore the stability of core (M = Cu, Ru, Rh, Pd, Ag, Os, Ir, Au)-shell (Pt) catalysts under harsh conditions, including solutions and reaction intermediates involved in the oxygen reduction reaction (ORR) in fuel cells. A pseudomorphic surface alloy (PSA) with a Pt monolayer (Pt 1ML) supported on an M surface, Pt 1ML/M(111) or (001), was considered as a model system. Different sets of candidate M cores were identified to achieve a stable Pt 1ML shell depending on the conditions. In vacuum conditions, the Pt 1ML shell can be stabilized on the mostmore » of M cores except Cu, Ag, and Au. The situation varies under various electrochemical conditions. Depending on the solutions and the operating reaction pathways of the ORR, different M should be considered. Pd and Ir are the only core metals studied, being able to keep the Pt ML shell intact in perchloric acid, sulfuric acid, phosphoric acid, and alkaline solutions as well as under the ORR conditions via different pathways. Ru and Os cores should also be paid attention, which only fall during the ORR via the *OOH intermediate. Rh core works well as long as the ORR does not undergo the pathway via *O intermediate. Our results show that PSAs can behave differently from the near surface alloy, Pt 1ML/M 1ML/Pt(111), highlighting the importance of considering both chemical environments and the atomic structures in rational design of highly stable core-shell nanocatalysts. Finally, the roles that d-band center of a core M played in determining the stability of supported Pt 1ML shell were also discussed.« less

Stabilization of Pt monolayer catalysts under harsh conditions of fuel cells

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

Zhang, Xiaoming; Yu, Shansheng; Zheng, Weitao, E-mail: wtzheng@jlu.edu.cn, E-mail: pingliu3@bnl.gov

2015-05-21

We employed density functional theory to explore the stability of core (M = Cu, Ru, Rh, Pd, Ag, Os, Ir, Au)-shell (Pt) catalysts under harsh conditions, including solutions and reaction intermediates involved in the oxygen reduction reaction (ORR) in fuel cells. A pseudomorphic surface alloy (PSA) with a Pt monolayer (Pt{sub 1ML}) supported on an M surface, Pt{sub 1ML}/M(111) or (001), was considered as a model system. Different sets of candidate M cores were identified to achieve a stable Pt{sub 1ML} shell depending on the conditions. In vacuum conditions, the Pt{sub 1ML} shell can be stabilized on the most ofmore » M cores except Cu, Ag, and Au. The situation varies under various electrochemical conditions. Depending on the solutions and the operating reaction pathways of the ORR, different M should be considered. Pd and Ir are the only core metals studied, being able to keep the Pt{sub ML} shell intact in perchloric acid, sulfuric acid, phosphoric acid, and alkaline solutions as well as under the ORR conditions via different pathways. Ru and Os cores should also be paid attention, which only fall during the ORR via the *OOH intermediate. Rh core works well as long as the ORR does not undergo the pathway via *O intermediate. Our results show that PSAs can behave differently from the near surface alloy, Pt{sub 1ML}/M{sub 1ML}/Pt(111), highlighting the importance of considering both chemical environments and the atomic structures in rational design of highly stable core-shell nanocatalysts. Finally, the roles that d-band center of a core M played in determining the stability of supported Pt{sub 1ML} shell were also discussed.« less

Storage stability of biodegradable polyethylene glycol microspheres

NASA Astrophysics Data System (ADS)

Jain, Era; Sheth, Saahil; Polito, Kristen; Sell, Scott A.; Zustiak, Silviya P.

2017-10-01

Degradable hydrogel microspheres are popular choices for multiple biomedical applications, including drug, protein, or cell carriers for minimally invasive delivery. Clinical transitioning of such new, sensitive pharmaceutical preparations requires investigation of storage methods that retain key properties for extended time. In this study, we sought to determine the influence of seven common storage conditions on the physical and mechanical properties of degradable polyethylene glycol (PEG) hydrogel microspheres: 25 °C, 4 °C, -80 °C, lyophilization/-20 °C, dimethyl sulfoxide/-80 °C, dimethyl sulfoxide/lyophilization/-20 °C, vacuum/-20 °C. We have outlined the storage conditions in detail and explained their effect on swelling ratio, stiffness and degradation rate post-storage. Additionally, we have implemented protein-loaded hydrogels to evaluate the effect of storage conditions on diffusivity as well as protein stability post-storage. We found that hydrogels could be stored short-term (1-4 d) under moist conditions (i.e. storage without drying) without a substantial loss of properties. For extended storage (7-28 d), they could be stored either at  -80 °C (moist condition) or vacuum drying (dry condition).

Computational design of a pH stable enzyme: understanding molecular mechanism of penicillin acylase's adaptation to alkaline conditions.

PubMed

Suplatov, Dmitry; Panin, Nikolay; Kirilin, Evgeny; Shcherbakova, Tatyana; Kudryavtsev, Pavel; Svedas, Vytas

2014-01-01

Protein stability provides advantageous development of novel properties and can be crucial in affording tolerance to mutations that introduce functionally preferential phenotypes. Consequently, understanding the determining factors for protein stability is important for the study of structure-function relationship and design of novel protein functions. Thermal stability has been extensively studied in connection with practical application of biocatalysts. However, little work has been done to explore the mechanism of pH-dependent inactivation. In this study, bioinformatic analysis of the Ntn-hydrolase superfamily was performed to identify functionally important subfamily-specific positions in protein structures. Furthermore, the involvement of these positions in pH-induced inactivation was studied. The conformational mobility of penicillin acylase in Escherichia coli was analyzed through molecular modeling in neutral and alkaline conditions. Two functionally important subfamily-specific residues, Gluβ482 and Aspβ484, were found. Ionization of these residues at alkaline pH promoted the collapse of a buried network of stabilizing interactions that consequently disrupted the functional protein conformation. The subfamily-specific position Aspβ484 was selected as a hotspot for mutation to engineer enzyme variant tolerant to alkaline medium. The corresponding Dβ484N mutant was produced and showed 9-fold increase in stability at alkaline conditions. Bioinformatic analysis of subfamily-specific positions can be further explored to study mechanisms of protein inactivation and to design more stable variants for the engineering of homologous Ntn-hydrolases with improved catalytic properties.

Computational Design of a pH Stable Enzyme: Understanding Molecular Mechanism of Penicillin Acylase's Adaptation to Alkaline Conditions

PubMed Central

Suplatov, Dmitry; Panin, Nikolay; Kirilin, Evgeny; Shcherbakova, Tatyana; Kudryavtsev, Pavel; Švedas, Vytas

2014-01-01

Protein stability provides advantageous development of novel properties and can be crucial in affording tolerance to mutations that introduce functionally preferential phenotypes. Consequently, understanding the determining factors for protein stability is important for the study of structure-function relationship and design of novel protein functions. Thermal stability has been extensively studied in connection with practical application of biocatalysts. However, little work has been done to explore the mechanism of pH-dependent inactivation. In this study, bioinformatic analysis of the Ntn-hydrolase superfamily was performed to identify functionally important subfamily-specific positions in protein structures. Furthermore, the involvement of these positions in pH-induced inactivation was studied. The conformational mobility of penicillin acylase in Escherichia coli was analyzed through molecular modeling in neutral and alkaline conditions. Two functionally important subfamily-specific residues, Gluβ482 and Aspβ484, were found. Ionization of these residues at alkaline pH promoted the collapse of a buried network of stabilizing interactions that consequently disrupted the functional protein conformation. The subfamily-specific position Aspβ484 was selected as a hotspot for mutation to engineer enzyme variant tolerant to alkaline medium. The corresponding Dβ484N mutant was produced and showed 9-fold increase in stability at alkaline conditions. Bioinformatic analysis of subfamily-specific positions can be further explored to study mechanisms of protein inactivation and to design more stable variants for the engineering of homologous Ntn-hydrolases with improved catalytic properties. PMID:24959852

Influence of sulfhydryl sites on metal binding by bacteria

NASA Astrophysics Data System (ADS)

Nell, Ryan M.; Fein, Jeremy B.

2017-02-01

The role of sulfhydryl sites within bacterial cell envelopes is still unknown, but the sites may control the fate and bioavailability of metals. Organic sulfhydryl compounds are important complexing ligands in aqueous systems and they can influence metal speciation in natural waters. Though representing only approximately 5-10% of the total available binding sites on bacterial surfaces, sulfhydryl sites exhibit high binding affinities for some metals. Due to the potential importance of bacterial sulfhydryl sites in natural systems, metal-bacterial sulfhydryl site binding constants must be determined in order to construct accurate models of the fate and distribution of metals in these systems. To date, only Cd-sulfhydryl binding has been quantified. In this study, the thermodynamic stabilities of Mn-, Co-, Ni-, Zn-, Sr- and Pb-sulfhydryl bacterial cell envelope complexes were determined for the bacterial species Shewanella oneidensis MR-1. Metal adsorption experiments were conducted as a function of both pH, ranging from 5.0 to 7.0, and metal loading, from 0.5 to 40.0 μmol/g (wet weight) bacteria, in batch experiments in order to determine if metal-sulfhydryl binding occurs. Initially, the data were used to calculate the value of the stability constants for the important metal-sulfhydryl bacterial complexes for each metal-loading condition studied, assuming a single binding reaction for the dominant metal-binding site type under the pH conditions of the experiments. For most of the metals that we studied, these calculated stability constant values increased significantly with decreasing metal loading, strongly suggesting that our initial assumption was not valid and that more than one type of binding occurs at the assumed binding site. We then modeled each dataset with two distinct site types with identical acidity constants: one site with a high metal-site stability constant value, which we take to represent metal-sulfhydryl binding and which dominates under low metal loading conditions, and another more abundant site that we term non-sulfhydryl sites that becomes important at high metal loadings. The resulting calculated stability constants do not vary significantly as a function of metal loading and yield reasonable fits to the observed adsorption behaviors as a function of both pH and metal loading. We use the results to calculate the speciation of metals bound by the bacterial envelope in realistic bacteria-bearing, heavy metal contaminated systems in order to demonstrate the potential importance of metal-sulfhydryl binding in the budget of bacterially-adsorbed metals under low metal-loading conditions.

Instabilities caused by floating-point arithmetic quantization.

NASA Technical Reports Server (NTRS)

Phillips, C. L.

1972-01-01

It is shown that an otherwise stable digital control system can be made unstable by signal quantization when the controller operates on floating-point arithmetic. Sufficient conditions of instability are determined, and an example of loss of stability is treated when only one quantizer is operated.

Aluminum and iron doped graphene for adsorption of methylated arsenic pollutants

NASA Astrophysics Data System (ADS)

Cortés-Arriagada, Diego; Toro-Labbé, Alejandro

2016-11-01

The ability of Al and Fe-doped graphene for the adsorption of trivalent and pentavalent methylated arsenic compounds was studied by quantum chemistry computations. The adsorption of trivalent methylarsenicals is reached with adsorption energies of 1.5-1.7 eV at neutral conditions; while, adsorption of pentavalent methylarsenicals reaches adsorption energies of 3.3-4.2 eV and 1.2-2.4 eV from neutral to low pH conditions, respectively. Moreover, the weakening of the interacting σAssbnd O bond in the pollutant structure played an important role in the stability of the adsorbent-adsorbate systems, determining the adsorption strength. In addition, the pollutant adsorption appears to be efficient in aqueous environments, with even high stability at ambient temperature; in this regard, it was determined that the trivalent and petavalent forms are mainly adsorbed in their neutral and anionic forms at neutral pH, respectively. Therefore, Al and Fe-doped graphene are considered as potential future materials for the removal of methylated arsenic pollutants.

Regeneration and molecular characterization of an intergeneric hybrid between Graphium putredinis and Trichoderma harzianum by protoplasmic fusion.

PubMed

Savitha, S; Sadhasivam, S; Swaminathan, K

2010-01-01

The fungal strains Graphium putredinis and Trichoderma harzianum were selected as parents for fusant development. Protoplasts were isolated using the combination of lysing enzymes Novozym 234 and cellulase with 0.6M KCl as osmotic stabilizer. The optimum conditions for release of viable protoplasts from the fungal mycelium viz. age of the mycelium, lytic enzymes, osmotic stabilizers, pH, incubation period and regeneration medium were determined. Intergeneric protoplast fusion was carried out using 50% polyethylene glycol with calcium chloride (CaCl(2)) and glycine buffer and the conditions for effective protoplast fusion, viz. fusogen, osmotic stabilizer, pH, incubation period and regeneration medium were optimized. At optimum conditions, the regeneration frequency of the fused protoplasts on potato dextrose agar (PDA) medium and fusion frequency were calculated. The regeneration frequency on non-selective (PDA) and selective media (PDA amended with starch) was determined for the parental and fusant strains in which, fusant showed a higher rate of regeneration. Fusant formation was confirmed by morphological markers (colony morphology and spore size and shape) and genetical markers like, mycelial protein pattern, restriction digestion pattern and random amplified polymorphic DNA (RAPD) analysis. The efficiency of these parental strains and their intergeneric fusant in the production of hydrolytic enzymes - amylases (treatment plant for sago factory effluent), cellulases (bioethanol), xylanases (bleaching agents for waste paper pulp) and proteases (additives in commercial detergents) - have probable applications in various industrial processes. (c) 2010 Elsevier Inc. All rights reserved.

Stability and bifurcation analysis on a ratio-dependent predator-prey model with time delay

NASA Astrophysics Data System (ADS)

Xu, Rui; Gan, Qintao; Ma, Zhien

2009-08-01

A ratio-dependent predator-prey model with time delay due to the gestation of the predator is investigated. By analyzing the corresponding characteristic equations, the local stability of a positive equilibrium and a semi-trivial boundary equilibrium is discussed, respectively. Further, it is proved that the system undergoes a Hopf bifurcation at the positive equilibrium. Using the normal form theory and the center manifold reduction, explicit formulae are derived to determine the direction of bifurcations and the stability and other properties of bifurcating periodic solutions. By means of an iteration technique, sufficient conditions are obtained for the global attractiveness of the positive equilibrium. By comparison arguments, the global stability of the semi-trivial equilibrium is also addressed. Numerical simulations are carried out to illustrate the main results.

Turbine Engine Stability/Instability With Rub Forces Axisymmetric Rotor-Support Stiffness

NASA Technical Reports Server (NTRS)

Gallardo, Vicente; Lawrence, Charles

2004-01-01

The stability/instability condition of a turbine rotor with axisymmetric supports is determined in the presence of gyroscopic loads and rub-induced destabilizing forces. A modal representation of the turbine engine is used, with one mode in each of the vertical and horizontal planes. The use of non-spinning rotor modes permits an explicit treatment of gyroscopic effects. The two linearized modal equations of motion of a rotor with axisymmetric supports are reduced to a single equation in a complex variable. The resulting eigenvalues yield explicit expressions at the stability boundary, for the whirl frequency as well as the required damping for stability in the presence of the available rub-induced destabilization. Conversely, the allowable destabilization in the presence of the available damping is also given.

Front and pulse solutions for the complex Ginzburg-Landau equation with higher-order terms.

PubMed

Tian, Huiping; Li, Zhonghao; Tian, Jinping; Zhou, Guosheng

2002-12-01

We investigate one-dimensional complex Ginzburg-Landau equation with higher-order terms and discuss their influences on the multiplicity of solutions. An exact analytic front solution is presented. By stability analysis for the original partial differential equation, we derive its necessary stability condition for amplitude perturbations. This condition together with the exact front solution determine the region of parameter space where the uniformly translating front solution can exist. In addition, stable pulses, chaotic pulses, and attenuation pulses appear generally if the parameters are out of the range. Finally, applying these analysis into the optical transmission system numerically we find that the stable transmission of optical pulses can be achieved if the parameters are appropriately chosen.

Activity and Stability of Biofilm Uricase of Lactobacillus plantarum for Uric Acid Biosensor

NASA Astrophysics Data System (ADS)

Iswantini, Dyah; Rachmatia, Rescy; Diana, Novita Rose; Nurhidayat, Novik; Akhiruddin; Saprudin, Deden

2016-01-01

Research of uric acid biosensor used a Lactobacillus plantarum was successfully conducted. Lactobacillus plantarum could produce uricase that could be used as uric acid biosensor. Therefore, lifetime of bacteria were quite short that caused the bacteria could not detect uric acid for a long time. To avoid this problem, development of biofilm for uric acid biosensor is important. Biofilms is a structured community of bacterial cells, stick together and are able to maintain a bacteria in an extreme environments. The purpose of present study was to determine and compare the activity of uricase produced by L. plantarum, deposited whithin biofilm and planktonic bacteria on glassy carbon electrode (GCEb & GCE), also to determine the stability of biofilm. The optimization process was conducted by using temperature, pH, and substrate concentration as the parameters. It showed that the activity of uricase within biofilm was able to increase the oxidation current. GCEb and GCE yielded the oxidation current in the amount of 47.24 μA and 23.04 μA, respectively, under the same condition. Results indicated that the optimum condition for uric acid biosensor using biofilm were pH 10, temperature of 40 oC, and uric acid concentration of 5 mM. The stability of GCEb decreased after 10 hours used, with decreasing percentage over 86.33%. This low stability probably caused by the unprotected active site of the enzyme that the enzyme is easier to experience the denaturation.

Recent Progress in the Structure Determination of GPCRs, a Membrane Protein Family with High Potential as Pharmaceutical Targets

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

Cherezov, Vadim; Abola, Enrique; Stevens, Raymond C.

2015-11-30

G protein-coupled receptors (GPCRs) constitute a highly diverse and ubiquitous family of integral membrane proteins, transmitting signals inside the cells in response to an assortment of disparate extra-cellular stimuli. Their strategic location on the cell surface and their involvement in crucial cellular and physiological processes turn these receptors into highly important pharmaceutical targets. Recent technological developments aimed at stabilization and crystallization of these receptors have led to significant breakthroughs in GPCR structure determination efforts. One of the successful approaches involved receptor stabilization with the help of a fusion partner combined with crystallization in lipidic cubic phase (LCP). The success ofmore » using an LCP matrix for crystallization is generally attributed to the creation of a more native, membrane-like stabilizing environment for GPCRs just prior to nucleation and to the formation of type I crystal lattices, thus generating highly ordered and strongly diffracting crystals. Here they describe protocols for reconstituting purified GPCRs in LCP, performing pre-crystallization assays, setting up crystallization trials in manual mode, detecting crystallization hits, optimizing crystallization conditions, harvesting, and collecting crystallographic data. The protocols provide a sensible framework for approaching crystallization of stabilized GPCRs in LCP, however, as in any crystallization experiment, extensive screening and optimization of crystallization conditions as well as optimization of protein construct and purification steps are required. The process remains risky and these protocols do not necessarily guarantee success.« less

Environmental behavior of cement-based stabilized foundry sludge products incorporating additives.

PubMed

Ruiz, M C; Irabien, A

2004-06-18

A series of experiments were conducted to stabilize the inorganic and organic pollutants in a foundry sludge from a cast iron activity using Portland cement as binder and three different types of additives, organophilic bentonite, lime and coal fly ash. Ecotoxicological and chemical behavior of stabilized mixes of foundry sludge were analyzed to assess the feasibility to immobilize both types of contaminants, all determined on the basis of compliance leaching tests. The incorporation of lime reduces the ecotoxicity of stabilized mixes and enhances stabilization of organic pollutants obtaining better results when a 50% of cement is replaced by lime. However, the alkalinity of lime increases slightly the leached zinc up to concentrations above the limit set under neutral conditions by the European regulations. The addition of organophilic bentonite and coal fly ash can immobilize the phenolic compounds but are inefficient to reduce the ecotoxicity and mobility of zinc of final products.

NASTRAN flutter analysis of advanced turbopropellers

NASA Technical Reports Server (NTRS)

Elchuri, V.; Smith, G. C. C.

1982-01-01

An existing capability developed to conduct modal flutter analysis of tuned bladed-shrouded discs in NASTRAN was modified and applied to investigate the subsonic unstalled flutter characteristics of advanced turbopropellers. The modifications pertain to the inclusion of oscillatory modal aerodynamic loads of blades with large (backward and forward) variable sweep. The two dimensional subsonic cascade unsteady aerodynamic theory was applied in a strip theory manner with appropriate modifications for the sweep effects. Each strip is associated with a chord selected normal to any spanwise reference curve such as the blade leading edge. The stability of three operating conditions of a 10-bladed propeller is analyzed. Each of these operating conditions is iterated once to determine the flutter boundary. A 5-bladed propeller is also analyzed at one operating condition to investigate stability. Analytical results obtained are in very good agreement with those from wind tunnel tests.

Physicochemical characterization and an injection formulation study of water insoluble ZCVI₄-2, a novel NO-donor anticancer compound.

PubMed

Gao, Yuan; Li, Li; Zhang, Jianjun; Su, Feng; Gong, Zhenhua; Lai, Yisheng; Zhang, Yihua

2012-07-01

ZCVI(4)-2 was a novel nitric oxide-releasing glycosyl derivative of oleanolic acid that displayed strong cytotoxicity selectively against human hepatocellular carcinoma in vitro and in vivo. In this study, ZCVI(4)-2 was characterized by FT-IR spectroscopy, differential scanning calorimetry, powder X-ray diffractometry, Raman spectroscopy, hygroscopicity and stability. A high performance liquid chromatography method was also established for the quantitative determination of solubility and additional stability profile of ZCVI(4)-2. ZCVI(4)-2 was found to be an amorphous and stable solid with low solubility of less than 10 μg/mL. Based on the solubilization tests that included methods of cosolvency and micellization, the solution mixture of 5% Solutol HS-15, 5% 1, 2-propylene glycol and 5% anhydrous ethanol was determined to be the system for the preparation of the ZCVI(4)-2 early injection solution. The effect of pH, temperature, light and injectable isotonic glucose or NaCl solution on ZCVI(4)-2 injection was also investigated. Good stability was observed at all testing conditions. Under the conditions studied, the NO-releasing rate and amount of ZCVI(4)-2 from the early injection solution in rat plasma demonstrated a promising therapeutic efficacy while maintaining a good safety profile.

Affective Modulation of Cognitive Control is Determined by Performance-Contingency and Mediated by Ventromedial Prefrontal and Cingulate Cortex

PubMed Central

King, Joseph A.; Korb, Franziska M.; Krebs, Ruth M.; Notebaert, Wim; Egner, Tobias

2013-01-01

Cognitive control requires a fine balance between stability, the protection of an on-going task-set, and flexibility, the ability to update a task-set in line with changing contingencies. It is thought that emotional processing modulates this balance, but results have been equivocal regarding the direction of this modulation. Here, we tested the hypothesis that a crucial determinant of this modulation is whether affective stimuli represent performance-contingent or task-irrelevant signals. Combining functional magnetic resonance imaging with a conflict task-switching paradigm, we contrasted the effects of presenting negative- and positive-valence pictures on the stability/flexibility trade-off in humans, depending on whether picture presentation was contingent on behavioral performance. Both the behavioral and neural expressions of cognitive control were modulated by stimulus valence and performance contingency: in the performance-contingent condition, cognitive flexibility was enhanced following positive pictures, whereas in the nonperformance-contingent condition, positive stimuli promoted cognitive stability. The imaging data showed that, as anticipated, the stability/flexibility trade-off per se was reflected in differential recruitment of dorsolateral frontoparietal and striatal regions. In contrast, the affective modulation of stability/flexibility shifts was mirrored, unexpectedly, by neural responses in ventromedial prefrontal and posterior cingulate cortices, core nodes of the “default mode” network. Our results demonstrate that the affective modulation of cognitive control depends on the performance contingency of the affect-inducing stimuli, and they document medial default mode regions to mediate the flexibility-promoting effects of performance-contingent positive affect, thus extending recent work that recasts these regions as serving a key role in on-task control processes. PMID:24155301

Straightening of a wavy strip: An elastic-plastic contact problem including snap-through

NASA Technical Reports Server (NTRS)

Fischer, D. F.; Rammerstorfer, F. G.

1980-01-01

The nonlinear behavior of a wave like deformed metal strip during the levelling process were calculated. Elastic-plastic material behavior as well as nonlinearities due to large deformations were considered. The considered problem lead to a combined stability and contact problem. It is shown that, despite the initially concentrated loading, neglecting the change of loading conditions due to altered contact domains may lead to a significant error in the evaluation of the nonlinear behavior and particularly to an underestimation of the stability limit load. The stability was examined by considering the load deflection path and the behavior of a load-dependent current stiffness parameter in combination with the determinant of the current stiffness matrix.

Boundary layer stability on a yawed spinning body of revolution and its effect on the magnus force and moment

NASA Technical Reports Server (NTRS)

Jacobson, I. D.; Morton, J. B.

1972-01-01

The parameters are established which are important to the stability of a boundary layer flow over a yawed spinning cylinder in a uniform stream. It is shown that transition occurs asymmetrically in general and this asymmetry can be important for the prediction of aerodynamic forces and moments (e.g., the Magnus effect). Instability of the steady-state boundary layer flow is determined using small disturbance theory. Although the approach is strictly valid only for the calculation of the conditions for stability in the small, experimental data indicate that in many problems, it provides a good estimate for the transition to turbulence.

Flight of frigatebirds inside clouds - energy gain, stability and control.

PubMed

Sachs, Gottfried; Weimerskirch, Henri

2018-07-07

Investigating the unique ability of frigatebirds of flying inside clouds, it is shown that they achieve a large energy gain by ascents to high altitudes in strong updrafts of trade cumulus clouds. Frigatebirds often perform that kind of flight, at daytime as well as in the night. This suggests that they are capable of flying inside clouds in a controlled and stabilized manner. The control requirements for ascents in terms of a circling flight in updrafts of trade cumulus clouds are analyzed, and the necessary aerodynamic control moments are determined. Based on a stability investigation, it is shown that there are restoring effects which act against disturbances causing possible deviations from the circling flight condition. The aerodynamic moments which effectuate that stabilization are identified. Furthermore, the problem of neutral azimuth stability which generally exists in the flight of birds and which is the reason for continually increasing deviations from the course is dealt with. It is shown for the circling flight mode of frigatebirds inside clouds that, here, deviations are small and remain constant, suggesting that a corrective control action is not required. This is particularly important for circling flight in conditions without a visual reference, like inside clouds. Copyright © 2018 Elsevier Ltd. All rights reserved.

Radioactive nuclear waste stabilization - Aspects of solid-state molecular engineering and applied geochemistry

NASA Technical Reports Server (NTRS)

Haggerty, S. E.

1983-01-01

Stabilization techniques for the storage of radioactive wastes are surveyed, with emphasis on immobilization in a primary barrier of synthetic rock. The composition, half-life, and thermal-emission characteristics of the wastes are shown to require thermally stable immobilization enduring at least 100,000 years. Glass materials are determined to be incapable of withstanding the expected conditions, average temperatures of 100-500 C for the first 100 years. The geological-time stability of crystalline materials, ceramics or synthetic rocks, is examined in detail by comparing their components with similar naturally occurring minerals, especially those containing the same radioactive elements. The high-temperature environment over the first 100 years is seen as stabilizing, since it can recrystallize radiation-induced metamicts. The synthetic-rock stabilization technique is found to be essentially feasible, and improvements are suggested, including the substitution of nepheline with freudenbergite and priderite for alkaline-waste stabilization, the maintenance of low oxygen fugacity, and the dilution of the synthetic-rock pellets into an inert medium.

Pulsational stabilities of a star in thermal imbalance - Comparison between the methods

NASA Technical Reports Server (NTRS)

Vemury, S. K.

1978-01-01

The stability coefficients for quasi-adiabatic pulsations for a model in thermal imbalance are evaluated using the dynamical energy (DE) approach, the total (kinetic plus potential) energy (TE) approach, and the small amplitude (SA) approaches. From a comparison among the methods, it is found that there can exist two distinct stability coefficients under conditions of thermal imbalance as pointed out by Demaret. It is shown that both the TE approaches lead to one stability coefficient, while both the SA approaches lead to another coefficient. The coefficient obtained through the energy approaches is identified as the one which determines the stability of the velocity amplitudes. For a prenova model with a thin hydrogen-burning shell in thermal imbalance, several radial modes are found to be unstable both for radial displacements and for velocity amplitudes. However, a new kind of pulsational instability also appears, viz., while the radial displacements are unstable, the velocity amplitudes may be stabilized through the thermal imbalance terms.

Strategy for assessment of the colloidal and biological stability of H1N1 influenza A viruses.

PubMed

Hämmerling, Frank; Lorenz-Cristea, Oliver; Baumann, Pascal; Hubbuch, Jürgen

2017-01-30

Current influenza vaccines are mostly formulated as liquids which requires a continuous cold chain to maintain the stability of the antigen. For development of vaccines with an increased stability at ambient temperatures, manifold parameters and their influences on the colloidal stability and activity of the antigen have to be understood. This work presents a strategy to examine both, the colloidal stability and the remaining biological activity of H1N1 influenza viruses under various conditions after an incubation of 40 days. H1N1 phase diagrams were generated for several pH values and different initial H1N1 and NaCl concentrations. It was shown that the highest H1N1 recoveries were obtained for pH 6 and that moderate amounts of NaCl are favorable for increased recoveries. In contrast to colloidal stability, the highest remaining HA activity was observed at pH 9. The electrostatic and hydrophobic surface properties of H1N1 were investigated to reveal the mechanisms accounting for the decrease in stability. Secondly, the capability of virus precipitation by polyethylene glycol in combination with determination of surface hydrophobicity was proven to be useful as a predictive tool to rank stability under different conditions. This methodology enables the rapid assessment of aggregation propensity of H1N1 formulations and the influence on the activity of the virus particles and might become a standard tool during the development of vaccine formulations. Copyright © 2016 Elsevier B.V. All rights reserved.

Effects of solution conditions on methionine oxidation in albinterferon alfa-2b and the role of oxidation in its conformation and aggregation.

PubMed

Chou, Danny K; Krishnamurthy, Rajesh; Manning, Mark Cornell; Randolph, Theodore W; Carpenter, John F

2013-02-01

Physical and chemical degradation of therapeutic proteins can occur simultaneously. In this study, our first objective was to investigate how solution conditions that impact conformational stability of albinterferon alfa-2b, a recombinant fusion protein, modulate rates of methionine (Met) oxidation. Another objective of this work was to determine whether oxidation affects conformation and rate of aggregation of the protein. The protein was subjected to oxidation in solutions of varying pH, ionic strength, and excipients by the addition of 0.02% tertiary-butyl hydroperoxide (TBHP). The rate of formation of Met-sulfoxide species was monitored by reversed-phase high-performance liquid chromatography and compared across solution conditions. Albinterferon alfa-2b exhibited susceptibility to Met oxidation during exposure to TBHP that was highly dependent on solution parameters, but there was not a clear correlation between oxidation rate and protein conformational stability. Met oxidation resulted in significant perturbation of both secondary and tertiary structure of albinterferon alfa-2b as shown by both far-ultraviolet (UV) and near-UV circular dichroism. Moreover, oxidation of the protein caused a noticeable reduction in the protein's resistance to thermal denaturation. Surprisingly, despite its negative effect on solution structure and conformational stability, oxidation actually reduced the protein's aggregation rate during agitation at room temperature as well as during quiescent incubation at 40°C. Oxidation of the protein resulted in improved colloidal stability of the protein, which is manifested by a more positive B(22) value in the oxidized protein. Thus, the reduced aggregation rate after oxidation suggests that increased colloidal stability of oxidized albinterferon alfa-2b counteracted oxidation-induced decreases in conformational stability. Copyright © 2012 Wiley Periodicals, Inc.

Influence of light and oxygen on the color stability of five calcium silicate-based materials.

PubMed

Vallés, Marta; Mercadé, Montse; Duran-Sindreu, Fernando; Bourdelande, Jose L; Roig, Miguel

2013-04-01

Difficult handling, long setting time, and potential discoloration are important drawbacks of white mineral trioxide aggregate (WMTA). The development of Biodentine, a recently developed calcium silicate-based material (CSM), has overcome some of these shortcomings; however, there are no available data on its color stability. A previous study showed that WMTA discolors under light irradiation in an oxygen-free environment. The present study evaluated the influence of light irradiation and oxygen on the color stability of 5 CSMs. Fifteen samples of 5 CSMs (ProRoot WMTA, Angelus WMTA, White Portland Cement [PC], PC with bismuth oxide, and Biodentine) were divided into 5 groups. Each group was exposed to different oxygen and light conditions. A spectrophotometer was used to determine the color of each specimen at 0, 120 seconds, and 5 days. Data were analyzed by using analysis of variance and Tukey honestly significant difference test. The materials PC with bismuth oxide, Angelus WMTA, and ProRoot WMTA showed dark discoloration after light irradiation in an oxygen-free environment, which was statistically significantly different from Biodentine and PC. In groups that were exposed to no light irradiation or to an oxygen atmosphere, all materials showed color stability over time, and no significant differences were observed among them. PC and Biodentine maintained color stability in all conditions over time and showed no significant differences. The combination of light and anaerobic conditions (similar to those in clinical situations) results in differences in color of the tested CSMs during a period of 5 days, of which Biodentine and PC demonstrated color stability. Copyright © 2013 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.

Stability analysis for discrete-time stochastic memristive neural networks with both leakage and probabilistic delays.

PubMed

Liu, Hongjian; Wang, Zidong; Shen, Bo; Huang, Tingwen; Alsaadi, Fuad E

2018-06-01

This paper is concerned with the globally exponential stability problem for a class of discrete-time stochastic memristive neural networks (DSMNNs) with both leakage delays as well as probabilistic time-varying delays. For the probabilistic delays, a sequence of Bernoulli distributed random variables is utilized to determine within which intervals the time-varying delays fall at certain time instant. The sector-bounded activation function is considered in the addressed DSMNN. By taking into account the state-dependent characteristics of the network parameters and choosing an appropriate Lyapunov-Krasovskii functional, some sufficient conditions are established under which the underlying DSMNN is globally exponentially stable in the mean square. The derived conditions are made dependent on both the leakage and the probabilistic delays, and are therefore less conservative than the traditional delay-independent criteria. A simulation example is given to show the effectiveness of the proposed stability criterion. Copyright © 2018 Elsevier Ltd. All rights reserved.

Experimental study of the effects of secondary air on the emissions and stability of a lean premixed combustor

NASA Technical Reports Server (NTRS)

Roffe, G.; Raman, R. S. V.

1981-01-01

Tests were run using a perforated plate flameholder with a relatively short attached recirculation zone and a vee gutter flameholder with a relatively long attached recirculation zone. Combustor streamlines were traced in cold flow tests at ambient pressure. The amount of secondary air entrainment in the recirculation zones of the flameholders was determined by tracer gas testing at cold flow ambient pressure conditions. Combustion tests were caried out at entrance conditions of 0.5 MPa/630K and emission of NOx, CO and unburned hydrocarbons were measured along with lean stability and flashback limits. The degree of entrainment increases as dilution air injection decreases. Flashback appears to be a function of overall equivalence ratio and resistance to flashback increases with increasing combustor entrance velocity. Lean stability limit appears to be a function of both primary zone and flameholder recirculation zone equivalence ratios and resistance to lean blowout increases with increasing combustor entrance velocity.

Investigation of stability in a two-delay model of the ultradian oscillations in glucose-insulin regulation

NASA Astrophysics Data System (ADS)

Huard, B.; Easton, J. F.; Angelova, M.

2015-09-01

In this paper, a two-delay model for the ultradian oscillatory behaviour of the glucose-insulin regulation system is studied. Hill functions are introduced to model nonlinear physiological interactions within this system and ranges on parameters reproducing biological oscillations are determined on the basis of analytical and numerical considerations. Local and global stability are investigated and delay-dependent conditions are obtained through the construction of Lyapunov-Krasovskii functionals. The effect of Hill parameters on these conditions, as well as the boundary of the stability region in the delay domain, are established for the first time. Numerical simulations demonstrate that the model with Hill functions represents well the oscillatory behaviour of the system with the advantage of incorporating new meaningful parameters. The influence of the time delays on the period of oscillations and the sensitivity of the latter to model parameters, in particular glucose infusion, are investigated. The model can contribute to the better understanding and treatment of diabetes.

Direct quantitation of fatty acids present in bacteria and fungi: stability of the cyclopropane ring to chlorotrimethylsilane.

PubMed

Eras, Jordi; Oró, Robert; Torres, Mercè; Canela, Ramon

2008-07-09

The stability of the cyclopropane ring and the fatty acid composition of microbial cells were determined using chlorotrimethylsilane as reagent with three different conditions 80 degrees C for 1 h, 60 degrees C for 1 h, and 60 degrees C for 2 h. Chlorotrimethylsilane permits a simultaneous extraction and derivatization of fatty acids. A basic method was used as reference. The bacteria, Escherichia coli, Burkholderia cepacia, and Lactobacillus brevis, and fungi Aspergillus niger and Gibberella fujikuroi were used. The stability of the cyclopropane ring on acidic conditions was tested using the cyclopropanecarboxylic acid and a commercial mixture of bacteria fatty acid methyl esters (BAME). Fisher's least significant difference test showed significant differences among the methods. The method using chlorotrimethylsilane and 1-pentanol for 1 h at 80 degrees C gave the best results in cyclopropane, hydroxyl, and total fatty acid recoveries. This procedure allows the fast and easy one-step direct extraction derivatization.

The Edge of Stability: Response Times and Delta Oscillations in Balanced Networks

PubMed Central

Gillary, Grant; Niebur, Ernst

2016-01-01

The standard architecture of neocortex is a network with excitation and inhibition in closely maintained balance. These networks respond fast and with high precision to their inputs and they allow selective amplification of patterned signals. The stability of such networks is known to depend on balancing the strengths of positive and negative feedback. We here show that a second condition is required for stability which depends on the relative strengths and time courses of fast (AMPA) and slow (NMDA) currents in the excitatory projections. This condition also determines the response time of the network. We show that networks which respond quickly to an input are necessarily close to an oscillatory instability which resonates in the delta range. This instability explains the existence of neocortical delta oscillations and the emergence of absence epilepsy. Although cortical delta oscillations are a network-level phenomenon, we show that in non-pathological networks, individual neurons receive sufficient information to keep the network in the fast-response regime without sliding into the instability. PMID:27689361

Protein half-life determines expression of proteostatic networks in podocyte differentiation.

PubMed

Schroeter, Christina B; Koehler, Sybille; Kann, Martin; Schermer, Bernhard; Benzing, Thomas; Brinkkoetter, Paul T; Rinschen, Markus M

2018-04-25

Podocytes are highly specialized, epithelial, postmitotic cells, which maintain the renal filtration barrier. When adapting to considerable metabolic and mechanical stress, podocytes need to accurately maintain their proteome. Immortalized podocyte cell lines are a widely used model for studying podocyte biology in health and disease in vitro. In this study, we performed a comprehensive proteomic analysis of the cultured human podocyte proteome in both proliferative and differentiated conditions at a depth of >7000 proteins. Similar to mouse podocytes, human podocyte differentiation involved a shift in proteostasis: undifferentiated podocytes have high expression of proteasomal proteins, whereas differentiated podocytes have high expression of lysosomal proteins. Additional analyses with pulsed stable-isotope labeling by amino acids in cell culture and protein degradation assays determined protein dynamics and half-lives. These studies unraveled a globally increased stability of proteins in differentiated podocytes. Mitochondrial, cytoskeletal, and membrane proteins were stabilized, particularly in differentiated podocytes. Importantly, protein half-lives strongly contributed to protein abundance in each state. These data suggest that regulation of protein turnover of particular cellular functions determines podocyte differentiation, a paradigm involving mitophagy and, potentially, of importance in conditions of increased podocyte stress and damage.-Schroeter, C. B., Koehler, S., Kann, M., Schermer, B., Benzing, T., Brinkkoetter, P. T., Rinschen, M. M. Protein half-life determines expression of proteostatic networks in podocyte differentiation.

Stabilization of hyperforin dicyclohexylammonium salt with dissolved albumin and albumin nanoparticles for studying hyperforin effects on 2D cultivation of keratinocytes in vitro.

PubMed

Füller, J; Kellner, T; Gaid, M; Beerhues, L; Müller-Goymann, C C

2018-05-01

Due to the limited chemical stability of the natural hyperforin molecule, a more stable form of hyperforin, i.e., the hyperforin dicyclohexylammonium salt (HYP-DCHA) has been used for ex vivo and in vitro experiments in recent years, but its actual stability under typical cell culture conditions has never been studied before. In this contribution the stability of HYP-DCHA was examined under typical cell culture conditions. Different cell culture media with and without fetal calf serum (FCS) supplementation were studied with regard to further stabilization of HYP-DCHA determined with HPLC analysis. Furthermore, albumin nanoparticles were examined as a stabilizing carrier system for HYP-DCHA. In this context, the interaction between HYP-DCHA and albumin nanoparticles (ANP) was examined with regard to size and loading with HYP . The effects of HYP-DCHA either supplied in cell culture medium or loaded on ANP on viability and cytotoxicity were studied in vitro on HaCaT monolayers (human keratinocyte cell line). HYP-DCHA supplied in FCS-containing medium was recovered completely after 24h of incubation. However, a lack of FCS caused a total loss of HYP-DCHA after less than 24h incubation time. Supplying HYP-DCHA loaded on ANP in an FCS-free medium resulted in a recovery of about 60% after 24h incubation. HYP-DCHA supplied in medium along with FCS showed a slow dose-dependent decrease in viability of HaCaT cells without any cytotoxic effects (antiproliferative effect). Treatment with HYP-DCHA with a lack of FCS resulted in a significantly faster decrease in viability which was mainly due to cytotoxicity. The latter was true for HYP-DHCA-loaded ANP where increased cytotoxicity was observed despite the presence of FCS. The results show that the stability of the widely used HYP-DCHA is rather limited under cell culture conditions. Especially a lack of FCS leads to degradation and/or oxidation of HYP-DCHA probably causing an increased cytotoxicity. In contrast, FCS supplementation fairly stabilizes HYP-DCHA under cell culture conditions while albumin nanoparticles may serve the same stabilization purpose despite increasing cytotoxic effects onto the cells themselves. Copyright © 2017 Elsevier B.V. All rights reserved.

Free energy landscapes for initiation and branching of protein aggregation.

PubMed

Zheng, Weihua; Schafer, Nicholas P; Wolynes, Peter G

2013-12-17

Experiments on artificial multidomain protein constructs have probed the early stages of aggregation processes, but structural details of the species that initiate aggregation remain elusive. Using the associative-memory, water-mediated, structure and energy model known as AWSEM, a transferable coarse-grained protein model, we performed simulations of fused constructs composed of up to four copies of the Titin I27 domain or its mutant I27* (I59E). Free energy calculations enable us to quantify the conditions under which such multidomain constructs will spontaneously misfold. Consistent with experimental results, the dimer of I27 is found to be the smallest spontaneously misfolding construct. Our results show how structurally distinct misfolded states can be stabilized under different thermodynamic conditions, and this result provides a plausible link between the single-molecule misfolding experiments under native conditions and aggregation experiments under denaturing conditions. The conditions for spontaneous misfolding are determined by the interplay among temperature, effective local protein concentration, and the strength of the interdomain interactions. Above the folding temperature, fusing additional domains to the monomer destabilizes the native state, and the entropically stabilized amyloid-like state is favored. Because it is primarily energetically stabilized, the domain-swapped state is more likely to be important under native conditions. Both protofibril-like and branching structures are found in annealing simulations starting from extended structures, and these structures suggest a possible connection between the existence of multiple amyloidogenic segments in each domain and the formation of branched, amorphous aggregates as opposed to linear fibrillar structures.

The SalGI restriction endonuclease. Purification and properties

PubMed Central

Maxwell, Anthony; Halford, Stephen E.

1982-01-01

The type II restriction endonuclease SalGI has been purified to near homogeneity. At least 80% of the protein remaining after the final stage of the preparation is SalGI restriction endonuclease; no contaminating nucleases remain detectable. The principal form of the protein under both native and denaturing conditions is a monomer of Mr about 29000. The optimal conditions for both enzyme stability and enzyme activity have been determined. ImagesFig. 1. PMID:6285898

Shelf-life of a 2.5% sodium hypochlorite solution as determined by Arrhenius equation.

PubMed

Nicoletti, Maria Aparecida; Siqueira, Evandro Luiz; Bombana, Antonio Carlos; Oliveira, Gabriella Guimarães de

2009-01-01

Accelerated stability tests are indicated to assess, within a short time, the degree of chemical degradation that may affect an active substance, either alone or in a formula, under normal storage conditions. This method is based on increased stress conditions to accelerate the rate of chemical degradation. Based on the equation of the straight line obtained as a function of the reaction order (at 50 and 70 degrees C) and using Arrhenius equation, the speed of the reaction was calculated for the temperature of 20 degrees C (normal storage conditions). This model of accelerated stability test makes it possible to predict the chemical stability of any active substance at any given moment, as long as the method to quantify the chemical substance is available. As an example of the applicability of Arrhenius equation in accelerated stability tests, a 2.5% sodium hypochlorite solution was analyzed due to its chemical instability. Iodometric titration was used to quantify free residual chlorine in the solutions. Based on data obtained keeping this solution at 50 and 70 degrees C, using Arrhenius equation and considering 2.0% of free residual chlorine as the minimum acceptable threshold, the shelf-life was equal to 166 days at 20 degrees C. This model, however, makes it possible to calculate shelf-life at any other given temperature.

On the stability of a variety of organic photovoltaic devices by IPCE and in situ IPCE analyses--the ISOS-3 inter-laboratory collaboration.

PubMed

Teran-Escobar, Gerardo; Tanenbaum, David M; Voroshazi, Eszter; Hermenau, Martin; Norrman, Kion; Lloyd, Matthew T; Galagan, Yulia; Zimmermann, Birger; Hösel, Markus; Dam, Henrik F; Jørgensen, Mikkel; Gevorgyan, Suren; Kudret, Suleyman; Maes, Wouter; Lutsen, Laurence; Vanderzande, Dirk; Würfel, Uli; Andriessen, Ronn; Rösch, Roland; Hoppe, Harald; Rivaton, Agnès; Uzunoğlu, Gülşah Y; Germack, David; Andreasen, Birgitta; Madsen, Morten V; Bundgaard, Eva; Krebs, Frederik C; Lira-Cantu, Monica

2012-09-07

This work is part of the inter-laboratory collaboration to study the stability of seven distinct sets of state-of-the-art organic photovoltaic (OPV) devices prepared by leading research laboratories. All devices have been shipped to and degraded at RISØ-DTU up to 1830 hours in accordance with established ISOS-3 protocols under defined illumination conditions. In this work, we apply the Incident Photon-to-Electron Conversion Efficiency (IPCE) and the in situ IPCE techniques to determine the relation between solar cell performance and solar cell stability. Different ageing conditions were considered: accelerated full sun simulation, low level indoor fluorescent lighting and dark storage. The devices were also monitored under conditions of ambient and inert (N(2)) atmospheres, which allows for the identification of the solar cell materials more susceptible to degradation by ambient air (oxygen and moisture). The different OPVs configurations permitted the study of the intrinsic stability of the devices depending on: two different ITO-replacement alternatives, two different hole extraction layers (PEDOT:PSS and MoO(3)), and two different P3HT-based polymers. The response of un-encapsulated devices to ambient atmosphere offered insight into the importance of moisture in solar cell performance. Our results demonstrate that the IPCE and the in situ IPCE techniques are valuable analytical methods to understand device degradation and solar cell lifetime.

Stability of a rigid rotor supported on oil-film journal bearings under dynamic load

NASA Technical Reports Server (NTRS)

Majumdar, B. C.; Brewe, D. E.

1987-01-01

Most published work relating to dynamically loaded journal bearings are directed to determining the minimum film thickness from the predicted journal trajectories. These do not give any information about the subsynchronous whirl stability of journal bearing systems since they do not consider the equations of motion. It is, however, necessary to know whether the bearing system operation is stable or not under such an operating condition. The stability characteristics of the system are analyzed. A linearized perturbation theory about the equilibrium point can predict the threshold of stability; however it does not indicate postwhirl orbit detail. The linearized method may indicate that a bearing is unstable for a given operating condition whereas the nonlinear analysis may indicate that it forms a stable limit cycle. For this reason, a nonlinear transient analysis of a rigid rotor supported on oil journal bearings under: (1) a unidirectional constant load, (2) a unidirectional periodic load, and (3) variable rotating load are performed. The hydrodynamic forces are calculated after solving the time-dependent Reynolds equation by a finite difference method with a successive overrelaxation scheme. Using these forces, equations of motion are solved by the fourth-order Runge-Kutta method to predict the transient behavior of the rotor. With the aid of a high-speed digital computer and graphics, the journal trajectories are obtained for several different operating conditions.

Stress state of rock mass under open pit mining in the influence zone of tectonic disturbances (in terms of the Oktorkoi Fault, North Tien Shan)

NASA Astrophysics Data System (ADS)

Kozhogulov, KCh; Nikolskaya, OV; Rybin, AK; Kuzikov, SI

2018-03-01

The qualitative connection between the crack growth direction and the orientation of the main axes of horizontal deformations in rocks mass in the area of the Boordin gold ore province is revealed. The effect of the rock mass quality (RQD) and contact conditions of crack surfaces on the stability index of pit wall rock mass is evaluated, and the influence of the rock mass quality index on the pit wall stability is determined.

Experimental Evaluation of Journal Bearing Stability and New Gas Wave Bearing Materials

NASA Technical Reports Server (NTRS)

Keith, Theo G., Jr.; Dimofte, Florin

1998-01-01

A gas journal bearing, with a wavy surfaces was tested in a range of speeds up to 18,000 RPM to determine its stability in an unloaded condition as a function of the wave amplitude. The bearing, was 50 mm in diameter, 58 mm long and had 0.01 65 mm radial clearance. Three waves were created on the inner surface by deforming the bearing sleeve. The ratio of the wave amplitude to the radial clearance (the wave amplitude ratio) was varied from zero to 0.3.

Species dispersal rates alter diversity and ecosystem stability in pond metacommunities.

PubMed

Howeth, Jennifer G; Leibold, Mathew A

2010-09-01

Metacommunity theory suggests that relationships between diversity and ecosystem stability can be determined by the rate of species dispersal among local communities. The predicted relationships, however, may depend upon the relative strength of local environmental processes and disturbance. Here we evaluate the role of dispersal frequency and local predation perturbations in affecting patterns of diversity and stability in pond plankton metacommunities. Pond metacommunities were composed of three mesocosm communities: one of the three communities maintained constant "press" predation from a selective predator, bluegill sunfish (Lepomis macrochirus); the second community maintained "press" conditions without predation; and the third community experienced recurrent "pulsed" predation from bluegill sunfish. The triads of pond communities were connected at either no, low (0.7%/d), or high (20%/d) planktonic dispersal. Richness and composition of zooplankton and stability of plankton biomass and ecosystem productivity were measured at local and regional spatial scales. Dispersal significantly affected diversity such that local and regional biotas at the low dispersal rate maintained the greatest number of species. The unimodal local dispersal-diversity relationship was predator-dependent, however, as selective press predation excluded species regardless of dispersal. Further, there was no effect of dispersal on beta diversity because predation generated local conditions that selected for distinct community assemblages. Spatial and temporal ecosystem stability responded to dispersal frequency but not predation. Low dispersal destabilized the spatial stability of producer biomass but stabilized temporal ecosystem productivity. The results indicate that selective predation can prevent species augmentation from mass effects but has no apparent influence on stability. Dispersal rates, in contrast, can have significant effects on both species diversity and ecosystem stability at multiple spatial scales in metacommunities.

Modelling and optimising of physicochemical features of walnut-oil beverage emulsions by implementation of response surface methodology: effect of preparation conditions on emulsion stability.

PubMed

Homayoonfal, Mina; Khodaiyan, Faramarz; Mousavi, Mohammad

2015-05-01

The major purpose of this study is to apply response surface methodology to model and optimise processing conditions for the preparation of beverage emulsions with maximum emulsion stability and viscosity, minimum particle size, turbidity loss rate, size index and peroxide value changes. A three-factor, five-level central composite design was conducted to estimate the effects of three independent variables: ultrasonic time (UT, 5-15 min), walnut-oil content (WO, 4-10% (w/w)) and Span 80 content (S80, 0.55-0.8). The results demonstrated the empirical models were satisfactorily (p < 0.0001) fitted to the experimental data. Evaluation of responses by analysis of variance indicated high coefficient determination values. The overall optimisation of preparation conditions was an UT of 14.630 min, WO content of 8.238% (w/w), and S80 content of 0.782% (w/w). Under this optimum region, responses were found to be 219.198, 99.184, 0.008, 0.008, 2.43 and 16.65 for particle size, emulsion stability, turbidity loss rate, size index, viscosity and peroxide value changes, respectively. Copyright © 2014 Elsevier Ltd. All rights reserved.

Theoretical speciation of ethylenediamine-N-(o-hydroxyphenylacetic)-N'-(p-hydroxyphenylacetic) acid (o,p-EDDHA) in agronomic conditions.

PubMed

Yunta, Felipe; García-Marco, Sonia; Lucena, Juan J

2003-08-27

The presence of ethylenediamine-N-(o-hydroxyphenylacetic)-N'-(p-hydroxyphenylacetic) acid (o,p-EDDHA) as the second largest component in commercial EDDHA iron chelates has recently been demonstrated. Here is reported the speciation of o,p-EDDHA by the application of a novel methodology through the determination of the complexing capacity, protonation, and Ca(2+), Mg(2+), Cu(2+), and Fe(3+) stability constants. The pM values and species distribution in solution, hydroponic, and soil conditions were obtained. Due to the para position of one phenol group in o,p-EDDHA, the protonation constants and Ca and Mg stability constants have different values from those of o,o-EDDHA and p,p-EDDHA regioisomers. o,p-EDDHA/Fe(3+) stability constants are higher than those of EDTA/Fe(3+) but lower than those of o,o-EDDHA/Fe(3+). The sequence obtained for pFe is o,o-EDDHA/Fe(3+) >/= o,p-EDDHA/Fe(3+) > EDTA/Fe(3+). o,p-EDDHA/Fe(3+) can be used as an iron chelate in hydroponic conditions. Also, it can be used in soils with limited Cu availability.

Using data from the Microsoft Kinect 2 to determine postural stability in healthy subjects: A feasibility trial

PubMed Central

Smeragliuolo, Anna H.; Long, John Davis; Bumanlag, Silverio Joseph; He, Victor; Lampe, Anna

2017-01-01

The objective of this study was to determine whether kinematic data collected by the Microsoft Kinect 2 (MK2) could be used to quantify postural stability in healthy subjects. Twelve subjects were recruited for the project, and were instructed to perform a sequence of simple postural stability tasks. The movement sequence was performed as subjects were seated on top of a force platform, and the MK2 was positioned in front of them. This sequence of tasks was performed by each subject under three different postural conditions: “both feet on the ground” (1), “One foot off the ground” (2), and “both feet off the ground” (3). We compared force platform and MK2 data to quantify the degree to which the MK2 was returning reliable data across subjects. We then applied a novel machine-learning paradigm to the MK2 data in order to determine the extent to which data from the MK2 could be used to reliably classify different postural conditions. Our initial comparison of force plate and MK2 data showed a strong agreement between the two devices, with strong Pearson correlations between the trunk centroids “Spine_Mid” (0.85 ± 0.06), “Neck” (0.86 ± 0.07) and “Head” (0.87 ± 0.07), and the center of pressure centroid inferred by the force platform. Mean accuracy for the machine learning classifier from MK2 was 97.0%, with a specific classification accuracy breakdown of 90.9%, 100%, and 100% for conditions 1 through 3, respectively. Mean accuracy for the machine learning classifier derived from the force platform data was lower at 84.4%. We conclude that data from the MK2 has sufficient information content to allow us to classify sequences of tasks being performed under different levels of postural stability. Future studies will focus on validating this protocol on large populations of individuals with actual balance impairments in order to create a toolkit that is clinically validated and available to the medical community. PMID:28196139

Effects of 30-, 60-, and 90-Day Bed Rest on Postural Control in Men and Women

NASA Technical Reports Server (NTRS)

Esteves, Julie; Taylor, Laura C.; Vanya, Robert D.; Dean, S. Lance; Wood, Scott J.

2011-01-01

INTRODUCTION Head-down-tilt bed rest (HDT) has been used as a safe gr ound-based analog to mimic and develop countermeasures for the physiological effects of spaceflight, including decrements in postural stability. The purpose of this investigation was to characterize the effects of 30-, 60-, and 90-day bed rest on postural control in men and women. METHODS Twenty-nine subjects (18M,11F) underwent 13 days of ambula tory acclimatization and were placed in 6? HDT for 30 (n=12), 60 (n=8), or 90 (n=9) days, followed by 14 days of ambulatory recovery. Computerized dynamic posturography (CDP) was used to assess changes in sensory and motor components of postural control, and recovery after HDT. Sensory Organization Tests (SOTs) objectively evaluate one?s ability to effectively use or suppress visual, vestibular, and proprioceptive information for postural control. Stability during the SOTs was assessed using peak-to-peak sway and convergence toward stability limits to derive an equilibrium score. Motor Control Tests (MCTs) evaluate one?s ability to recover from unexpected support surface perturbations, with performance determined by center-of-pressure path length. Whole-body kinematic data were collected to determine body-sway strategy used to maintain stability during each condition. Baselines were determined pre-HDT. Recovery was tracked post-HDT on days 0, 1, 2, and 4. RESULTS Immediately after HDT, subjects showed decreased performance on most SOTs, primarily on sway-referenced support conditions, typically returning to baseline levels within 4 days. MCT performance was not significantly affected. There were no significant gender or duration differences in performance. Kinematic data revealed a tendency to use ankle strategy to maintain an upright stance during most SOT conditions. Interestingly, six subjects (2M,4F) experienced orthostatic intolerance and were unable to complete day 0 testing. CONCLUSION HDT mimics some un loading mechanisms of spaceflight and elicits orthostatic issues present post-spaceflight (contributing to instability); however, it does not sufficiently address the vestibular dysfunction which occurs post-spaceflight.

Using data from the Microsoft Kinect 2 to determine postural stability in healthy subjects: A feasibility trial.

PubMed

Dehbandi, Behdad; Barachant, Alexandre; Smeragliuolo, Anna H; Long, John Davis; Bumanlag, Silverio Joseph; He, Victor; Lampe, Anna; Putrino, David

2017-01-01

The objective of this study was to determine whether kinematic data collected by the Microsoft Kinect 2 (MK2) could be used to quantify postural stability in healthy subjects. Twelve subjects were recruited for the project, and were instructed to perform a sequence of simple postural stability tasks. The movement sequence was performed as subjects were seated on top of a force platform, and the MK2 was positioned in front of them. This sequence of tasks was performed by each subject under three different postural conditions: "both feet on the ground" (1), "One foot off the ground" (2), and "both feet off the ground" (3). We compared force platform and MK2 data to quantify the degree to which the MK2 was returning reliable data across subjects. We then applied a novel machine-learning paradigm to the MK2 data in order to determine the extent to which data from the MK2 could be used to reliably classify different postural conditions. Our initial comparison of force plate and MK2 data showed a strong agreement between the two devices, with strong Pearson correlations between the trunk centroids "Spine_Mid" (0.85 ± 0.06), "Neck" (0.86 ± 0.07) and "Head" (0.87 ± 0.07), and the center of pressure centroid inferred by the force platform. Mean accuracy for the machine learning classifier from MK2 was 97.0%, with a specific classification accuracy breakdown of 90.9%, 100%, and 100% for conditions 1 through 3, respectively. Mean accuracy for the machine learning classifier derived from the force platform data was lower at 84.4%. We conclude that data from the MK2 has sufficient information content to allow us to classify sequences of tasks being performed under different levels of postural stability. Future studies will focus on validating this protocol on large populations of individuals with actual balance impairments in order to create a toolkit that is clinically validated and available to the medical community.

How Does the Gibbs Inequality Condition Affect the Stability and Detachment of Floating Spheres from the Free Surface of Water?

PubMed

Feng, Dong-xia; Nguyen, Anh V

2016-03-01

Floating objects on the air-water interfaces are central to a number of everyday activities, from walking on water by insects to flotation separation of valuable minerals using air bubbles. The available theories show that a fine sphere can float if the force of surface tension and buoyancies can support the sphere at the interface with an apical angle subtended by the circle of contact being larger than the contact angle. Here we show that the pinning of the contact line at the sharp edge, known as the Gibbs inequality condition, also plays a significant role in controlling the stability and detachment of floating spheres. Specifically, we truncated the spheres with different angles and used a force sensor device to measure the force of pushing the truncated spheres from the interface into water. We also developed a theoretical modeling to calculate the pushing force that in combination with experimental results shows different effects of the Gibbs inequality condition on the stability and detachment of the spheres from the water surface. For small angles of truncation, the Gibbs inequality condition does not affect the sphere detachment, and hence the classical theories on the floatability of spheres are valid. For large truncated angles, the Gibbs inequality condition determines the tenacity of the particle-meniscus contact and the stability and detachment of floating spheres. In this case, the classical theories on the floatability of spheres are no longer valid. A critical truncated angle for the transition from the classical to the Gibbs inequality regimes of detachment was also established. The outcomes of this research advance our understanding of the behavior of floating objects, in particular, the flotation separation of valuable minerals, which often contain various sharp edges of their crystal faces.

Etanercept (Enbrel®) alternative storage at ambient temperature.

PubMed

Shannon, Edel; Daffy, Joanne; Jones, Heather; Paulson, Andrea; Vicik, Steven M

2017-01-01

Biologic disease-modifying antirheumatic drugs, including tumor necrosis factor inhibitors such as etanercept (Enbrel ® ), have improved outcomes for patients with rheumatic and other inflammatory diseases, with sustained remission being the optimal goal for patients with rheumatoid arthritis. Flexible and convenient treatment options, compatible with modern lifestyle, are important in helping patients maintain treatment and manage their disease. Etanercept drug product (DP) is available in lyophilized powder (Lyo) for solution injection, prefilled syringe, and prefilled pen presentations and is typically stored under refrigerated conditions. We aimed to generate a comprehensive analytical data package from stability testing of key quality attributes, consistent with regulatory requirements, to determine whether the product profile of etanercept is maintained at ambient temperature. Test methods assessing key attributes of purity, quality, potency, and safety were performed over time, following storage of etanercept DP presentations under a range of conditions. Results and statistical analysis from stability testing (based on size exclusion high-performance liquid chromatography, hydrophobic interaction chromatography, and sodium dodecyl sulfate-polyacrylamide gel electrophoresis Coomassie) across all etanercept presentations (10 and 25 mg/vial Lyo DP; 25 and 50 mg prefilled syringe DP; 50 mg prefilled pen DP) showed key stability-indicating parameters were within acceptable limits through the alternative storage condition of 25°C±2°C for 1 month. Stability testing performed in line with regulatory requirements supports a single period of storage for etanercept DP at an alternative storage condition of 25°C±2°C for up to 1 month within the approved expiry of the product. This alternative storage condition represents further innovation in the etanercept product lifecycle, providing greater flexibility and enhanced overall convenience for patients.

A validated stability-indicating RP-HPLC method for levofloxacin in the presence of degradation products, its process related impurities and identification of oxidative degradant.

PubMed

Lalitha Devi, M; Chandrasekhar, K B

2009-12-05

The objective of current study was to develop a validated specific stability indicating reversed-phase liquid chromatographic method for the quantitative determination of levofloxacin as well as its related substances determination in bulk samples, pharmaceutical dosage forms in the presence of degradation products and its process related impurities. Forced degradation studies were performed on bulk sample of levofloxacin as per ICH prescribed stress conditions using acid, base, oxidative, water hydrolysis, thermal stress and photolytic degradation to show the stability indicating power of the method. Significant degradation was observed during oxidative stress and the degradation product formed was identified by LCMS/MS, slight degradation in acidic stress and no degradation was observed in other stress conditions. The chromatographic method was optimized using the samples generated from forced degradation studies and the impurity spiked solution. Good resolution between the peaks corresponds to process related impurities and degradation products from the analyte were achieved on ACE C18 column using the mobile phase consists a mixture of 0.5% (v/v) triethyl amine in sodium dihydrogen orthophosphate dihydrate (25 mM; pH 6.0) and methanol using a simple linear gradient. The detection was carried out at 294 nm. The limit of detection and the limit of quantitation for the levofloxacin and its process related impurities were established. The stressed test solutions were assayed against the qualified working standard of levofloxacin and the mass balance in each case was in between 99.4 and 99.8% indicating that the developed LC method was stability indicating. Validation of the developed LC method was carried out as per ICH requirements. The developed LC method was found to be suitable to check the quality of bulk samples of levofloxacin at the time of batch release and also during its stability studies (long term and accelerated stability).

Engineering proteins with tunable thermodynamic and kinetic stabilities.

PubMed

Pey, Angel L; Rodriguez-Larrea, David; Bomke, Susanne; Dammers, Susanne; Godoy-Ruiz, Raquel; Garcia-Mira, Maria M; Sanchez-Ruiz, Jose M

2008-04-01

It is widely recognized that enhancement of protein stability is an important biotechnological goal. However, some applications at least, could actually benefit from stability being strongly dependent on a suitable environment variable, in such a way that enhanced stability or decreased stability could be realized as required. In therapeutic applications, for instance, a long shelf-life under storage conditions may be convenient, but a sufficiently fast degradation of the protein after it has performed the planned molecular task in vivo may avoid side effects and toxicity. Undesirable effects associated to high stability are also likely to occur in food-industry applications. Clearly, one fundamental factor involved here is the kinetic stability of the protein, which relates to the time-scale of the irreversible denaturation processes and which is determined to some significant extent by the free-energy barrier for unfolding (the barrier that "separates" the native state from the highly-susceptible-to-irreversible-alterations nonnative states). With an appropriate experimental model, we show that strong environment-dependencies of the thermodynamic and kinetic stabilities can be achieved using robust protein engineering. We use sequence-alignment analysis and simple computational electrostatics to design stabilizing and destabilizing mutations, the latter introducing interactions between like charges which are screened out at high salt. Our design procedures lead naturally to mutating regions which are mostly unstructured in the transition state for unfolding. As a result, the large salt effect on the thermodynamic stability of our consensus plus charge-reversal variant translates into dramatic changes in the time-scale associated to the unfolding barrier: from the order of years at high salt to the order of days at low salt. Certainly, large changes in salt concentration are not expected to occur in biological systems in vivo. Hence, proteins with strong salt-dependencies of the thermodynamic and kinetic stabilities are more likely to be of use in those cases in which high-stability is required only under storage conditions. A plausible scenario is that inclusion of high salt in liquid formulations will contribute to a long protein shelf-life, while the lower salt concentration under the conditions of the application will help prevent the side effects associated with high-stability which may potentially arise in some therapeutic and food-industry applications. From a more general viewpoint, this work shows that consensus engineering and electrostatic engineering can be readily combined and clarifies relevant aspects of the relation between thermodynamic stability and kinetic stability in proteins. (c) 2007 Wiley-Liss, Inc.

Glutamine Synthetase Isoenzymes in the Green Soil Alga Stichococcus bacillaris Naeg.

PubMed

Ahmad, I; Hellebust, J A

1987-02-01

Two forms of glutamine synthetase (GS(1) and GS(2)) have been separated from cells of Stichococcus bacillaris by fast protein liquid chromatography. The activities of the two isoenzymes were influenced by the composition of the media employed; thiol reagents were essential for stabilizing GS(2) but they suppressed GS(1) activity. The activity of each isoenzyme was, therefore, determined following separate purification procedures. Growth conditions influenced both isoenzymes; GS(2) showed maximum activity under photoautotrophic conditions, whereas GS(1) showed maximum activity under heterotrophic conditions.

Glutamine Synthetase Isoenzymes in the Green Soil Alga Stichococcus bacillaris Naeg. 1

PubMed Central

Ahmad, Iftikhar; Hellebust, Johan A.

1987-01-01

Two forms of glutamine synthetase (GS1 and GS2) have been separated from cells of Stichococcus bacillaris by fast protein liquid chromatography. The activities of the two isoenzymes were influenced by the composition of the media employed; thiol reagents were essential for stabilizing GS2 but they suppressed GS1 activity. The activity of each isoenzyme was, therefore, determined following separate purification procedures. Growth conditions influenced both isoenzymes; GS2 showed maximum activity under photoautotrophic conditions, whereas GS1 showed maximum activity under heterotrophic conditions. PMID:16665232

Cold denaturation and 2H2O stabilization of a staphylococcal nuclease mutant.

PubMed Central

Antonino, L C; Kautz, R A; Nakano, T; Fox, R O; Fink, A L

1991-01-01

Cold denaturation is now recognized as a general property of proteins but has been observed only under destabilizing conditions, such as moderate denaturant concentration or low pH. By destabilizing the protein using site-directed mutagenesis, we have observed cold denaturation at pH 7.0 in the absence of denaturants in a mutant of staphylococcal nuclease, which we call NCA S28G for a hybrid protein between staphylococcal nuclease and concanavalin A in which there is the point mutation Ser-28----Gly. The temperature of maximum stability (tmax) as determined by circular dichroism (CD) was 18.1 degrees C, and the midpoints of the thermal unfolding transitions (tm) were 0.6 degrees C and 30.0 degrees C. These values may be compared with the tm of 52.5 degrees C for wild-type staphylococcal nuclease, for which no cold denaturation was observed under these conditions. When the stability of the mutant was examined in 2H2O by NMR, CD, or fluorescence, a substantial increase in the amount of folded protein at the tmax was noted as well as a decrease in tmax, reflecting increased stability. PMID:1652762

Evaluation of accelerated UV and thermal testing for benzene formation in beverages containing benzoate and ascorbic acid.

PubMed

Nyman, Patricia J; Wamer, Wayne G; Begley, Timothy H; Diachenko, Gregory W; Perfetti, Gracia A

2010-04-01

Under certain conditions, benzene can form in beverages containing benzoic and ascorbic acids. The American Beverage Assn. (ABA) has published guidelines to help manufacturers mitigate benzene formation in beverages. These guidelines recommend accelerated testing conditions to test product formulations, because exposure to ultraviolet (UV) light and elevated temperature over the shelf life of the beverage may result in benzene formation in products containing benzoic and ascorbic acids. In this study, the effects of UVA exposure on benzene formation were determined. Benzene formation was examined for samples contained in UV stabilized and non-UV stabilized packaging. Additionally, the usefulness of accelerated thermal testing to simulate end of shelf-life benzene formation was evaluated for samples containing either benzoic or ascorbic acid, or both. The 24 h studies showed that under intense UVA light benzene levels increased by as much as 53% in model solutions stored in non-UV stabilized bottles, whereas the use of UV stabilized polyethylene terephthalate bottles reduced benzene formation by about 13% relative to the non-UV stabilized bottles. Similar trends were observed for the 7 d study. Retail beverages and positive and negative controls were used to study the accelerated thermal testing conditions. The amount of benzene found in the positive controls and cranberry juice suggests that testing at 40 degrees C for 14 d may more reliably simulate end of shelf-life benzene formation in beverages. Except for cranberry juice, retail beverages were not found to contain detectable amounts of benzene (<0.05 ng/g) at the end of their shelf lives.

Cooperative control theory and integrated flight and propulsion control

NASA Technical Reports Server (NTRS)

Schmidt, David K.; Schierman, John D.

1995-01-01

The major contribution of this research was the exposition of the fact that airframe and engine interactions could be present, and their effects could include loss of stability and performance of the control systems. Also, the significance of two directional, as opposed to one-directional, coupling was identified and explained. A multivariable stability and performance analysis methodology was developed, and applied to several candidate aircraft configurations. In these example evaluations, the significance of these interactions was underscored. Also exposed was the fact that with interactions present along with some integrated control approaches, the engine command/limiting logic (which represents an important nonlinear component of the engine control system) can impact closed-loop airframe/engine system stability. Finally, a brief investigation of control-law synthesis techniques appropriate for the class of systems was pursued, and it was determined that multivariable techniques, including model-following formulations of LQG and/or H infinity methods, showed promise. However, for practical reasons, decentralized control architectures are preferred, which is an architecture incompatible with these synthesis methods. The major contributions of the second phase of the grant was the development of conditions under which no decentralized controller could achieve closed loop system requirements on stability and/or performance. Sought were conditions that depended only on properties of the plant and the requirement, and independent of any particular control law or synthesis approach. Therefore, they could be applied a priori, before synthesis of a candidate control law. Under this grant, such conditions were found regarding stability, and encouraging initial results were obtained regarding performance.

Application of linear Raman spectroscopy for the determination of acetone decomposition.

PubMed

Eichmann, Simone Christine; Trost, Johannes; Seeger, Thomas; Zigan, Lars; Leipertz, Alfred

2011-06-06

Acetone (CH₃)₂CO is a common tracer for laser-induced fluorescence (LIF) to investigate mixture formation processes and temperature fields in combustion applications. Since the fluorescence signal is a function of temperature and pressure, calibration measurements in high pressure and high temperature cells are necessary. However, there is a lack of reliable data of tracer stability at these harsh conditions for technical application. A new method based on the effect of spontaneous Raman scattering is proposed to analyze the thermal stability of the tracer directly in the LIF calibration cell. This is done by analyzing the gas composition regarding educts and products of the reaction. First measurements at IC engine relevant conditions up to 750 K and 30 bar are presented.

Influence of storage conditions on the stability of monomeric anthocyanins studied by reversed-phase high-performance liquid chromatography.

PubMed

Morais, Helena; Ramos, Cristina; Forgács, Esther; Cserháti, Tibor; Oliviera, José

2002-04-25

The effect of light, storage time and temperature on the decomposition rate of monomeric anthocyanin pigments extracted from skins of grape (Vitis vinifera var. Red globe) was determined by reversed-phase high-performance liquid chromatography (RP-HPLC). The impact of various storage conditions on the pigment stability was assessed by stepwise regression analysis. RP-HPLC separated well the five anthocyanins identified and proved the presence of other unidentified pigments at lower concentrations. Stepwise regression analysis confirmed that the overall decomposition rate of monomeric anthocyanins, peonidin-3-glucoside and malvidin-3-glucoside significantly depended on the time and temperature of storage, the effect of storage time being the most important. The presence or absence of light exerted a negligible impact on the decomposition rate.

Stability evaluation of modernized bank protections in a culvert construction

NASA Astrophysics Data System (ADS)

Cholewa, Mariusz; Plesiński, Karol; Kamińska, Katarzyna; Wójcik, Izabela

2018-02-01

The paper presents stability evaluation of the banks of the Wilga River on a chosen stretch in Koźmice Wielkie, Małopolska Province. The examined stretch included the river bed upstream from the culvert on a district road. The culvert construction, built over four decades ago, was disassembled in 2014. The former construction, two pipes that were 1.4 m in diameter, was entirely removed. The investor decided to build a new construction in the form of insitu poured reinforced concrete with a 4 x 2 m cross section. Change of geometry and different location in relation to the river current caused increase in the flow velocity and, as a consequence, erosion of both protected and natural banks. Groundwater conditions were determined based on the geotechnical tests that were carried out on soil samples taken from the banks and the river bed. Stability calculations of natural slopes of the Wilga River and the ones protected with riprap indicate mistakes in the design project concerning construction of the river banks. The purpose of the study was to determine the stability of the Wilga River banks on a selected section adjacent to the rebuilt culvert. Stability of a chosen cross section was analysed in the paper. Presented conclusions are based on the results of geotechnical tests and numerical calculations.

Thermal Stability of RP-2 for Hydrocarbon Boost Regenerative Cooling

NASA Technical Reports Server (NTRS)

Kleinhenz, Julie E.; Deans, Matthew C.; Stiegemeier, Benjamin R.; Psaras, Peter M.

2013-01-01

A series of tests were performed in the NASA Glenn Research Centers Heated Tube Facility to study the heat transfer and thermal stability behavior of RP-2 under conditions similar to those found in rocket engine cooling channels. It has long been known that hydrocarbon fuels, such as RP-2, can decompose at high temperature to form deposits (coke) which can adversely impact rocket engine cooling channel performance. The heated tube facility provides a simple means to study these effects. Using resistively heated copper tubes in a vacuum chamber, flowing RP-2 was heated to explore thermal effects at a range of test conditions. Wall temperature (850-1050F) and bulk fluid temperature (300-500F) were varied to define thermal decomposition and stability at each condition. Flow velocity and pressure were fixed at 75 fts and 1000 psia, respectively. Additionally, five different batches of RP-2 were tested at identical conditions to examine any thermal stability differences resulting from batch to batch compositional variation. Among these tests was one with a potential coke reducing additive known as 1,2,3,4-Tetrahydroquinoline (THQ). While copper tubes were used for the majority of tests, two exploratory tests were performed with a copper alloy known as GRCop-42. Each tube was instrumented with 15 thermocouples to examine the temperature profile, and carbon deposition at each thermocouple location was determined post-test in an oxidation furnace. In many tests, intermittent local temperature increases were observed visually and in the thermocouple data. These hot spots did not appear to correspond with a higher carbon deposition.

Examining the effect of altered redox conditions on deep soil organic matter stability

NASA Astrophysics Data System (ADS)

Gabriel, C.; Kellman, L. M.; Ziegler, S. E.

2013-12-01

Since subsoil horizons contribute significantly to terrestrial carbon (C) budgets, understanding the influence of disturbances such as forest harvesting on subsoil C stability is critical. Clearcut harvesting leads to changes in the soil physico-chemical environment, including altering redox conditions arising from changes in soil hydrology that increase soil saturation, soil temperature, and pH. These physico-chemical changes have the potential to alter the adsorption of soil organic matter (SOM) to minerals, particularly at depth where SOM is primarily associated with mineral phases. The objective of this study was to determine the effect of differing redox states (aerobic vs. anaerobic) and temperature upon SOM stability of forested soils representative of the Acadian Forest Region of Eastern North America. Composite soil samples through depth (0-10, 10-20, 20-35, and 35-50 cm) from a mature red spruce forest (110 years) were incubated under optimum (aerobic) or saturated (anaerobic) conditions for 1 or 4 months at two temperatures (5 and 15 C). Following incubation, soil leachate was analyzed for dissolved organic carbon (DOC), and UV-vis absorbance in order to determine soil C losses and its optical character. Specific UV-vis absorbance SUVA (254 nm) and spectral slope ratios were calculated in order to assess the composition of chromophoric dissolved organic matter (CDOM). Preliminary results from the 1 month incubation indicate that under anaerobic conditions, all depths released DOC with a higher SUVA than under aerobic conditions, with the largest change observed in the 0-10 cm depth increment. Soil incubated at 5 C produced leachate with significantly less DOC and with a lower absorbance compared to 15 C under both redox conditions. These results suggest that both temperature and redox state are important in determining the aromaticity of DOC released from soils. Spectral slope ratios revealed that a greater proportion of CDOM of lower molecular weight (MW) compounds were released from deep mineral podzolic soils when saturated (high SUVA, low spectral slope), while higher MW CDOM were released from shallow soil strata (low SUVA, high spectral slope). This is consistent with research that indicates plant-derived SOM and microbial products each dominate in shallow and deep mineral soils, respectively. These preliminary results suggest that alterations to the redox state of a forested podzolic soil may have the potential to alter the mobilization of SOM, its composition and associated soil carbon stores.

Influence of external extrusion on stability of hydrogen molecule and its chaotic behavior

NASA Astrophysics Data System (ADS)

Jarosik, M. W.; SzczÈ©śniak, R.; Durajski, A. P.; Kalaga, J. K.; Leoński, W.

2018-01-01

We have determined the stability conditions of the hydrogen molecule under the influence of an external force of harmonic-type explicitly dependent on the amplitude (A) and frequency (Ω). The ground state of the molecule has been determined in the framework of the Born-Oppenheimer approximation, whereas the energy of the electronic subsystem has been calculated using the Hubbard model including all two-site electron interactions. The diagram of RT0(A ,Ω) , where RT0 denotes the distance between protons after the fixed initial time T0, allowed us to visualize the area of the instability with the complicated structure. We have shown that the vibrations of the hydrogen molecule have a chaotic nature for some points of the instability region. In addition to the amplitude and frequency of the extrusion, the control parameter of the stability of the molecule is the external force associated with pressure. The increase in its value causes the disappearance of the area of the instability and chaotic vibrations.

Some remarks on the compatibility between determinism and unpredictability.

PubMed

Franceschelli, Sara

2012-09-01

Determinism and unpredictability are compatible since deterministic flows can produce, if sensitive to initial conditions, unpredictable behaviors. Within this perspective, the notion of scenario to chaos transition offers a new form of predictability for the behavior of sensitive to initial condition systems under the variation of a control parameter. In this paper I first shed light on the genesis of this notion, based on a dynamical systems approach and on considerations of structural stability. I then suggest a link to the figure of epigenetic landscape, partially inspired by a dynamical systems perspective, and offering a theoretical framework to apprehend developmental noise. Copyright © 2012 Elsevier Ltd. All rights reserved.

MATLAB Stability and Control Toolbox Trim and Static Stability Module

NASA Technical Reports Server (NTRS)

Kenny, Sean P.; Crespo, Luis

2012-01-01

MATLAB Stability and Control Toolbox (MASCOT) utilizes geometric, aerodynamic, and inertial inputs to calculate air vehicle stability in a variety of critical flight conditions. The code is based on fundamental, non-linear equations of motion and is able to translate results into a qualitative, graphical scale useful to the non-expert. MASCOT was created to provide the conceptual aircraft designer accurate predictions of air vehicle stability and control characteristics. The code takes as input mass property data in the form of an inertia tensor, aerodynamic loading data, and propulsion (i.e. thrust) loading data. Using fundamental nonlinear equations of motion, MASCOT then calculates vehicle trim and static stability data for the desired flight condition(s). Available flight conditions include six horizontal and six landing rotation conditions with varying options for engine out, crosswind, and sideslip, plus three take-off rotation conditions. Results are displayed through a unique graphical interface developed to provide the non-stability and control expert conceptual design engineer a qualitative scale indicating whether the vehicle has acceptable, marginal, or unacceptable static stability characteristics. If desired, the user can also examine the detailed, quantitative results.

Pessimistic Determination of Mechanical Conditions and Micro/macroeconomic Evaluation of Mine Pillar Replacement

NASA Astrophysics Data System (ADS)

Chen, Qingfa; Zhao, Fuyu

2017-12-01

Numerous pillars are left after mining of underground mineral resources using the open stope method or after the first step of the partial filling method. The mineral recovery rate can, however, be improved by replacement recovery of pillars. In the present study, the relationships among the pillar type, minimum pillar width, and micro/macroeconomic factors were investigated from two perspectives, namely mechanical stability and micro/macroeconomic benefit. Based on the mechanical stability formulas for ore and artificial pillars, the minimum width for a specific pillar type was determined using a pessimistic criterion. The microeconomic benefit c of setting an ore pillar, the microeconomic benefit w of artificial pillar replacement, and the economic net present value (ENPV) of the replacement process were calculated. The values of c and w were compared with respect to ENPV, based on which the appropriate pillar type and economical benefit were determined.

Impact of short range hydrophobic interactions and long range electrostatic forces on the aggregation kinetics of a monoclonal antibody and a dual-variable domain immunoglobulin at low and high concentrations.

PubMed

Kumar, Vineet; Dixit, Nitin; Zhou, Liqiang Lisa; Fraunhofer, Wolfgang

2011-12-12

The purpose of this work was to determine the nature of long and short-range forces governing protein aggregation kinetics at low and high concentrations for a monoclonal antibody (IgG1) and a dual-variable-domain immunoglobulin (DVD-Ig). Protein-protein interactions (PPI) were studied under dilute conditions by utilizing the methods of static (B(22)) and dynamic light scattering (k(D)). PPI in solutions containing minimal ionic strengths were characterized to get detailed insights into the impact of ionic strength on aggregation. Microcalorimetry and susceptibility to denature at air-liquid interface were used to assess the tertiary structure and quiescent stability studies were conducted to study aggregation characteristics. Results for IgG1 showed that electrostatic interactions governed protein aggregation kinetics both under dilute and concentrated conditions (i.e., 5 mg/mL and 150 mg/mL). For DVD-Ig molecules, on the other hand, although electrostatic interactions governed protein aggregation under dilute conditions, hydrophobic forces clearly determined the kinetics at high concentrations. This manuscript shows for the first time that short-range hydrophobic interactions can outweigh electrostatic forces and play an important role in determining protein aggregation at high concentrations. Additionally, results show that although higher-order virial coefficients become significant under low ionic strength conditions, removal of added charges may be used to enhance the aggregation stability of dilute protein formulations. Copyright © 2011 Elsevier B.V. All rights reserved.

What you see is what you step: the horizontal-vertical illusion increases toe clearance in older adults during stair ascent.

PubMed

Foster, Richard J; Whitaker, David; Scally, Andrew J; Buckley, John G; Elliott, David B

2015-05-01

Falls on stairs are a significant cause of morbidity and mortality in elderly people. A simple safety strategy to avoid tripping on stairs is increasing foot clearance. We determined whether a horizontal-vertical illusion superimposed onto stairs to create an illusory perceived increase in stair-riser height would increase stair ascent foot clearance in older participants. Preliminary experiments determined the optimum parameters for the horizontal-vertical illusion. Fourteen older adults (mean age ± 1 SD, 68.5 ± 7.4 years) ascended a three-step staircase with the optimized version of the horizontal-vertical illusion (spatial frequency: 12 cycles per stair riser) positioned either on the bottom or top stair only, or on the bottom and top stair simultaneously. These were compared to a control condition, which had a plain stair riser with edge highlighters positioned flush with each stair-tread edge. Foot clearance and measures of postural stability were compared across conditions. The optimized illusion on the bottom and top stair led to a significant increase in foot clearance over the respective stair edge, compared to the control condition. There were no significant decreases in postural stability. An optimized horizontal-vertical visual illusion led to significant increases in foot clearance in older adults when ascending a staircase, but the effects did not destabilize their postural stability. Inclusion of the horizontal-vertical illusion on raised surfaces (e.g., curbs) or the bottom and top stairs of staircases could improve stair ascent safety in older adults.

Parametrically excited multidegree-of-freedom systems with repeated frequencies

NASA Astrophysics Data System (ADS)

Nayfeh, A. H.

1983-05-01

An analysis is presented of the linear response of multidegree-of-freedom systems with a repeated frequency of order three to a harmonic parametric excitation. The method of multiple scales is used to determine the modulation of the amplitudes and phases for two cases: fundamental resonance of the modes with the repeated frequency and combination resonance involving these modes and another mode. Conditions are then derived for determining the stability of the motion.

Method of fan sound mode structure determination computer program user's manual: Microphone location program

NASA Technical Reports Server (NTRS)

Pickett, G. F.; Wells, R. A.; Love, R. A.

1977-01-01

A computer user's manual describing the operation and the essential features of the microphone location program is presented. The Microphone Location Program determines microphone locations that ensure accurate and stable results from the equation system used to calculate modal structures. As part of the computational procedure for the Microphone Location Program, a first-order measure of the stability of the equation system was indicated by a matrix 'conditioning' number.

Investigation of the Low-Speed Stability and Control Characteristics of a 1/10-Scale Model of the Douglas XF4D-1 Airplane in the Langley Free-Flight Tunnel TED No. NACA DE 349

NASA Technical Reports Server (NTRS)

Johnson, Joseph L.

1951-01-01

An investigation of the low-speed, power-off stability and control characteristics of a 1/10-scale model of the Douglas XF4D-1 airplane has been made in the Langley free-flight tunnel. The model was flown with leading-edge slats retracted and extended over a lift-coefficient range from 0.5 to the stall. Only relatively low-altitude conditions were simulated and no attempt was made to determine the effect on the stability characteristics of freeing the controls. The longitudinal stability and control characteristics of the model were satisfactory for all conditions investigated except near the stall with slats extended, where the model had a slight nosing-up tendency. The lateral stability and control characteristics of the model were considered satisfactory for all conditions investigated except near the stall with slats retracted, where a change in sign of the static- directional-stability parameter Cn(sub beta) caused the model to be directionally divergent. The addition of an extension to the top of the vertical tail did not increase Cn(sub beta) enough to eliminate the directional divergence of the model, but a large increase in Cn(sub beta) that was obtainable by artificial means appeared to eliminate the divergence and flights near the stall could be made. Artificially increasing the stability derivative-Cn(sub r) (yawing moment due to yawing) and Cn(sub p) (yawing moment due to rolling) had little effect on the divergence for the range of these parameters investigated. Calculations indicate that the damping of the lateral oscillation of the airplane with slats retracted or extended will be satisfactory at sea level but will be only marginally satisfactory at 40,000 feet.

Stability-indicating RP-HPLC method for the simultaneous determination of escitalopram oxalate and clonazepam.

PubMed

Kakde, Rajendra B; Satone, Dinesh D; Gadapayale, Kamalesh K; Kakde, Megha G

2013-07-01

The objective of the current study was to develop a validated, specific stability-indicating reversed-phase liquid chromatographic (LC) method for the quantitative determination of escitalopram oxalate and clonazepam and their related substances in bulk drugs and pharmaceutical dosage forms in the presence of degradation products. Forced degradation studies were performed on the pure drugs of escitalopram oxalate and clonazepam, as per the stress conditions prescribed by the International Conference on Harmonization (ICH) using acid, base, oxidation, thermal stress and photolytic degradation to show the stability-indicating power of the method. Significant degradation was observed during acid and alkaline hydrolysis and no degradation was observed in other stress conditions. The chromatographic method was optimized using the samples generated from forced degradation studies. Good resolution between the peaks corresponded to the active pharmaceutical ingredients, escitalopram oxalate and clonazepam, and degradation products from the analyte were achieved on an ODS Hypersil C18 column (250 × 4.6 mm) using a mobile phase consisting of a mixture of acetonitrile-50 mM phosphate buffer + 10 mM triethylamine (70:30, v/v). The detection was conducted at 268 nm. The limit of detection and the limit of quantitation for escitalopram oxalate and clonazepam were established. The stress test solutions were assayed against the qualified working standards of escitalopram oxalate and clonazepam, which indicated that the developed LC method was stability-indicating. Validation of the developed LC method was conducted as per ICH requirements. The developed LC method was found to be suitable to check the quality of bulk samples of escitalopram oxalate and clonazepam.

Interfacial Chemical Interactions in the (Alumina/Graphite/Al Alloys) System: Thermodynamic Modeling and Experimental Results

NASA Astrophysics Data System (ADS)

Gelbstein, M.; Edry, I.; Froumin, N.; Frage, N.

2009-04-01

The stability of alumina-coated graphite couples in liquid Al is investigated in the 1373 to 1573 K temperature range. A thermodynamic model was carried out to determine the mechanisms controlling the couple stability and the effect of alloying Al with high melting point element for instance U (up to 3 at. pct). It was established that the dissolved uranium dose not play any role in the interfacial interactions and that the couple stability is governed by the interactions with Al resulting in the release of gaseous products. The experiments focused on wetting kinetics under conditions allowing for an in-situ reduction of the alumina coating by the liquid Al. The experimental results confirm the predictions of the thermodynamic analysis.

Similar folds with different stabilization mechanisms: the cases of prion and doppel proteins

PubMed Central

Colacino, Stefano; Tiana, Guido; Colombo, Giorgio

2006-01-01

Background Protein misfolding is the main cause of a group of fatal neurodegenerative diseases in humans and animals. In particular, in Prion-related diseases the normal cellular form of the Prion Protein PrP (PrPC) is converted into the infectious PrPSc through a conformational process during which it acquires a high β-sheet content. Doppel is a protein that shares a similar native fold, but lacks the scrapie isoform. Understanding the molecular determinants of these different behaviours is important both for biomedical and biophysical research. Results In this paper, the dynamical and energetic properties of the two proteins in solution is comparatively analyzed by means of long time scale explicit solvent, all-atom molecular dynamics in different temperature conditions. The trajectories are analyzed by means of a recently introduced energy decomposition approach (Tiana et al, Prot. Sci. 2004) aimed at identifying the key residues for the stabilization and folding of the protein. Our analysis shows that Prion and Doppel have two different cores stabilizing the native state and that the relative contribution of the nucleus to the global stability of the protein for Doppel is sensitively higher than for PrP. Moreover, under misfolding conditions the Doppel core is conserved, while the energy stabilization network of PrP is disrupted. Conclusion These observations suggest that different sequences can share similar native topology with different stabilizing interactions and that the sequences of the Prion and Doppel proteins may have diverged under different evolutionary constraints resulting in different folding and stabilization mechanisms. PMID:16857062

Flight Measurements to Determine Effect of a Spring-Loaded Tab on Longitudinal Stability of an Airplane

NASA Technical Reports Server (NTRS)

Hunter, Paul A.; Reeder, John P.

1946-01-01

In conjunction with a program of research on the general problem of stability of airplanes in the climbing condition, tests have been made of a spring-loaded tb which. is referred to as a ?springy tab,? installed on the elevator of a low-wing scout bomber. The tab was arranged to deflect upward with decrease in speed which caused an increase in the pull force required to trim at low speeds and thereby increased the stick-free static longitudinal stability of the airplane. It was found that the springy tab would increase the stick-free stability in all flight conditions, would reduce the danger of inadvertent stalling because of the definite pull force required to stall the airplane with power on, would reduce the effect of center-of-gravity position on stick-free static stability, and would have little effect on the elevator stick forces in accelerated f11ght. Another advantage of the springy tab is that it might be used to provide almost any desired variation of elevator stick force with speed by adjusting the tab hinge-moment characteristics and the variation of spring moment with tab deflection. Unlike the bungee and the bobweight, the springy tab would provide stick-free static stability without requiring a pull force to hold the stick back while taxying. A device similar to the springy tab may be used on the rudder or ailerons to eliminate undesirable trim-force variations with speed.

Optimization of the canola oil based vitamin E nanoemulsions stabilized by food grade mixed surfactants using response surface methodology.

PubMed

Mehmood, Tahir

2015-09-15

The objective of the present study was to prepare canola oil based vitamin E nanoemulsions by using food grade mixed surfactants (Tween:80 and lecithin; 3:1) to replace some concentration of nonionic surfactants (Tween 80) with natural surfactant (soya lecithin) and to optimize their preparation conditions. RBD (Refined, Bleached and Deodorized) canola oil and vitamin E acetate were used in water/vitamin E/oil/surfactant system due to their nutritional benefits and oxidative stability, respectively. Response surface methodology (RSM) was used to optimize the preparation conditions. The effects of homogenization pressure (75-155MPa), oil concentrations (4-12% w/w), surfactant concentrations (3-11% w/w) and vitamin E acetate contents (0.4-1.2% w/w) on the particle size and emulsion stability were studied. RSM analysis has shown that the experimental data could be fitted well into second-order polynomial model with the coefficient of determinations of 0.9464 and 0.9278 for particle size and emulsion stability, respectively. The optimum values of independent variables were 135MPa homogenization pressure, 6.18% oil contents, 6.39% surfactant concentration and 1% vitamin E acetate concentration. The optimized response values for particle size and emulsion stability were 150.10nm and 0.338, respectively. Whereas, the experimental values for particle size and nanoemulsion stability were 156.13±2.3nm and 0.328±0.015, respectively. Copyright © 2015 Elsevier Ltd. All rights reserved.

The Influence of Tablet Formulation, Drug Concentration, and pH Modification on the Stability of Extemporaneously Compounded Levothyroxine Suspensions.

PubMed

Svirskis, Darren; Lin, Shao-Wei; Brown, Helen; Sangaroomthong, Annie; Shin, Daniel; Wang, Ziqi; Xu, Hongtao; Dean, Rebecca; Vareed, Preetika; Jensen, Maree; Wu, Zimei

2018-01-01

Three brands of levothyroxine tablets are currently available in New Zealand (Eltroxin, Mercury Pharma, Synthroid) for extemporaneous compounding into suspensions. This study aims to determine whether tablet brand (i.e., formulation), concentration, storage conditions, as well as pH, impact the stability of compounded levothyroxine suspensions. Using the three available brands of levothyroxine tablets, suspensions were compounded at concentrations of 15 µg/mL and 25 µg/mL and stored at 4°C and 22°C. Samples were withdrawn weekly for 4 weeks, and chemical stability was evaluated using high-performance liquid chromatographic analysis. Physical appearance, ease of resuspension, and pH were also monitored weekly. To evaluate the effect on drug stability, pH modifiers were added to a suspension. As demonstrated by high-performance liquid chromatographic analysis, the suspensions compounded from the Eltroxin and Mercury Pharma tablets were more stable (>90% remaining after 4 weeks) than Synthroid across both storage conditions and concentrations. The drug was more stable at the higher concentration of 25 µg/mL than at 15 µg/mL. Levothyroxine was stable when pH was increased to pH 8 through the addition of sodium citrate; stability was reduced at a lower pH. Storage temperature did not affect the stability of the suspensions during the 4-week study. This is the first study demonstrating the impact of tablet brand, with different excipients, and drug concentrations on stability, and thus the beyond-use date of the compounded levothyroxine liquid formulations. The pH control achieved by sodium citrate, either as an excipient in tablets or an additive during compounding, improved drug stability. Copyright© by International Journal of Pharmaceutical Compounding, Inc.

Evaluation of accelerated stability test conditions for medicated chewing gums.

PubMed

Maggi, Lauretta; Conte, Ubaldo; Nhamias, Alain; Grenier, Pascal; Vergnault, Guy

2013-10-01

The overall stability of medicated chewing gums is investigated under different storage conditions. Active substances with different chemical stabilities in solid state are chosen as model drugs. The dosage form is a three layer tablet obtained by direct compression. The gum core contains the active ingredient while the external layers are formulated to prevent gum adhesion to the punches of the tableting machine. Two accelerated test conditions (40°C/75% RH and 30°C/65% RH) are performed for 6 months. Furthermore, a long-term stability test at room conditions is conducted to verify the predictability of the results obtained from the stress tests. Some drugs are stable in all the conditions tested, but other drugs, generally considered stable in solid dosage forms, have shown relevant stability problems particularly when stress test conditions are applied to this particular semi-solid dosage forms. For less stable drugs, the stress conditions of 40°C/75% RH are not always predictable of chewing gum stability at room temperature and may produce false negative; intermediate conditions, 30°C/65% RH, are more predictive for this purpose, the results of drug content found after 6 months at intermediate stress conditions and 12 months at room conditions are generally comparable. But the results obtained show that only long-term conditions stability tests gave consistent results. During aging, the semi solid nature of the gum base itself, may also influence the drug delivery rate during chewing and great attention should be given also to the dissolution stability.

On the nonlinear stability of the unsteady, viscous flow of an incompressible fluid in a curved pipe

NASA Technical Reports Server (NTRS)

Shortis, Trudi A.; Hall, Philip

1995-01-01

The stability of the flow of an incompressible, viscous fluid through a pipe of circular cross-section curved about a central axis is investigated in a weakly nonlinear regime. A sinusoidal pressure gradient with zero mean is imposed, acting along the pipe. A WKBJ perturbation solution is constructed, taking into account the need for an inner solution in the vicinity of the outer bend, which is obtained by identifying the saddle point of the Taylor number in the complex plane of the cross-sectional angle co-ordinate. The equation governing the nonlinear evolution of the leading order vortex amplitude is thus determined. The stability analysis of this flow to periodic disturbances leads to a partial differential system dependent on three variables, and since the differential operators in this system are periodic in time, Floquet theory may be applied to reduce this system to a coupled infinite system of ordinary differential equations, together with homogeneous uncoupled boundary conditions. The eigenvalues of this system are calculated numerically to predict a critical Taylor number consistent with the analysis of Papageorgiou. A discussion of how nonlinear effects alter the linear stability analysis is also given, and the nature of the instability determined.

Production development of organic nonflammable spacecraft potting, encapsulating and conformal coating compounds. Volume 3: Appendices

NASA Technical Reports Server (NTRS)

Lieberman, S. L.

1974-01-01

Appendices are presented which include: statement of work; material vendor contacts; formulation/processing data sheet; upward propagation test; flammability test conditions/results sheet; odor test; vacuum stability requirements; flammability test facility; determination of offgassing products and carbon monoxide test; and pneumatic and mechanical impact test guidelines.

Extemporaneous clobazam suspensions for paediatric use prepared from commercially available tablets and pure drug.

PubMed

Buontempo, F; Moretton, M A; Quiroga, E; Chiappetta, D A

2013-01-01

Two clobazam aqueous suspensions for paediatric oral usage (5 mg/ml) were investigated to determinate its physicochemical stability under different storage conditions. Formulations were stored at 4 and 25 °C and the clobazam content was determined by High Performance Liquid Chromatography. Each sample was analyzed by triplicate at different time points (0, 7, 14, 28 and 56 days). Liquid suspensions were successfully formulated from pure drug and commercially available tablets. In both cases, samples showed suitable physical stability. Clobazam was chemically stable in aqueous suspension during the 56 days of the study at the two storage temperatures. All the tried oral liquid formulations can be conserved at 4 and 25 °C at least 56-day period. Copyright © 2013 SEFH. Published by AULA MEDICA. All rights reserved.

Analytical method for the simultaneous determination of polyfunctional amines used as monomers in the manufacture of food packaging materials.

PubMed

Paseiro-Cerrato, R; de Quirós, A Rodríguez-Bernaldo; Sendón, Raquel; Bustos, Juana; Ruíz, E; Cruz, J M; Paseiro-Losada, P

2011-10-07

This paper describes the development of a multi-analyte method for the determination of polyfunctional amines commonly used as monomers in the manufacture of food contact materials. Amines were analyzed by high-performance-liquid chromatography with diode-array detection (HPLC-DAD) after derivatization with dansyl chloride. The chromatographic analysis and the derivatization conditions were optimized. The proposed method was validated in terms of linearity, limits of detection and repeatabilities. The method showed an excellent sensitivity (LOD≤0.05 μg/mL) and appropriate repeatabilites (RSD (n=7)≤5%)). LC-MS/MS was used as a confirmatory technique. The stability of the amines in five food simulants (distilled water, 3% acetic acid, 10% ethanol, 50% ethanol and olive oil) under the most common testing conditions (10 days at 40 °C) was also studied. Results showed that amines had an acceptable stability in aqueous simulants but in the olive oil a loss of 100% was observed for all analytes. Copyright © 2011. Published by Elsevier B.V.

Aggregation factor analysis for protein formulation by a systematic approach using FTIR, SEC and design of experiments techniques.

PubMed

Feng, Yan Wen; Ooishi, Ayako; Honda, Shinya

2012-01-05

A simple systematic approach using Fourier transform infrared (FTIR) spectroscopy, size exclusion chromatography (SEC) and design of experiments (DOE) techniques was applied to the analysis of aggregation factors for protein formulations in stress and accelerated testings. FTIR and SEC were used to evaluate protein conformational and storage stabilities, respectively. DOE was used to determine the suitable formulation and to analyze both the main effect of single factors and the interaction effect of combined factors on aggregation. Our results indicated that (i) analysis at a low protein concentration is not always applicable to high concentration formulations; (ii) an investigation of interaction effects of combined factors as well as main effects of single factors is effective for improving conformational stability of proteins; (iii) with the exception of pH, the results of stress testing with regard to aggregation factors would be available for suitable formulation instead of performing time-consuming accelerated testing; (iv) a suitable pH condition should not be determined in stress testing but in accelerated testing, because of inconsistent effects of pH on conformational and storage stabilities. In summary, we propose a three-step strategy, using FTIR, SEC and DOE techniques, to effectively analyze the aggregation factors and perform a rapid screening for suitable conditions of protein formulation. Copyright © 2011 Elsevier B.V. All rights reserved.

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

Kuzmina, L.K.

The research deals with different aspects of mathematical modelling and the analysis of complex dynamic non-linear systems as a consequence of applied problems in mechanics (in particular those for gyrosystems, for stabilization and orientation systems, control systems of movable objects, including the aviation and aerospace systems) Non-linearity, multi-connectedness and high dimensionness of dynamical problems, that occur at the initial full statement lead to the need of the problem narrowing, and of the decomposition of the full model, but with safe-keeping of main properties and of qualitative equivalence. The elaboration of regular methods for modelling problems in dynamics, the generalization ofmore » reduction principle are the main aims of the investigations. Here, uniform methodology, based on Lyapunov`s methods, founded by N.G.Ohetayev, is developed. The objects of the investigations are considered with exclusive positions, as systems of singularly perturbed class, treated as ones with singular parametrical perturbations. It is the natural extension of the statements of N.G.Chetayev and P.A.Kuzmin for parametrical stability. In paper the systematical procedures for construction of correct simplified models (comparison ones) are developed, the validity conditions of the transition are determined the appraisals are received, the regular algorithms of engineering level are obtained. Applicabilitelly to the stabilization and orientation systems with the gyroscopic controlling subsystems, these methods enable to build the hierarchical sequence of admissible simplified models; to determine the conditions of their correctness.« less

Stability-indicating RP-HPLC Method for the Simultaneous Determination of Sitagliptin and Simvastatin in Tablets

PubMed Central

Ramalingam, P.; Bhaskar, V. Udaya; Reddy, Y. Padmanabha; Kumar, K. Vinod

2014-01-01

A new stability-indicating high-performance liquid chromatographic method for simultaneous analysis of sitagliptin and simvastatin in pharmaceutical dosage form was developed and validated. The mobile phase consisted of methanol and water (70:30, v/v) with 0.2 % of n-heptane sulfonic acid adjusted to pH 3.0 with ortho phosphoric acid was used. Retentions of sitagliptin and simvastatin were 4.3 min and 30.4 min, respectively with a flow rate of 1 ml/min on C8 (Qualisil BDS, 250×4.6 mm, 5 μ). Eluents were detected at 253 nm using photodiode diode array detector. The linear regression analysis data for the linearity plot showed correlation coefficient values of 0.9998 and 0.9993 for sitagliptin and simvastatin, with respective concentration ranges of 20-150 μg/ml and 8-60 μg/ml. The relative standard deviation for inter-day precision was lower than 2.0%. The assay of sitagliptin and simvastatin was determined in tablet dosage form was found to be within limits. Both drugs were subjected to a variety of stress conditions such as acidic, basic, oxidation, photolytic, neutral and thermal stress in order to achieve adequate degradation. Results revealed that considerable degradation was found in all stress conditions except oxidative degradations. The method has proven specificity for stability indicating assay method. PMID:25425754

Stability of cosmetic emulsion containing different amount of hemp oil.

PubMed

Kowalska, M; Ziomek, M; Żbikowska, A

2015-08-01

The aim of the study was to determine the optimal conditions, that is the content of hemp oil and time of homogenization to obtain stable dispersion systems. For this purpose, six emulsions were prepared, their stability was examined empirically and the most correctly formulated emulsion composition was determined using a computer simulation. Variable parameters (oil content and homogenization time) were indicated by the optimization software based on Kleeman's method. Physical properties of the synthesized emulsions were studied by numerous techniques involving particle size analysis, optical microscopy, Turbiscan test and viscosity of emulsions. The emulsion containing 50 g of oil and being homogenized for 6 min had the highest stability. Empirically determined parameters proved to be consistent with the results obtained using the computer software. The computer simulation showed that the most stable emulsion should contain from 30 to 50 g of oil and should be homogenized for 2.5-6 min. The computer software based on Kleeman's method proved to be useful for quick optimization of the composition and production parameters of stable emulsion systems. Moreover, obtaining an emulsion system with proper stability justifies further research extended with sensory analysis, which will allow the application of such systems (containing hemp oil, beneficial for skin) in the cosmetic industry. © 2015 Society of Cosmetic Scientists and the Société Française de Cosmétologie.

Impact of lysozyme on stability mechanism of nanozirconia aqueous suspension

NASA Astrophysics Data System (ADS)

Szewczuk-Karpisz, Katarzyna; Wiśniewska, Małgorzata

2016-08-01

The effect of lysozyme (LSZ) presence on the zirconium(IV) oxide (ZrO2) aqueous suspension stability was examined. The applied zirconia contains mesopores (with a diameter about 30 nm) and its mean particle size is about 100 nm. To determine the stability mechanism of ZrO2 suspension in the biopolymer presence, the adsorption and electrokinetic (surface charge density and zeta potential) measurements were performed in the pH range 3-10. The lysozyme adsorption on the nanozirconia surface proceeds mainly through electrostatic forces. Under solid-polymer repulsion conditions, there is no adsorption of lysozyme (pH < 6, CNaCl 0.01 mol/dm3). The increase of solution ionic strength to 0.2 mol/dm3 causes screening of unfavourable forces and biopolymer adsorption becomes possible. The LSZ addition to the ZrO2 suspension influences its stability. At pH 3, 4.6 and 7.6, slight improvement of the system stability was obtained. In turn, at pH 9 considerable destabilization of nanozirconia particles covered by polymeric layers occurs.

On the stability of fast rotating magentodiscs

NASA Astrophysics Data System (ADS)

Neupane, B. R.; Delamere, P. A.; Ma, X.

2016-12-01

In this study, a steady-state, self-consistent magnetodisc model (i.e., Caudal [1986] model based on in-situ observational temperature and density profile) has been developed to systematically investigate the stability of fast rotationing magnetodiscs, which is fundamentally important to the dynamics of Jupiter's and Saturn's magnetospheres. Comparison between model and observational data (magnetic field component normal to the equatorial plane) suggests that Saturn's magnetodisc equilibrium is dominated by the heavy and cold plasma, where the centrifugal force cannot be ignored. In contrast, the hot tenuous plasma contribution, in which the centrifugal force can be ignored, should be small. In general, the stability of the Saturn's magnetosphere is determined by the competition between the radial decrease of flux tube content and radial increase of flux tube entropy. The profiles of flux tube content and flux tube entropy are expected to vary under different solar wind dynamic pressure conditions, consequently changing the stability of the magnetosphere. We will discuss stability during solar wind compression and expansion.

The stability of gadolinium-based contrast agents in human serum: A reanalysis of literature data and association with clinical outcomes.

PubMed

Prybylski, John P; Semelka, Richard C; Jay, Michael

2017-05-01

To reanalyze literature data of gadolinium (Gd)-based contrast agents (GBCAs) in plasma with a kinetic model of dissociation to provide a comprehensive assessment of equilibrium conditions for linear GBCAs. Data for the release of Gd from GBCAs in human serum was extracted from a previous report in the literature and fit to a kinetic dissociation/association model. The conditional stabilities (logK cond ) and percent intact over time were calculated using the model rate constants. The correlations between clinical outcomes and logK cond or other stability indices were determined. The release curves for Omniscan®, gadodiamide, OptiMARK®, gadoversetamide Magnevist® and Multihance® were extracted and all fit well to the kinetic model. The logK cond s calculated from the rate constants were on the order of ~4-6, and were not significantly altered by excess ligand or phosphate. The stability constant based on the amount intact by the initial elimination half-life of GBCAs in plasma provided good correlation with outcomes observed in patients. Estimation of the kinetic constants for GBCA dissociation/association revealed that their stability in physiological fluid is much lower than previous approaches would suggest, which correlates well with deposition and pharmacokinetic observations of GBCAs in human patients. Copyright © 2017 Elsevier Inc. All rights reserved.

Enzyme stability, thermodynamics and secondary structures of α-amylase as probed by the CD spectroscopy.

PubMed

Kikani, B A; Singh, S P

2015-11-01

An amylase of a thermophilic bacterium, Bacillus sp. TSSC-3 (GenBank Number, EU710557) isolated from the Tulsi Shyam hot spring reservoir (Gujarat, India) was purified to the homogeneity in a single step on phenyl sepharose 6FF. The molecular weight of the enzyme was 25kD, while the temperature and pH optima for the enzyme catalysis were 80°C and 7, respectively. The purified enzyme was highly thermostable with broad pH stability and displayed remarkable resistance against surfactants, chelators, urea, guanidine HCl and various solvents as well. The stability and changes in the secondary structure of the enzyme under various extreme conditions were determined by the circular dichroism (CD) spectroscopy. The stability trends and the changes in the α-helices and β-sheets were analyzed by Mean Residual Ellipticity (MRE) and K2D3. The CD data confirmed the structural stability of the enzyme under various harsh conditions, yet it indicated reduced α-helix content and increased β-sheets upon denaturation. The thermodynamic parameters; deactivation rate constant, half-life, changes in entropy, enthalpy, activation energy and Gibb's free energy indicated that the enzyme-substrate reactions were highly stable. The overall profile of the enzyme: high thermostability, alkalitolerance, calcium independent nature, dextrose equivalent values and resistance against chemical denaturants, solvents and surfactants suggest its commercial applications. Copyright © 2015 Elsevier B.V. All rights reserved.

Intervention criterion and control research for active front steering with consideration of road adhesion

NASA Astrophysics Data System (ADS)

Wu, Xiaojian; Zhou, Bing; Wen, Guilin; Long, Lefei; Cui, Qingjia

2018-04-01

A multi-objective active front steering (AFS) control system considering the road adhesion constraint on vehicle stability is developed using the sliding mode control (SMC) method. First, an identification function combined with the relationship between the yaw rate and the steering angle is developed to determine whether the tyre state is linear or nonlinear. On this basis, an intervention criterion for the AFS system is proposed to improve vehicle handling and stability in emergent conditions. A sideslip angle stability domain enveloped by the upper, lower, left, and right boundaries, as well as the constraint of road adhesion coefficient, is constructed based on the ? phase-plane method. A dynamic weighting coefficient to coordinate the control of yaw rate and sideslip angle, and a control strategy that considers changing control objectives based on the desired yaw rate, the desired sideslip angle, and their proportional weights, are proposed for the SMC controller. Because road adhesion has a significant effect on vehicle stability and to meet the control algorithm's requirement of real-time access to vehicle states, a unscented Kalman filter-based state observer is proposed to estimate the adhesion coefficient and the required states. Finally, simulations are performed using high and low road adhesion conditions in a Matlab/Simulink environment, and the results show that the proposed AFS control system promptly intervenes according to the intervention criterion, effectively improving vehicle handling and stability.

Clay facial masks: physicochemical stability at different storage temperatures.

PubMed

Zague, Vivian; de Almeida Silva, Diego; Baby, André Rolim; Kaneko, Telma Mary; Velasco, Maria Valéria Robles

2007-01-01

Clay facial masks--formulations that contain a high percentage of solids dispersed in a liquid vehicle--have become of special interest due to specific properties presented by clays, such as particle size, cooling index, high adsorption capacity, and plasticity. Although most of the physicochemical properties of clay dispersions have been studied, specific aspects concerning the physicochemical stability of clay mask products remain unclear. This work aimed at investigating the accelerated physicochemical stability of clay mask formulations stored at different temperatures. Formulations were subjected to centrifuge testing and to thermal treatment for 15 days, during which temperature was varied from -5.0 degrees to 45.0 degrees C. The apparent viscosity and visual aspect (homogeneity) of all formulations were affected by temperature variation, whereas color, odor, and pH value remained unaltered. These results, besides the estimation of physicochemical stability under aging, can be useful in determining the best storage conditions for clay-based formulations.

Nonlinear dynamics of autonomous vehicles with limits on acceleration

NASA Astrophysics Data System (ADS)

Davis, L. C.

2014-07-01

The stability of autonomous vehicle platoons with limits on acceleration and deceleration is determined. If the leading-vehicle acceleration remains within the limits, all vehicles in the platoon remain within the limits when the relative-velocity feedback coefficient is equal to the headway time constant [k=1/h]. Furthermore, if the sensitivity α>1/h, no collisions occur. String stability for small perturbations is assumed and the initial condition is taken as the equilibrium state. Other values of k and α that give stability with no collisions are found from simulations. For vehicles with non-negligible mechanical response, simulations indicate that the acceleration-feedback-control gain might have to be dynamically adjusted to obtain optimal performance as the response time changes with engine speed. Stability is demonstrated for some perturbations that cause initial acceleration or deceleration greater than the limits, yet do not cause collisions.

Investigation of the Stability and Control Characteristics of a 1/10-Scale Model of the Chance Vought XF7U-1 Airplane in the Langley Free-Flight Tunnel, TED No. NACA DE306

NASA Technical Reports Server (NTRS)

Draper, John W.; Hewes, Donald E.

1948-01-01

At the request of the Bureau of Aeronautics, Navy Department, a stability and control investigation of a 1/10-scale model of the Chance Vought XF7U-1 airplane has been conducted in the Langley free-flight tunnel. Results of force end flight tests to determine the power-off stability and control characteristics of the model with slats retracted and extended are presented herein. The longitudinal and lateral stability characteristics were satisfactory for both the slats retracted and extended conditions over the lift range up to the stall. With the slats retracted, the stall was fairly gentle but the model rolled off out of control. With the slats extended, control could be maintained at the stall so that the wings could be kept level even as the model dropped.

Overview of waste stabilization with cement.

PubMed

Batchelor, B

2006-01-01

Cement can treat a variety of wastes by improving physical characteristics (solidification) and reducing the toxicity and mobility of contaminants (stabilization). Potentially adverse waste-binder interactions are an important consideration because they can limit solidification. Stabilization occurs when a contaminant is converted from the dissolved (mobile) phase to a solid (immobile) phase by reactions, such as precipitation, sorption, or substitution. These reactions are often strongly affected by pH, so the presence of components of the waste that control pH are critical to stabilization reactions. Evaluating environmental impacts can be accomplished in a tiered strategy in which simplest approach would be to measure the maximum amount of contaminant that could be released. Alternatively, the sequence of release can be determined, either by microcosm tests that attempt to simulate conditions in the disposal zone or by mechanistic models that attempt to predict behavior using fundamental characteristics of the treated waste.

The effects of viscosity on the stability of a trailing-line vortex in compressible flow

NASA Technical Reports Server (NTRS)

Stott, Jillian A. K.; Duck, Peter W.

1994-01-01

We consider the effects of viscosity on the inviscid stability of the Batchelor vortex in a compressible flow. The problem is tackled asymptotically, in the limit of large (streamwise and azimuthal) wavenumbers, together with large Mach numbers. Previous studies, with viscous effects neglected, found that the nature of the solution passes through different regimes as the Mach number increases, relative to the wavenumber. This structure persists when viscous effects are included in the analysis. In the present study the mode present in the incompressible case ceases to be unstable at high Mach numbers and a center mode forms, whose stability characteristics are determined primarily by conditions close to the vortex axis. We find generally that viscosity has a stabilizing influence on the flow, while in the case of center modes, viscous effects become important at much larger Reynolds numbers than for the first class of disturbance.

A feedback control strategy for the airfoil system under non-Gaussian colored noise excitation.

PubMed

Huang, Yong; Tao, Gang

2014-09-01

The stability of a binary airfoil with feedback control under stochastic disturbances, a non-Gaussian colored noise, is studied in this paper. First, based on some approximated theories and methods the non-Gaussian colored noise is simplified to an Ornstein-Uhlenbeck process. Furthermore, via the stochastic averaging method and the logarithmic polar transformation, one dimensional diffusion process can be obtained. At last by applying the boundary conditions, the largest Lyapunov exponent which can determine the almost-sure stability of the system and the effective region of control parameters is calculated.

A feedback control strategy for the airfoil system under non-Gaussian colored noise excitation

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

Huang, Yong, E-mail: hy@njust.edu.cn, E-mail: taogang@njust.edu.cn; Tao, Gang, E-mail: hy@njust.edu.cn, E-mail: taogang@njust.edu.cn

2014-09-01

The stability of a binary airfoil with feedback control under stochastic disturbances, a non-Gaussian colored noise, is studied in this paper. First, based on some approximated theories and methods the non-Gaussian colored noise is simplified to an Ornstein-Uhlenbeck process. Furthermore, via the stochastic averaging method and the logarithmic polar transformation, one dimensional diffusion process can be obtained. At last by applying the boundary conditions, the largest Lyapunov exponent which can determine the almost-sure stability of the system and the effective region of control parameters is calculated.

Stabilization of the composition of the gas medium of a repetitively pulsed CO2 laser by means of hopcalite

NASA Astrophysics Data System (ADS)

Baranov, V. Iu.; Drokov, G. F.; Kuzmenko, V. A.; Mezhevov, V. S.; Pigulskaia, V. V.

1986-05-01

Results of experiments in which hopcalite was used to stabilize the composition of the gas medium of repetitively pulsed and monopulse CO2 lasers are reported. In particular, the mechanisms of the decrease in the catalyst activity with time under conditions for catalyst regeneration are determined. It is shown that the use of hopcalite has made it possible to achieve long-term operation of a high-power repetitively pulsed CO2 laser without changing the gas mixture in a closed circuit. Some details related to the use of hopcalite are discussed.

Dynamics and statics of nonaxisymmetric and symmetric liquid bridges

NASA Technical Reports Server (NTRS)

Alexander, J. Iwan D.; Resnick, Andrew H.; Kaukler, William F.; Zhang, Yiqiang

1994-01-01

This program of theoretical and experimental ground-based research focuses on the understanding of the dynamics and stability limits of nonaxisymmetric and symmetric liquid bridges. There are three basic objectives: First, to determine the stability limits of nonaxisymmetric liquid bridges held between non-coaxial parallel disks, Second, to examine the dynamics of nonaxisymmetric bridges and nonaxisymmetric oscillations of initially axisymmetric bridges. The third objective is to experimentally investigate the vibration sensitivity of liquid bridges under terrestrial and low gravity conditions. Some of these experiments will require a low gravity environment and the ground-based research will culminate in a definitive flight experiment.

Impact of aerobic stabilization on the characteristics of treatment sludge in the leather tanning industry.

PubMed

Cokgor, Emine Ubay; Aydinli, Ebru; Tas, Didem Okutman; Zengin, Gulsum Emel; Orhon, Derin

2014-01-01

The efficiency of aerobic stabilization on the treatment sludge generated from the leather industry was investigated to meet the expected characteristics and conditions of sludge prior to landfill. The sludge types subjected to aerobic stabilization were chemical treatment sludge, biological excess sludge, and the mixture of both chemical and biological sludges. At the end of 23 days of stabilization, suspended solids, volatile suspended solids and total organic carbon removal efficiencies were determined as 17%, 19% and 23% for biological sludge 31%, 35% and 54% for chemical sludge, and 32%, 34% and 63% for the mixture of both chemical and biological sludges, respectively. Model simulations of the respirometric oxygen uptake rate measurements showed that the ratio of active biomass remained the same at the end of the stabilization for all the sludge samples. Although mixing the chemical and biological sludges resulted in a relatively effective organic carbon and solids removal, the level of stabilization achieved remained clearly below the required level of organic carbon content for landfill. These findings indicate the potential risk of setting numerical restrictions without referring to proper scientific support.

Adaptive gait responses to awareness of an impending slip during treadmill walking.

PubMed

Yang, Feng; Kim, JaeEun; Munoz, Jose

2016-10-01

The awareness of potential slip risk has been shown to cause protective changes to human gait during overground walking. It remains unknown if such adaptations to walking pattern also exist when ambulating on a treadmill. This study sought to determine whether and to what extent individuals, when being aware of a potential slip risk during treadmill walking, could adjust their gait pattern to improve their dynamic stability against backward balance loss in response to the impending slip hazard. Fifty-four healthy young subjects (age: 23.9±4.7years) participated in this study. Subjects' gait pattern was measured under two conditions: walking on a treadmill without (or normal walking) and with (or aware walking) the awareness of the potential slip perturbation. During both walking conditions, subjects' full body kinematics were gathered by using a motion capture system. Spatial gait parameters and the dynamic gait stability against backward balance were compared between the two walking conditions. The results revealed that subjects proactively adopted a "cautious gait" during aware walking compared with the normal walking. The cautious gait, which was achieved by taking a shorter step and a more flatfoot landing, positioned the body center of mass closer to the base of support, improving participants' dynamic stability and increasing their resistance against a possible slip-related fall. The finding from this study could provide insights into the dynamic stability control when individuals anticipate potential slip risk during treadmill walking. Copyright © 2016 Elsevier B.V. All rights reserved.

Study of quality and stability of ursodeoxycholic acid formulations for oral pediatric administration.

PubMed

Santoveña, A; Sánchez-Negrín, E; Charola, L; Llabrés, M; Fariña, J B

2014-12-30

This paper describes a rational method of characterizing the biopharmaceutical stability of two oral suspensions of ursodeoxycholic acid (UDCA) used in pediatrics. Because there is no commercial presentation of UDCA that can administer appropriate doses for infants and children, an active pharmaceutical ingredient (API) formulation is required. Due to its very low solubility and low dose in the formula (1.5%), two different suspensions with minimal use of excipients were studied, avoiding the use of complex additives and those not recommended by the European Medicines Agency (EMA). Adherence to Standard Operating Procedure (SOP) allows the preparation of formulations with appropriately sized and stable particles, and suitable rheological behavior in withdrawing the dose after stirring. Dose uniformity, expressed as mass and content variability, was determined using the criteria of the European and the United States Pharmacopoeia. Additionally, dose content variation of every mass determined was studied. A rational method was developed for determining the dose uniformity of UDCA in suspensions, whether freshly prepared or after storage under different conditions for 30 and 60 days. This method permits detection of differences between doses taken at different heights in the vessel at various times and storage conditions. UDCA was stable under all conditions studied, requiring the presence of glycerol in the formulation to obtain the declared API value after stirring. Storage of UDCA suspensions in a refrigerator increased variability between doses. Copyright © 2014 Elsevier B.V. All rights reserved.

Emulsions Stabilized by Chitosan-Modified Silica Nanoparticles: pH Control of Structure-Property Relations.

PubMed

Alison, Lauriane; Demirörs, Ahmet F; Tervoort, Elena; Teleki, Alexandra; Vermant, Jan; Studart, Andre R

2018-05-29

In food-grade emulsions, particles with an appropriate surface modification can be used to replace surfactants and potentially enhance the stability of emulsions. During the life cycle of products based on such emulsions, they can be exposed to a broad range of pH conditions and hence it is crucial to understand how pH changes affect stability of emulsions stabilized by particles. Here, we report on a comprehensive study of the stability, microstructure, and macroscopic behavior of pH-controlled oil-in-water emulsions containing silica nanoparticles modified with chitosan, a food-grade polycation. We found that the modified colloidal particles used as stabilizers behave differently depending on the pH, resulting in unique emulsion structures at multiple length scales. Our findings are rationalized in terms of the different emulsion stabilization mechanisms involved, which are determined by the pH-dependent charges and interactions between the colloidal building blocks of the system. At pH 4, the silica particles are partially hydrophobized through chitosan modification, favoring their adsorption at the oil-water interface and the formation of Pickering emulsions. At pH 5.5, the particles become attractive and the emulsion is stabilized by a network of agglomerated particles formed between the droplets. Finally, chitosan aggregates form at pH 9 and these act as the emulsion stabilizers under alkaline conditions. These insights have important implications for the processing and use of particle-stabilized emulsions. On one hand, changes in pH can lead to undesired macroscopic phase separation or coalescence of oil droplets. On the other hand, the pH effect on emulsion behavior can be harnessed in industrial processing, either to tune their flow response by altering the pH between processing stages or to produce pH-responsive emulsions that enhance the functionality of the emulsified end products.

Evaluation of the stability of a mixture of volatile organic compounds on sorbents for the determination of emissions from indoor materials and products using thermal desorption/gas chromatography/mass spectrometry.

PubMed

Brown, Veronica M; Crump, Derrick R; Plant, Neil T; Pengelly, Ian

2014-07-11

The standard method for the determination of volatile organic compounds (VOCs) in indoor and test chamber air (ISO 16000-6:2011) specifies sampling onto the sorbent Tenax TA followed by analysis using thermal desorption/gas chromatography/mass spectrometry (TD/GC/MS). The informative Annex D to the standard suggests the use of multi-sorbent samplers to extend the volatility range of compounds which can be determined. The aim of this study was to investigate the storage performance of Tenax TA and two multi-sorbent tubes loaded with a mixture of nine VOCs of relevance for material emissions testing. The sorbent combinations tested were quartz wool/Tenax TA/Carbograph™ 5TD and quartz wool/Tenax TA/Carbopack™ X. A range of loading levels, loading conditions (humidities and air volume), storage times (1-4 weeks) and storage conditions (refrigerated and ambient) were investigated. Longer term storage trials (up to 1 year) were conducted with Tenax TA tubes to evaluate the stability of tubes used for proficiency testing (PT) of material emissions analyses. The storage performance of the multi-sorbent tubes tested was found to be equal to that for Tenax TA, with recoveries after 4 weeks storage of within about 10% of the amounts loaded. No consistent differences in recoveries were found for the different loading or storage conditions. The longer term storage trials also showed good recovery for these compounds, although two other compounds, hexanal and BHT, were found to be unstable when stored on Tenax TA. The results of this study provide confidence in the stability of nine analytes for up to 4 weeks on two multi-sorbent tubes for material emissions testing and the same compounds loaded on Tenax TA sorbent for a recently introduced PT scheme for material emissions testing. Copyright © 2014 Elsevier B.V. All rights reserved.

Validation of a French version of the Sleep Condition Indicator: a clinical screening tool for insomnia disorder according to DSM-5 criteria.

PubMed

Bayard, Sophie; Lebrun, Cindy; Maudarbocus, Khaalid Hassan; Schellaert, Vanessa; Joffre, Alicia; Ferrante, Esther; Le Louedec, Marie; Cournoulat, Alice; Gely-Nargeot, Marie-Christine; Luik, Annemarie I

2017-12-01

Insomnia disorder is frequent in the population, yet there is no French screening instrument available that is based on the updated DSM-5 criteria. We evaluated the validity and reliability of the French version of an insomnia screening instrument based on DSM-5 criteria, the Sleep Condition Indicator, in a population-based sample of adults. A total of 366 community-dwelling participants completed a face-to-face clinical interview to determine insomnia disorder against DSM-5 criteria and several questionnaires including the French Sleep Condition Indicator version. Three-hundred and twenty-nine participants completed the Sleep Condition Indicator again after 1 month. Statistical analyses were performed to determine the reliability, construct validity, divergent validity and temporal stability of the French translation of the Sleep Condition Indicator. In addition, an explanatory factor analysis was performed to assess the underlying structure. The internal consistency (α = 0.87) and temporal stability (r = 0.86, P < 0.001) of the French Sleep Condition Indicator were high. When using the previously defined cut-off value of ≤ 16, the area under the receiver operating characteristic curve was 0.93 with a sensitivity of 95% and a specificity of 75%. Additionally, good construct and divergent validity were demonstrated. The factor analyses showed a two-factor structure with a focus on sleep and daytime effects. The French version of the Sleep Condition Indicator demonstrates satisfactory psychometric properties while being a useful instrument in detecting cases of insomnia disorder, consistent with features of DSM-5, in the general population. © 2017 European Sleep Research Society.

Vibration and flutter characteristics of the SR7L large-scale propfan

NASA Technical Reports Server (NTRS)

August, Richard; Kaza, Krishna Rao V.

1988-01-01

An investigation of the vibration characteristics and aeroelastic stability of the SR7L Large-Scale Advanced Propfan was performed using a finite element blade model and an improved aeroelasticity code. Analyses were conducted for different blade pitch angles, blade support conditions, number of blades, rotational speeds, and freestream Mach numbers. A finite element model of the blade was used to determine the blade's vibration behavior and sensitivity to support stiffness. The calculated frequencies and mode shape obtained with this model agreed well with the published experimental data. A computer code recently developed at NASA Lewis Research Center and based on three-dimensional, unsteady, lifting surface aerodynamic theory was used for the aeroelastic analysis to examine the blade's stability at a cruise condition of Mach 0.8 at 1700 rpm. The results showed that the blade is stable for that operating point. However, a flutter condition was predicted if the cruise Mach number was increased to 0.9.

A full-scale wind tunnel investigation of a helicopter bearingless main rotor. [Ames 40 by 80 Wind Tunnel

NASA Technical Reports Server (NTRS)

Warmbrodt, W.; Mccloud, J. L., II

1981-01-01

A helicopter bearingless main rotor was tested. Areas of investigation included aeroelastic stability, aerodynamic performance, and rotor loads as a function of collective pitch setting, RPM, airspeed and shaft angle. The rotor/support system was tested with the wind tunnel balance dampers installed and, subsequently, removed. Modifications to the rotor hub were tested. These included a reduction in the rotor control system stiffness and increased flexbeam structural damping. The primary objective of the test was to determine aeroelastic stability of the fundamental flexbeam/blade chordwise bending mode. The rotor was stable for all conditions. Damping of the rotor chordwise bending mode increases with increased collective pitch angle at constant operating conditions. No significant decrease in rotor damping occured due to frequency coalescence between the blade chordwise fundamental bending mode and the support system.

Space Shuttle stability and control flight test techniques

NASA Technical Reports Server (NTRS)

Cooke, D. R.

1980-01-01

A unique approach for obtaining vehicle aerodynamic characteristics during entry has been developed for the Space Shuttle. This is due to the high cost of Shuttle testing, the need to open constraints for operational flights, and the fact that all flight regimes are flown starting with the first flight. Because of uncertainties associated with predicted aerodynamic coefficients, nine flight conditions have been identified at which control problems could occur. A detailed test plan has been developed for testing at these conditions and is presented. Due to limited testing, precise computer initiated maneuvers are implemented. These maneuvers are designed to optimize the vehicle motion for determining aerodynamic coefficients. Special sensors and atmospheric measurements are required to provide stability and control flight data during an entire entry. The techniques employed in data reduction are proven programs developed and used at NASA/DFRC.

Optimization of extraction of novel pectinase enzyme discovered in red pitaya (Hylocereus polyrhizus) peel.

PubMed

Zohdi, Nor Khanani; Amid, Mehrnoush

2013-11-20

Plant peels could be a potential source of novel pectinases for use in various industrial applications due to their broad substrate specificity with high stability under extreme conditions. Therefore, the extraction conditions of a novel pectinase enzyme from pitaya peel was optimized in this study. The effect of extraction variables, namely buffer to sample ratio (2:1 to 8:1, X₁), extraction temperature (-15 to +25 °C, X₂) and buffer pH (4.0 to 12.0, X₃) on specific activity, temperature stability, storage stability and surfactant agent stability of pectinase from pitaya peel was investigated. The study demonstrated that the optimum conditions for the extraction of pectinase from pitaya sources could improve the enzymatic characteristics of the enzyme and protect its activity and stability during the extraction procedure. The optimum extraction conditions cause the pectinase to achieve high specific activity (15.31 U/mg), temperature stability (78%), storage stability (88%) and surfactant agent stability (83%). The most desirable conditions to achieve the highest activity and stability of pectinase enzyme from pitaya peel were the use of 5:1 buffer to sample ratio at 5 °C and pH 8.0.

Accelerated Stability Testing of a Clobetasol Propionate-Loaded Nanoemulsion as per ICH Guidelines.

PubMed

Ali, Mohammad Sajid; Alam, Mohammad Sarfaraz; Alam, Nawazish; Anwer, Tarique; Safhi, Mohammed Mohsen A

2013-01-01

The physical and chemical degradation of drugs may result in altered therapeutic efficacy and even toxic effects. Therefore, the objective of this work was to study the stability of clobetasol propionate (CP) in a nanoemulsion. The nanoemulsion formulation containing CP was prepared by the spontaneous emulsification method. For the formulation of the nanoemulsion, Safsol, Tween 20, ethanol, and distilled water were used. The drug was incorporated into an oil phase in 0.05% w/v. The lipophilic nature of the drug led to the O/W nanoemulsion formulation. This was characterized by droplet size, pH, viscosity, conductivity, and refractive index. Stability studies were performed as per ICH guidelines for a period of three months. The shelf life of the nanoemulsion formulation was also determined after performing accelerated stability testing (40°C ± 2°C and 75% ± 5% RH). We also performed an intermediate stability study (30°C ± 2°C/65% RH ± 5% RH). It was found that the droplet size, conductivity, and refractive index were slightly increased, while the viscosity and pH slightly decreased at all storage conditions during the 3-month period. However, the changes in these parameters were not statistically significant (p≥0.05). The degradation (%) of the optimized nanoemulsion of CP was determined and the shelf life was found to be 2.18 years at room temperature. These studies confirmed that the physical and chemical stability of CP were enhanced in the nanoemulsion formulation.

Study of the thermal stability of studtite by in situ Raman spectroscopy and DFT calculations

NASA Astrophysics Data System (ADS)

Colmenero, Francisco; Bonales, Laura J.; Cobos, Joaquín; Timón, Vicente

2017-03-01

The design of a safe spent nuclear fuel repository requires the knowledge of the stability of the secondary phases which precipitate when water reaches the fuel surface. Studtite is recognized as one of the secondary phases that play a key-role in the mobilization of the radionuclides contained in the spent fuel. Thereby, it has been identified as a product formed under oxidation conditions at the surface of the fuel, and recently found as a corrosion product in the Fukushima-Daiichi nuclear plant accident. Thermal stability is one of the properties that should be determined due to the high temperature of the fuel. In this work we report a detailed analysis of the structure and thermal stability of studtite. The structure has been studied both by experimental techniques (SEM, TGA, XRD and Raman spectroscopy) and theoretical DFT electronic structure and spectroscopic calculations. The comparison of the results allows us to perform for the first time the Raman bands assignment of the whole spectrum. The thermal stability of studtite has been analyzed by in situ Raman spectroscopy, with the aim of studying the effect of the heating rate and the presence of water. For this purpose, a new cell has been designed. The results show that studtite is stable under dry conditions only at temperatures below 30 °C, in contrast with the higher temperatures published up to date ( 130 °C). Opposite behaviour has been found when studtite is in contact with water; under these conditions studtite is stable up to 90 °C, what is consistent with the encounter of this phase after the Fukushima-Daiichi accident.

Study of the thermal stability of studtite by in situ Raman spectroscopy and DFT calculations.

PubMed

Colmenero, Francisco; Bonales, Laura J; Cobos, Joaquín; Timón, Vicente

2017-03-05

The design of a safe spent nuclear fuel repository requires the knowledge of the stability of the secondary phases which precipitate when water reaches the fuel surface. Studtite is recognized as one of the secondary phases that play a key-role in the mobilization of the radionuclides contained in the spent fuel. Thereby, it has been identified as a product formed under oxidation conditions at the surface of the fuel, and recently found as a corrosion product in the Fukushima-Daiichi nuclear plant accident. Thermal stability is one of the properties that should be determined due to the high temperature of the fuel. In this work we report a detailed analysis of the structure and thermal stability of studtite. The structure has been studied both by experimental techniques (SEM, TGA, XRD and Raman spectroscopy) and theoretical DFT electronic structure and spectroscopic calculations. The comparison of the results allows us to perform for the first time the Raman bands assignment of the whole spectrum. The thermal stability of studtite has been analyzed by in situ Raman spectroscopy, with the aim of studying the effect of the heating rate and the presence of water. For this purpose, a new cell has been designed. The results show that studtite is stable under dry conditions only at temperatures below 30°C, in contrast with the higher temperatures published up to date (~130°C). Opposite behaviour has been found when studtite is in contact with water; under these conditions studtite is stable up to 90°C, what is consistent with the encounter of this phase after the Fukushima-Daiichi accident. Copyright © 2016 Elsevier B.V. All rights reserved.

Effect of buffer and antioxidant on stability of a mercaptopurine suspension.

PubMed

Aliabadi, Hamidreza Montazeri; Romanick, Marcel; Desai, Sunil; Lavasanifar, Afsaneh

2008-03-01

The stability of standard and modified mercaptopurine suspensions when stored at room temperature and under refrigerated conditions to test the feasibility of increasing shelf life was studied. A 50-mg/mL mercaptopurine suspension was compounded by adding simple syrup, cherry syrup, and sterile water for irrigation to triturated mercaptopurine tablets for the initial reference formulation. Three additional formulations were prepared by adding an antioxidant (ascorbic acid 10 mg), a buffer (sodium phosphate monobasic monohydrate 500 mg), and a combination of antioxidant and buffer to the reference formulation. Each compounded batch was divided into two parts and stored in amber bottles at room temperature (19-23 degrees C) or under refrigerated conditions (4-8 degrees C). Analysis through high-performance liquid chromatography determined mercaptopurine levels after three and seven days and weekly thereafter for at least two weeks after shelf life was reached under specified storage conditions. Solutions with at least 93% of the original mercaptopurine concentration and with no observable sign of aggregation or cake formation were considered stable. The reference suspension of mercaptopurine showed an acceptable physical and chemical stability of up to 5 weeks when stored at room temperature. The addition of ascorbic acid extended the shelf life of the compounded suspension to 11 weeks. However, the addition of sodium phosphate monobasic did not improve the stability of mercaptopurine in the suspension. The results showed a higher stability for all formulations after storage at room temperature compared with those stored in a refrigerator. A standard oral suspension of mercaptopurine contained an acceptable drug concentration for up to 5 weeks when stored at room temperature. The addition of ascorbic acid at a concentration of 0.1% w/v to the standard formulation increased the suspension's shelf life at room temperature to 11 weeks.

Experimental Investigation of Flame Stability in Porous Media Burners

NASA Astrophysics Data System (ADS)

Mohaddes, Danyal; Sobhani, Sadaf; Boigne, Emeric; Muhunthan, Priyanka; Ihme, Matthias

2017-11-01

Porous media burners (PMBs) facilitate the stabilization of a flame inside the pores of a solid porous material, and have benefits when compared to traditional burners in terms of emissions reduction and operating envelope extension. PMBs can potentially find application in a wide variety of domains, including household and industrial heating, internal combustion engines, and gas turbine engine combustors. The current study aims to motivate the use of PMBs in such applications on a thermodynamic basis, and subsequently compares the performance of two PMB designs. To this end, an experiment was devised and conducted to determine the stable operating conditions of a continuously varying and a discontinuously varying pore diameter profile PMB. In addition to investigating the stability regime of each design, pressure drop and axial temperatures were measured and compared at different operating conditions. The collected experimental data will be used both to inform computational studies of combustion within porous media and to aid in future optimizations of the design of PMBs. This work is supported by a Leading Edge Aeronautics Research for NASA (LEARN) Grant (Award No. NNX15AE42A).

The Effects of Predator Evolution and Genetic Variation on Predator-Prey Population-Level Dynamics.

PubMed

Cortez, Michael H; Patel, Swati

2017-07-01

This paper explores how predator evolution and the magnitude of predator genetic variation alter the population-level dynamics of predator-prey systems. We do this by analyzing a general eco-evolutionary predator-prey model using four methods: Method 1 identifies how eco-evolutionary feedbacks alter system stability in the fast and slow evolution limits; Method 2 identifies how the amount of standing predator genetic variation alters system stability; Method 3 identifies how the phase lags in predator-prey cycles depend on the amount of genetic variation; and Method 4 determines conditions for different cycle shapes in the fast and slow evolution limits using geometric singular perturbation theory. With these four methods, we identify the conditions under which predator evolution alters system stability and shapes of predator-prey cycles, and how those effect depend on the amount of genetic variation in the predator population. We discuss the advantages and disadvantages of each method and the relations between the four methods. This work shows how the four methods can be used in tandem to make general predictions about eco-evolutionary dynamics and feedbacks.

[Influence of Restricting the Ankle Joint Complex Motions on Gait Stability of Human Body].

PubMed

Li, Yang; Zhang, Junxia; Su, Hailong; Wang, Xinting; Zhang, Yan

2016-10-01

The purpose of this study is to determine how restricting inversion-eversion and pronation-supination motions of the ankle joint complex influences the stability of human gait.The experiment was carried out on a slippery level ground walkway.Spatiotemporal gait parameter,kinematics and kinetics data as well as utilized coefficient of friction(UCOF)were compared between two conditions,i.e.with restriction of the ankle joint complex inversion-eversion and pronation-supination motions(FIXED)and without restriction(FREE).The results showed that FIXED could lead to a significant increase in velocity and stride length and an obvious decrease in double support time.Furthermore,FIXED might affect the motion angle range of knee joint and ankle joint in the sagittal plane.In FIXED condition,UCOF was significantly increased,which could lead to an increase of slip probability and a decrease of gait stability.Hence,in the design of a walker,bipedal robot or prosthetic,the structure design which is used to achieve the ankle joint complex inversion-eversion and pronation-supination motions should be implemented.

A hydrophilic interaction liquid chromatography-mass spectrometry (HILIC-MS) based metabolomics study on colour stability of ovine meat.

PubMed

Subbaraj, Arvind K; Kim, Yuan H Brad; Fraser, Karl; Farouk, Mustafa M

2016-07-01

Meat colour is one of the cues available to the consumer to gauge overall meat quality and wholesomeness. Colour stability of meat is determined by several factors both inherent to the animal and post-slaughter conditions, including ageing, storage/packaging and display times. A hydrophilic interaction liquid chromatography-mass spectrometry (HILIC-MS) based metabolomics study was undertaken to identify and compare polar metabolites between ovine meat samples that were exposed to different durations of ageing, storage conditions, and display times. Primary metabolites comprising amino acids, sugars, nucleotides, nucleosides, organic acids and their breakdown products were mainly identified as discriminating factors. For the first time, boron complexes of sugar and malic acid were also tentatively identified. As expected, most compounds identified were related to myoglobin chemistry, and compounds with antioxidant properties were found in higher levels in colour stable samples. Supplementary studies identifying semi-polar, non-polar and volatile compounds will provide a holistic understanding of the chemical basis of colour stability in ovine meat. Copyright © 2016 Elsevier Ltd. All rights reserved.

Solid-state thermal behavior and stability studies of theophylline-citric acid cocrystals prepared by neat cogrinding or thermal treatment

NASA Astrophysics Data System (ADS)

Hsu, Po-Chun; Lin, Hong-Liang; Wang, Shun-Li; Lin, Shan-Yang

2012-08-01

To investigate the thermal behavior of cocrystal formed between anhydrous theophylline (TP) and anhydrous citric acid (CA) by neat manual cogrinding or thermal treatment, DSC and FTIR microspectroscopy with curve-fitting analysis were applied. The physical mixture and 60-min ground mixture were stored at 55±0.5 °C/40±2% RH condition to determine their stability behavior. Typical TP-CA cocrystals were prepared by slow solvent evaporation method. Results indicate that the cogrinding process could gradually induce the cocrystal formation between TP and CA. The IR spectral peak shift from 3495 to 3512 cm-1 and the stepwise appearance of several new IR peaks at 1731, 1712, 1676, 1651, 1557 and 1265 cm-1 with cogrinding time suggest that the mechanism of TP-CA cocrystal formation was evidenced by interacting TP with CA through the intermolecular O-H···O hydrogen bonding. The stability of 60-min ground mixture of TP-CA was confirmed at 55±0.5 °C/40±2% RH condition over a storage time of 60 days.

Improvement of Stability and Antioxidant Activities by Using Phycocyanin - Chitosan Encapsulation Technique

NASA Astrophysics Data System (ADS)

Suzery, Meiny; Hadiyanto; Majid, Dian; Setyawan, Deny; Sutanto, Heri

2017-02-01

Encapsulation is a coating process to improve the stability of bioactive compounds. Phycocyanin with high antioxidant activity has been encapsulated with chitosan in microcapsules form. In this study aims to determine the best conditions in the encapsulation process using the extrusion method, characterization of the physicochemical properties of the microcapsules, antioxidant activity test using DPPH, in vitro release performance and evaluate the storage stability against temperature. The results of the encapsulation process is obtained: Na-TPP is better than Na-citrate as crosslinker and chitosan content 3% as a coating with ratio of chitosan to phycocyanin ratio 1: 1. Test of antioxidant activity also showed encapsulation with chitosan content 3% has the highest antioxidant activity. Morphological analysis microcapsules were found to have compact spherical shape with diameter range 900-1000 µm. In vitro release testing showed a quick release in an acidic environment (SGF) for 2 hours and slowly release under alkaline conditions (SIF) for 8 hours under mechanical stirring at 37°C. Phycocyanin much more stable against temperature during storage in microcapsules.

Determination of Polymer Additives-Antioxidants, Ultraviolet Stabilizers, Plasticizers and Photoinitiators in Plastic Food Package by Accelerated Solvent Extraction Coupled with High-Performance Liquid Chromatography.

PubMed

Li, Bo; Wang, Zhi-Wei; Lin, Qin-Bao; Hu, Chang-Ying; Su, Qi-Zhi; Wu, Yu-Mei

2015-07-01

An analytical method for the quantitative determination of 4 antioxidants, 9 ultraviolet (UV) stabilizers, 12 phthalate plasticizers and 2 photoinitiators in plastic food package using accelerated solvent extraction (ASE) coupled with high-performance liquid chromatography-photodiode array detector (HPLC-PDA) has been developed. Parameters affecting the efficiency in the process such as extraction and chromatographic conditions were studied in order to determine operating conditions. The analytical method of ASE-HPLC showed good linearity with good correlation coefficients (R ≥ 0.9833). The limits of detection and quantification were between 0.03 and 0.30 µg mL(-1) and between 0.10 and 1.00 µg mL(-1) for 27 analytes. Average spiked recoveries for most analytes in samples were >70.4% at 10, 20 and 40 µg g(-1) spiked levels, except UV-9 and Irganox 1010 (58.6 and 64.0% spiked at 10 µg g(-1), respectively), the relative standard deviations were in the range from 0.4 to 15.4%. The methodology has been proposed for the analysis of 27 polymer additives in plastic food package. © The Author 2014. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Insight of DFT and ab initio atomistic thermodynamics on the surface stability and morphology of In2O3

NASA Astrophysics Data System (ADS)

Zhang, Minhua; Wang, Wenyi; Chen, Yifei

2018-03-01

In2O3 catalysts show remarkable activity and selectivity in methanol synthesis from CO2 hydrogenation. In order to get insight into the surface stability of this catalyst, density functional theory and ab initio atomistic thermodynamics method were used to investigate the surface free energies of various facets as a function of oxygen chemical potential, as well as the influences of temperature, pressure and gas compositions. The results show that the (111) facet presents lowest surface free energy under oxygen-rich condition, while the indium-terminated (100) facet is the most stable one under oxygen-lean condition. Moreover, we applied Wulff construction to determine the equilibrium shape of In2O3 with different oxygen chemical potentials. The equilibrium shape under oxygen-lean condition is cubic, which only expose (100) facet, while, the equilibrium shape under oxygen-rich condition is octahedron, which only expose (111) facet. Meanwhile, the results agree well with what is observed experimentally. It is further predicted that Wulff shape of In2O3 exists in a truncated octahedron morphology in which the (100) surface becomes predominant plane under CO2 hydrogenation reaction conditions.

Gravity-oriented satellite dynamics subject to gravitational and active damping torques

NASA Astrophysics Data System (ADS)

Sarychev, V. A.; Gutnik, S. A.

2018-01-01

The dynamics of the rotational motion of a satellite moving in the central Newtonian field of force over a circular orbit under the effect of gravitational and active damping torques, which depend on the satellite angular velocity projections, has been investigated. The paper proposes a method of determining all equilibrium positions (equilibrium orientations) of a satellite in the orbital coordinate system for specified values of damping coefficients and principal central moments of inertia. The conditions of their existence have been obtained. For a zero equilibrium position where the axes of the satellite-centered coordinate system coincide with the axes of the orbital coordinate system, the necessary and sufficient conditions for asymptotic stability are obtained using the Routh-Hurwitz criterion. A detailed analysis of the regions where the conditions of the asymptotic stability of a zero equilibrium position are fulfilled have been obtained depending on three dimensionless parameters of the problem, and the numerical study of the process of attenuation of satellite's spatial oscillations for various damping coefficients has been carried out. It has been shown that there is a wide range of damping parameters from which, by choosing the necessary values, one can provide the asymptotic stability of satellite's zero equilibrium position in the orbital coordinate system.

Nanoparticle dispersion in environmentally relevant culture media: a TiO2 case study and considerations for a general approach

NASA Astrophysics Data System (ADS)

Horst, Allison M.; Ji, Zhaoxia; Holden, Patricia A.

2012-08-01

Nanoparticle exposure in toxicity studies requires that nanoparticles are bioavailable by remaining highly dispersed in culture media. However, reported dispersion approaches are variable, mostly study-specific, and not transferable owing to their empirical basis. Furthermore, many published approaches employ proteinaceous dispersants in rich laboratory media, both of which represent end members in environmental scenarios. Here, a systematic approach was developed to disperse initially agglomerated TiO2 nanoparticles (Aeroxide® TiO2 P25, Evonik, NJ; primary particle size range 6.4-73.8 nm) in oligotrophic culture medium for environmentally relevant bacterial toxicity studies. Based on understanding particle-particle interactions in aqueous media and maintaining environmental relevance, the approach involves (1) quantifying the relationship between pH and zeta potential to determine the point of zero charge of select nanoparticles in water; (2) nominating, then testing and selecting, environmentally relevant stabilizing agents; and (3) dispersing via "condition and capture" whereby stock dry powder nanoparticles are sonicated in pre-conditioned (with base, or acid, plus stabilizing agent) water, then diluted into culture media. The "condition and capture" principle is transferable to other nanoparticle and media chemistries: simultaneously, mechanically and electrostatically, nanoparticles can be dispersed with surrounding stabilizers that coat and sterically hinder reagglomeration in the culture medium.

An empirically based steady state friction law and implications for fault stability

NASA Astrophysics Data System (ADS)

Spagnuolo, E.; Nielsen, S.; Violay, M.; Di Toro, G.

2016-04-01

Empirically based rate-and-state friction laws (RSFLs) have been proposed to model the dependence of friction forces with slip and time. The relevance of the RSFL for earthquake mechanics is that few constitutive parameters define critical conditions for fault stability (i.e., critical stiffness and frictional fault behavior). However, the RSFLs were determined from experiments conducted at subseismic slip rates (V < 1 cm/s), and their extrapolation to earthquake deformation conditions (V > 0.1 m/s) remains questionable on the basis of the experimental evidence of (1) large dynamic weakening and (2) activation of particular fault lubrication processes at seismic slip rates. Here we propose a modified RSFL (MFL) based on the review of a large published and unpublished data set of rock friction experiments performed with different testing machines. The MFL, valid at steady state conditions from subseismic to seismic slip rates (0.1 µm/s < V < 3 m/s), describes the initiation of a substantial velocity weakening in the 1-20 cm/s range resulting in a critical stiffness increase that creates a peak of potential instability in that velocity regime. The MFL leads to a new definition of fault frictional stability with implications for slip event styles and relevance for models of seismic rupture nucleation, propagation, and arrest.

Physical and Chemical Stability of Budesonide Mucoadhesive Oral Suspensions (MucoLox).

PubMed

Ip, Kendice; Carvalho, Maria; Shan, Ashley; Banov, Daniel

2017-01-01

Budesonide is a corticosteroid that has been shown effective in the treatment of eosinophilic esophagitis, but there are currently no commercial medicines to treat this chronic allergic/immune condition, despite its prevalence in the U.S. Therefore, pharmaceutical compounding is the alternative choice to meet the therapeutic need of eosinophilic esophagitis patients. Two budesonide mucoadhesive oral suspensions (1 mg/10 mL and 2 mg/10 mL) were developed using the compounding vehicle MucoLox, a proprietary mucoadhesive polymer blend that promotes mucosal adhesion. The physical and chemical stability of the oral suspensions was tested over a period of 182 days, at room temperature and refrigerated conditions, in order to determine the corresponding beyond-use date. The physical characterization consisted in observing all samples for color/appearance and odor, and testing for pH and density, whereas the chemical characterization consisted in ultra-performance liquid chromatography assay testing. Both oral suspensions were proven physically and chemically stable, and the ultra-performance liquid chromatography method was proven stability indicating. As a result, the beyond-use date of the budesonide 1-mg/10-mL and 2-mg/10-mL mucoadhesive oral suspensions (MucoLox), in amber plastic bottles, is six months at both room temperature and refrigerated conditions. Copyright© by International Journal of Pharmaceutical Compounding, Inc.

A simplified approach for slope stability analysis of uncontrolled waste dumps.

PubMed

Turer, Dilek; Turer, Ahmet

2011-02-01

Slope stability analysis of municipal solid waste has always been problematic because of the heterogeneous nature of the waste materials. The requirement for large testing equipment in order to obtain representative samples has identified the need for simplified approaches to obtain the unit weight and shear strength parameters of the waste. In the present study, two of the most recently published approaches for determining the unit weight and shear strength parameters of the waste have been incorporated into a slope stability analysis using the Bishop method to prepare slope stability charts. The slope stability charts were prepared for uncontrolled waste dumps having no liner and leachate collection systems with pore pressure ratios of 0, 0.1, 0.2, 0.3, 0.4 and 0.5, considering the most critical slip surface passing through the toe of the slope. As the proposed slope stability charts were prepared by considering the change in unit weight as a function of height, they reflect field conditions better than accepting a constant unit weight approach in the stability analysis. They also streamline the selection of slope or height as a function of the desired factor of safety.

Thermal control/oxidation resistant coatings for titanium-based alloys

NASA Technical Reports Server (NTRS)

Clark, Ronald K.; Wallace, Terryl A.; Cunnington, George R.; Wiedemann, Karl E.

1992-01-01

Extensive research and development efforts have been expended toward development of thermal control and environmental protection coatings for NASP and generic hypersonic vehicle applications. The objective of the coatings development activities summarized here was to develop light-weight coatings for protecting advanced titanium alloys from oxidation in hypersonic vehicle applications. A number of new coating concepts have been evaluated. Coated samples were exposed to static oxidation tests at temperatures up to 1000 C using a thermogravimetric apparatus. Samples were also exposed to simulated hypersonic flight conditions for up to 10 hr to determine their thermal and chemical stability and catalytic efficiency. The emittance of samples was determined before and after exposure to simulated hypersonic flight conditions.

LMI-based stability and performance conditions for continuous-time nonlinear systems in Takagi-Sugeno's form.

PubMed

Lam, H K; Leung, Frank H F

2007-10-01

This correspondence presents the stability analysis and performance design of the continuous-time fuzzy-model-based control systems. The idea of the nonparallel-distributed-compensation (non-PDC) control laws is extended to the continuous-time fuzzy-model-based control systems. A nonlinear controller with non-PDC control laws is proposed to stabilize the continuous-time nonlinear systems in Takagi-Sugeno's form. To produce the stability-analysis result, a parameter-dependent Lyapunov function (PDLF) is employed. However, two difficulties are usually encountered: 1) the time-derivative terms produced by the PDLF will complicate the stability analysis and 2) the stability conditions are not in the form of linear-matrix inequalities (LMIs) that aid the design of feedback gains. To tackle the first difficulty, the time-derivative terms are represented by some weighted-sum terms in some existing approaches, which will increase the number of stability conditions significantly. In view of the second difficulty, some positive-definitive terms are added in order to cast the stability conditions into LMIs. In this correspondence, the favorable properties of the membership functions and nonlinear control laws, which allow the introduction of some free matrices, are employed to alleviate the two difficulties while retaining the favorable properties of PDLF-based approach. LMI-based stability conditions are derived to ensure the system stability. Furthermore, based on a common scalar performance index, LMI-based performance conditions are derived to guarantee the system performance. Simulation examples are given to illustrate the effectiveness of the proposed approach.

Preserving enzymatic activity and enhancing biochemical stability of glutathione transferase by soluble additives under free and tethered conditions.

PubMed

Karamitros, Christos S; Labrou, Nikolaos E

2017-09-01

In the present study, we report the effect of four different soluble additives (sucrose, lactitol, superfloc c577, and dextran sulfate) on the stability of glutathione transferase 1 enzyme from Zea mays (ZmGSTF1-1) under free and tethered conditions at 4 and 25 °C. Among all additives, the best stabilizing effects were observed in the case of superfloc c577 and sucrose at both tested temperatures, yet at distinct concentrations at each condition. Those two stabilizing agents were further combined and potential positive synergistic effects were investigated. In addition, we assessed the long-term storage and operational stability of ZmGSTF1-1 under tethered conditions in the presence of additives, which provided the most conducive effects on its stability under free conditions. Our results strongly suggest that the presence of additives may be beneficial to the stability of the enzyme under both free and tethered conditions. Thermodynamic analysis of the free enzyme in the presence of sucrose, which exhibited the best stabilizing effect at both temperatures, shed light on the possible mechanism of action. Given the considerable importance of the development of GST-based biosensors with prolonged stability, the present work may be of general interest to researchers in the field of applied enzymology. © 2016 International Union of Biochemistry and Molecular Biology, Inc.

A computational examination of directional stability for smooth and chined forebodies at high-alpha

NASA Technical Reports Server (NTRS)

Ravi, Ramakrishnan; Mason, William H.

1992-01-01

Computational Fluid Dynamics (CFD) has been used to study aircraft forebody flowfields at low-speed, angle-of-attack conditions with sideslip. The purpose is to define forebody geometries which provide good directional stability characteristics under these conditions. The flows over the experimentally investigated F-5A forebody and chine type configuration, previously computed by the authors, were recomputed with better grid topology and resolution. The results were obtained using a modified version of CFL3D (developed at NASA Langley) to solve either the Euler equations or the Reynolds equations employing the Baldwin-Lomax turbulence model with the Degani-Schiff modification to account for massive crossflow separation. Based on the results, it is concluded that current CFD methods can be used to investigate the aerodynamic characteristics of forebodies to achieve desirable high angle-of-attack characteristics. An analytically defined generic forebody model is described, and a parametric study of various forebody shapes was then conducted to determine which shapes promote a positive contribution to directional stability at high angle-of-attack. An unconventional approach for presenting the results is used to illustrate how the positive contribution arises. Based on the results of this initial parametric study, some guidelines for aerodynamic design to promote positive directional stability are presented.

Thermal Stability of Oil Palm Empty Fruit Bunch (OPEFB) Nanocrystalline Cellulose: Effects of post-treatment of oven drying and solvent exchange techniques

NASA Astrophysics Data System (ADS)

Indarti, E.; Marwan; Wanrosli, W. D.

2015-06-01

Nanocrystallinecellulose (NCC) from biomass is a promising material with huge potentials in various applications. A big challenge in its utilization is the agglomeration of the NCC's during processing due to hydrogen bonding among the cellulose chains when in close proximity to each other. Obtaining NCC's in a non-agglomerated and non-aqueous condition is challenging. In the present work NCC's was isolated from oil palm empty fruit bunch (OPEFB) using TEMPO-oxidation reaction method. To obtain non-agglomerated and non-aqueous products, the NCC's underwent post-treatment using oven drying (OD) and solvent exchanged (SE) techniques. The thermal stability of all samples was determined from TGA and DTG profiles whilst FTIR was used to analyzethe chemical modifications that occurred under these conditions. NCC-SE has better thermal stability than the NCC-OD and its on-set degradation temperature and residue are also higher. FTIR analysis shows that NCC-SE has a slightly different chemical composition whereby the absorption band at 1300 cm-1 (due to C-O symmetric stretching) is absent as compared to NCC-OD indicating that in NCC-SE the carboxylate group is in acid form which contribute to its thermal stability

Predicting stability of DNA duplexes in solutions containing magnesium and monovalent cations.

PubMed

Owczarzy, Richard; Moreira, Bernardo G; You, Yong; Behlke, Mark A; Walder, Joseph A

2008-05-13

Accurate predictions of DNA stability in physiological and enzyme buffers are important for the design of many biological and biochemical assays. We therefore investigated the effects of magnesium, potassium, sodium, Tris ions, and deoxynucleoside triphosphates on melting profiles of duplex DNA oligomers and collected large melting data sets. An empirical correction function was developed that predicts melting temperatures, transition enthalpies, entropies, and free energies in buffers containing magnesium and monovalent cations. The new correction function significantly improves the accuracy of predictions and accounts for ion concentration, G-C base pair content, and length of the oligonucleotides. The competitive effects of potassium and magnesium ions were characterized. If the concentration ratio of [Mg (2+)] (0.5)/[Mon (+)] is less than 0.22 M (-1/2), monovalent ions (K (+), Na (+)) are dominant. Effects of magnesium ions dominate and determine duplex stability at higher ratios. Typical reaction conditions for PCR and DNA sequencing (1.5-5 mM magnesium and 20-100 mM monovalent cations) fall within this range. Conditions were identified where monovalent and divalent cations compete and their stability effects are more complex. When duplexes denature, some of the Mg (2+) ions associated with the DNA are released. The number of released magnesium ions per phosphate charge is sequence dependent and decreases surprisingly with increasing oligonucleotide length.

Nonlinear stability of Halley comethosheath with transverse plasma motion

NASA Technical Reports Server (NTRS)

Srivastava, Krishna M.; Tsurutani, Bruce T.

1994-01-01

Weakly nonlinear Magneto Hydrodynamic (MHD) stability of the Halley cometosheath determined by the balance between the outward ion-neutral drag force and the inward Lorentz force is investigated including the transverse plasma motion as observed in the flanks with the help of the method of multiple scales. The eigenvalues and the eigenfunctions are obtained for the linear problem and the time evolution of the amplitude is obtained using the solvability condition for the solution of the second order problem. The diamagnetic cavity boundary and the adjacent layer of about 100 km thickness is found unstable for the travelling waves of certain wave numbers. Halley ionopause has been observed to have strong ripples with a wavelength of several hundred kilometers. It is found that nonlinear effects have stabilizing effect.

Stability diagram for dense suspensions of model colloidal Al2O3 particles in shear flow.

PubMed

Hecht, Martin; Harting, Jens; Herrmann, Hans J

2007-05-01

In Al2O3 suspensions, depending on the experimental conditions, very different microstructures can be found, comprising fluidlike suspensions, a repulsive structure, and a clustered microstructure. For technical processing in ceramics, the knowledge of the microstructure is of importance, since it essentially determines the stability of a workpiece to be produced. To enlighten this topic, we investigate these suspensions under shear by means of simulations. We observe cluster formation on two different length scales: the distance of nearest neighbors and on the length scale of the system size. We find that the clustering behavior does not depend on the length scale of observation. If interparticle interactions are not attractive the particles form layers in the shear flow. The results are summarized in a stability diagram.

Lipid oxidation and color changes of goose meat stored under vacuum and modified atmosphere conditions.

PubMed

Orkusz, A; Haraf, G; Okruszek, A; Werenska-Sudnik, M

2017-03-01

The objective of the work was to investigate the color and lipid oxidation changes of goose breast meat packaged in vacuum and modified atmosphere (MA) conditions consisting of 80% O2, 20% CO2, and stored in refrigerated conditions at 4°C. Color stability was monitored by determining total heme pigments concentration; relative concentration of myoglobin, oxymyoglobin, and metmyoglobin; parameters of color L*, a*, b*, and sensory evaluation of the surface color. Lipid stability was measured by determining thiobarbituric acid reactive substances (TBARS). The samples were examined in 24 h after slaughter (unpacked muscles) and on d 4, 7, 9, 11 of storage (muscles packed in vacuum and in MA). Through the time of storage, samples packed in MA had higher TBARS values in comparison to the meat packed in vacuum. For samples packed in two types of atmospheres, the total pigments concentration decreased gradually within 11 d of storage. It was observed that relative metmyoglobin concentration increased whereas relative oxymyoglobin concentration decreased in total heme pigments in the MA stored muscle. The relative concentration of all three myoglobin forms sample packed in vacuum remained unchanged. The color parameters (L*, a*, b*) did not change for 11 d of storage for the vacuum packed meat. The value of the color parameter a* decreased and the value of the color parameters L* and b* increased in the samples packaged in MA. The data prove that if you store goose meat in MA (consisting of 80% O2, 20% CO2) or vacuum, the unchanged surface color is preserved for 9 and 11 day, respectively.Vacuum appears to be a better method as regards the maintaining of lipid stability in goose meat. © 2016 Poultry Science Association Inc.

Phase Stability Determinations of DWPF Waste Glasses

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

Marra, S.L.

1999-10-22

Liquid high-level nuclear waste will be immobilized at the Savannah River Site (SRS) by vitrification in borosilicate glass. To fulfill this requirement, glass samples were heat treated at various times and temperatures. These results will provide guidance to the repository program about conditions to be avoided during shipping, handling and storage of DWPF canistered waste forms.

Impact of Oral Fluid Collection Device on Cannabinoid Stability Following Smoked Cannabis

PubMed Central

Anizan, Sébastien; Bergamaschi, Mateus M.; Barnes, Allan J.; Milman, Garry; Desrosiers, Nathalie; Lee, Dayong; Gorelick, David A.; Huestis, Marilyn A.

2014-01-01

Evaluation of cannabinoid stability in authentic oral fluid (OF) is critical, as most OF stability studies employed fortified or synthetic OF. Participants (n=16) smoked a 6.8% delta-9-tetrahydrocannabinol (THC) cigarette, and baseline concentrations of THC, 11-nor-9-carboxy-THC (THCCOOH), cannabidiol (CBD), and cannabinol (CBN) were determined within 24h in 16 separate pooled samples (collected 1h before to 10.5 or 13h after smoking). OF was collected with the StatSure Saliva Sampler™ and Oral-Eze® devices. Oral-Eze samples were re-analyzed after room temperature (RT) storage for 1 week, and for both devices after 4°C for 1 and 4 weeks, and –20°C for 4 and 24 weeks. Concentrations ±20% from initial concentrations were considered stable. With the StatSure device, all cannabinoids were within 80-120% median %baseline for all storage conditions. Individual THC, CBD, CBN and THCCOOH pool concentrations were stable in 100%, 100%, 80-94% and >85%, respectively, across storage conditions. With the Oral-Eze device, at RT or refrigerated storage (for 1 and 4 weeks), THC, CBD and THCCOOH were stable in 94-100%, 78-89% and 93-100% of samples, respectively, while CBN concentrations were 53–79% stable. However, after 24 weeks at -20°C, stability decreased, especially for CBD, with a median of 56% stability. Overall, the collection devices’ elution/stabilizing buffers provided good stability for OF cannabinoids, with the exception of the more labile CBN. To ensure OF cannabinoid concentration accuracy, these data suggest analysis within 4 weeks at 4°C storage for Oral-Eze collection and within 4 weeks at 4°C or 24 weeks at -20°C for StatSure collection. PMID:24995604

Effects of anticaking agents and relative humidity on the physical and chemical stability of powdered vitamin C.

PubMed

Lipasek, Rebecca A; Taylor, Lynne S; Mauer, Lisa J

2011-09-01

Vitamin C is an essential nutrient that is widely used by the food industry in the powder form for both its nutritional and functional properties. However, vitamin C is deliquescent, and deliquescence has been linked to physical and chemical instabilities. Anticaking agents are often added to powder systems to delay or prevent caking, but little is known about their effect on the chemical stability of powders. In this study, various anticaking agents (calcium phosphate, calcium silicate, calcium stearate, corn starch, and silicon dioxide) were combined with sodium ascorbate at 2% and 50% w/w ratios and stored at various relative humidities (23%, 43%, 64%, 75%, 85%, and 98% RHs). Chemical and physical stability and moisture sorption were monitored over time. Additionally, saturated solution samples were stored at various pHs to determine the effect of surface pH and dissolution on the vitamin degradation rate. Storage RH, time, and anticaking agent type and ratio all significantly affected (P < 0.05) moisture sorption and vitamin C stability. Silicon dioxide and calcium silicate (50% w/w) and calcium stearate (at both ratios) were the only anticaking agents to improve the physical stability of powdered sodium ascorbate while none of the anticaking agents improved its chemical stability. However, corn starch and calcium stearate had the least adverse effect on chemical stability. Dissolution rate and pH were also important factors affecting the chemical and physical stability of the powders. Therefore, monitoring storage environmental conditions and anticaking agent usage are important for understanding the stability of vitamin C. Anticaking agent type and ratio significantly affected the physical and chemical stability of vitamin C over time and over a range of RHs. No anticaking agent improved the chemical stability of the vitamin, and most caused an increase in chemical degradation even if physical stability was improved. It is possible that anticaking agents would greatly affect other chemically labile deliquescent ingredients, and therefore, anticaking agent usage and storage conditions should be monitored in blended powder systems. © 2011 Institute of Food Technologists®

Changing Places and Partners: Associations of Neighborhood Conditions With Sexual Network Turnover Among African American Adults Relocated From Public Housing.

PubMed

Linton, Sabriya L; Cooper, Hannah L F; Luo, Ruiyan; Karnes, Conny; Renneker, Kristen; Haley, Danielle F; Dauria, Emily F; Hunter-Jones, Josalin; Ross, Zev; Wingood, Gina M; Adimora, Adaora A; Bonney, Loida; Rothenberg, Richard

2017-05-01

Neighborhood conditions and sexual network turnover have been associated with the acquisition of HIV and other sexually transmitted infections (STIs). However, few studies investigate the influence of neighborhood conditions on sexual network turnover. This longitudinal study used data collected across 7 visits from a predominantly substance-misusing cohort of 172 African American adults relocated from public housing in Atlanta, Georgia, to determine whether post-relocation changes in exposure to neighborhood conditions influence sexual network stability, the number of new partners joining sexual networks, and the number of partners leaving sexual networks over time. At each visit, participant and sexual network characteristics were captured via survey, and administrative data were analyzed to describe the census tracts where participants lived. Multilevel models were used to longitudinally assess the relationships of tract-level characteristics to sexual network dynamics over time. On average, participants relocated to neighborhoods that were less economically deprived and violent, and had lower alcohol outlet densities. Post-relocation reductions in exposure to alcohol outlet density were associated with fewer new partners joining sexual networks. Reduced perceived community violence was associated with more sexual partners leaving sexual networks. These associations were marginally significant. No post-relocation changes in place characteristics were significantly associated with overall sexual network stability. Neighborhood social context may influence sexual network turnover. To increase understanding of the social-ecological determinants of HIV/STIs, a new line of research should investigate the combined influence of neighborhood conditions and sexual network dynamics on HIV/STI transmission over time.

Stability and pre-formulation development of a plant-produced anthrax vaccine candidate.

PubMed

Jones, R Mark; Burke, Michael; Dubose, Devon; Chichester, Jessica A; Manceva, Slobodanka; Horsey, April; Streatfield, Stephen J; Breit, Jeff; Yusibov, Vidadi

2017-10-04

Second generation anthrax vaccines focus on the use of recombinant protective antigen (rPA) to elicit a strong, toxin neutralizing antibody responses in immunized subjects. The main difference between the rPA vaccines compared to the current licensed vaccine, anthrax vaccine absorbed (AVA), is the rPA vaccines are highly purified preparations of only rPA. These second generation rPA vaccines strive to elicit strong immune responses with substantially fewer doses than AVA while provoking less side effects. Many of the rPA candidates have shown to be effective in pre-clinical studies, but most of the second generation molecules have stability issues which reduce their efficacy over time. These stability issues are evident even under refrigerated conditions and thus emphasis has been directed to stabilizing the rPA molecule and determining an optimized final formulation. Stabilization of vaccines for long-term storage is a major challenge in the product development life cycle. The effort required to identify suitable formulations can be slow and expensive. The ideal storage for stockpiled vaccines would allow the candidate to withstand years of storage at ambient temperatures. The Fraunhofer Center for Molecular Biotechnology is developing a plant-produced rPA vaccine candidate that shows instability when stored under refrigerated conditions in a solution, as is typical for rPA vaccines. Increased stability of our plant-produced rPA vaccine candidate was achieved in a spray dried powder formulation that could eliminate the need for conventional cold chain allowing greater confidence to stockpile vaccine for civilian and military biodefense. Copyright © 2017 Elsevier Ltd. All rights reserved.

Transport and deposition of carbon at catchment scale: stabilization mechanisms approach

NASA Astrophysics Data System (ADS)

Martínez-Mena, María; Almagro, María; Díaz-Pereira, Elvira; García-Franco, Noelia; Boix-Fayos, Carolina

2016-04-01

Terrestrial sedimentation buries large amounts of organic carbon (OC) annually, contributing to the terrestrial carbon sink. The temporal significance of this sink will strongly depend on the attributes of the depositional environment, but also on the characteristics of the OC reaching these sites and its stability upon deposition. The fate of the redistributed OC will ultimately depend on the mechanisms of its physical and chemical protection against decomposition, its turnover rates and the conditions under which the OC is stored in sedimentary settings. This framework is more complex in Mediterranean river basins where sediments are often redistributed under a range of environmental conditions in ephemeral, intermittent and perennial fluvial courses, sometimes within the same catchment. The OC stabilization mechanisms and their relations with aggregation at different transport and sedimentary deposits is under those conditions highly uncertain. The main objective of this work was to characterize the stabilization and mineralization of OC in sediments in transit (suspended load), at a range of depositional settings (alluvial bars, reservoir sediments) and soils from the source areas in a sub-catchment (111 km2) at the headwaters of the Segura catchment in South East Spain. In order to obtain a deeper knowledge on the predominant stabilization mechanism corresponding to each erosional phase, the following organic carbon fractionation method was carried out: Four aggregate size classes were distinguished by sieving (large and small macroaggregates, free microaggregates, and free silt plus clay fraction), and the microaggregates occluded within macroaggregates (SMm) were isolated. As a further step, an oxidation of the OC occluded in silt plus clay fraction and that of the free silt plus clay fraction was performed to estimate the oxidant resistant OC pool. Measured OC in these fractions can be related to three functional pools: active (free particulate organic matter), slow (carbon associated to clay and silt or stabilized in aggregates) and passive (oxidation-resistant OC). In addition, the potential mineralized C (incubation method) in each deposit and soil was determined. Preliminary results indicate a higher OC content in the suspended sediments in transit and in the reservoir deposited sediments than in the alluvial bars, being in all sediments the total OC content lower than in the source soils. Slow and passive pools prevailed in suspended sediments and in reservoir sediments compared to alluvial bars, indicating different OC stabilization mechanisms. In addition, in the alluvial bars, mineralization rates were higher in bars located in channels with ephemeral flow conditions and vegetated areas than in bars located in channels with perennial flow conditions.

A comprehensive approach for the determination of extractable and leachable metals in pharmaceutical products by inductively-coupled plasma.

PubMed

Zuccarello, Daniel J; Murphy, Michael P; Meyer, Richard F; Winslow, Paul A

2009-01-01

A comprehensive digestive approach for determining the extractable and leachable metals in pharmaceutical products by inductively-coupled plasma is investigated. This study examines several acid digestion strategies for packaging materials, containers, and formulated products for complete trace metals analysis. Packaging materials, a food product, and a simulated drug product are evaluated for leachable metals by stressing the materials under accelerated stability conditions. Trace metal profiles of 64 elements for these materials are reported.

Stability of the rhizosphere and endophytic bacterial communities associated with Arabidopsis thaliana (L.) Heynh under impact of cosmic factors

NASA Astrophysics Data System (ADS)

Kordium, V. A.; Adamchuk-Chala, N. I.; Moshinec, H. V.

The orbital experiment will involve a growing of Arabidopsis plant seed to seed in the presence of a plant probiotic bacteria consortium introduced into the system The purpose of experiment is to characterize microbial community associated with Arabidopsis thaliana and determine how consortium of introduced bacteria along with the endemic plant-associated bacteria influences the plant development reproductive system and seed formation in spaceflight conditions The first study will be an examination of the survival of model bacteria in on the inoculated plant The second complex study is to examine the plant traits in particular the ultrastructure of root statocytes in order to determine whether the plant development proceeds normally under microgravity conditions on background of introduced bacteria and to assess the structural changes occurring in the cotyledons generative organs and seeds The third set of observations will concern studies of the structure of microbial community associated with Arabidopsis plants with traditional and molecular tools The fourth part of the work will be an examination of mobile genetic elements that can play a role in adaptation of bacteria to the spaceflight conditions however they may affect the stability of bacterial endo- and rhizosphere communities The final part of the proposal initiates the study of possible risk of the bacterial consortium use for a plant inoculation in spaceflight conditions An evaluation of this risk will be performed via examination of expression of the Klebsiella

A novel accelerated oxidative stability screening method for pharmaceutical solids.

PubMed

Zhu, Donghua Alan; Zhang, Geoff G Z; George, Karen L S T; Zhou, Deliang

2011-08-01

Despite the fact that oxidation is the second most frequent degradation pathway for pharmaceuticals, means of evaluating the oxidative stability of pharmaceutical solids, especially effective stress testing, are still lacking. This paper describes a novel experimental method for peroxide-mediated oxidative stress testing on pharmaceutical solids. The method utilizes urea-hydrogen peroxide, a molecular complex that undergoes solid-state decomposition and releases hydrogen peroxide vapor at elevated temperatures (e.g., 30°C), as a source of peroxide. The experimental setting for this method is simple, convenient, and can be operated routinely in most laboratories. The fundamental parameter of the system, that is, hydrogen peroxide vapor pressure, was determined using a modified spectrophotometric method. The feasibility and utility of the proposed method in solid form selection have been demonstrated using various solid forms of ephedrine. No degradation was detected for ephedrine hydrochloride after exposure to the hydrogen peroxide vapor for 2 weeks, whereas both anhydrate and hemihydrate free base forms degraded rapidly under the test conditions. In addition, both the anhydrate and the hemihydrate free base degraded faster when exposed to hydrogen peroxide vapor at 30°C under dry condition than at 30°C/75% relative humidity (RH). A new degradation product was also observed under the drier condition. The proposed method provides more relevant screening conditions for solid dosage forms, and is useful in selecting optimal solid form(s), determining potential degradation products, and formulation screening during development. Copyright © 2011 Wiley-Liss, Inc.

Conformally non-flat spacetime representing dense compact objects

NASA Astrophysics Data System (ADS)

Singh, Ksh. Newton; Bhar, Piyali; Rahaman, Farook; Pant, Neeraj; Rahaman, Mansur

2017-06-01

A new conformally non-flat interior spacetime embedded in five-dimensional (5D) pseudo Euclidean space is explored in this paper. We proceed our calculation with the assumption of spherically symmetric anisotropic matter distribution and Karmarkar condition (necessary condition for class one). This solution is free from geometrical singularity and well-behaved in all respects. We ansatz a new type of metric potential g11 and solve for the metric potential g00 via Karmarkar condition. Further, all the physical parameters are determined from Einstein’s field equations using the two metric potentials. All the constants of integration are determined using boundary conditions. Due to its conformally non-flat character, it can represent bounded configurations. Therefore, we have used it to model two compact stars Vela X-1 and Cyg X-2. Indeed, the obtained masses and radii of these two objects from our solution are well matched with those observed values given in [T. Gangopadhyay et al., Mon. Not. R. Astron. Soc. 431, 3216 (2013)] and [J. Casares et al., Mon. Not. R. Astron. Soc. 401, 2517 (2010)]. The equilibrium of the models is investigated from generalized TOV-equation. We have adopted [L. Herrera’s, Phys. Lett. A 165, 206 (1992)] method and static stability criterion of Harisson-Zeldovich-Novikov [B. K. Harrison et al., Gravitational Theory and Gravitational Collapse (University of Chicago Press, 1965); Ya. B. Zeldovich and I. D. Novikov, Relativistic Astrophysics, Vol. 1, Stars and Relativity (University of Chicago Press, 1971)] to analyze the stability of the models.

Evaluation of Interference of Cellular Phones on Electronic Apex Locators: An In Vitro Study.

PubMed

Sidhu, Preena; Shankargouda, Swapnil; Dicksit, Daniel DevaPrakash; Mahdey, Haydar Majeed; Muzaffar, Danish; Arora, Shelly

2016-04-01

Use of mobile phone has been prohibited in many hospitals to prevent interference with medical devices. Electromagnetic radiation emitted from cellular phones might interfere with electronic working length determination. The purpose of this in vitro study was to evaluate the effect of a smart phone (Samsung Galaxy Note Edge) on working length determination of electronic apex locators (EALs) Propex II and Rootor. Fifteen intact, non-carious single-rooted teeth were decoronated at the cementoenamel junction. Visually, working length was determined by using a #15 K-file under stereomicroscope (×20). The effect of cellular phones on electronic working length (EWL) was determined under 2 experimental settings: (1) in a closed room with poor signal strength and (2) in a polyclinic set up with good signal strength and 5 conditions: (1) electronically, without cellular phone in room; (2) electronically, with cellular phone in physical contact with EAL; (3) electronically, with mobile phone in physical contact with EAL and in calling mode for a period of 25 seconds; (4) electronically, mobile phone placed at a distance of 40 cm from the EAL; and (5) electronically, mobile phone placed at a distance of 40 cm and in calling mode for a period of 25 seconds. The EWL was measured 3 times per tooth under each condition. Stability of the readings was scored from 1 to 3: (1) good stability, (2) stable reading after 1 attempt, and (3) stable reading after 2 attempts. The data were compared by using analysis of variance. The EWL measurements were not influenced by the presence of cellular phone and could be determined under all experimental conditions. Within the limitations of this study, it can be concluded that mobile phones do not interfere with the EWL determination. Copyright © 2016 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.

Sensory Bias Predicts Postural Stability, Anxiety, and Cognitive Performance in Healthy Adults Walking in Novel Discordant Conditions

NASA Technical Reports Server (NTRS)

Brady, Rachel A.; Batson, Crystal D.; Peters, Brian T.; Mulavara, Ajitkumar P.; Bloomberg, Jacob J.

2010-01-01

We designed a gait training study that presented combinations of visual flow and support surface manipulations to investigate the response of healthy adults to novel discordant sensorimotor conditions. We aimed to determine whether a relationship existed between subjects visual dependence and their scores on a collective measure of anxiety, cognition, and postural stability in a new discordant environment presented at the conclusion of training (Transfer Test). A treadmill was mounted to a motion base platform positioned 2 m behind a large visual screen. Training consisted of three walking sessions, each within a week of the previous visit, that presented four 5-minute exposures to various combinations of support surface and visual scene manipulations, all lateral sinusoids. The conditions were scene translation only, support surface translation only, simultaneous scene and support surface translations in-phase, and simultaneous scene and support surface translations 180 out-of-phase. During the Transfer Test, the trained participants received a 2-minute novel exposure. A visual sinusoidal roll perturbation, with twice the original flow rate, was superimposed on a sinusoidal support surface roll perturbation that was 90 out of phase with the scene. A high correlation existed between normalized torso translation, measured in the scene-only condition at the first visit, and a combined measure of normalized heart rate, stride frequency, and reaction time at the transfer test. Results suggest that visually dependent participants experience decreased postural stability, increased anxiety, and increased reaction times compared to their less visually dependent counterparts when negotiating novel discordant conditions.

Effects of Storage Conditions on Consumer and Chemical Assessments of Raw ‘Nonpareil’ Almonds Over a Two‐Year Period

PubMed Central

Pleasance, Emily A.; Pegg, Ronald B.; Swanson, Ruthann B.; Cheely, Anna N.; Huang, Guangwei; Parrish, Daniel R.; Kerrihard, Adrian L.

2018-01-01

Abstract Raw almonds are a major commodity, yet much is unknown about how storage conditions determine their shelf life. The storage stability, as measured by consumer assessments and chemical measures, of raw almonds was determined for samples stored in cardboard boxes and polypropylene packaging for 2 years at 4, 15, 25, and 35 °C, and at 50% and 65% relative humidity (RH). Samples stored in unlined cartons always failed (>25% rejection) before their counterparts stored in polypropylene bags under identical environmental conditions. Models determined that polypropylene packaging (as opposed to unlined cardboard cartons) extended the time until sample rejection by more than 7 months. Temperature and RH were both negatively associated with storage time until failure. Flavor was a greater contributor to consumer acceptability than texture or odor, while peroxide values and free fatty acids were of greater importance in predicting raw almond consumer quality than measures of conjugated dienes or 2‐thiobarbituric acid‐reactive substances. Practical Application The results of this study will allow almond producers to determine packaging types and environmental storage conditions that provide shelf life of a specified time. PMID:29355948

Binding of Cu(II) ions to peptides studied by fluorescence spectroscopy and isothermal titration calorimetry.

PubMed

Makowska, Joanna; Żamojć, Krzysztof; Wyrzykowski, Dariusz; Uber, Dorota; Wierzbicka, Małgorzata; Wiczk, Wiesław; Chmurzyński, Lech

2016-01-15

Steady-state and time-resolved fluorescence quenching measurements supported by Isothermal Titration Calorimetry (ITC) were used to study the interactions of Cu(2+) with four peptides. Two of them were taken from the N-terminal part of the FBP28 protein (formin binding protein) WW domain: Tyr-Lys-Thr-Ala-Asp-Gly-Lys-Thr-Tyr-NH2 (D9) and its mutant Tyr-Lys-Thr-Ala-Asn-Gly-Lys-Thr-Tyr-NH2 (D9_M) as well as two mutated peptides from the B3 domain of the immunoglobulin binding protein G derived from Streptococcus: Asp-Val-Ala-Thr-Tyr-Thr-NH2 (J1) and Glu-Val-Ala-Thr-Tyr-Thr-NH2 (J2). The measurements were carried out at 298.15K in 20mM 2-(N-morpholino)ethanesulfonic acid (MES) buffer solution with a pH of 6. The fluorescence of all peptides was quenched by Cu(2+) ions. The stoichiometry, conditional stability constants and thermodynamic parameters for the interactions of the Cu(2+) ions with D9 and D9_M were determined from the calorimetric data. The values of the conditional stability constants were additionally determined from fluorescence quenching measurements and compared with those obtained from calorimetric studies. There was a good correlation between data obtained from the two techniques. On the other hand, the studies revealed that J1 and J2 do not exhibit an affinity towards metal ions. The obtained results prove that fluorescence quenching experiments may be successfully used in order to determine stability constants of complexes with fluorescent ligands. Finally, based on the obtained results, the coordinating properties of the peptides towards the Cu(2+) ions are discussed. Copyright © 2015 Elsevier B.V. All rights reserved.

Binding of Cu(II) ions to peptides studied by fluorescence spectroscopy and isothermal titration calorimetry

NASA Astrophysics Data System (ADS)

Makowska, Joanna; Żamojć, Krzysztof; Wyrzykowski, Dariusz; Uber, Dorota; Wierzbicka, Małgorzata; Wiczk, Wiesław; Chmurzyński, Lech

2016-01-01

Steady-state and time-resolved fluorescence quenching measurements supported by Isothermal Titration Calorimetry (ITC) were used to study the interactions of Cu2 + with four peptides. Two of them were taken from the N-terminal part of the FBP28 protein (formin binding protein) WW domain: Tyr-Lys-Thr-Ala-Asp-Gly-Lys-Thr-Tyr-NH2 (D9) and its mutant Tyr-Lys-Thr-Ala-Asn-Gly-Lys-Thr-Tyr-NH2 (D9_M) as well as two mutated peptides from the B3 domain of the immunoglobulin binding protein G derived from Streptococcus: Asp-Val-Ala-Thr-Tyr-Thr-NH2 (J1) and Glu-Val-Ala-Thr-Tyr-Thr-NH2 (J2). The measurements were carried out at 298.15 K in 20 mM 2-(N-morpholino)ethanesulfonic acid (MES) buffer solution with a pH of 6. The fluorescence of all peptides was quenched by Cu2 + ions. The stoichiometry, conditional stability constants and thermodynamic parameters for the interactions of the Cu2 + ions with D9 and D9_M were determined from the calorimetric data. The values of the conditional stability constants were additionally determined from fluorescence quenching measurements and compared with those obtained from calorimetric studies. There was a good correlation between data obtained from the two techniques. On the other hand, the studies revealed that J1 and J2 do not exhibit an affinity towards metal ions. The obtained results prove that fluorescence quenching experiments may be successfully used in order to determine stability constants of complexes with fluorescent ligands. Finally, based on the obtained results, the coordinating properties of the peptides towards the Cu2 + ions are discussed.

Harmonic Balance Computations of Fan Aeroelastic Stability

NASA Technical Reports Server (NTRS)

Bakhle, Milind A.; Reddy, T. S. R.

2010-01-01

A harmonic balance (HB) aeroelastic analysis, which has been recently developed, was used to determine the aeroelastic stability (flutter) characteristics of an experimental fan. To assess the numerical accuracy of this HB aeroelastic analysis, a time-domain aeroelastic analysis was also used to determine the aeroelastic stability characteristics of the same fan. Both of these three-dimensional analysis codes model the unsteady flowfield due to blade vibrations using the Reynolds-averaged Navier-Stokes (RANS) equations. In the HB analysis, the unsteady flow equations are converted to a HB form and solved using a pseudo-time marching method. In the time-domain analysis, the unsteady flow equations are solved using an implicit time-marching approach. Steady and unsteady computations for two vibration modes were carried out at two rotational speeds: 100 percent (design) and 70 percent (part-speed). The steady and unsteady results obtained from the two analysis methods compare well, thus verifying the recently developed HB aeroelastic analysis. Based on the results, the experimental fan was found to have no aeroelastic instability (flutter) at the conditions examined in this study.

Color profiles and stability of acylated and nonacylated anthocyanins as novel pigment sources in a lipstick model: A viable alternative to synthetic colorants.

PubMed

Westfall, Alexandra; Giusti, Mónica

Cosmetics, such as lipstick, can affect an individual's perception of attractiveness and morale. Consumer concern with the safety of synthetic colorants has made the need for alternative natural color sources increasingly urgent. Our goal was to evaluate the feasibility of anthocyanin (ACN) extracts as colorants in lipstick formulations. Lipstick formulations were colored with ACN-rich materials. Accelerated environmental testing typical of the cosmetic industry were used: incubation at 20°, 37°, and 45°C for 12 weeks and temperature abuse cycles between 20°/37°C or -20°/20°C. Color (CIELab) and total monomeric ACN (pH-differential) changes were monitored to determine shelf stability of the product. All formulations exhibited acceptable color for lipsticks. Shelf stability was determined to exceed 2 year based on the accelerated testing conditions. Formulations containing cyanidin as their main ACN were the most stable (elderberry, purple corn, and purple sweet potato). ACNs could be used as suitable alternatives to synthetic colorants in lipid-based topical formulations.

Identification of a Novel Reference Gene for Apple Transcriptional Profiling under Postharvest Conditions

PubMed Central

Storch, Tatiane Timm; Pegoraro, Camila; Finatto, Taciane; Quecini, Vera; Rombaldi, Cesar Valmor; Girardi, César Luis

2015-01-01

Reverse Transcription quantitative PCR (RT-qPCR) is one of the most important techniques for gene expression profiling due to its high sensibility and reproducibility. However, the reliability of the results is highly dependent on data normalization, performed by comparisons between the expression profiles of the genes of interest against those of constitutively expressed, reference genes. Although the technique is widely used in fruit postharvest experiments, the transcription stability of reference genes has not been thoroughly investigated under these experimental conditions. Thus, we have determined the transcriptional profile, under these conditions, of three genes commonly used as reference—ACTIN (MdACT), PROTEIN DISULPHIDE ISOMERASE (MdPDI) and UBIQUITIN-CONJUGATING ENZYME E2 (MdUBC)—along with two novel candidates—HISTONE 1 (MdH1) and NUCLEOSSOME ASSEMBLY 1 PROTEIN (MdNAP1). The expression profile of the genes was investigated throughout five experiments, with three of them encompassing the postharvest period and the other two, consisting of developmental and spatial phases. The transcriptional stability was comparatively investigated using four distinct software packages: BestKeeper, NormFinder, geNorm and DataAssist. Gene ranking results for transcriptional stability were similar for the investigated software packages, with the exception of BestKeeper. The classic reference gene MdUBC ranked among the most stably transcribed in all investigated experimental conditions. Transcript accumulation profiles for the novel reference candidate gene MdH1 were stable throughout the tested conditions, especially in experiments encompassing the postharvest period. Thus, our results present a novel reference gene for postharvest experiments in apple and reinforce the importance of checking the transcription profile of reference genes under the experimental conditions of interest. PMID:25774904

Identification of a novel reference gene for apple transcriptional profiling under postharvest conditions.

PubMed

Storch, Tatiane Timm; Pegoraro, Camila; Finatto, Taciane; Quecini, Vera; Rombaldi, Cesar Valmor; Girardi, César Luis

2015-01-01

Reverse Transcription quantitative PCR (RT-qPCR) is one of the most important techniques for gene expression profiling due to its high sensibility and reproducibility. However, the reliability of the results is highly dependent on data normalization, performed by comparisons between the expression profiles of the genes of interest against those of constitutively expressed, reference genes. Although the technique is widely used in fruit postharvest experiments, the transcription stability of reference genes has not been thoroughly investigated under these experimental conditions. Thus, we have determined the transcriptional profile, under these conditions, of three genes commonly used as reference--ACTIN (MdACT), PROTEIN DISULPHIDE ISOMERASE (MdPDI) and UBIQUITIN-CONJUGATING ENZYME E2 (MdUBC)--along with two novel candidates--HISTONE 1 (MdH1) and NUCLEOSSOME ASSEMBLY 1 PROTEIN (MdNAP1). The expression profile of the genes was investigated throughout five experiments, with three of them encompassing the postharvest period and the other two, consisting of developmental and spatial phases. The transcriptional stability was comparatively investigated using four distinct software packages: BestKeeper, NormFinder, geNorm and DataAssist. Gene ranking results for transcriptional stability were similar for the investigated software packages, with the exception of BestKeeper. The classic reference gene MdUBC ranked among the most stably transcribed in all investigated experimental conditions. Transcript accumulation profiles for the novel reference candidate gene MdH1 were stable throughout the tested conditions, especially in experiments encompassing the postharvest period. Thus, our results present a novel reference gene for postharvest experiments in apple and reinforce the importance of checking the transcription profile of reference genes under the experimental conditions of interest.

Anions adsorption onto nanoparticles: effects on colloid stability and mobility in the environment

NASA Astrophysics Data System (ADS)

Missana, Tiziana; Benedicto, Ana; Mayordomo, Natalia; Alonso, Ursula

2013-04-01

Nanoparticles and colloids can enhance the contaminant transport in groundwater, if the contaminant is irreversibly adsorbed onto their surface; additionally colloids must be stable and mobile under the chemical conditions of the environment of interest. Colloid stability and mobility are factors directly related to the chemistry of the water, which determines the charge and size of the particles, but these colloidal properties can also be affected by the contaminant adsorption. This last point, which is potentially very relevant on the overall colloid-driven transport, is scarcely investigated. The evaluation of the stability of a colloidal system is generally carried out by measuring the aggregation kinetic after the change of a specific chemical condition, mainly pH or ionic strength of the aqueous solution. The effect of anion adsorption onto the stability of colloidal systems is mostly neglected. Parameters of the nanoparticles,as the point of zero charge (pH PCZ) or the isoelectric point (pH IEP) are determined with "inert" electrolytes and this might not be representative of their real behavior in natural systems. In this work, the effects of the Se(IV) (selenite) adsorption on alumina (Al2O3) nanoparticles have been analyzed. Selenite adsorption was studied in a wide range of pH (2-12) and ionic strengths (0.0005 - 0.1 M in NaClO4) and the effect of the adsorption on the main properties of the colloids (size and charge) were analyzed. Se adsorption on Al2O3 is almost independent of the ionic strength and decreases with increasing pH; sorption data were successfully fit by surface complexation modeling. Selenite adsorption (at medium-high surface occupancies) clearly affected the stability of Al2O3 colloids, with a clear shift of the isoelectric point towards more acid pH and enhancing colloid aggregation when the ionic strength increases. Considering the obtained results, the effect of anions in the chemical composition of natural water, frequently not accounted for in stability studies, will be discussed, as well as their implications on possible colloid-driven selenite transport in the environment.

Stabilizing Conditional Standard Errors of Measurement in Scale Score Transformations

ERIC Educational Resources Information Center

Moses, Tim; Kim, YoungKoung

2017-01-01

The focus of this article is on scale score transformations that can be used to stabilize conditional standard errors of measurement (CSEMs). Three transformations for stabilizing the estimated CSEMs are reviewed, including the traditional arcsine transformation, a recently developed general variance stabilization transformation, and a new method…

Method for accurate determination of dissociation constants of optical ratiometric systems: chemical probes, genetically encoded sensors, and interacting molecules.

PubMed

Pomorski, Adam; Kochańczyk, Tomasz; Miłoch, Anna; Krężel, Artur

2013-12-03

Ratiometric chemical probes and genetically encoded sensors are of high interest for both analytical chemists and molecular biologists. Their high sensitivity toward the target ligand and ability to obtain quantitative results without a known sensor concentration have made them a very useful tool in both in vitro and in vivo assays. Although ratiometric sensors are widely used in many applications, their successful and accurate usage depends on how they are characterized in terms of sensing target molecules. The most important feature of probes and sensors besides their optical parameters is an affinity constant toward analyzed molecules. The literature shows that different analytical approaches are used to determine the stability constants, with the ratio approach being most popular. However, oversimplification and lack of attention to detail results in inaccurate determination of stability constants, which in turn affects the results obtained using these sensors. Here, we present a new method where ratio signal is calibrated for borderline values of intensities of both wavelengths, instead of borderline ratio values that generate errors in many studies. At the same time, the equation takes into account the cooperativity factor or fluorescence artifacts and therefore can be used to characterize systems with various stoichiometries and experimental conditions. Accurate determination of stability constants is demonstrated utilizing four known optical ratiometric probes and sensors, together with a discussion regarding other, currently used methods.

Data Obtained in the Flight Measurements to Determine the Stability and Control Characteristics of a C-54D Airplane (AAF No. 42-72713) and a Summary of the Test Program

NASA Technical Reports Server (NTRS)

Talmage, Donald B.; Reeder, John P.

1947-01-01

The flight investigation of the C-54D airplane was initiated to determine the necessity of changes or additions to existing handling-qualities requirements to cove the case of instrument approaches with large airplanes. This paper gives a brief synopsis of the results and presents the measured data of tests to determine the stability and control characteristics. It was found that no new requirements were necessary to cover the problems of instrument approaches. The C-54D airplane tested met the Amy and Navy stability and control requirements except for the following items. The control-system friction with autopilot installed vas double that allowed by the requirements. The amount of friction was found to impair the controllability of the airplane in precision flying. The lateral and directional characteristics were good except that the maximum pb/2V was slightly below the minimum required, and the elevator-control forces to obtain the maximum pb/2V at low speeds were above the Army and Navy requirements. The longitudinal stability and control characteristics were good except that the elevator-control forces exceeded the limits of the Army and Navy requirements in turns and in landings. The stalling characteristics were considered good in all conditions with the stall warning in the form of tail buffeting occurring at speeds approximately 5 miles per hour above the stall.

Electrostatic Interactions at the Dimer Interface Stabilize the E. coli β Sliding Clamp.

PubMed

Purohit, Anirban; England, Jennifer K; Douma, Lauren G; Tondnevis, Farzaneh; Bloom, Linda B; Levitus, Marcia

2017-08-22

Sliding clamps are ring-shaped oligomeric proteins that encircle DNA and associate with DNA polymerases for processive DNA replication. The dimeric Escherichia coli β-clamp is closed in solution but must adopt an open conformation to be assembled onto DNA by a clamp loader. To determine what factors contribute to the stability of the dimer interfaces in the closed conformation and how clamp dynamics contribute to formation of the open conformation, we identified conditions that destabilized the dimer and measured the effects of these conditions on clamp dynamics. We characterized the role of electrostatic interactions in stabilizing the β-clamp interface. Increasing salt concentration results in decreased dimer stability and faster subunit dissociation kinetics. The equilibrium dissociation constant of the dimeric clamp varies with salt concentration as predicted by simple charge-screening models, indicating that charged amino acids contribute to the remarkable stability of the interface at physiological salt concentrations. Mutation of a charged residue at the interface (Arg-103) weakens the interface significantly, whereas effects are negligible when a hydrophilic (Ser-109) or a hydrophobic (Ile-305) amino acid is mutated instead. It has been suggested that clamp opening by the clamp loader takes advantage of spontaneous opening-closing fluctuations at the clamp's interface, but our time-resolved fluorescence and fluorescence correlation experiments rule out conformational fluctuations that lead to a significant fraction of open states. Copyright © 2017 Biophysical Society. Published by Elsevier Inc. All rights reserved.

Aircraft measurement of ozone turbulent flux in the atmospheric boundary layer

NASA Astrophysics Data System (ADS)

Affre, Ch.; Carrara, A.; Lefebre, F.; Druilhet, A.; Fontan, J.; Lopez, A.

In May 1995, the "Chimie-Creil 95" experiment was undertaken in the north of France. The field data are first used to validate the methodology for airborne measurement of ozone flux. A certain number of methodological problems due to the location of the fast ozone sensor inside the airplane are, furthermore discussed. The paper describes the instrumentation of the ARAT (Avion de Recherche Atmosphérique et de Télédétection), an atmospheric research and remote-sensing aircraft used to perform the airborne measurements, the area flown over, the meteorological conditions and boundary layer stability conditions. These aircraft measurements are then used to determine ozone deposition velocity and values are proposed for aerodynamic, bulk transfer coefficients (ozone and momentum). The paper also establishes the relationship between the normalised standard deviation and stability parameters ( z/ L) for ozone, temperature, humidity and vertical velocity. The laws obtained are then presented.

Bouncing ball problem: stability of the periodic modes.

PubMed

Barroso, Joaquim J; Carneiro, Marcus V; Macau, Elbert E N

2009-02-01

Exploring all its ramifications, we give an overview of the simple yet fundamental bouncing ball problem, which consists of a ball bouncing vertically on a sinusoidally vibrating table under the action of gravity. The dynamics is modeled on the basis of a discrete map of difference equations, which numerically solved fully reveals a rich variety of nonlinear behaviors, encompassing irregular nonperiodic orbits, subharmonic and chaotic motions, chattering mechanisms, and also unbounded nonperiodic orbits. For periodic motions, the corresponding conditions for stability and bifurcation are determined from analytical considerations of a reduced map. Through numerical examples, it is shown that a slight change in the initial conditions makes the ball motion switch from periodic to chaotic orbits bounded by a velocity strip v=+/-Gamma(1-epsilon) , where Gamma is the nondimensionalized shaking acceleration and epsilon the coefficient of restitution which quantifies the amount of energy lost in the ball-table collision.

Transcriptome Wide Annotation of Eukaryotic RNase III Reactivity and Degradation Signals

PubMed Central

Gagnon, Jules; Lavoie, Mathieu; Catala, Mathieu; Malenfant, Francis; Elela, Sherif Abou

2015-01-01

Detection and validation of the RNA degradation signals controlling transcriptome stability are essential steps for understanding how cells regulate gene expression. Here we present complete genomic and biochemical annotations of the signals required for RNA degradation by the dsRNA specific ribonuclease III (Rnt1p) and examine its impact on transcriptome expression. Rnt1p cleavage signals are randomly distributed in the yeast genome, and encompass a wide variety of sequences, indicating that transcriptome stability is not determined by the recurrence of a fixed cleavage motif. Instead, RNA reactivity is defined by the sequence and structural context in which the cleavage sites are located. Reactive signals are often associated with transiently expressed genes, and their impact on RNA expression is linked to growth conditions. Together, the data suggest that Rnt1p reactivity is triggered by malleable RNA degradation signals that permit dynamic response to changes in growth conditions. PMID:25680180

Modeling of in-use stability for tablets and powders in bottles.

PubMed

Waterman, Kenneth C; Chen, Lili; Waterman, Philip; MacDonald, Bruce C; Monahan, Andrew P; Scrivens, Garry

2016-10-01

A model is presented for determining the time when an active pharmaceutical ingredient in tablets/powders will remain within its specification limits during an in-use period; that is, when a heat-induction sealed bottle is opened for fixed time periods and where tablets are removed at fixed time points. This model combines the Accelerated Stability Assessment Program to determine the impact on degradation rates of relative humidity (RH) with calculations of the RH as a function of time for the dosage forms under in-use conditions. These calculations, in a conservative approach, assume that the air inside bottles with broached heat-induction seals completely exchanges with the external environment during periods when the bottle remains open. The solid dosages are assumed to sorb water at estimable rates during these openings. When bottles are capped, the moisture vapor transmission rate can be estimated to determine the changing RH inside the bottles between opening events. The impact of silica gel desiccants can also be included in the modeling.

Laboratory sample stability. Is it possible to define a consensus stability function? An example of five blood magnitudes.

PubMed

Gómez Rioja, Rubén; Martínez Espartosa, Débora; Segovia, Marta; Ibarz, Mercedes; Llopis, María Antonia; Bauça, Josep Miquel; Marzana, Itziar; Barba, Nuria; Ventura, Monserrat; García Del Pino, Isabel; Puente, Juan José; Caballero, Andrea; Gómez, Carolina; García Álvarez, Ana; Alsina, María Jesús; Álvarez, Virtudes

2018-05-05

The stability limit of an analyte in a biological sample can be defined as the time required until a measured property acquires a bias higher than a defined specification. Many studies assessing stability and presenting recommendations of stability limits are available, but differences among them are frequent. The aim of this study was to classify and to grade a set of bibliographic studies on the stability of five common blood measurands and subsequently generate a consensus stability function. First, a bibliographic search was made for stability studies for five analytes in blood: alanine aminotransferase (ALT), glucose, phosphorus, potassium and prostate specific antigen (PSA). The quality of every study was evaluated using an in-house grading tool. Second, the different conditions of stability were uniformly defined and the percent deviation (PD%) over time for each analyte and condition were scattered while unifying studies with similar conditions. From the 37 articles considered as valid, up to 130 experiments were evaluated and 629 PD% data were included (106 for ALT, 180 for glucose, 113 for phosphorus, 145 for potassium and 85 for PSA). Consensus stability equations were established for glucose, potassium, phosphorus and PSA, but not for ALT. Time is the main variable affecting stability in medical laboratory samples. Bibliographic studies differ in recommedations of stability limits mainly because of different specifications for maximum allowable error. Definition of a consensus stability function in specific conditions can help laboratories define stability limits using their own quality specifications.

Validation of a stability-indicating hydrophilic interaction liquid chromatographic method for the quantitative determination of vitamin k3 (menadione sodium bisulfite) in injectable solution formulation.

PubMed

Ghanem, Mashhour M; Abu-Lafi, Saleh A; Hallak, Hussein O

2013-01-01

A simple, specific, accurate, and stability-indicating method was developed and validated for the quantitative determination of menadione sodium bisulfite in the injectable solution formulation. The method is based on zwitterionic hydrophilic interaction liquid chromatography (ZIC-HILIC) coupled with a photodiode array detector. The desired separation was achieved on the ZIC-HILIC column (250 mm × 4.6 mm, 5 μm) at 25°C temperature. The optimized mobile phase consisted of an isocratic solvent mixture of 200mM ammonium acetate (NH4AC) solution and acetonitrile (ACN) (20:80; v/v) pH-adjusted to 5.7 by glacial acetic acid. The mobile phase was fixed at 0.5 ml/min and the analytes were monitored at 261 nm using a photodiode array detector. The effects of the chromatographic conditions on the peak retention, peak USP tailing factor, and column efficiency were systematically optimized. Forced degradation experiments were carried out by exposing menadione sodium bisulfite standard and the injectable solution formulation to thermal, photolytic, oxidative, and acid-base hydrolytic stress conditions. The degradation products were well-resolved from the main peak and the excipients, thus proving that the method is a reliable, stability-indicating tool. The method was validated as per ICH and USP guidelines (USP34/NF29) and found to be adequate for the routine quantitative estimation of menadione sodium bisulfite in commercially available menadione sodium bisulfite injectable solution dosage forms.

Study of thermal stability and degradation of fire resistant candidate polymers for aircraft interiors

NASA Technical Reports Server (NTRS)

Hsu, M. T. S.

1976-01-01

The thermochemistry of bismaleimide resins and phenolphthalein polycarbonate was studied. Both materials are fire-resistant polymers and may be suitable for aircraft interiors. The chemical composition of the polymers has been determined by nuclear magnetic resonance and infrared spectroscopy and by elemental analysis. Thermal properties of these polymers have been characterized by thermogravimetric analyses. Qualitative evaluation of the volatile products formed in pyrolysis under oxidative and non-oxidative conditions has been made using infrared spectrometry. The residues after pyrolysis were analyzed by elemental analysis. The thermal stability of composite panel and thermoplastic materials for aircraft interiors was studied by thermogravimetric analyses.

A comprehensive model to determine the effects of temperature and species fluctuations on reaction rates in turbulent reaction flows

NASA Technical Reports Server (NTRS)

Magnotti, F.; Diskin, G.; Matulaitis, J.; Chinitz, W.

1984-01-01

The use of silane (SiH4) as an effective ignitor and flame stabilizing pilot fuel is well documented. A reliable chemical kinetic mechanism for prediction of its behavior at the conditions encountered in the combustor of a SCRAMJET engine was calculated. The effects of hydrogen addition on hydrocarbon ignition and flame stabilization as a means for reduction of lengthy ignition delays and reaction times were studied. The ranges of applicability of chemical kinetic models of hydrogen-air combustors were also investigated. The CHARNAL computer code was applied to the turbulent reaction rate modeling.

Development of postural control and maturation of sensory systems in children of different ages a cross-sectional study.

PubMed

Sá, Cristina Dos Santos Cardoso de; Boffino, Catarina Costa; Ramos, Renato Teodoro; Tanaka, Clarice

To evaluate the stability, postural adjustments and contributions of sensory information for postural control in children. 40 boys and 40 girls were equally divided into groups of 5, 7, 9 and 12 years (G5, G7, G9 and G12). All children were submitted to dynamic posturography using a modified sensory organization test, using four sensory conditions: combining stable or sway referencing platform with eyes opened, or closed. The area and displacements of the center of pressure were used to determine stability, while the adjustments were used to measure the speed of the center of pressure displacements. These measurements were compared between groups and test conditions. Stability tends to increase with age and to decrease with sensory manipulation with significant differences between G5 and G7 in different measures. G7 differed from G12 under the conditions of stable and sway platform with eyes open. G9 did not differ from G12. Similar behavior was observed for adjustments, especially in anterior-posterior directions. Postural stability and adjustments were associated with age and were influenced by sensory manipulation. The ability to perform anterior-posterior adjustments was more evident and sensory maturation occurred firstly on the visual system, then proprioceptive system, and finally, the vestibular system, reaching functional maturity at nine years of age. Seven-year-olds seem to go through a period of differentiated singularity in postural control. Copyright © 2017 Associação Brasileira de Pesquisa e Pós-Graduação em Fisioterapia. Publicado por Elsevier Editora Ltda. All rights reserved.

Power Output Stability Research for Harvesting Automobile Exhaust Energy with Heat Capacity Material as Intermediate Medium

NASA Astrophysics Data System (ADS)

Xiao, Longjie; He, Tianming; Mei, Binyu; Wang, Yiping; Wang, Zongsong; Tan, Gangfeng

2018-01-01

Automobile exhaust energy thermoelectric utilization can promote energy-saving and emission-reduction. Unexpected urban traffic conditions lead to the hot-end temperature instability of the exhaust pipe-mounted thermoelectric generator (TEG), and influence the TEG power generation efficiency. The heat conduction oil circulation located at the hot-end could smooth the temperature fluctuation, at the expense of larger system size and additional energy supply. This research improves the TEG hot-end temperature stability by installing solid heat capacity material (SHCM) to the area between the outer wall of the exhaust pipe and the TEG, which has the merits of simple structure, light weight and no additional energy consumption. The exhaust temperature and flow rate characteristics with various driving conditions are firstly studied for the target engine. Then the convective heat transfer models of SHCM's hot-end and thermoelectric material's cold-end are established. Meanwhile, SHCM thermal properties' effects on the amplitude and response speed of the TEG hot-end temperature are studied. The candidate SHCM with the characteristics of low thermal resistance and high heat capacity is determined. And the heat transfer model going through from TEG's hot-end to the cold-end is established. The results show that the SHCM significantly improves the TEG hot-end temperature stability but slightly reduces the average power output. When the engine working conditions change a lot, the SHCM's improvement on the TEG hot-end temperature stability is more significant, but the reduction of the average power output becomes more remarkable.

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

Sanders, L.K.; Xian, W.; Guaqueta, C.

The aim for deterministic control of the interactions between macroions in aqueous media has motivated widespread experimental and theoretical work. Although it has been well established that like-charged macromolecules can aggregate under the influence of oppositely charged condensing agents, the specific conditions for the stability of such aggregates can only be determined empirically. We examine these conditions, which involve an interplay of electrostatic and osmotic effects, by using a well defined model system composed of F-actin, an anionic rod-like polyelectrolyte, and lysozyme, a cationic globular protein with a charge that can be genetically modified. The structure and stability of actin-lysozymemore » complexes for different lysozyme charge mutants and salt concentrations are examined by using synchrotron x-ray scattering and molecular dynamics simulations. We provide evidence that supports a structural transition from columnar arrangements of F-actin held together by arrays of lysozyme at the threefold interstitial sites of the actin sublattice to marginally stable complexes in which lysozyme resides at twofold bridging sites between actin. The reduced stability arises from strongly reduced partitioning of salt between the complex and the surrounding solution. Changes in the stability of actin-lysozyme complexes are of biomedical interest because their formation has been reported to contribute to the persistence of airway infections in cystic fibrosis by sequestering antimicrobials such as lysozyme. We present x-ray microscopy results that argue for the existence of actin-lysozyme complexes in cystic fibrosis sputum and demonstrate that, for a wide range of salt conditions, charge-reduced lysozyme is not sequestered in ordered complexes while retaining its bacterial killing activity.« less

Power Output Stability Research for Harvesting Automobile Exhaust Energy with Heat Capacity Material as Intermediate Medium

NASA Astrophysics Data System (ADS)

Xiao, Longjie; He, Tianming; Mei, Binyu; Wang, Yiping; Wang, Zongsong; Tan, Gangfeng

2018-06-01

Automobile exhaust energy thermoelectric utilization can promote energy-saving and emission-reduction. Unexpected urban traffic conditions lead to the hot-end temperature instability of the exhaust pipe-mounted thermoelectric generator (TEG), and influence the TEG power generation efficiency. The heat conduction oil circulation located at the hot-end could smooth the temperature fluctuation, at the expense of larger system size and additional energy supply. This research improves the TEG hot-end temperature stability by installing solid heat capacity material (SHCM) to the area between the outer wall of the exhaust pipe and the TEG, which has the merits of simple structure, light weight and no additional energy consumption. The exhaust temperature and flow rate characteristics with various driving conditions are firstly studied for the target engine. Then the convective heat transfer models of SHCM's hot-end and thermoelectric material's cold-end are established. Meanwhile, SHCM thermal properties' effects on the amplitude and response speed of the TEG hot-end temperature are studied. The candidate SHCM with the characteristics of low thermal resistance and high heat capacity is determined. And the heat transfer model going through from TEG's hot-end to the cold-end is established. The results show that the SHCM significantly improves the TEG hot-end temperature stability but slightly reduces the average power output. When the engine working conditions change a lot, the SHCM's improvement on the TEG hot-end temperature stability is more significant, but the reduction of the average power output becomes more remarkable.

Substituent effects and pH profiles for stability constants of arylboronic acid diol esters.

PubMed

Martínez-Aguirre, Mayte A; Villamil-Ramos, Raul; Guerrero-Alvarez, Jorge A; Yatsimirsky, Anatoly K

2013-05-17

Stability constants of boronic acid diol esters in aqueous solution have been determined potentiometrically for a series of meta-, para-substituted phenylboronic acids and diols of variable acidity. The constants β(11-1) for reactions between neutral forms of reactants producing the anionic ester plus proton follow the Hammett equation with ρ depending on pKa of diol and varying from 2.0 for glucose to 1.29 for 4-nitrocatechol. Observed stability constants (K(obs)) measured by UV-vis and fluorometric titrations at variable pH for esters of 4,5-dihydroxy-1,3-benzenedisulfonate (Tiron) generally agree with those expected on the basis of β(11-1) values, but the direct fitting of K(obs) vs pH profiles gives shifted pKa values both for boronic acids and diol as a result of significant interdependence of fitting parameters. The subsituent effects on absorption and fluorescence spectra of Tiron arylboronate esters are characterized. The K(obs) for Tiron determined by (11)B NMR titrations are approximately 1 order of magnitude smaller than those determined by UV-vis titrations under identical conditions. A general equation, which makes possible an estimate of β(11-1) for any pair of boronic acid and diol from their pKa values, is proposed on the basis of established Brönsted-type correlation of Hammett parameters for β(11-1) with acidity of diols. The equation allows one to calculate stability constants expected only on basis of acid-base properties of the components, thus permitting more strict evaluation of contributions of additional factors such as steric or charge effects to the ester stability.

The effect of simulated acid rain on the stabilization of cadmium in contaminated agricultural soils treated with stabilizing agents.

PubMed

Zhu, Hao; Wu, Chunfa; Wang, Jun; Zhang, Xumei

2018-04-16

Stabilization technology is one of widely used remediation technologies for cadmium (Cd)-contaminated agricultural soils, but stabilized Cd in soil may be activated again when external conditions such as acid rain occurred. Therefore, it is necessary to study the effect of acid rain on the performance of different stabilizing agents on Cd-polluted agriculture soils. In this study, Cd-contaminated soils were treated with mono-calcium phosphate (MCP), mono-ammonium phosphate (MAP), and artificial zeolite (AZ) respectively and incubated 3 months. These treatments were followed by two types of simulated acid rain (sulfuric acid rain and mixed acid rain) with three levels of acidity (pH = 3.0, 4.0, and 5.6). The chemical forms of Cd in the soils were determined by Tessier's sequential extraction procedure, and the leaching toxicities of Cd in the soils were assessed by toxicity characteristic leaching procedure (TCLP). The results show that the three stabilizing agents could decrease the mobility of Cd in soil to some degree with or without simulated acid rain (SAR) treatment. The stabilization performances followed the order of AZ < MAP < MCP. Acid rain soaking promoted the activation of Cd in stabilized soil, and both anion composition and pH of acid rain were two important factors that influenced the stabilization effect of Cd.

Geobiochemistry: Placing Biochemistry in Its Geochemical Context

NASA Astrophysics Data System (ADS)

Shock, E.; Boyer, G. M.; Canovas, P. A., III; Prasad, A.; Dick, J. M.

2014-12-01

Goals of geobiochemistry include simultaneously evaluating the relative stabilities of microbial cells and minerals, and predicting how the composition of biomolecules can change in response to the progress of geochemical reactions. Recent developments in theoretical geochemistry make it possible to predict standard thermodynamic properties of proteins, nucleotides, lipids, and many metabolites including the constituents of the citric acid cycle, at all temperatures and pressures where life is known to occur, and beyond. Combining these predictions with constraints from geochemical data makes it possible to assess the relative stabilities of biomolecules. Resulting independent predictions of the environmental occurrence of homologous proteins and lipid side-chains can be compared with observations from metagenomic and metalipidomic data to quantify geochemical driving forces that shape the composition of biomolecules. In addition, the energetic costs of generating biomolecules from within a diverse range of habitable environments can be evaluated in terms of prevailing geochemical variables. Comparisons of geochemical bioenergetic calculations across habitats leads to the generalization that the availability of H2 determines the cost of autotrophic biosynthesis relative to the aquatic environment external to microbial cells, and that pH, temperature, pressure, and availability of C, N, P, and S are typically secondary. Increasingly reduced conditions, which are determined by reactions of water with mineral surfaces and mineral assemblages, allow many biosynthetic reactions to shift from costing energy to releasing energy. Protein and lipid synthesis, as well as the reverse citric acid cycle, become energy-releasing processes under these conditions. The resulting energy balances that determine habitability contrast dramatically with assumptions derived from oxic surface conditions, such as those where human biochemistry operates.

Effect of the presence of cationic polyacrylamide on the surface properties of aqueous alumina suspension-stability mechanism

NASA Astrophysics Data System (ADS)

Wiśniewska, Małgorzata; Chibowski, Stanisław; Urban, Teresa

2014-11-01

The effects of solution pH and the content of cationic groups in polyacrylamide (PAM) macromolecules on the stability mechanism of aqueous alumina suspension were investigated. The following experimental techniques were applied: spectrophotometry, potentiometric titration, microelectrophoresis, viscosimetry and turbidimetry. They enable determination of polymer adsorbed amount, surface charge density and zeta potential of solid particles in the presence and absence of PAM, as well as thickness of polymer adsorption layer, size of macromolecules in the solution and stability of the Al2O3-polymer systems, respectively. The obtained results indicate that adsorption of PAM increases with the increasing pH, whereas the thickness of polymeric adsorption layer decreases. Additionally, the greater the number of cationic groups in the PAM chains is, the higher adsorption was found. The polymer presence influences on the alumina suspension stability. At pH 3 and 6 the slight deterioration of stability conditions of solid particle covered with polyacrylamide was observed. At pH 9 the systems containing polymer are unstable, similarly to the suspension without PAM, but the mechanism of their destabilization is different.

Nanobubbles in confined solution: Generation, contact angle, and stability.

PubMed

Wei, Jiachen; Zhang, Xianren; Song, Fan; Shao, Yingfeng

2018-02-14

The formation of gas bubbles presents a frequent challenge to microfluidic operations, for which fluids are geometrically confined to a microscale space. Here, to understand the mechanism of nucleating gas bubbles in microfluidic devices, we investigate the formation and stability of nanobubbles in confined solutions. Our molecular dynamics simulations show that while pinning of the contact line is a prerequisite for the stability of surface nanobubbles in open systems that can exchange gas with surrounding environment, in confined solutions, stable nanobubbles can exist even without pinning. In supersaturated condition, stable bubbles can be found in confined solutions with acute or obtuse contact angle, depending on the substrate hydrophobicity. We also demonstrate that when open to the bulk solution, the stable nanobubbles in closed systems would become unstable unless both supersaturation and pinning of the contact line are satisfied. Our results not only shed light on the design of novel heterogeneous surfaces for generating nanobubbles in confined space with controllable shape and stability but also address the crucial effect of gas exchange with the surroundings in determining the stability of nanobubbles.

Nanobubbles in confined solution: Generation, contact angle, and stability

NASA Astrophysics Data System (ADS)

Wei, Jiachen; Zhang, Xianren; Song, Fan; Shao, Yingfeng

2018-02-01

The formation of gas bubbles presents a frequent challenge to microfluidic operations, for which fluids are geometrically confined to a microscale space. Here, to understand the mechanism of nucleating gas bubbles in microfluidic devices, we investigate the formation and stability of nanobubbles in confined solutions. Our molecular dynamics simulations show that while pinning of the contact line is a prerequisite for the stability of surface nanobubbles in open systems that can exchange gas with surrounding environment, in confined solutions, stable nanobubbles can exist even without pinning. In supersaturated condition, stable bubbles can be found in confined solutions with acute or obtuse contact angle, depending on the substrate hydrophobicity. We also demonstrate that when open to the bulk solution, the stable nanobubbles in closed systems would become unstable unless both supersaturation and pinning of the contact line are satisfied. Our results not only shed light on the design of novel heterogeneous surfaces for generating nanobubbles in confined space with controllable shape and stability but also address the crucial effect of gas exchange with the surroundings in determining the stability of nanobubbles.

Boosting antibody developability through rational sequence optimization.

PubMed

Seeliger, Daniel; Schulz, Patrick; Litzenburger, Tobias; Spitz, Julia; Hoerer, Stefan; Blech, Michaela; Enenkel, Barbara; Studts, Joey M; Garidel, Patrick; Karow, Anne R

2015-01-01

The application of monoclonal antibodies as commercial therapeutics poses substantial demands on stability and properties of an antibody. Therapeutic molecules that exhibit favorable properties increase the success rate in development. However, it is not yet fully understood how the protein sequences of an antibody translates into favorable in vitro molecule properties. In this work, computational design strategies based on heuristic sequence analysis were used to systematically modify an antibody that exhibited a tendency to precipitation in vitro. The resulting series of closely related antibodies showed improved stability as assessed by biophysical methods and long-term stability experiments. As a notable observation, expression levels also improved in comparison with the wild-type candidate. The methods employed to optimize the protein sequences, as well as the biophysical data used to determine the effect on stability under conditions commonly used in the formulation of therapeutic proteins, are described. Together, the experimental and computational data led to consistent conclusions regarding the effect of the introduced mutations. Our approach exemplifies how computational methods can be used to guide antibody optimization for increased stability.

Effect of Nickel Concentration on Bias Reliability and Thermal Stability of Thin-Film Transistors Fabricated by Ni-Metal-Induced Crystallization

NASA Astrophysics Data System (ADS)

Lai, Ming-Hui; Sermon Wu, YewChung; Huang, Jung-Jie

2012-01-01

Ni-metal-induced crystallization (MIC) of amorphous Si (α-Si) has been employed to fabricate low-temperature polycrystalline silicon (poly-Si) thin-film transistors (TFTs). Although the high leakage current is a major issue in the performance of conventional MIC-TFTs since Ni contamination induces deep-level state traps, it can be greatly improved by using well-known technologies to reduce Ni contamination. However, for active-matrix organic light-emitting diode (AMOLED) display applications, the bias reliability and thermal stability are major concerns especially when devices are operated under a hot carrier condition and in a high-temperature environment. It will be interesting to determine how the bias reliability and thermal stability are affected by the reduction of Ni concentration. In the study, the effect of Ni concentration on bias reliability and thermal stability was investigated. We found that a device exhibited high immunity against hot-carrier stress and elevated temperatures. These findings demonstrated that reducing the Ni concentration in MIC films was also beneficial for bias reliability and thermal stability.

Impact of Basal Conditions on Grounding-Line Retreat

NASA Astrophysics Data System (ADS)

Koellner, S. J.; Parizek, B. R.; Alley, R. B.; Muto, A.; Holschuh, N.; Nowicki, S.

2017-12-01

An often-made assumption included in ice-sheet models used for sea-level projections is that basal rheology is constant throughout the domain of the simulation. The justification in support of this assumption is that physical data for determining basal rheology is limited and a constant basal flow law can adequately approximate current as well as past behavior of an ice-sheet. Prior studies indicate that beneath Thwaites Glacier (TG) there is a ridge-and-valley bedrock structure which likely promotes deformation of soft tills within the troughs and sliding, more akin to creep, over the harder peaks; giving rise to a spatially variable basal flow law. Furthermore, it has been shown that the stability of an outlet glacier varies with the assumed basal rheology, so accurate projections almost certainly need to account for basal conditions. To test the impact of basal conditions on grounding-line evolution forced by ice-shelf perturbations, we modified the PSU 2-D flowline model to enable the inclusion of spatially variable basal rheology along an idealized bedrock profile akin to TG. Synthetic outlet glacier "data" were first generated under steady-state conditions assuming a constant basal flow law and a constant basal friction coefficient field on either a linear or bumpy sloping bed. In following standard procedures, a suite of models were then initialized by assuming different basal rheologies and then determining the basal friction coefficients that produce surface velocities matching those from the synthetic "data". After running each of these to steady state, the standard and full suite of models were forced by drastically reducing ice-shelf buttressing through side-shear and prescribed basal-melting perturbations. In agreement with previous findings, results suggest a more plastic basal flow law enhances stability in response to ice-shelf perturbations by flushing ice from farther upstream to sustain the grounding-zone mass balance required to prolong the current grounding-line position. Mixed rheology beds tend to mimic the retreat of the higher-exponent bed, a behavior enhanced over bumps as the stabilizing ridges tap into ice from local valleys. Thus, accounting for variable basal conditions in ice-sheet model projections is critical for improving both the timing and magnitude of retreat.

Flutter of Darrieus wind turbine blades

NASA Technical Reports Server (NTRS)

Ham, N. D.

1978-01-01

The testing of Darrieus wind turbines has indicated that under certain conditions, serious vibrations of the blades can occur, involving flatwise bending, torsion, and chordwise bending. A theoretical method of predicting the aeroelastic stability of the coupled bending and torsional motion of such blades with a view to determining the cause of these vibrations, and a means of suppressing them was developed.

Evaluation program for secondary spacecraft cells: Cycle life test

NASA Technical Reports Server (NTRS)

Harkness, J. D.

1979-01-01

The service life and storage stability for several storage batteries were determined. The batteries included silver-zinc batteries, nickel-cadmium batteries, and silver-cadmium batteries. The cell performance characteristics and limitations are to be used by spacecraft power systems planners and designers. A statistical analysis of the life cycle prediction and cause of failure versus test conditions is presented.

Development and Validation of highly Sensitive Stability Indicating Spectrofluorimetric Method for Determination of Amlodipine in Pharmaceutical Preparations and Human Plasma.

PubMed

Mohamed, Abdel-Maaboud I; Omar, Mahmoud A; Hammad, Mohamed A; Mohamed, Abobakr A

2016-11-01

A highly sensitive and simple spectrofluorimetric method was developed for the determination of Amlodipine besylate (AML) in its pharmaceutical formulations and spiked human plasma. The proposed method is based on the investigation of the fluorescence spectral behaviour of AML in Tween-80 micellar system. In aqueous solution, the fluorescence intensity of AML was greatly enhanced (160 %) in the presence of Tween-80. The fluorescence intensity was measured at 427 nm after excitation at 385 nm. The fluorescence-concentration plot was rectilinear over the concentration range 0.1-4.0 μg/ml, with lower detection limit of 0.03 μg/ml. The suggested method was successfully applied for the analysis of AML in its commercial tablets alone or in combination with either Atorvastatin or Valsartan. The application of the proposed method was extended to the assay of AML in spiked human plasma and stability studies of AML after exposure to different forced degradation conditions, such as acidic, alkaline, photo- and oxidative conditions, according to ICH guidelines. The results were statistically compared to those obtained by comparison methods and were found to be in good agreement.

Determination of degradation products and process related impurities of asenapine maleate in asenapine sublingual tablets by UPLC

NASA Astrophysics Data System (ADS)

Kumar, Nitin; Sangeetha, D.; Kalyanraman, L.

2017-11-01

For determination of process related impurities and degradation products of asenapine maleate in asenapine sublingual Tablets, a reversed phase, stability indicating UPLC method was developed. Acetonitrile, methanol and potassium dihydrogen phosphate buffer with tetra-n- butyl ammonium hydrogen sulphate as ion pair (pH 2.2; 0.01 M) at flow rate of 0.2 ml/min were used in gradient elution mode. Separation was achieved by using acquity BEH Shield RP18 column (1.7 μm, 2.1 mm×100 mm) at 35 ºC. UV detection was performed at 228 nm. Subsequently the liquid chromatography method was validated as per ICH. The drug product was exposed to the stress conditions of acid hydrolysis, base hydrolysis, water hydrolysis, oxidative, thermal, and photolytic. In oxidative stress and thermal stress significant degradation was observed. All the degradation products were well separated from analyte peak and its impurities. Stability indicating nature of the method was proved by demonstrating the peak purity of Asenapine peak in all the stressed samples. The mass balance was found >95% for all the stress conditions. Based on method validation, the method was found specific, linear, accurate, precise, rugged and robust.

Determining temperature limits of drilling fluids

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

Thuren, J.B.; Chenevert, M.E.; Huang, W.T.W.

A capillary three tube viscometer has been designed which allows the measurement of rheological properties of time dependent non-Newtonian fluids in laminar flow at high temperture and pressure. The objective of this investigation is to determine the temperature stability of clay-water suspensions containing various drilling fluid additives. The additives studied consisted of viscosifiers, filtrate reducers, and chemical thinners. The temperature range studied is from room temperature to 550{sup 0}F. The system pressure is consistently maintained above the vapor pressure. The Bentonite and water standardized base mud used is equivalent to a 25 ppB fluid. Stabilization of the base mud ismore » necessary to obtain steady state laminar flow conditions and to obtain reliable temperature thinning effects with each temperature interval under investigation. Generally the temperature levels are maintained for one hour until 550{sup 0}F is attained. The last interval is then maintained until system fluid degradation occurs. Rheological measurements are obtained from differential pressure transducers located in a three diameter tube test section and externally at ambient conditions from a Baroid Rotational Viscometer. The power law model for non-Newtonian fluids is used to correlate the data.« less

Game Theoretical Analysis on Cooperation Stability and Incentive Effectiveness in Community Networks.

PubMed

Song, Kaida; Wang, Rui; Liu, Yi; Qian, Depei; Zhang, Han; Cai, Jihong

2015-01-01

Community networks, the distinguishing feature of which is membership admittance, appear on P2P networks, social networks, and conventional Web networks. Joining the network costs money, time or network bandwidth, but the individuals get access to special resources owned by the community in return. The prosperity and stability of the community are determined by both the policy of admittance and the attraction of the privileges gained by joining. However, some misbehaving users can get the dedicated resources with some illicit and low-cost approaches, which introduce instability into the community, a phenomenon that will destroy the membership policy. In this paper, we analyze on the stability using game theory on such a phenomenon. We propose a game-theoretical model of stability analysis in community networks and provide conditions for a stable community. We then extend the model to analyze the effectiveness of different incentive policies, which could be used when the community cannot maintain its members in certain situations. Then we verify those models through a simulation. Finally, we discuss several ways to promote community network's stability by adjusting the network's properties and give some proposal on the designs of these types of networks from the points of game theory and stability.

Stability analysis of spacecraft power systems

NASA Technical Reports Server (NTRS)

Halpin, S. M.; Grigsby, L. L.; Sheble, G. B.; Nelms, R. M.

1990-01-01

The problems in applying standard electric utility models, analyses, and algorithms to the study of the stability of spacecraft power conditioning and distribution systems are discussed. Both single-phase and three-phase systems are considered. Of particular concern are the load and generator models that are used in terrestrial power system studies, as well as the standard assumptions of load and topological balance that lead to the use of the positive sequence network. The standard assumptions regarding relative speeds of subsystem dynamic responses that are made in the classical transient stability algorithm, which forms the backbone of utility-based studies, are examined. The applicability of these assumptions to a spacecraft power system stability study is discussed in detail. In addition to the classical indirect method, the applicability of Liapunov's direct methods to the stability determination of spacecraft power systems is discussed. It is pointed out that while the proposed method uses a solution process similar to the classical algorithm, the models used for the sources, loads, and networks are, in general, more accurate. Some preliminary results are given for a linear-graph, state-variable-based modeling approach to the study of the stability of space-based power distribution networks.

Flight Test Results on the Stability and Control of the F-15 Quiet Spike(TradeMark) Aircraft

NASA Technical Reports Server (NTRS)

Moua, Cheng M.; McWherter, Shaun C.; Cox, Timothy H.; Gera, Joe

2012-01-01

The Quiet Spike F-15B flight research program investigated supersonic shock reduction using a 24-ft sub-scale telescoping nose boom on an F-15B airplane. The program primary flight test objective was to collect flight data for aerodynamic and structural models validation up to 1.8 Mach. Other objectives were to validate the mechanical feasibility of a morphing fuselage at the operational conditions and determine the near-field shock wave characterization. The stability and controls objectives were to assess the effect of the spike on the stability, controllability, and handling qualities of the aircraft and to ensure adequate stability margins across the entire research flight envelop. The two main stability and controls issues were the effects of the telescoping nose boom influenced aerodynamics on the F-15B aircraft flight dynamics and air data and angle of attack sensors. This paper reports on the stability and controls flight envelope clearance methods and flight test analysis of the F-15B Quiet Spike. Brief pilot commentary on typical piloting tasks, approach and landing, refueling task, and air data sensitivity to the flight control system are also discussed in this report.

Experimental Investigation of Diffuser Pressure-ratio Control with Shock-positioning Limit on 28-inch Ram-jet Engine

NASA Technical Reports Server (NTRS)

Dunbar, William R; Wentworth, Carl B; Crowl, Robert J

1957-01-01

The performance of a control system designed for variable thrust applications was determined in an altitude free-jet facility at various Mach numbers, altitudes and angles of attack for a wide range of engine operation. The results are presented as transient response characteristics for step disturbances in fuel flow and stability characteristics as a function of control constants and engine operating conditions. The results indicate that the control is capable of successful operation over the range of conditions tested, although variations in engine gains preclude optimum response characteristics at all conditions with fixed control constants.

Hover test of a full-scale hingeless helicopter rotor: Aeroelastic stability, performance and loads data. [wind tunnel tests

NASA Technical Reports Server (NTRS)

Peterson, R. L.; Warmbrodt, W.

1984-01-01

A hover test of a full-scale, hingeless rotor system was conducted in the NASA Ames 40- by 80-foot wind tunnel. The rotor was tested on the Ames rotor test apparatus. Rotor aeroelastic stability, performance, and loads at various rotational speeds and thrust coefficients were investigated. The primary objective was to determine the inplane stability characteristics of the rotor system. Rotor inplane damping data were obtained for operation between 350 and 425 rpm (design speed), and for thurst coefficients between 0.0 and 0.12. The rotor was stable for all conditions tested. At constant rotor rotational speed, a minimum inplane dampling level was obtained at a thrust coefficient approximately = 0.02. At constant rotor lift, a minimum in rotor inplane damping was measured at 400 rpm.

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.

Dynamics of morphological evolution in experimental Escherichia coli populations.

PubMed

Cui, F; Yuan, B

2016-08-30

Here, we applied a two-stage clonal expansion model of morphological (cell-size) evolution to a long-term evolution experiment with Escherichia coli. Using this model, we derived the incidence function of the appearance of cell-size stability, the waiting time until this morphological stability, and the conditional and unconditional probabilities of morphological stability. After assessing the parameter values, we verified that the calculated waiting time was consistent with the experimental results, demonstrating the effectiveness of the two-stage model. According to the relative contributions of parameters to the incidence function and the waiting time, cell-size evolution is largely determined by the promotion rate, i.e., the clonal expansion rate of selectively advantageous organisms. This rate plays a prominent role in the evolution of cell size in experimental populations, whereas all other evolutionary forces were found to be less influential.

Transformations of C2-C4 alcohols on the surface of a copper catalyst

NASA Astrophysics Data System (ADS)

Magaeva, A. A.; Lyamina, G. V.; Sudakova, N. N.; Shilyaeva, L. P.; Vodyankina, O. V.

2007-10-01

The interaction of monoatomic alcohols C2-C4 with the surface of a copper catalyst preliminarily oxidized under various conditions was studied by the temperature-programmed reaction method to determine the detailed mechanism of partial oxidation. The conditions of oxygen preadsorption on the surface of copper for the preparation of the desired products were determined. The selective formation of carbonyl compounds was shown to occur at the boundary between reduced and oxidized copper surface regions. The role played by Cu2O was the deep oxidation of alcohols to CO2. Alcohols with branched hydrocarbon structures experienced parallel partial oxidation and dehydrogenation, which was related to the high stability of intermediate keto-type compounds.

Further Results on Finite-Time Partial Stability and Stabilization. Applications to Nonlinear Control Systems

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

Jammazi, Chaker

2009-03-05

The paper gives Lyapunov type sufficient conditions for partial finite-time and asymptotic stability in which some state variables converge to zero while the rest converge to constant values that possibly depend on the initial conditions. The paper then presents partially asymptotically stabilizing controllers for many nonlinear control systems for which continuous asymptotically stabilizing (in the usual sense) controllers are known not to exist.

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

Taketomo, C.K.; Chu, S.A.; Cheng, M.H.

The stability of captopril in powder papers under three different storage conditions was determined. Captopril 12.5-mg tablets were triturated with lactose to a final concentration of 2 mg of captopril in 100 mg of powder. A total of 240 powder papers were prepared and stored in class A prescription vials (80 papers), 002G plastic zip-lock bags (80 papers), and Moisture Proof Barrier Bags (80 papers). Immediately after preparation and at 1, 2, 3, 4, 8, 12, and 24 weeks of storage at room temperature, powder papers under each storage condition were reweighed and the contents were assayed for captopril concentrationmore » by a stability-indicating high-performance liquid chromatographic method. More than 90% of the initial captopril concentration was retained under all storage conditions during the first 12 weeks of the study. Captopril disulfide, a degradation product, was detected in one sample stored in a plastic zip-lock bag at 24 weeks. Captopril was stable for the entire 24-week period in powder papers stored in either the class A prescription vial or the Moisture Proof Barrier Bag. Captopril in powder papers is stable for at least 12 weeks when stored at room temperature under all three storage conditions.« less

Minimalist, standard and no footwear on static and dynamic postural stability following jump landing.

PubMed

Zech, Astrid; Argubi-Wollesen, Andreas; Rahlf, Anna-Lina

2015-01-01

In recreational sports, uncushioned, light-weight and minimalist shoes are increasingly used to imitate barefoot situations. Uncertainty exists whether these shoes provide sufficient stability during challenging movements. In this randomised crossover study, 35 healthy distance runners performed jump landing stabilisation and single-leg stance tests on a force plate, using four conditions in random order: barefoot, uncushioned minimalist shoes, cushioned ultraflexible shoes and standard running shoes. Ground reaction force (GRF) and centre of pressure (COP) data were used to determine unilateral jump landing stabilisation time and COP sway velocity during single-leg stance. Repeated measures analysis of variance revealed significant footwear interactions for medial-lateral (p < 0.001) and anterior-posterior COP sway velocity during standing (p < 0.001). The barefoot condition produced significantly greater postural sway velocities (p < 0.001) compared to all footwear conditions. No significant effects were found for jump landing stabilisation time. In conclusion, the results of this study indicate that increased shoe flexibility and reduced sole support have no, or only minor influence on static and dynamic postural control, and therefore, may not increase the risk of traumatic events during sports activities. However, barefoot conditions should be considered carefully when adequate postural control is needed.

Gallic Acid Grafted Chitosan Has Enhanced Oxidative Stability in Bulk Oils.

PubMed

Gim, Seo Yeong; Hong, Seungmi; Kim, Mi-Ja; Lee, JaeHwan

2017-07-01

Gallic acid (GA) was grafted in chitosan and the effects of GA grafted chitosan (GA-g-CS) on the oxidative stability in bulk oil was tested at 60 and 140 °C. To text oxidative stability in oils, headspace oxygen content, conjugated dienoic acid (CDA) value, p-anisidine value (p-AV), and acid value were determined. Chitosan itself did not show antioxidative or prooxidative effects in oils at 60 °C. However, GA-g-CS and GA acted as antioxidants at 60 °C. At 140 °C heating with moisture supplied condition, different results were observed. GA-g-CS acted as antioxidants based on the results of CDA and p-AV. However, chitosan showed the highest oxidative stability based on results of acid value and brown color formation at 140 °C. This could be due to reduction of moisture content by chitosan. GA was continuously released from GA-g-CS in bulk oil. This might have provided extra antioxidant activities to oils. © 2017 Institute of Food Technologists®.

Stability of vertical magnetic chains

PubMed Central

2017-01-01

A linear stability analysis is performed for a pair of coaxial vertical chains made from permanently magnetized balls under the influence of gravity. While one chain rises from the ground, the other hangs from above, with the remaining ends separated by a gap of prescribed length. Various boundary conditions are considered, as are situations in which the magnetic dipole moments in the two chains are parallel or antiparallel. The case of a single chain attached to the ground is also discussed. The stability of the system is examined with respect to three quantities: the number of balls in each chain, the length of the gap between the chains, and a single dimensionless parameter which embodies the competition between magnetic and gravitational forces. Asymptotic scaling laws involving these parameters are provided. The Hessian matrix is computed in exact form, allowing the critical parameter values at which the system loses stability and the respective eigenmodes to be determined up to machine precision. A comparison with simple experiments for a single chain attached to the ground shows good agreement. PMID:28293135

Stability of vertical magnetic chains

NASA Astrophysics Data System (ADS)

Schönke, Johannes; Fried, Eliot

2017-02-01

A linear stability analysis is performed for a pair of coaxial vertical chains made from permanently magnetized balls under the influence of gravity. While one chain rises from the ground, the other hangs from above, with the remaining ends separated by a gap of prescribed length. Various boundary conditions are considered, as are situations in which the magnetic dipole moments in the two chains are parallel or antiparallel. The case of a single chain attached to the ground is also discussed. The stability of the system is examined with respect to three quantities: the number of balls in each chain, the length of the gap between the chains, and a single dimensionless parameter which embodies the competition between magnetic and gravitational forces. Asymptotic scaling laws involving these parameters are provided. The Hessian matrix is computed in exact form, allowing the critical parameter values at which the system loses stability and the respective eigenmodes to be determined up to machine precision. A comparison with simple experiments for a single chain attached to the ground shows good agreement.

Investigating Strategies to Increase Persistence and Success Rates among Anatomy & Physiology Students: A Case Study at Austin Community College District

NASA Astrophysics Data System (ADS)

Vedartham, Padmaja B.

Snap-through buckling provides an intricate force-displacement relationship for study. With the possibility for multiple limit points and pitchfork bifurcations and large regions of instability, experimental validation of numerical analysis can become difficult. This requires stabilization of unstable static equilibria, for which limited prior research exists. For all but the simplest cases, more than one actuator is needed, increasing the complexity of the experiment to the point of intractability without a control system. In this thesis, the necessary conditions for stabilization of a buckled beam with pinned boundaries under transverse loading were determined. By combining various nonlinear solution methods, a control system was created that could stabilize any branch of the force-displacement response. Experimental traversal of an unstable branch are presented along with other unstable static equilibrium configurations. The control system had numerical limitations, losing convergence near singular points. The groundwork for experimental stabilization was validated and demonstrated.

Potential phosphorus eutrophication mitigation strategy: Biochar carbon composition, thermal stability and pH influence phosphorus sorption.

PubMed

Ngatia, L W; Hsieh, Y P; Nemours, D; Fu, R; Taylor, R W

2017-08-01

Phosphorus (P) eutrophication is a major pollution problem globally, with unprecedented amount of P emanating from agricultural sources. But little is known about the optimization of soil-biochar P sorption capacity. The study objective was to determine how biochar feedstocks and pyrolysis conditions influences carbon (C) thermal stability, C composition and pH and in turn influence the phosphorus sorption optimization. Biochar was produced from switchgrass, kudzu and Chinese tallow at 200, 300, 400, 500, 550, 650,750 °C. Carbon thermal stability was determined by multi-element scanning thermal analysis (MESTA), C composition was determined using solid state 13 C NMR. Phosphorus sorption was determined using a mixture of 10% biochar and 90% sandy soil after incubation. Results indicate increased P sorption (P < 0.0001) and decreased P availability (P < 0.0001) with increasing biochar pyrolysis temperature. However, optimum P sorption was feedstock specific with switchgrass indicating P desorption between 200 and 550 °C. Phosphorus sorption was in the order of kudzu > switchgrass > Chinese tallow. Total C, C thermal stability, aromatic C and alkalinity increased with elevated pyrolysis temperature. Biochar alkalinity favored P sorption. There was a positive relationship between high thermal stable C and P sorption for Kudzu (r = 0.62; P = 0.0346) and Chinese tallow (r = 0.73; P = 0.0138). In conclusion, biochar has potential for P eutrophication mitigation, however, optimum biochar pyrolysis temperature for P sorption is feedstock specific and in some cases might be out of 300-500 °C temperature range commonly used for agronomic application. High thermal stable C dominated by aromatic C and alkaline pH seem to favor P sorption. Copyright © 2017 Elsevier Ltd. All rights reserved.

Totally S-protected hyaluronic acid: Evaluation of stability and mucoadhesive properties as liquid dosage form.

PubMed

Pereira de Sousa, Irene; Suchaoin, Wongsakorn; Zupančič, Ožbej; Leichner, Christina; Bernkop-Schnürch, Andreas

2016-11-05

It is the aim of this study to synthesize hyaluronic acid (HA) derivatives bearing mucoadhesive properties and showing prolonged stability at pH 7.4 and under oxidative condition as liquid dosage form. HA was modified by thiolation with l-cysteine (HA-SH) and by conjugation with 2-mercaptonicotinic acid-l-cysteine ligand to obtain an S-protected derivative (HA-MNA). The polymers were characterized by determination of thiol group content and mercaptonicotinic acid content. Cytotoxicity, stability and mucoadhesive properties (rheological evaluation and tensile test) of the polymers were evaluated. HA-SH and HA-MNA could be successfully synthesized with a degree of modification of 5% and 9% of the total moles of carboxylic acid groups, respectively. MTT assay revealed no toxicity for the polymers. HA-SH resulted to be unstable both at pH 7.4 and under oxidative conditions, whereas HA-MNA was stable under both conditions. Rheological assessment showed a 52-fold and a 3-fold increase in viscosity for HA-MNA incubated with mucus compared to unmodified HA and HA-SH, respectively. Tensile evaluation carried out with intestinal and conjunctival mucosa confirmed the higher mucoadhesive properties of HA-MNA compared to HA-SH. According to the presented results, HA-MNA appears to be a potent excipient for the formulation of stable liquid dosage forms showing comparatively high mucodhesive properties. Copyright © 2016 Elsevier Ltd. All rights reserved.

Surface complexation modeling of proton and Cd adsorption onto an algal cell wall.

PubMed

Kaulbach, Emily S; Szymanowski, Jennifer E S; Fein, Jeremy B

2005-06-01

This study quantifies Cd adsorption onto the cell wall of the algal species Pseudokirchneriella subcapitata by applying a surface complexation approach to model the observed adsorption behavior. We use potentiometric titrations to determine deprotonation constants and site concentrations for the functional groups on the algal cell wall. Adsorption and desorption kinetics experiments illustrate that adsorption of Cd onto the cell wall is rapid and reversible, except under low pH conditions. Adsorption experiments conducted as a function of pH and total Cd concentration yield the stoichiometry and site-specific stability constants for the important Cd-algal surface complexes. We model the acid/base properties of the algal cell wall by invoking four discrete surface functional group types, with pKa values of 3.9 +/- 0.3, 5.4 +/- 0.1, 7.6 +/- 0.3, and 9.6 +/- 0.4. The results of the Cd adsorption experiments indicate that the first, third, and fourth sites contribute to Cd adsorption under the experimental conditions, with calculated log stability constant values of 4.1 +/- 0.5, 5.4 +/- 0.5, and 6.1 +/- 0.4, respectively. Our results suggest that the stabilities of the Cd-surface complexes are high enough for algal adsorption to affect the fate and transport of Cd under some conditions and that on a per gram basis, algae and bacteria exhibit broadly similar extents of Cd adsorption.

Stability Study on Steel Structural Columns with Initial Blast Damage under High Temperatures

NASA Astrophysics Data System (ADS)

Baoxin, Qi; Yan, Shi; Li, Peng

2018-03-01

Blast may bring light-weight steel columns with initial damages, resulting in lowering its critical fire-resistance temperature whose reduced amplitude is relevant to the form and degree of the damages. Finite element analysis software ANSYS was used in the paper to analyze the issue of the fire-resistance temperature of the column with the blast damages, and the coupling method for heat and structure was applied during the simulation. The emphasis was laid on parametric factors of axial compression ratio, the form and the degree of the initial damages, as well as the confined condition at the ends of the columns. The numerical results showed that the fire-resistance temperature will lower as increasing of the axial compression ratio, the form and the degree of the initial damages and it will be also affected by the restraint conditions at the ends of the columns. The critical stress formula with initial bending damage under elevated temperature was set up under flexural small deformation condition, then the stability coefficient was determined and the method for evaluating the limit temperature of the column was put forward. The theoretical result was also compared with that of the finite element method (FEM). The results both showed that the stability capacity for the damaged columns was dramatically reduced as increasing the temperature and the initial damage level.

An empirically based steady state friction law and implications for fault stability

PubMed Central

Nielsen, S.; Violay, M.; Di Toro, G.

2016-01-01

Abstract Empirically based rate‐and‐state friction laws (RSFLs) have been proposed to model the dependence of friction forces with slip and time. The relevance of the RSFL for earthquake mechanics is that few constitutive parameters define critical conditions for fault stability (i.e., critical stiffness and frictional fault behavior). However, the RSFLs were determined from experiments conducted at subseismic slip rates (V < 1 cm/s), and their extrapolation to earthquake deformation conditions (V > 0.1 m/s) remains questionable on the basis of the experimental evidence of (1) large dynamic weakening and (2) activation of particular fault lubrication processes at seismic slip rates. Here we propose a modified RSFL (MFL) based on the review of a large published and unpublished data set of rock friction experiments performed with different testing machines. The MFL, valid at steady state conditions from subseismic to seismic slip rates (0.1 µm/s < V < 3 m/s), describes the initiation of a substantial velocity weakening in the 1–20 cm/s range resulting in a critical stiffness increase that creates a peak of potential instability in that velocity regime. The MFL leads to a new definition of fault frictional stability with implications for slip event styles and relevance for models of seismic rupture nucleation, propagation, and arrest. PMID:27667875

A novel analytical method for pharmaceutical polymorphs by terahertz spectroscopy and the optimization of crystal form at the discovery stage.

PubMed

Ikeda, Yukihiro; Ishihara, Yoko; Moriwaki, Toshiya; Kato, Eiji; Terada, Katsuhide

2010-01-01

A novel analytical method for the determination of pharmaceutical polymorphs was developed using terahertz spectroscopy. It was found out that each polymorph of a substance showed a specific terahertz absorption spectrum. In particular, analysis of the second derivative spectrum was enormously beneficial in the discrimination of closely related polymorphs that were difficult to discern by powder X-ray diffractometry. Crystal forms that were obtained by crystallization from various solvents and stored under various conditions were specifically characterized by the second derivative of each terahertz spectrum. Fractional polymorphic transformation for substances stored under stressed conditions was also identified by terahertz spectroscopy during solid-state stability test, but could not be detected by powder X-ray diffractometry. Since polymorphs could be characterized clearly by terahertz spectroscopy, further physicochemical studies could be conducted in a timely manner. The development form of compound examined was determined by the results of comprehensive physicochemical studies that included thermodynamic relationships, as well as chemical and physicochemical stability. In conclusion, terahertz spectroscopy, which has unique power in the elucidation of molecular interaction within a crystal lattice, can play more important role in physicochemical research. Terahertz spectroscopy has a great potential as a tool for polymorphic determination, particularly since the second derivative of the terahertz spectrum possesses high sensitivity for pharmaceutical polymorphs.

Influence of light exposure and oxidative status on the stability of vitamins A and D₃ during the storage of fortified soybean oil.

PubMed

Hemery, Youna M; Fontan, Laura; Moench-Pfanner, Regina; Laillou, Arnaud; Berger, Jacques; Renaud, Cécile; Avallone, Sylvie

2015-10-01

Food fortification is implemented to address vitamins A and D deficiencies in numerous countries. The stability of vitamins A and D3 was assessed during a two-month period reproducing the usual oil storage conditions before sale to consumers. Soybean oils with different oxidative status and vitamin E contents were stored in the dark, semi-dark, or exposed to natural light. Lipid peroxidation took place after 3 weeks of storage in dark conditions. After 2 months, the vitamin A and D3 losses reached 60-68% and 61-68%, respectively, for oils exposed to natural light, and 32-39% and 24-44% in semi-dark conditions. The determining factors of vitamin A and D3 losses were (in decreasing order) the storage time, the exposure to light and the oxidative status of the oil, whereas vitamin E content had a protective role. Improving these parameters is thus essential to make vitamins A and D fortification in oils more efficient. Copyright © 2015. Published by Elsevier Ltd.

Lipid and colour stability of Milano-type sausages: effect of packing conditions.

PubMed

Zanardi, E; Dorigoni, V; Badiani, A; Chizzolini, R

2002-05-01

Lipid and colour oxidative changes in Milano-type fermented sausages were studied in relation to packing conditions and extended storage under fluorescent light. Matured sausages were sliced and packed under vacuum or in protective atmosphere (100% N(2)) and exposed in a display cabinet to mimic commercial conditions of light and temperature for 2 months. Lipid oxidation was measured by the determination of thiobarbituric acid reactive substances (TBARS) and cholesterol oxidation products (COP), whereas the oxidation of nitrosylmyoglobin was evaluated by a trained sensory panel. Lipid oxidation and discolouration were positively related in vacuum-packed sausages: TBARS and COP values increased significantly concurrently with increasing brown scores. Protective atmosphere came out to be more efficient than vacuum in controlling fatty acid oxidation and, to a lesser extent, cholesterol and pigment degradation: TBARS values remained constant during the whole storage period whereas cholesterol oxides and brown colour scores gradually increased but remained lower than those of vacuum-packed sausages. Higher residual oxygen in vacuum packing could be responsible for the observed differences in oxidative stability.

Evolution of the Shape of Detached GeSi Crystals in Microgravity

NASA Technical Reports Server (NTRS)

Volz, M. P.; Mazuruk, K.

2013-01-01

A series of GeSi crystal growth experiments are planned to be conducted in the Low Gradient Furnace (LGF) onboard the International Space Station. An objective of these experiments is to understand the mechanisms of detached Bridgman growth, a process in which a gap exists between the growing semiconductor crystal and the crucible wall. Crystals grown without wall contact have superior quality to otherwise similar crystals grown in direct contact with a container, especially with respect to impurity incorporation, formation of dislocations, and residual stress in crystals. Numerical calculations are used to determine the conditions in which a gap can exist. According to crystal shape stability theory, only some of these gap widths will be dynamically stable. Beginning with a crystal diameter that differs from stable conditions, the transient crystal growth process is analyzed. In microgravity, dynamic stability depends only on capillary effects and is decoupled from heat transfer. Depending on the initial conditions and growth parameters, the crystal shape will evolve towards the crucible wall, towards a stable gap width, or towards the center of the crucible, collapsing the meniscus.

Survival of Antarctic Cryptoendolithic Fungi in Simulated Martian Conditions On Board the International Space Station.

PubMed

Onofri, Silvano; de Vera, Jean-Pierre; Zucconi, Laura; Selbmann, Laura; Scalzi, Giuliano; Venkateswaran, Kasthuri J; Rabbow, Elke; de la Torre, Rosa; Horneck, Gerda

2015-12-01

Dehydrated Antarctic cryptoendolithic communities and colonies of the rock inhabitant black fungi Cryomyces antarcticus (CCFEE 515) and Cryomyces minteri (CCFEE 5187) were exposed as part of the Lichens and Fungi Experiment (LIFE) for 18 months in the European Space Agency's EXPOSE-E facility to simulated martian conditions aboard the International Space Station (ISS). Upon sample retrieval, survival was proved by testing colony-forming ability, and viability of cells (as integrity of cell membrane) was determined by the propidium monoazide (PMA) assay coupled with quantitative PCR tests. Although less than 10% of the samples exposed to simulated martian conditions were able to proliferate and form colonies, the PMA assay indicated that more than 60% of the cells and rock communities had remained intact after the "Mars exposure." Furthermore, a high stability of the DNA in the cells was demonstrated. The results contribute to assessing the stability of resistant microorganisms and biosignatures on the surface of Mars, data that are valuable information for further search-for-life experiments on Mars. Endoliths-Eukaryotes-Extremophilic microorganisms-Mars-Radiation resistance.

Fault-tolerant control of large space structures using the stable factorization approach

NASA Technical Reports Server (NTRS)

Razavi, H. C.; Mehra, R. K.; Vidyasagar, M.

1986-01-01

Large space structures are characterized by the following features: they are in general infinite-dimensional systems, and have large numbers of undamped or lightly damped poles. Any attempt to apply linear control theory to large space structures must therefore take into account these features. Phase I consisted of an attempt to apply the recently developed Stable Factorization (SF) design philosophy to problems of large space structures, with particular attention to the aspects of robustness and fault tolerance. The final report on the Phase I effort consists of four sections, each devoted to one task. The first three sections report theoretical results, while the last consists of a design example. Significant results were obtained in all four tasks of the project. More specifically, an innovative approach to order reduction was obtained, stabilizing controller structures for plants with an infinite number of unstable poles were determined under some conditions, conditions for simultaneous stabilizability of an infinite number of plants were explored, and a fault tolerance controller design that stabilizes a flexible structure model was obtained which is robust against one failure condition.

A priori stability results for PFC

NASA Astrophysics Data System (ADS)

Rossiter, J. A.

2017-02-01

Despite its popularity in industry and obvious efficacy, predictive functional control has few rigorous a priori stability results in the literature. In many cases, common sense and intuition with some trial and error are the main design tools. This paper seeks to tackle that gap by providing some analysis of the control law and showing what forms of stability assurances can be given and how these depend on the user choices of coincidence horizon and desired closed-loop pole. The conditions are separated into necessary, but not sufficient conditions for stability and, conversely, sufficient but not necessary conditions. Numerical examples demonstrate the efficacy of these conditions and the ease of use.

Crystal structure of Earth's inner core: A first-principles study

NASA Astrophysics Data System (ADS)

Moustafa, S. G.; Schultz, A. J.; Zurek, E.; Kofke, D. A.

2017-12-01

Since the detection of the Earth's solid inner core (IC) by Lehmann in 1936, its composition and crystal structure (which are essential to understand Earth's evolution) have been controversial. While seismological measurements (e.g. PREM) can give a robust estimation of the density, pressure, and elasticity of the IC, they cannot be directly used to determine its composition and/or crystal structure. Experimentally, reaching the extreme IC conditions ( 330 GPa and 6000 K) and getting reliable measurements is very challenging. First-principles calculations provide a viable alternative that can work as a powerful investigative tool. Although several attempts have been made to assess phase stability at IC conditions computationally, they often use a low level of theory for electronic structure (e.g., classical force-field), adopt approximate methods (e.g., quasiharmonic approximation, fixed hcp-c/a), or do not consider finite-size effects. The study of phase stability using accurate first-principles methods is hampered in part by the difficulty of computing the free energy (FE), the central thermodynamic quantity that determines stability, while including anharmonic and finite-size effects. Additional difficulty related to the IC in particular is introduced by the dynamical instability of one of the IC candidate structures (bcc) at low temperature. Recently [1-3], we introduced a novel method (denoted as "harmonically mapped averaging", or HMA) to efficiently measure anharmonic properties (e.g. FE, pressure, elastic modulus) by molecular simulation, yielding orders of magnitude CPU speedup compared to conventional methods. We have applied this method to the hcp candidate phase of iron at the IC conditions, obtaining first-principles anharmonic FE values with unprecedented accuracy and precision [4]. We have now completed and report HMA calculations to assess the phase stability of all IC candidate phases (fcc/hcp/bcc). This knowledge is the prerequisite for interpreting the geophysical and geochemical constraints of the IC (e.g. anisotropy and low rigidity); which should be a key ingredient in the longstanding debate about the nature of the Earth's IC. References[1] 10.1103/PhysRevE.92.043303[2] 10.1021/acs.jctc.6b00018[3] 10.1021/acs.jctc.6b01082[4] 10.1103/PhysRevB.96.014117

Local and global stability for Lotka-Volterra systems with distributed delays and instantaneous negative feedbacks

NASA Astrophysics Data System (ADS)

Faria, Teresa; Oliveira, José J.

This paper addresses the local and global stability of n-dimensional Lotka-Volterra systems with distributed delays and instantaneous negative feedbacks. Necessary and sufficient conditions for local stability independent of the choice of the delay functions are given, by imposing a weak nondelayed diagonal dominance which cancels the delayed competition effect. The global asymptotic stability of positive equilibria is established under conditions slightly stronger than the ones required for the linear stability. For the case of monotone interactions, however, sharper conditions are presented. This paper generalizes known results for discrete delays to systems with distributed delays. Several applications illustrate the results.

Wear Behavior of an Unstable Knee: Stabilization via Implant Design?

PubMed Central

Reinders, Jörn; Kretzer, Jan Philippe

2014-01-01

Background. Wear-related failures and instabilities are frequent failure mechanisms of total knee replacements. High-conforming designs may provide additional stability for the joint. This study analyzes the effects of a ligamentous insufficiency on the stability and the wear behavior of a high-conforming knee design. Methods. Two simulator wear tests were performed on a high-conforming total knee replacement design. In the first, a ligamentous-stable knee replacement with a sacrificed anterior cruciate ligament was simulated. In the second, a ligamentous-unstable knee with additionally insufficient posterior cruciate ligament and medial collateral ligament was simulated. Wear was determined gravimetrically and wear particles were analyzed. Implant kinematics was recorded during simulation. Results. Significantly higher wear rates (P ≤ 0.001) were observed for the unstable knee (14.58 ± 0.56 mg/106 cycles) compared to the stable knee (7.97 ± 0.87 mg/106 cycles). A higher number of wear particles with only small differences in wear particle characteristics were observed. Under unstable knee conditions, kinematics increased significantly for translations and rotations (P ≤ 0.01). This increase was mainly attributed to higher tibial posterior translation and internal rotations. Conclusion. Higher kinematics under unstable test conditions is a result of insufficient stabilization via implant design. Due to the higher kinematics, increased wear was observed in this study. PMID:25276820

Effect of thermal treatment on the quality of cloudy apple juice.

PubMed

Krapfenbauer, Gottfried; Kinner, Mathias; Gössinger, Manfred; Schönlechner, Regine; Berghofer, Emmerich

2006-07-26

Apple juice from eight different varieties of apples was heated at high-temperature (60-90 degrees C) and short-time (20-100 s) (HTST) combinations. To determine the effect of heating conditions on enzymatic browning and cloud stability in apple juices, the activity of polyphenol oxidase and pectinesterase was analyzed and correlated with the thermal treatment conditions and the quality of the juice. Additional investigations included the measurement of pH value, soluble solid content, titratable acidity, color, and turbidity after 3 and 6 months. The results showed that HTST treatment at 80 degrees C already inactivated polyphenol oxidase, whereas pectinesterase activity was reduced to half and could even at 90 degrees C not be inactivated completely. In fact, highest residual pectinesterase activity was found at 60 degrees C. Heating at 70 degrees C caused stable pectinesterase activity and even a slight increase for 50 and 100 s heating times. Turbidity and lightness increased after HTST treatment. In particular, differences in cloud stability between the varieties were measured. HTST parameters did not correlate with the residual cloud stability after 6 months. The sensory evaluation revealed that only a few combinations were distinguishable. The best stability of cloud and color in relation to heat impact was achieved by HTST treatment between 70 degrees C/100 s and 80 degrees C/20 s.

Synthesis and chemical characterization of the novel agronomically relevant pentadentate chelate 2-(2-((2-hydroxybenzyl)amino)ethylamino)-2-(2-hydroxyphenyl)acetic acid (DCHA).

PubMed

López-Rayo, Sandra; Hernández, Diana; Lucena, Juan J; Escudero, Rosa; Gómez-Gallego, Mar; Sierra, Miguel A

2010-07-14

Iron chelates analogous to o,o-EDDHA/Fe(3+) are the fertilizers chosen to treat iron chlorosis in plants growing on calcareous soil. The isomer o,p-EDDHA/Fe(3+) presents less stability but faster assimilation by the plant than o,o-EDDHA/Fe(3+), because only five coordinating groups are able to complex Fe(3+). The new chelating agent 2-(2-((2-hydroxybenzyl)amino)ethylamino)-2-(2-hydroxyphenyl)acetic acid (DCHA) has been synthesized to obtain an iron fertilizer with intermediate stability between o,o-EDDHA/Fe(3+) and o,p-EDDHA/Fe(3+) and with fast assimilation. Its synthesis has been done starting from phenol, N-acetylethylendiamine, glyoxylic acid, and NaOH in a three-step sequence. The purity of the DCHA chelating agent, its protonation, and Ca(2+), Mg(2+), Fe(3+), and Cu(2+) stability constants, together with its ability to maintain iron in solution in different agronomic conditions, have been determined. The results indicate that the chelate DCHA/Fe(3+) has intermediate stability between those of o,o-EDDHA/Fe(3+) and o,p-EDDHA/Fe(3+) complexes and that it is capable of maintaining the Fe(3+) in agronomic conditions. This new chelating agent may be effective in correcting iron chlorosis in plants.

Improvements in SiC{sub w}/Al{sub 2}O{sub 3} composites through colloidally stabilized suspensions

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

Crimp, M.J.; Oppermann, D.A.; Zhang, M.

1994-12-31

Through manipulation of colloidal parameters, suspensions of SiC(whisker)/Al{sub 2}O{sub 3} were prepared, at 5, 10 and 20 vol% SiC whisker, using processing conditions established in Stable Suspension{copyright}. Utilizing Hogg, Healy and Furstenau`s modifications to DLVO theory, this program predicts stability conditions for composite suspensions. Variations in the suspension pH induce changes in the attractive/repulsive interactions between components. This type of interaction in turn influences the packing and green density. Composite suspensions were prepared, freeze dried, then cold consolidated. The distribution of the SiC whiskers within the Al{sub 2}O{sub 3} matrix was determined from SEM micrographs and the composite green densitymore » correlated to the extent of homo- versus heterostability within the composite suspension. The green density of the pure Al{sub 2}O{sub 3} and the 5 vol% SiC whisker additions was the highest at the pH of maximum stability for each interaction. In contrast, at whisker additions of 10 and 20 vol%, the green density is the highest at a pH of low heterostability.« less

Full scale wind tunnel investigation of a bearingless main helicopter rotor. [Ames 40 by 80 foot wind tunnel test using the BO-105 helicopter

NASA Technical Reports Server (NTRS)

1980-01-01

A stability test program was conducted to determine the effects of airspeed, collective pitch, rotor speed and shaft angle on stability and loads at speeds beyond that attained in the BMR/BO-105 flight test program. Loads and performance data were gathered at forward speeds up to 165 knots. The effect of cyclic pitch perturbations on rotor response was investigated at simulated level flight conditions. Two configuration variations were tested for their effect on stability. One variable was the control system stiffness. An axially softer pitch link was installed in place of the standard BO-105 pitch link. The second variation was the addition of elastomeric damper strips to increase the structural damping. The BMR was stable at all conditions tested. At fixed collective pitch, shaft angle and rotor speed, damping generally increased between hover and 60 knots, remained relatively constant from 60 to 90 knots, then decreased above 90 knots. Analytical predictions are in good agreement with test data up to 90 knots, but the trend of decreasing damping above 90 knots is contrary to the theory.

Coloring attributes of betalains: a key emphasis on stability and future applications.

PubMed

Martins, Natália; Roriz, Custódio Lobo; Morales, Patricia; Barros, Lillian; Ferreira, Isabel C F R

2017-04-19

Organoleptic characteristics largely determine food acceptance, selection, and subsequent consumption. Therefore, food colorants are extremely important in the food industry. However, based on the latest findings related to the side effects and toxicity issues of some synthetic colorants, consumers worldwide have shown increasing interest in natural alternatives. Betalains are good examples of natural colorants and therefore the present study reviews the main sources of these pigments, their structural elucidation and biosynthetic pathways, their chemical instability to different environmental factors, as well as their potential uses at the industrial level and also for pharmaceutical and cosmetic purposes, due to their ability to act as functional ingredients and health enhancers/promoters. Betalain natural pigments represent a promising and safe alternative to synthetic dyes, but their chemical instability has limited their widespread use. Temperature, pH, water activity, oxygen, light, chelating agents, the presence of other compounds, pigment concentration, storage, and processing conditions are the most important factors affecting their stability. It is, therefore, very important to establish optimum processing conditions to maximize the stability of betalains and their extraction yields, focusing on their effective use as natural food colorants, functional ingredients and value-added food products.

Stability studies of crude plant material of Bacopa monnieri and quantitative determination of bacopaside I and bacoside A by HPLC.

PubMed

Srivastava, Pratibha; Raut, Hema N; Puntambekar, Hemalata M; Desai, Anagha C

2012-01-01

Bacopa monnieri (BM) contains several dammarane-type triterpenoid saponins including bacopaside I and bacoside A. These bioactive compounds may be used as chemical markers for the quality control of different BM products used for promoting mental health and intellect. Quantification of bacopaside I and bacoside A in crude plant material of BM stored under the stability study conditions by HPLC. Crude BM samples were stored at long-term (LS; 30°C and 65% RH), accelerated (AS; 40°C and 75% RH) and real-time (RT) study conditions. HPLC of BM extracts was carried out using a LiChroCART Purospher® STAR RP-18 endcapped column along with a guard column, Purospher STAR RP 18e 4.0 4.0 mm 5 µm using a gradient of acetonitrile (A) and water containing 0.05% (v/v) orthophosphoric acid (B) at a flow rate 1.5 mL/min with UV detection at 205 nm. The linear range of bacopaside I and bacoside A was 0.2 to 1 mg/mL. With the help of a regression equation the coefficient of determination (r²) values for bacopaside I and bacoside A were found to be > 0.999 and > 0.994 respectively. Relative standard deviation (RSD) values were < 4.0 for all the concentrations injected (n = 3). The HPLC study indicated that BM samples kept under LS condition are rich in saponin contents as compared with the samples stored under AS and RT study conditions. The study indicated that BM plant material should be used fresh to obtain maximum concentration of active saponins or it should be stored under LS conditions up to 3 months. Copyright © 2012 John Wiley & Sons, Ltd.

Cellular effects of the microtubule-targeting agent peloruside A in hypoxia-conditioned colorectal carcinoma cells.

PubMed

Řehulka, Jiří; Annadurai, Narendran; Frydrych, Ivo; Znojek, Pawel; Džubák, Petr; Northcote, Peter; Miller, John H; Hajdúch, Marián; Das, Viswanath

2017-07-01

Hypoxia is a prominent feature of solid tumors, dramatically remodeling microtubule structures and cellular pathways and contributing to paclitaxel resistance. Peloruside A (PLA), a microtubule-targeting agent, has shown promising anti-tumor effects in preclinical studies. Although it has a similar mode of action to paclitaxel, it binds to a distinct site on β-tubulin that differs from the classical taxane site. In this study, we examined the unexplored effects of PLA in hypoxia-conditioned colorectal HCT116 cancer cells. Cytotoxicity of PLA was determined by cell proliferation assay. The effects of a pre-exposure to hypoxia on PLA-induced cell cycle alterations and apoptosis were examined by flow cytometry, time-lapse imaging, and western blot analysis of selected markers. The hypoxia effect on stabilization of microtubules by PLA was monitored by an intracellular tubulin polymerization assay. Our findings show that the cytotoxicity of PLA is not altered in hypoxia-conditioned cells compared to paclitaxel and vincristine. Furthermore, hypoxia does not alter PLA-induced microtubule stabilization nor the multinucleation of cells. PLA causes cyclin B1 and G2/M accumulation followed by apoptosis. The cellular and molecular effects of PLA have been determined in normoxic conditions, but there are no reports of PLA effects in hypoxic cells. Our findings reveal that hypoxia preconditioning does not alter the sensitivity of HCT116 to PLA. These data report on the cellular and molecular effects of PLA in hypoxia-conditioned cells for the first time, and will encourage further exploration of PLA as a promising anti-tumor agent. Copyright © 2017 Elsevier B.V. All rights reserved.

Measuring the emulsification dynamics and stability of self-emulsifying drug delivery systems.

PubMed

Vasconcelos, Teófilo; Marques, Sara; Sarmento, Bruno

2018-02-01

Self-emulsifying drug delivery systems (SEDDS) are one of the most promising technologies in the drug delivery field, particularly for addressing solubility and bioavailability issues of drugs. The development of these drug carriers excessively relies in visual observations and indirect determinations. The present manuscript intended to describe a method able to measure the emulsification of SEDDS, both micro and nano-emulsions, able to measure the droplet size and to evaluate the physical stability of these formulations. Additionally, a new process to evaluate the physical stability of SEDDS after emulsification was also proposed, based on a cycle of mechanical stress followed by a resting period. The use of a multiparameter continuous evaluation during the emulsification process and stability was of upmost value to understand SEDDS emulsification process. Based on this method, SEDDS were classified as fast and slow emulsifiers. Moreover, emulsification process and stabilization of emulsion was subject of several considerations regarding the composition of SEDDS as major factor that affects stability to physical stress and the use of multicomponent with different properties to develop a stable and robust SEDDS formulation. Drug loading level is herein suggested to impact droplets size of SEDDS after dispersion and SEDDS stability to stress conditions. The proposed protocol allows an online measurement of SEDDS droplet size during emulsification and a rationale selection of excipients based on its emulsification and stabilization performance. Copyright © 2017. Published by Elsevier B.V.

SiC Composite for Fuel Structure Applications

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

Yueh, Ken

Extensive evaluation was performed to determine the suitability of using SiC composite as a boiling water reactor (BWR) fuel channel material. A thin walled SiC composite box, 10 cm in dimension by approximately 1.5 mm wall thickness was fabricated using chemical vapor deposition (CVD) for testing. Mechanical test results and performance evaluations indicate the material could meet BWR channel mechanical design requirement. However, large mass loss of up to 21% was measured in in-pile corrosion test under BWR-like conditions in under 3 months of irradiation. A fresh sister sample irradiated in a follow-up cycle under PWR conditions showed no measureablemore » weight loss and thus supports the hypothesis that the oxidizing condition of the BWR-like coolant chemistry was responsible for the high corrosion rate. A thermodynamic evaluation showed SiC is not stable and the material may oxidize to form SiO 2 and CO 2. Silica has demonstrated stability in high temperature steam environment and form a protective oxide layer under severe accident conditions. However, it does not form a protective layer in water under normal BWR operational conditions due to its high solubility. Corrosion product stabilization by modifying the SiC CVD surface is an approach evaluated in this study to mitigate the high corrosion rate. Titanium and zirconium have been selected as stabilizing elements since both TiSiO 4 and ZrSiO 4 are insoluble in water. Corrosion test results in oxygenated water autoclave indicate TiSiO4 does not form a protective layer. However, zirconium doped test samples appear to form a stable continuous layer of ZrSiO 4 during the corrosion process. Additional process development is needed to produce a good ZrSiC coating to verify functionality of the mitigation concept.« less

Concerning the production of free radicals in proteins by ultraviolet light.

NASA Technical Reports Server (NTRS)

Androes, G. M.; Gloria, H. R.; Reinisch, R. F.

1972-01-01

The response to UV light of several solid proteins and model compounds has been studied in vacuum and at low temperature, using electron paramagnetic resonance techniques. The results indicate that the details of amino acid composition and sequence, and the tertiary structure of a protein are important in determining both the rate of, and the mechanism for, the production of free radicals, and in determining the conditions under which sulfur-type radicals can be produced. The results presented are related to enzyme inactivation and to the UV stability of proteins generally.

GC-MS quantitation of fragrance compounds suspected to cause skin reactions. 1.

PubMed

Chaintreau, Alain; Joulain, Daniel; Marin, Christophe; Schmidt, Claus-Oliver; Vey, Matthias

2003-10-22

Recent changes in European legislation require monitoring of 24 volatile compounds in perfumes as they might elicit skin sensitization. This paper reports a GC-MS quantitation procedure for their determination in fragrance concentrates. GC and MS conditions were optimized for a routine use: analysis within 30 min, solvent and internal standard selection, and stock solution stability. Calibration curves were linear in the range of 2-100 mg/L with coefficients of determination in excess of 0.99. The method was tested using real perfumes spiked with known amounts of reference compounds.

Distortion of Magnetic Fields in a Starless Core II: 3D Magnetic Field Structure of FeSt 1-457

NASA Astrophysics Data System (ADS)

Kandori, Ryo; Tamura, Motohide; Tomisaka, Kohji; Nakajima, Yasushi; Kusakabe, Nobuhiko; Kwon, Jungmi; Nagayama, Takahiro; Nagata, Tetsuya; Tatematsu, Ken'ichi

2017-10-01

Three-dimensional (3D) magnetic field information on molecular clouds and cores is important for revealing their kinematical stability (magnetic support) against gravity, which is fundamental for studying the initial conditions of star formation. In the present study, the 3D magnetic field structure of the dense starless core FeSt 1-457 is determined based on the near-infrared polarimetric observations of the dichroic polarization of background stars and simple 3D modeling. With an obtained angle of line-of-sight magnetic inclination axis {θ }{inc} of 45^\\circ +/- 10^\\circ and previously determined plane-of-sky magnetic field strength {B}{pol} of 23.8 ± 12.1 μ {{G}}, the total magnetic field strength for FeSt 1-457 is derived to be 33.7 ± 18.0 μ {{G}}. The critical mass of FeSt 1-457, evaluated using both magnetic and thermal/turbulent support is {M}{cr}=3.70+/- 0.92 {M}⊙ , which is identical to the observed core mass, {M}{core}=3.55+/- 0.75 {M}⊙ . We thus conclude that the stability of FeSt 1-457 is in a condition close to the critical state. Without infalling gas motion and no associated young stars, the core is regarded to be in the earliest stage of star formation, I.e., the stage just before the onset of dynamical collapse following the attainment of a supercritical condition. These properties could make FeSt 1-457 one of the best starless cores for future studies of the initial conditions of star formation.

Activity and stability of a complex bacterial soil community under simulated Martian conditions

NASA Astrophysics Data System (ADS)

Hansen, Aviaja Anna; Merrison, Jonathan; Nørnberg, Per; Aagaard Lomstein, Bente; Finster, Kai

2005-04-01

A simulation experiment with a complex bacterial soil community in a Mars simulation chamber was performed to determine the effect of Martian conditions on community activity, stability and survival. At three different depths in the soil core short-term effects of Martian conditions with and without ultraviolet (UV) exposure corresponding to 8 Martian Sol were compared. Community metabolic activities and functional diversity, measured as glucose respiration and versatility in substrate utilization, respectively, decreased after UV exposure, whereas they remained unaffected by Martian conditions without UV exposure. In contrast, the numbers of culturable bacteria and the genetic diversity were unaffected by the simulated Martian conditions both with and without UV exposure. The genetic diversity of the soil community and of the colonies grown on agar plates were evaluated by denaturant gradient gel electrophoresis (DGGE) on DNA extracts. Desiccation of the soil prior to experimentation affected the functional diversity by decreasing the versatility in substrate utilization. The natural dominance of endospores and Gram-positive bacteria in the investigated Mars-analogue soil may explain the limited effect of the Mars incubations on the survival and community structure. Our results suggest that UV radiation and desiccation are major selecting factors on bacterial functional diversity in terrestrial bacterial communities incubated under simulated Martian conditions. Furthermore, these results suggest that forward contamination of Mars is a matter of great concern in future space missions.

ACOSS Six (Active Control of Space Structures)

DTIC Science & Technology

1981-10-01

modes, specially useful simpler conditions for ensuring closed-loop asymptotic stability are also derived. In addition, conditions for robustness of...in this initial study of FOCL stability and robustness . Such a condition is strong but not unreasonable nor unrealistic. Many useful simple in- sights...smallest possible feedback gains) and many interesting numerical results on closed-loop stability and robustness of the modal-dashpot designs. The

Flight Controllability Limits and Related Human Transfer Functions as Determined from Simulator and Flight Tests

NASA Technical Reports Server (NTRS)

Taylor, Lawrence W., Jr.; Day, Richard E.

1961-01-01

A simulator study and flight tests were performed to determine the levels of static stability and damping necessary to enable a pilot to control the longitudinal and lateral-directional dynamics of a vehicle for short periods of time. Although a basic set of aerodynamic characteristics was used, the study was conducted so that the results would be applicable to a wide range of flight conditions and configurations. Novel piloting techniques were found which enabled the pilot to control the vehicle at conditions that were otherwise uncontrollable. The influence of several critical factors in altering the controllability limits was also investigated. Several human transfer functions were used which gave fairly good representations of the controllability limits determined experimentally for the short-period longitudinal, directional, and lateral modes. A transfer function with approximately the same gain and phase angle as the pilot at the controlling frequencies along the controllability limits was also derived.

Determination of surface stress by Seasat-SASS - A case study with JASIN data

NASA Technical Reports Server (NTRS)

Liu, W. T.; Large, W. G.

1981-01-01

The values of sea surface stress determined with the dissipation method and those determined with a surface-layer model from observations on F.S. Meteor during the Joint Air-Sea Interaction (JASIN) Experiment are compared with the backscatter coefficients measured by the scatterometer SASS on the satellite Seasat. This study demonstrates that SASS can be used to determine surface stress directly as well as wind speed. The quality of the surface observations used in the calibration of the retrieval algorithms, however, is important. This sample of measurements disagrees with the predictions by the existing wind retrieval algorithm under non-neutral conditions and the discrepancies depend on atmospheric stability.

Synthesis and application of hydroxyapatite and fluoroapatite to scorodite encapsulation

NASA Astrophysics Data System (ADS)

Katsarou, Lydia

Recent research has investigated the precipitation of crystalline scorodite (FeAsO4˙2H2O) as a method to stabilise arsenic for disposal due to its good stability performance according to EPA's TCLP test. It has been determined, however, that scorodite releases arsenic in significant concentrations under alkaline pH or under anoxic conditions. With the objective of enhancing the stability of scorodite, its encapsulation with minerals inert to pH and redox potential variations is considered in this work. Such encapsulation materials are hydroxyapatite (HAP-Ca5(PO4)3OH) and fluoroapatite (FAP-Ca5(PO4)3F), the two most stable of the calcium phosphates. The work described in this thesis includes: 1) the preparation of hydroxyapatite and fluoroapatite powders and their characterisation, 2) the synthesis of crystalline scorodite under atmospheric conditions and its characterisation, 3) the encapsulation of scorodite with hydroxyapatite and fluoroapatite, and 4) the long term stability testing of the encapsulated solids. Hydroxyapatite and fluoroapatite were prepared first by homogeneous precipitation from a metastable solution, to which "Ca" and "PO4" source reagents of different concentrations were added at variable rates. The crystallinity of the produced materials was found to increase with temperature. Crystalline scorodite was produced by seeded crystallisation in ambient pressure. For the encapsulation of the scorodite particles various methods of direct precipitation by controlled supersaturation were attempted, by adjusting the pH and adding/mixing feed solutions of individual calcium and phosphate source reagents. Heterogeneous deposition of HAP on scorodite proved rather difficult. Optimum results were obtained via prior conditioning of the scorodite substrate in a calcium solution and employment of low agitation regime and high (37 °C rather than 22°C) temperature. The stability tests were done in oxic and anoxic environments and their results demonstrated that the encapsulated solids had enhanced stability, since the release of arsenic was lower than it was for naked scorodite. The presence of gypsum was found to help reduce the release of arsenic further as well as phosphorus under oxic, but not anoxic conditions due to possible interaction with the sulphite ions used as reducing agent.

Wind Tunnel Testing of Various Disk-Gap-Band Parachutes

NASA Technical Reports Server (NTRS)

Cruz, Juan R.; Mineck, Raymond E.; Keller, Donald F.; Bobskill, Maria V.

2003-01-01

Two Disk-Gap-Band model parachute designs were tested in the NASA Langley Transonic Dynamics Tunnel. The purposes of these tests were to determine the drag and static stability coefficients of these two model parachutes at various subsonic Mach numbers in support of the Mars Exploration Rover mission. The two model parachute designs were designated 1.6 Viking and MPF. These model parachute designs were chosen to investigate the tradeoff between drag and static stability. Each of the parachute designs was tested with models fabricated from MIL-C-7020 Type III or F-111 fabric. The reason for testing model parachutes fabricated with different fabrics was to evaluate the effect of fabric permeability on the drag and static stability coefficients. Several improvements over the Viking-era wind tunnel tests were implemented in the testing procedures and data analyses. Among these improvements were corrections for test fixture drag interference and blockage effects, and use of an improved test fixture for measuring static stability coefficients. The 1.6 Viking model parachutes had drag coefficients from 0.440 to 0.539, while the MPF model parachutes had drag coefficients from 0.363 to 0.428. The 1.6 Viking model parachutes had drag coefficients 18 to 22 percent higher than the MPF model parachute for equivalent fabric materials and test conditions. Model parachutes of the same design tested at the same conditions had drag coefficients approximately 11 to 15 percent higher when manufactured from F-111 fabric as compared to those fabricated from MIL-C-7020 Type III fabric. The lower fabric permeability of the F-111 fabric was the source of this difference. The MPF model parachutes had smaller absolute statically stable trim angles of attack as compared to the 1.6 Viking model parachutes for equivalent fabric materials and test conditions. This was attributed to the MPF model parachutes larger band height to nominal diameter ratio. For both designs, model parachutes fabricated from F-111 fabric had significantly greater statically stable absolute trim angles of attack at equivalent test conditions as compared to those fabricated from MILC-7020 Type III fabric. This reduction in static stability exhibited by model parachutes fabricated from F-111 fabric was attributed to the lower permeability of the F-111 fabric. The drag and static stability coefficient results were interpolated to obtain their values at Mars flight conditions using total porosity as the interpolating parameter.

Monoterpene persistence in the sapwood and heartwood of longleaf pine stumps: assessment of differences in composition and stability under field conditions

Treesearch

Thomas L. Eberhardt; Philip M. Sheridan; Jolie M. Mahfouz

2009-01-01

Monoterpenes in exudates, phloem and sapwood have received considerable attention relative to the active defenses of pine trees. However, little is known about the composition and function of the heartwood monoterpenes. To address this deficiency, monoterpene contents and relative compositions were determined for sapwood and heartwood samples from longleaf pine (Pinus...

Cerium-based metal organic frameworks with UiO-66 architecture: synthesis, properties and redox catalytic activity.

PubMed

Lammert, Martin; Wharmby, Michael T; Smolders, Simon; Bueken, Bart; Lieb, Alexandra; Lomachenko, Kirill A; Vos, Dirk De; Stock, Norbert

2015-08-14

A series of nine Ce(iv)-based metal organic frameworks with the UiO-66 structure containing linker molecules of different sizes and functionalities were obtained under mild synthesis conditions and short reaction times. Thermal and chemical stabilities were determined and a Ce-UiO-66-BDC/TEMPO system was successfully employed for the aerobic oxidation of benzyl alcohol.

Stability-indicating UPLC method for determining related substances and degradants in dronedarone.

PubMed

Pydimarry, Surya Prakash Rao; Cholleti, Vijay Kumar; Vangala, Ranga Reddy

2014-08-01

A simple, sensitive and reproducible method was developed on ultra-performance liquid chromatography coupled with photodiode array detection for the quantitative determination of dronedarone hydrochloride (DRO) in drug substance and pharmaceutical dosage forms. The method is applicable for the quantification of related substances and assays of drug substances. Chromatographic separation was achieved on Acquity UPLC BEH C8 100 mm, 2.1 mm and 1.7 µm columns, using gradient elution within a short run time of 10.0 min. The eluted compounds were monitored at 288 nm, the flow rate was 0.5 mL/min and the column oven temperature was maintained at 40°C. The resolution of DRO and 11 impurities (potentials and by-products) was greater than 2.0 for all pairs of components. The high correlation coefficient value (>0.9995) indicates the clear correlations between the concentrations of investigated compound and their peak areas within the test ranges. The repeatability and intermediate precision, expressed by the relative standard deviation, were less than 2.5%. The accuracy and validity of the method were further ascertained by performing recovery studies via a spike method. The accuracy of the method, expressed as relative error, was satisfactory. No interference was observed from concomitant substances normally added to the tablets. DRO was subjected to the stress conditions of oxidative, acid, base, hydrolytic, thermal and photolytic degradation. DRO was found to degrade significantly in acid and base stress conditions and to remain stable in thermal, photolytic degradation, oxidative and hydrolytic conditions. The degradation products were well resolved from primary peak and its impurities, proving that the method is stability indicating. The developed method was validated as per International Conference on Harmonization guidelines with respect to specificity, limit of detection, limit of quantification, linearity, accuracy, precision, solution stability and robustness. This method is also suitable for the determination of DRO drug substance and pharmaceutical dosage forms. © The Author [2013]. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

PET Imaging Stability Measurements During Simultaneous Pulsing of Aggressive MR Sequences on the SIGNA PET/MR System.

PubMed

Deller, Timothy W; Khalighi, Mohammad Mehdi; Jansen, Floris P; Glover, Gary H

2018-01-01

The recent introduction of simultaneous whole-body PET/MR scanners has enabled new research taking advantage of the complementary information obtainable with PET and MRI. One such application is kinetic modeling, which requires high levels of PET quantitative stability. To accomplish the required PET stability levels, the PET subsystem must be sufficiently isolated from the effects of MR activity. Performance measurements have previously been published, demonstrating sufficient PET stability in the presence of MR pulsing for typical clinical use; however, PET stability during radiofrequency (RF)-intensive and gradient-intensive sequences has not previously been evaluated for a clinical whole-body scanner. In this work, PET stability of the GE SIGNA PET/MR was examined during simultaneous scanning of aggressive MR pulse sequences. Methods: PET performance tests were acquired with MR idle and during simultaneous MR pulsing. Recent system improvements mitigating RF interference and gain variation were used. A fast recovery fast spin echo MR sequence was selected for high RF power, and an echo planar imaging sequence was selected for its high heat-inducing gradients. Measurements were performed to determine PET stability under varying MR conditions using the following metrics: sensitivity, scatter fraction, contrast recovery, uniformity, count rate performance, and image quantitation. A final PET quantitative stability assessment for simultaneous PET scanning during functional MRI studies was performed with a spiral in-and-out gradient echo sequence. Results: Quantitation stability of a 68 Ge flood phantom was demonstrated within 0.34%. Normalized sensitivity was stable during simultaneous scanning within 0.3%. Scatter fraction measured with a 68 Ge line source in the scatter phantom was stable within the range of 40.4%-40.6%. Contrast recovery and uniformity were comparable for PET images acquired simultaneously with multiple MR conditions. Peak noise equivalent count rate was 224 kcps at an effective activity concentration of 18.6 kBq/mL, and the count rate curves and scatter fraction curve were consistent for the alternating MR pulsing states. A final test demonstrated quantitative stability during a spiral functional MRI sequence. Conclusion: PET stability metrics demonstrated that PET quantitation was not affected during simultaneous aggressive MRI. This stability enables demanding applications such as kinetic modeling. © 2018 by the Society of Nuclear Medicine and Molecular Imaging.

Evaluation of Laser Stabilization and Imaging Systems for LCLS-II - Final Paper

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

Barry, Matthew

2015-08-20

By combining the top performing commercial laser beam stabilization system with the most ideal optical imaging configuration, the beamline for the Linear Accelerator Coherent Light Source II (LCLS-II) will deliver the highest quality and most stable beam to the cathode. To determine the optimal combination, LCLS-II beamline conditions were replicated and the systems tested with a He-Ne laser. The Guidestar-II and MRC active laser beam stabilization systems were evaluated for their ideal positioning and stability. Both a two and four lens optical imaging configuration was then evaluated for beam imaging quality, magnification properties, and natural stability. In their best performancesmore » when tested over fifteen hours, Guidestar-II kept the beam stable over approximately 70-110um while the MRC system kept it stable over approximately 90-100um. During short periods of time, Guidestar-II kept the beam stable between 10-20um, but was more susceptible to drift over time, while the MRC system maintained the beam between 30-50um with less overall drift. The best optical imaging configuration proved to be a four lens system that images to the iris located in the cathode room and from there, imaged to the cathode. The magnification from the iris to the cathode was 2:1, within an acceptable tolerance to the expected 2.1:1 magnification. The two lens configuration was slightly more stable in small periods of time (less than 10 minutes) without the assistance of a stability system, approximately 55um compared to approximately 70um, but the four lens configurations beam image had a significantly flatter intensity distribution compared to the two lens configuration which had a Gaussian distribution. A final test still needs to be run with both stability systems running at the same time through the four lens system. With this data, the optimal laser beam stabilization system can be determined for the beamline of LCLS-II.« less

Influence of Temperature and Humidity on the Stability of Carotenoids in Biofortified Maize (Zea mays L.) Genotypes during Controlled Postharvest Storage.

PubMed

Ortiz, Darwin; Rocheford, Torbert; Ferruzzi, Mario G

2016-04-06

Maize is a staple crop that has been the subject of biofortification efforts to increase the natural content of provitamin A carotenoids. Although significant progress toward increasing provitamin A carotenoid content in maize varieties has been made, postharvest handling factors that influence carotenoid stability during storage have not been fully established. The objectives of this study were to determine carotenoid profiles of six selected provitamin A biofortified maize genotypes at various developmental stages and assess the stability of carotenoids in maize kernels during controlled storage conditions (12 month period), including elevated temperature and relative humidity. There were no significant changes in the content of individual carotenoids within genotypes during kernel development from 45 days after pollination through the time of harvest. Carotenoid losses through traditional grain drying were also minimal (<9%). However, the stability of carotenoids in maize kernels over storage time after harvest was found to be dependent on both temperature and humidity, with variation observed among genotypes. Different forms of provitamin A carotenoids follow similar degradation rates. The genotype C17xDE3 had a degradation rate 2 times faster than those of the other genotypes evaluated (P < 0.001). These differences in carotenoid stability under controlled storage were attributed, in part, to observed differences in the physical properties of the kernels (surface area and porosity). These results support the notion that effective control of moisture content and temperature of the kernels during storage conditions is essential to reduce the speed of degradative reactions.

Preliminary 1 month stability screening of cosmetic multiple emulsions (W/O/W) prepared using cetyl dimethicone copolyol and Polysorbate 80.

PubMed

Khan, H; Akhtar, N; Mahmood, T; Jameel, A; Mohsin, S

2015-02-01

The objective of this work was to develop W/O/W emulsions with different concentration of paraffin oil, lipophilic (cetyl dimethicone copolyol) and hydrophilic emulsifiers (polysorbate 80) and to check their stability at different storage conditions. Approximately, 20 formulations (W/O/W) multiple emulsions were prepared, and their stability was checked at different storage conditions for the period of 30 days. Stability of some multiple emulsions ME12, ME13, ME14, ME19 and ME20 was also checked with carbomer as viscosity-enhancing agent. Microscopic analysis for droplet size determination and rheological characterization of most stable multiple emulsions, that is, ME20 were also performed. It was observed that stability of multiple emulsion increases with the addition of gelling agent. Formulation (ME20) with 13.6% paraffin oil, 2.4% cetyl dimethicone copolyol and 0.8% polysorbate 80 was found more stable at 25°C and 40°C for the period of 30 days. Rheological analysis indicated a decrease in viscosity with the passage of time, while droplet size analysis indicated an increase in droplet size with the passage of time. As a conclusion of this work, a stable multiple emulsion with 13.6% paraffin oil, 2.4% cetyl dimethicone copolyol and 0.8% polysorbate 80 can be formulated and can be further studied for any active ingredient for cosmetic purposes. © 2014 Society of Cosmetic Scientists and the Société Française de Cosmétologie.

Distinct structural changes detected by X-ray fiber diffraction in stabilization of F-actin by lowering pH and increasing ionic strength.

PubMed

Oda, T; Makino, K; Yamashita, I; Namba, K; Maéda, Y

2001-02-01

Lowering pH or raising salt concentration stabilizes the F-actin structure by increasing the free energy change associated with its polymerization. To understand the F-actin stabilization mechanism, we studied the effect of pH, salt concentration, and cation species on the F-actin structure. X-ray fiber diffraction patterns recorded from highly ordered F-actin sols at high density enabled us to detect minute changes of diffraction intensities and to precisely determine the helical parameters. F-actin in a solution containing 30 mM NaCl at pH 8 was taken as the control. F-actin at pH 8, 30 to 90 mM NaCl or 30 mM KCl showed a helical symmetry of 2.161 subunits per turn of the 1-start helix (12.968 subunits/6 turns). Lowering pH from 8 to 6 or replacing NaCl by LiCl altered the helical symmetry to 2.159 subunits per turn (12.952/6). The diffraction intensity associated with the 27-A meridional layer-line increased as the pH decreased but decreased as the NaCl concentration increased. None of the solvent conditions tested gave rise to significant changes in the pitch of the left-handed 1-start helix (approximately 59.8 A). The present results indicate that the two factors that stabilize F-actin, relatively low pH and high salt concentration, have distinct effects on the F-actin structure. Possible mechanisms will be discussed to understand how F-actin is stabilized under these conditions.

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

Boggs, S. Jr.; Livermore, D.; Seitz, M.G.

Dissolved humic substances (humic and fulvic acids) occur in surface waters and groundwaters in concentrations ranging from less than 1 mg(C)/L to more than 100 mg(C)/L. Humic substances are strong complexing agents for many trace metals in the environment and are also capable of forming stable soluble complexes or chelates with radionuclides. Concentrations of humic materials as low as 1 mg(C)/L can produce a detectable increase in the mobility of some actinide elements by forming soluble complexes that inhibit sorption of the radionuclides onto rock materials. The stability of trace metal- or radionuclide-organic complexes is commonly measured by an empiricallymore » determined conditional stability constant (K'), which is based on the ratio of complexed metal (radionuclide) in solution to the product concentration of uncomplexed metal and humic complexant. Larger values of stability constants indicate greater complex stability. The stability of radionuclide-organic complexes is affected both by concentration variables and envionmental factors. In general, complexing is favored by increased of radionuclide, increased pH, and decreased ionic strength. Actinide elements are generally most soluble in their higher oxidation states. Radionuclides can also form stable, insoluble complexes with humic materials that tend to reduce radionuclide mobility. These insoluble complexes may be radionuclide-humate colloids that subsequently precipitate from solution, or complexes of radionuclides and humic substances that sorb to clay minerals or other soil particulates strongly enough to immobilize the radionuclides. Colloid formation appears to be favored by increased radionuclide concentration and lowered pH; however, the conditions that favor formation of insoluble complexes that sorb to particulates are still poorly understood. 129 refs., 25 figs., 19 tabs.« less

Validated stability-indicating HPLC method for the determination of pridinol mesylate. Kinetics study of its degradation in acid medium.

PubMed

Bianchini, Romina M; Castellano, Patricia M; Kaufman, Teodoro S

2008-12-01

The stability of pridinol mesylate (PRI) was investigated under different stress conditions, including hydrolytic, oxidative, photolytic and thermal, as recommended by the ICH guidelines. Relevant degradation was found to take place under acidic (0.1N HCl) and photolytic (visible and long-wavelength UV-light) conditions, both yielding the product resulting from water elimination (ELI), while submission to an oxidizing environment gave the N-oxidation derivative (NOX). The standards of these degradation products were synthesized and characterized by IR, (1)H and (13)C NMR spectroscopy. A simple, sensitive and specific HPLC method was developed for the quantification of PRI, ELI and NOX in bulk drug, and the conditions were optimized by means of a statistical design strategy. The separation employs a C(18) column and a 51:9:40 (v/v/v) mixture of MeOH, 2-propanol and potassium phosphate solution (50mM, pH 6.0), as mobile phase, delivered at 1.0 ml min(-1); the analytes were detected and quantified at 220 nm. The method was validated, demonstrating to be accurate and precise (repeatability and intermediate precision levels) within the corresponding linear ranges of PRI (0.1-1.5 mg ml(-1); r=0.9983, n=18) and both impurities (0.1-1.3% relative to PRI, r=0.9996 and 0.9995 for ELI and NOX, respectively, n=18). Robustness against small modifications of pH and percentage of the aqueous mobile phase was ascertained and the limits of quantification of the analytes were also determined (0.4 and 0.5 microg ml(-1); 0.04% and 0.05% relative to PRI for ELI and NOX, respectively). Peak purity indices (>0.9997), obtained with the aid of diode-array detection, and satisfactory resolution (R(s)>2.0) between PRI and its impurities established the specificity of the determination, all these results proving the stability-indicating capability of the method. The kinetics of the degradation of PRI in acid medium was also studied, determining that this is a first-order process with regards to drug concentration, with an activation energy of 25.5 Kcal mol(-1) and a t(1/2)=10,830 h, in 0.1N HCl at 38 degrees C.

An eco-friendly direct spectrofluorimetric method for the determination of irreversible tyrosine kinase inhibitors, neratinib and pelitinib: application to stability studies.

PubMed

Maher, H M; Alzoman, N Z; Shehata, S M

2017-03-01

A new rapid and simple stability-indicating spectrofluorimetric method has been developed for the determination of two irreversible tyrosine kinase inhibitors (TKIs), neratinib (NER) and pelitinib (PEL). The method is based upon measurement of the native fluorescence intensity of both drugs at λ ex 270 nm in aqueous borate buffer solutions (pH 10.5). The fluorescence intensity recorded at 545 nm (NER) and 465 nm (PEL) were rectilinear over the concentration range of 0.1-10 μg/mL for both drugs with a high correlation coefficient (r > 0.999). The proposed method provided low limits of detection and of quantitation of 0.07, 0.11 μg/mL (NER) and 0.02, 0.05 μg/mL (PEL), respectively. The method was successfully applied for the determination of NER and PEL in bulk powder. The proposed methods were fully validated as per the International Conference on Harmonisation (ICH) guidelines. The application of the method was extended to stability studies of both NER and PEL under different forced-degradation conditions (acidic-induced, base-induced, oxidative, wet heat, and photolytic degradation). Moreover, the kinetics of the base-induced and oxidative degradation of both drugs was investigated and the pseudo-first-order rate constants and half-lives were estimated at different temperatures. Also, an Arrhenius plot was applied to predict the stability behaviour of the two drugs at room temperature. Copyright © 2016 John Wiley & Sons, Ltd. Copyright © 2016 John Wiley & Sons, Ltd.

Factors influencing initial cup stability in total hip arthroplasty.

PubMed

Amirouche, Farid; Solitro, Giovanni; Broviak, Stefanie; Gonzalez, Mark; Goldstein, Wayne; Barmada, Riad

2014-12-01

One of the main goals in total hip replacement is to preserve the integrity of the hip kinematics, by well positioning the cup and to make sure its initial stability is congruent and attained. Achieving the latter is not trivial. A finite element model of the cup-bone interface simulating a realistic insertion and analysis of different scenarios of cup penetration, insertion, under-reaming and loading is investigated to determine certain measurable factors sensitivity to stress-strain outcome. The insertion force during hammering and its relation to the cup penetration during implantation is also investigated with the goal of determining the initial stability of the acetabular cup during total hip arthroplasty. The mathematical model was run in various configurations to simulate 1 and 2mm of under-reaming at various imposed insertion distances to mimic hammering and insertion of cup insertion into the pelvis. Surface contact and micromotion at the cup-bone interface were evaluated after simulated cup insertion and post-operative loading conditions. The results suggest a direct correlation between under-reaming and insertion force used to insert the acetabular cup on the micromotion and fixation at the cup-bone interface. While increased under-reaming and insertion force result in an increase amount of stability at the interface, approximately the same percentage of surface contact and micromotion reduction can be achieved with less insertion force. We need to exercise caution to determine the optimal configuration which achieves a good conformity without approaching the yield strength for bone. Copyright © 2014 Elsevier Ltd. All rights reserved.

Deep Boreholes Seals Subjected to High P,T conditions - Proposed Experimental Studies

NASA Astrophysics Data System (ADS)

Caporuscio, F.

2015-12-01

Deep borehole experimental work will constrain the P,T conditions which "seal" material will experience in deep borehole crystalline rock repositories. The rocks of interest to this study include mafic (amphibolites) and silicic (granitic gneiss) end members. The experiments will systematically add components to capture discrete changes in both water and EBS component chemistries. Experiments in the system wall rock-clay-concrete-groundwater will evaluate interactions among components, including: mineral phase stability, metal corrosion rates and thermal limits. Based on engineered barrier studies, experimental investigations will move forward with three focusses. First, evaluation of interaction between "seal" materials and repository wall rock (crystalline) under fluid-saturated conditions over long-term (i.e., six-month) experiments; which reproduces the thermal pulse event of a repository. Second, perform experiments to determine the stability of zeolite minerals (analcime-wairakitess) under repository conditions. Both sets of experiments are critically important for understanding mineral paragenesis (zeolites and/or clay transformations) associated with "seals" in contact with wall rock at elevated temperatures. Third, mineral growth at the metal interface is a principal control on the survivability (i.e. corrosion) of waste canisters in a repository. The objective of this planned experimental work is to evaluate physio-chemical processes for 'seal' components and materials relevant to deep borehole disposal. These evaluations will encompass multi-laboratory efforts for the development of seals concepts and application of Thermal-Mechanical-Chemical (TMC) modeling work to assess barrier material interactions with subsurface fluids and other barrier materials, their stability at high temperatures, and the implications of these processes to the evaluation of thermal limits.

Cell-cell and cell-surface interactions mediated by cellulose and a novel exopolysaccharide contribute to Pseudomonas putida biofilm formation and fitness under water-limiting conditions.

PubMed

Nielsen, Lindsey; Li, Xiaohong; Halverson, Larry J

2011-05-01

The composition of the exopolysaccharide matrix of Pseudomonas putida mt2 biofilms is relatively undefined as well as the contributions of each polymer to ecological fitness. Here, we describe the role of two putative exopolysaccharide gene clusters, putida exopolysaccharide A (pea) and bacterial cellulose (bcs) in biofilm formation and stability, rhizosphere colonization and matrix hydration under water-limiting conditions. Our findings suggest that pea is involved in the production of a novel glucose, galactose, and mannose-rich polymer that contributes to cell-cell interactions necessary for pellicle and biofilm formation and stability. In contrast, Bcs plays a minor role in biofilm formation and stability, although it does contribute to rhizosphere colonization based on a competition assay. We show that pea expression is highly induced transiently under water-limiting conditions but only slightly by high osmolarity, as determined by qRT-PCR. In contrast, both forms of water stress highly induced bcs expression. Cells deficient in making one or more exopolysaccharide experienced greater dehydration-mediated cell-envelope stress, leading to increased alginate promoter activity. However, this did not lead to increased exopolysaccharide production, except in bcs or pea mutants unable to produce alginate, indicating that P. putida compensates by producing, presumably more Pea or Bcs exopolysaccharides, to facilitate biofilm hydration. Collectively, the data suggest that Pea and Bcs contribute to biofilm formation and in turn their presence contributes to fitness under water-limiting conditions, but not to the extent of alginate. © 2011 Society for Applied Microbiology and Blackwell Publishing Ltd.

Dynamic remedial action scheme using online transient stability analysis

NASA Astrophysics Data System (ADS)

Shrestha, Arun

Economic pressure and environmental factors have forced the modern power systems to operate closer to their stability limits. However, maintaining transient stability is a fundamental requirement for the operation of interconnected power systems. In North America, power systems are planned and operated to withstand the loss of any single or multiple elements without violating North American Electric Reliability Corporation (NERC) system performance criteria. For a contingency resulting in the loss of multiple elements (Category C), emergency transient stability controls may be necessary to stabilize the power system. Emergency control is designed to sense abnormal conditions and subsequently take pre-determined remedial actions to prevent instability. Commonly known as either Remedial Action Schemes (RAS) or as Special/System Protection Schemes (SPS), these emergency control approaches have been extensively adopted by utilities. RAS are designed to address specific problems, e.g. to increase power transfer, to provide reactive support, to address generator instability, to limit thermal overloads, etc. Possible remedial actions include generator tripping, load shedding, capacitor and reactor switching, static VAR control, etc. Among various RAS types, generation shedding is the most effective and widely used emergency control means for maintaining system stability. In this dissertation, an optimal power flow (OPF)-based generation-shedding RAS is proposed. This scheme uses online transient stability calculation and generator cost function to determine appropriate remedial actions. For transient stability calculation, SIngle Machine Equivalent (SIME) technique is used, which reduces the multimachine power system model to a One-Machine Infinite Bus (OMIB) equivalent and identifies critical machines. Unlike conventional RAS, which are designed using offline simulations, online stability calculations make the proposed RAS dynamic and adapting to any power system configuration and operating state. The generation-shedding cost is calculated using pre-RAS and post-RAS OPF costs. The criteria for selecting generators to trip is based on the minimum cost rather than minimum amount of generation to shed. For an unstable Category C contingency, the RAS control action that results in stable system with minimum generation shedding cost is selected among possible candidate solutions. The RAS control actions update whenever there is a change in operating condition, system configuration, or cost functions. The effectiveness of the proposed technique is demonstrated by simulations on the IEEE 9-bus system, the IEEE 39-bus system, and IEEE 145-bus system. This dissertation also proposes an improved, yet relatively simple, technique for solving Transient Stability-Constrained Optimal Power Flow (TSC-OPF) problem. Using the SIME method, the sets of dynamic and transient stability constraints are reduced to a single stability constraint, decreasing the overall size of the optimization problem. The transient stability constraint is formulated using the critical machines' power at the initial time step, rather than using the machine rotor angles. This avoids the addition of machine steady state stator algebraic equations in the conventional OPF algorithm. A systematic approach to reach an optimal solution is developed by exploring the quasi-linear behavior of critical machine power and stability margin. The proposed method shifts critical machines active power based on generator costs using an OPF algorithm. Moreover, the transient stability limit is based on stability margin, and not on a heuristically set limit on OMIB rotor angle. As a result, the proposed TSC-OPF solution is more economical and transparent. The proposed technique enables the use of fast and robust commercial OPF tool and time-domain simulation software for solving large scale TSC-OPF problem, which makes the proposed method also suitable for real-time application.

Guidelines for the practical stability studies of anticancer drugs: a European consensus conference.

PubMed

Bardin, C; Astier, A; Vulto, A; Sewell, G; Vigneron, J; Trittler, R; Daouphars, M; Paul, M; Trojniak, M; Pinguet, F

2011-07-01

Stability studies performed by the pharmaceutical industry are only designed to fulfill licensing requirements. Thus, post-dilution or -reconstitution stability data are frequently limited to 24h only for bacteriological reasons regardless of the true chemical stability which could, in many cases, be longer. In practice, the pharmacy-based centralized preparation may require infusions to be made several days in advance to provide, for example, the filling of ambulatory devices for continuous infusions or batch preparations for dose banding. Furthermore, a non-justified limited stability for expensive products is obviously very costly. Thus, there is a compelling need for additional stability data covering practical uses of anticancer drugs. A European conference consensus was held in France, May 2010, under the auspices of the French Society of Oncology Pharmacy (SFPO) to propose adapted rules on stability in practical situations and guidelines to perform corresponding stability studies. For each anticancer drug, considering their therapeutic index, the pharmacokinetics/pharmacodynamics (PK/PD) variability, specific clinical use and risks related to degradation products, the classical limit of 10% of degradation can be inappropriate. Therefore, acceptance limits must be clinically relevant and should be defined for each drug individually. Design of stability studies has to reflect the different needs of the clinical practice (preparation for the week-ends, outpatient transportations, implantable devices, dose banding…). It is essential to use validated stability-indicating methods, separating degradation products being formed in the practical use of the drug. Sequential temperature designs should be encouraged to replicate problems seen in daily practice such as rupture of the cold-chain or temperature-cycling between refrigerated storage and ambient in-use conditions. Stressed conditions are recommended to evaluate not only the role of classical variables (pH, temperature, light) but also the mechanical stress. Physical stability such as particles' formation should be systematically evaluated. The consensus conference focused on the need to perform more studies on the stability of biotherapies, including a minimum of three complementary separating methods and a careful evaluation of submicron aggregates. The determination of the biological activity of proteins could be also useful. A guideline on the practical stability of anticancer drugs is proposed to cover current clinical and pharmaceutical practice. It should contribute to improved security of use, optimization of centralized handling and reduced costs. Finally, we have attempted to establish a new drug stability paradigm based on practical clinical needs, to complement regulatory guidelines which are essentially orientated to the stability of manufactured drugs. Copyright © 2011 Elsevier Masson SAS. All rights reserved.

Aquaporin-1 Deficiency Protects Against Myocardial Infarction by Reducing Both Edema and Apoptosis in Mice

PubMed Central

Li, Lihua; Weng, Zhiyong; Yao, Chenjuan; Song, Yuanlin; Ma, Tonghui

2015-01-01

Many studies have determined that AQP1 plays an important role in edema formation and resolution in various tissues via water transport across the cell membrane. The aim of this research was to determine both if and how AQP1 is associated with cardiac ischemic injury, particularly the development of edema following myocardial infarction (MI). AQP1+/+ and AQP1−/− mice were used to create the MI model. Under physiological conditions, AQP1−/− mice develop normally; however, in the setting of MI, they exhibit cardioprotective properties, as shown by reduced cardiac infarct size determined via NBT staining, improved cardiac function determined via left ventricular catheter measurements, decreased AQP1-dependent myocardial edema determined via water content assays, and decreased apoptosis determined via TUNEL analysis. Cardiac ischemia caused by hypoxia secondary to AQP1 deficiency stabilized the expression of HIF-1α in endothelial cells and subsequently decreased microvascular permeability, resulting in the development of edema. The AQP1-dependent myocardial edema and apoptosis contributed to the development of MI. AQP1 deficiency protected cardiac function from ischemic injury following MI. Furthermore, AQP1 deficiency reduced microvascular permeability via the stabilization of HIF-1α levels in endothelial cells and decreased cellular apoptosis following MI. PMID:26348407

40 CFR 86.1312-2007 - Filter stabilization and microbalance workstation environmental conditions, microbalance...

Code of Federal Regulations, 2010 CFR

2010-07-01

... 40 Protection of Environment 19 2010-07-01 2010-07-01 false Filter stabilization and microbalance workstation environmental conditions, microbalance specifications, and particulate matter filter handling and... Particulate Exhaust Test Procedures § 86.1312-2007 Filter stabilization and microbalance workstation...

40 CFR 86.1312-2007 - Filter stabilization and microbalance workstation environmental conditions, microbalance...

Code of Federal Regulations, 2013 CFR

2013-07-01

... 40 Protection of Environment 20 2013-07-01 2013-07-01 false Filter stabilization and microbalance workstation environmental conditions, microbalance specifications, and particulate matter filter handling and... Particulate Exhaust Test Procedures § 86.1312-2007 Filter stabilization and microbalance workstation...

40 CFR 86.1312-2007 - Filter stabilization and microbalance workstation environmental conditions, microbalance...

Code of Federal Regulations, 2012 CFR

2012-07-01

... 40 Protection of Environment 20 2012-07-01 2012-07-01 false Filter stabilization and microbalance workstation environmental conditions, microbalance specifications, and particulate matter filter handling and... Particulate Exhaust Test Procedures § 86.1312-2007 Filter stabilization and microbalance workstation...

40 CFR 86.1312-2007 - Filter stabilization and microbalance workstation environmental conditions, microbalance...

Code of Federal Regulations, 2011 CFR

2011-07-01

... 40 Protection of Environment 19 2011-07-01 2011-07-01 false Filter stabilization and microbalance workstation environmental conditions, microbalance specifications, and particulate matter filter handling and... Particulate Exhaust Test Procedures § 86.1312-2007 Filter stabilization and microbalance workstation...

Stability analysis of fractional-order Hopfield neural networks with time delays.

PubMed

Wang, Hu; Yu, Yongguang; Wen, Guoguang

2014-07-01

This paper investigates the stability for fractional-order Hopfield neural networks with time delays. Firstly, the fractional-order Hopfield neural networks with hub structure and time delays are studied. Some sufficient conditions for stability of the systems are obtained. Next, two fractional-order Hopfield neural networks with different ring structures and time delays are developed. By studying the developed neural networks, the corresponding sufficient conditions for stability of the systems are also derived. It is shown that the stability conditions are independent of time delays. Finally, numerical simulations are given to illustrate the effectiveness of the theoretical results obtained in this paper. Copyright © 2014 Elsevier Ltd. All rights reserved.

Identification of new impurities of enalapril maleate on oxidation in the presence of magnesium monoperoxyphthalate.

PubMed

Toporisic, Rebeka; Mlakar, Anita; Hvala, Jernej; Prislan, Iztok; Zupancic-Kralj, Lucija

2010-06-05

Stress stability testing and forced degradation were used to determine the stability of enalapril maleate (EM) and to find a degradation pathway for the drug. The degradation impurities, formed under different stressed conditions, were investigated by HPLC and UPLC-MS methods. HPLC analysis showed several degradation impurities of which several were already determined, but on oxidation in the presence of magnesium monoperoxyphthalate (MMPP) several impurities of EM were observed which were not yet characterized. The HPLC methods for determination of EM were validated. The linearity of HPLC method was established in the concentration range between 0.5 and 10 microg/mL with correlation coefficient greater than 0.99. The LOD of EM was 0.2 microg/mL and LOQ was 0.5 microg/mL. The validated HPLC method was used to determine the degradation impurities in samples after stress stability testing and forced degradation of EM. In order to identify new degradation impurities of EM after forced degradation UPLC-MS/MS(n), Orbitrap has been used. It was found that new impurities are oxidation products: (S)-1-((S)-2-((S)-1-ethoxy-4-(o,m,p-hydroxyphenyl)-1-oxobutan-2-ylamino)propanoyl)pyrrolidine-2-carboxylic acid, (2S)-1-((2S)-2-((2S)-1-ethoxy-4-hydroxy-1-oxo-4-phenylbutan-2-ylamino)propanoyl)pyrrolidine-2-carboxylic acid. (S)-2-(3-phenylpropylamino)-1-(pyrrolidin-1-yl)propan-1-one was identified as a new degradation impurity. Copyright (c) 2010. Published by Elsevier B.V.

A validated specific stability-indicating RP-HPLC assay method for Ambrisentan and its related substances.

PubMed

Narayana, M B V; Chandrasekhar, K B; Rao, B M

2014-09-01

A validated specific stability-indicating reverse-phase liquid chromatographic method was developed for the quantitative determination of Ambrisentan as well as its related substances in bulk samples, pharmaceutical dosage forms in the presence of degradation products and its related impurities. Forced degradation studies were performed on bulk samples of Ambrisentan as per the ICH-prescribed stress conditions using acid, base, oxidative, thermal stress and photolytic degradation to show the stability-indicating power of the LC method. Significant degradation in acidic, basic stress conditions was observed and no degradation was observed in other stress conditions. The chromatographic method was optimized using the samples generated from the forced degradation studies and the impurity-spiked solution. Good resolution between the peaks corresponds to Ambrisentan-related impurities and degradation products from the analyte were achieved on a SunFire C18 column using a mobile phase consisting of a mixture of potassium dihydrogen orthophosphate at a pH adjusted to 2.5 with ortho-phosphoric acid in water and a mixture of acetonitrile:methanol using a simple linear gradient. The detection was carried out at 225 nm. The limit of detection and the limit of quantification for the Ambrisentan and its related impurities were established. The stressed test solutions were assayed against the qualified working standard of Ambrisentan and the mass balance in each case was between 98.9 and 100.3%, indicating that the developed LC method was stability indicating. Validation of the developed LC method was carried out as per the ICH requirements. The developed method was found to be suitable to check the quality of bulk samples of Ambrisentan at the time of batch release and also during its storage (long-term and accelerated stability). © The Author [2013]. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Cost-effective alternative to nano-encapsulation: Amorphous curcumin-chitosan nanoparticle complex exhibiting high payload and supersaturation generation.

PubMed

Nguyen, Minh Hiep; Yu, Hong; Kiew, Tie Yi; Hadinoto, Kunn

2015-10-01

While the wide-ranging therapeutic activities of curcumin have been well established, its successful delivery to realize its true therapeutic potentials faces a major challenge due to its low oral bioavailability. Even though nano-encapsulation has been widely demonstrated to be effective in enhancing the bioavailability of curcumin, it is not without drawbacks (i.e. low payload and costly preparation). Herein we present a cost-effective bioavailability enhancement strategy of curcumin in the form of amorphous curcumin-chitosan nanoparticle complex (or curcumin nanoplex in short) exhibiting a high payload (>80%). The curcumin nanoplex was prepared by a simple yet highly efficient drug-polysaccharide complexation method that required only mixing of the curcumin and chitosan solutions under ambient condition. The effects of (1) pH and (2) charge ratio of chitosan to curcumin on the (i) physical characteristics of the nanoplex (i.e. size, colloidal stability and payload), (ii) complexation efficiency, and (iii) production yield were investigated from which the optimal preparation condition was determined. The nanoplex formation was found to favor low acidic pH and charge ratio below unity. At the optimal condition (i.e. pH 4.4. and charge ratio=0.8), stable curcumin nanoplex (≈260nm) was prepared at >90% complexation efficiency and ≈50% production yield. The amorphous state stability, colloidal stability, and in vitro non-cytotoxicity of the nanoplex were successfully established. The curcumin nanoplex produced prolonged supersaturation (3h) in the presence of hydroxypropyl methylcellulose (HPMC) at five times of the saturation solubility of curcumin. In addition, curcumin released from the nanoplex exhibited improved chemical stability owed to the presence of chitosan. Both results (i.e. high supersaturation and improved chemical stability) bode well for the ability of the curcumin nanoplex to enhance the bioavailability of curcumin clinically. Copyright © 2015 Elsevier B.V. All rights reserved.

The hip fluid seal--Part II: The effect of an acetabular labral tear, repair, resection, and reconstruction on hip stability to distraction.

PubMed

Nepple, Jeffrey J; Philippon, Marc J; Campbell, Kevin J; Dornan, Grant J; Jansson, Kyle S; LaPrade, Robert F; Wijdicks, Coen A

2014-04-01

The acetabular labrum is theorized to be important to normal hip function by providing stability to distraction forces through the suction effect of the hip fluid seal. The purpose of this study was to determine the relative contributions of the hip capsule and labrum to the distractive stability of the hip, and to characterize hip stability to distraction forces in six labral conditions: intact labrum, labral tear, labral repair (looped vs. through sutures), partial resection, labral reconstruction with iliotibial band, and complete resection. Eight cadaveric hips with a mean age of 47.8 years (SD 4.3, range 41-51 years) were included. For each condition, the hip seal was broken by distracting the hip at a rate of 0.33 mm/s while the required force, energy, and negative intra-articular pressure were measured. For comparisons between labral conditions, measurements were normalized to the intact labral state (percent of intact). The relative contribution of the labrum to distractive stability was greatest at 1 and 2 mm of displacement, where it was significantly greater than the role of the capsule and accounted for 77 % (SD 27 %, p = 0.006) and 70 % (SD 7 %, p = 0.009) of total distractive stability, respectively. The relative contribution of the capsule to distractive stability increased with progressive displacement, providing 41 % (SD 49 %) and 52 % (SD 53 %) of distractive stability at 3 and 5 mm of distraction, respectively. The maximal distraction force required to break the hip seal in the intact labral state (capsule removed) varied from 124 to 150 N. Labral tear, partial resection, and complete resection resulted in average maximal distraction forces of 76 % (SD 34 %), 29 % (SD 26 %), and 27 % (SD 22 %), respectively, compared to the intact state. Through type labral repairs resulted in significantly greater improvements (from the labral tear state) in maximal negative pressure generated, compared to looped type repairs (median increase; +32 vs. -9 %, p = 0.029). Labral reconstruction resulted in a mean maximal distraction force of 66 % (SD 35 %), with a significant improvement of 37 % compared to partial labral resection (p < 0.001). The acetabular labrum was the primary hip stabilizer to distraction forces at small displacements (1-2 mm). Partial labral resection significantly decreased the distractive strength of the hip fluid seal. Labral reconstruction significantly improved distractive stability, compared to partial labral resection. The results of this study may provide insight into the relative importance of the capsule and labrum to distractive stability of the hip and may help to explain hip microinstability in the setting of labral disease.

Derivation of charts for determining the horizontal tail load variation with any elevator motion

NASA Technical Reports Server (NTRS)

Pearson, Henry A

1943-01-01

The equations relating the wing and tail loads are derived for a unit elevator displacement. These equations are then converted into a nondimensional form and charts are given by which the wing- and tail-load-increment variation may be determined under dynamic conditions for any type of elevator motion and for various degrees of airplane stability. In order to illustrate the use of the charts, several examples are included in which the wing and tail loads are evaluated for a number of types of elevator motion. Methods are given for determining the necessary derivatives from results of wind-tunnel tests when such tests are available.

Determination of traces of silver in waters by anion exchange and atomic absorption spectrophotometry

USGS Publications Warehouse

Chao, T.T.; Fishman, M. J.; Ball, J.W.

1969-01-01

A method has been developed for the accurate determination of 0.1-1 ??g of silver per liter of water. The method permits stabilization of silver in water without loss to container walls. Optimum conditions have been established for the complete recovery of silver from water with an anion-exchange column, for quantitative elution of silver from the resin, and for measurement of silver by atomic absorption spectrophotometry after chelation with ammonium pyrrolidine dithiocarbamate and extraction of the chelate with MIBK. Silver in the 1-10 ??g 1 range can be determined by extraction without pre-concentration on an ion-exchange resin. ?? 1969.

Evaluation of some antioxidants in radiation vulcanized ethylene-propylene diene (EPDM) rubber

NASA Astrophysics Data System (ADS)

Abdel-Aziz, M. M.; Basfar, A. A.

2001-12-01

Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) have been used to study the oxidation of γ-ray vulcanized ethylene-propylene diene rubber (EPDM) stabilized with various types of antioxidants. The antioxidants used were pentaerythrityl tetrakis(3,5-di-tert-butyl(-4-hydroxyphenyl))propionate (Irganox 1010), Irganox 1035, Irganox 1520D, as primary antioxidants; Irganox B561 and Irganox B900, as synergistic blends; hindered amine light stabilizer (HALS), i.e. Tinuvin 622 LD; N-isopropyl- N-phenyl- p-phenylene diamine (IPPD) and trimethyl quinoline (TMQ) and their mixtures. The measurements were carried out under atmospheric conditions. The effects of antioxidant type and its selected concentration were determined and mechanism of reaction proposed.

Artificial blood circulation: stabilization, physiological control, and optimization.

PubMed

Lerner, A Y

1990-04-01

The requirements for creating an efficient Artificial Blood Circulation System (ABCS) have been determined. A hierarchical three-level adaptive control system is suggested for ABCS to solve the following problems: stabilization of the circulation conditions, left and right pump coordination, physiological control for maintaining a proper relation between the cardiac output and the level of gas exchange required for metabolism, and optimization of the system behavior. The adaptations to varying load and body parameters will be accomplished using the signals which characterize the real-time computer-processed values of correlations between the changes in hydraulic resistance of blood vessels, or the changes in aortic pressure, and the oxygen (or carbon dioxide) concentration.

Stability Analysis of Flow Induced by the Traveling Magnetic Field

NASA Technical Reports Server (NTRS)

Mazuruk, Konstantin

2003-01-01

Re-circulating flow in molten metal columns can be conveniently induced by the axisymmetric traveling magnetic field. A number of applications can benefit from this technique, such as mixing under microgravity environment, or.crysta1 growth from metallic melts. For small magnetic field excitations, the flow is laminar and stationary. As the imposed field increases, a more complex flow will set up in the cylindrical column. Conditions for stable laminar flow are of importance for practical applications. In this work, a linear stability analysis is performed in order to determine the onset of the bifurcation in the system. Here the analysis is restricted to the axisymmetric modes and the low-frequency regime.

Stability Analysis of Flow Induced by the Traveling Magnetic Field

NASA Technical Reports Server (NTRS)

Mazuruk, Konstantin

2003-01-01

Re-circulating flow in molten metal columns can be conveniently induced by the axisymmetric traveling magnetic field. A number of applications can benefit from this technique, such as mixing under microgravity environment, or crysta1 growth from metallic melts. For small magnetic field excitations, the flow is laminar and stationary. As the imposed field increases, a more complex flow will set up in the cylindrical column. Conditions for stable laminar flow are of importance for practical applications. In this work, a linear stability analysis is performed in order to determine the onset of the bifurcation in the system. Here the analysis is restricted to the axisymmetric modes and the low-frequency regime.

Theoretical stability in coefficient inverse problems for general hyperbolic equations with numerical reconstruction

NASA Astrophysics Data System (ADS)

Yu, Jie; Liu, Yikan; Yamamoto, Masahiro

2018-04-01

In this article, we investigate the determination of the spatial component in the time-dependent second order coefficient of a hyperbolic equation from both theoretical and numerical aspects. By the Carleman estimates for general hyperbolic operators and an auxiliary Carleman estimate, we establish local Hölder stability with either partial boundary or interior measurements under certain geometrical conditions. For numerical reconstruction, we minimize a Tikhonov functional which penalizes the gradient of the unknown function. Based on the resulting variational equation, we design an iteration method which is updated by solving a Poisson equation at each step. One-dimensional prototype examples illustrate the numerical performance of the proposed iteration.

[Culture conditions of engineered strain of L-asparaginase and the recombinant plasmid stability].

PubMed

Wang, Y; Qian, S; Ye, J; Meng, G; Zhang, S

1999-12-01

The growth curves of engineered strain JM105(pASN) were different in LB and M-3 media. The expression level and activity of L-asparaginase were affected apparently by both biomass and induction time. Glucose repression of production of L-asparaginase was found. The stability of the recombinant plasmid pASN in different host strains and in LB and M-3 media was determined. After cultivation inLB broth and M-3 media at 30 degrees C for more than 50 generations without antibiotic selection, then induced at 42 degrees C for up to 5 h, the engineered strains were proved to be stable, except for DHA alpha (pASN).

Generation of sub-optical-cycle, carrier-envelope-phase--insensitive, extreme-uv pulses via nonlinear stabilization in a waveguide

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

Sandhu, Arvinder S.; Gagnon, Etienne; Paul, Ariel

2006-12-15

We present evidence for a new regime of high-harmonic generation in a waveguide where bright, sub-optical-cycle, quasimonochromatic, extreme ultraviolet (EUV) light is generated via a mechanism that is relatively insensitive to carrier-envelope phase fluctuations. The interplay between the transient plasma which determines the phase matching conditions and the instantaneous laser intensity which drives harmonic generation gives rise to a new nonlinear stabilization mechanism in the waveguide, localizing the phase-matched EUV emission to within sub-optical-cycle duration. The sub-optical-cycle EUV emission generated by this mechanism can also be selectively optimized in the spectral domain by simple tuning of parameters.

Anchoring of development workings in a zone of influence of mining in case of the level anchoring system

NASA Astrophysics Data System (ADS)

Demin, V. F.; Fofanov, O. B.; Demina, T. V.; Yavorskiy, V. V.

2017-02-01

Regularities of the change of the stress-strain state of coal containing rock masses, depending on mining-geological factors, were revealed. These factors allow establishing rational parameters of anchoring of wall rocks to enhance the stability of development workings. Specific conditions of the deflected mode, displays of rock pressure, terms of maintenance depending on technological parameters are investigated. Researches allowed determining the degree of their development influence on the efficiency of application of the anchoring of the hollow making and will allow a reasonable application of anchoring certificates, provide stability of the rocks mining and reduce expenses on its realization and maintenance.

Unexpected Ground-State Structure and Mechanical Properties of Ir₂Zr Intermetallic Compound.

PubMed

Zhang, Meiguang; Cao, Rui; Zhao, Meijie; Du, Juan; Cheng, Ke

2018-01-10

Using an unbiased structure searching method, a new orthorhombic Cmmm structure consisting of ZrIr 12 polyhedron building blocks is predicted to be the thermodynamic ground-state of stoichiometric intermetallic Ir₂Zr in Ir-Zr systems. The formation enthalpy of the Cmmm structure is considerably lower than that of the previously synthesized Cu₂Mg-type phase, by ~107 meV/atom, as demonstrated by the calculation of formation enthalpy. Meanwhile, the phonon dispersion calculations further confirmed the dynamical stability of Cmmm phase under ambient conditions. The mechanical properties, including elastic stability, rigidity, and incompressibility, as well as the elastic anisotropy of Cmmm -Ir₂Zr intermetallic, have thus been fully determined. It is found that the predicted Cmmm phase exhibits nearly elastic isotropic and great resistance to shear deformations within the (100) crystal plane. Evidence of atomic bonding related to the structural stability for Ir₂Zr were manifested by calculations of the electronic structures.

Modelling and tuning for a time-delayed vibration absorber with friction

NASA Astrophysics Data System (ADS)

Zhang, Xiaoxu; Xu, Jian; Ji, Jinchen

2018-06-01

This paper presents an integrated analytical and experimental study to the modelling and tuning of a time-delayed vibration absorber (TDVA) with friction. In system modelling, this paper firstly applies the method of averaging to obtain the frequency response function (FRF), and then uses the derived FRF to evaluate the fitness of different friction models. After the determination of the system model, this paper employs the obtained FRF to evaluate the vibration absorption performance with respect to tunable parameters. A significant feature of the TDVA with friction is that its stability is dependent on the excitation parameters. To ensure the stability of the time-delayed control, this paper defines a sufficient condition for stability estimation. Experimental measurements show that the dynamic response of the TDVA with friction can be accurately predicted and the time-delayed control can be precisely achieved by using the modelling and tuning technique provided in this paper.

The stability of nonlinear dynamos and the limited role of kinematic growth rates

NASA Astrophysics Data System (ADS)

Brandenburg, A.; Krause, F.; Meinel, R.; Moss, D.; Tuominen, I.

1989-04-01

The growth rate behavior of several kinematic dynamo models was investigated in the context of the observation that, as a rule, a magnetic field of a single symmetry dominates in the sun and other cosmic objects. For all dynamo models considered, it is shown that, as the dynamo numbers increase, the kinematic growth rates of fields of different parities are asymptotically equal, indicating that growth rates do not dominate the final state of the field. The possibility that the stability of different solutions of nonlinear dynamos determines the final state was then investigated. Dynamo models in spherical geometry were found in which both symmetric and antisymmetric solutions are stable. The kind of symmetry finally established depends in these cases on the initial conditions, i.e., on the history of the object. It is noted that the basic mechanism stabilizing or destabilizing different solutions is not well understood.

The stability of a trailing-line vortex in compressible flow

NASA Technical Reports Server (NTRS)

Stott, Jillian A. K.; Duck, Peter W.

1992-01-01

We consider the inviscid stability of the Batchelor (1964) vortex in a compressible flow. The problem is tackled numerically and also asymptotically, in the limit of large (aximuthal and streamwise) wavenumbers, together with large Mach numbers. The nature of the solution passes through different regimes as the Mach number increases, relative to the wavenumbers. At very high wavenumbers and Mach numbers, the mode which is present in the incompressible case ceases to be unstable, while new 'center mode' forms, whose stability characteristics, are determined primarily by conditions close to the vortex axis. We find that generally the flow becomes less unstable as the Mach number increases, and that the regime of instability appears generally confined to disturbances in a direction counter to the direction of the rotation of the swirl of the vortex. Throughout the paper, comparison is made between our numerical results and results obtained from the various asymptotic theories.