Amperometric detector for gas chromatography based on a silica sol-gel solid electrolyte.

PubMed

Steinecker, William H; Miecznikowski, Krzysztof; Kulesza, Pawel J; Sandlin, Zechariah D; Cox, James A

2017-11-01

An electrochemical cell comprising a silica sol-gel solid electrolyte, a working electrode that protrudes into a gas phase, and reference and counter electrodes that contact the solid electrolyte comprises an amperometric detector for gas chromatography. Under potentiostatic conditions, a current related to the concentration of an analyte in the gas phase is produced by its oxidation at the three-phase boundary among the sol-gel, working electrode, and the gas phase. The sol-gel is processed to contain an electrolyte that also serves as a humidistat to maintain a constant water activity even in the presence the gas chromatographic mobile phase. Response was demonstrated toward a diverse set of analytes, namely hydrogen, 1,2-ethandithiol, phenol, p-cresol, and thioanisole. Using flow injection amperometry of hydrogen with He as the carrier gas, 90% of the steady-state current was achieved in < 1s at a flow rate of 20mLmin -1 . A separation of 1,2-ethandithiol, phenol, p-cresol, and thioanisole at a 2.2mLmin -1 flow rate was achieved with respective detection limits (k = 3 criterion) of 4, 1, 3, and 70 ppmv when the working electrode potential was 800mV. Copyright © 2017 Elsevier B.V. All rights reserved.

Electrolyte-free Amperometric Immunosensor using a Dendritic Nanotip†

PubMed Central

Kim, Jong-Hoon; Hiraiwa, Morgan; Lee, Hyun-Boo; Lee, Kyong-Hoon; Cangelosi, Gerard A.; Chung, Jae-Hyun

2013-01-01

Electric detection using a nanocomponent may lead to platforms for rapid and simple biosensing. Sensors composed of nanotips or nanodots have been described for highly sensitive amperometry enabled by confined geometry. However, both fabrication and use of nanostructured sensors remain challenging. This paper describes a dendritic nanotip used as an amperometric biosensor for highly sensitive detection of target bacteria. A dendritic nanotip is structured by Si nanowires coated with single-walled carbon nanotubes (SWCNTs) for generation of a high electric field. For reliable measurement using the dendritic structure, Si nanowires were uniformly fabricated by ultraviolet (UV) lithography and etching. The dendritic structure effectively increased the electric current density near the terminal end of the nanotip according to numerical computation. The electrical characteristics of a dendritic nanotip with additional protein layers was studied by cyclic voltammetry and I–V measurement in deionized (DI) water. When the target bacteria dielectrophoretically captured onto a nanotip were bound with fluorescence antibodies, the electric current through DI water decreased. Measurement results were consistent with fluorescence- and electron microscopy. The sensitivity of the amperometry was 10 cfu/sample volume (103 cfu/mL), which was equivalent to the more laborious fluorescence measurement method. The simple configuration of a dendritic nanotip can potentially offer an electrolyte-free detection platform for sensitive and rapid biosensors. PMID:23585927

Electrolyte-free Amperometric Immunosensor using a Dendritic Nanotip.

PubMed

Kim, Jong-Hoon; Hiraiwa, Morgan; Lee, Hyun-Boo; Lee, Kyong-Hoon; Cangelosi, Gerard A; Chung, Jae-Hyun

2013-01-01

Electric detection using a nanocomponent may lead to platforms for rapid and simple biosensing. Sensors composed of nanotips or nanodots have been described for highly sensitive amperometry enabled by confined geometry. However, both fabrication and use of nanostructured sensors remain challenging. This paper describes a dendritic nanotip used as an amperometric biosensor for highly sensitive detection of target bacteria. A dendritic nanotip is structured by Si nanowires coated with single-walled carbon nanotubes (SWCNTs) for generation of a high electric field. For reliable measurement using the dendritic structure, Si nanowires were uniformly fabricated by ultraviolet (UV) lithography and etching. The dendritic structure effectively increased the electric current density near the terminal end of the nanotip according to numerical computation. The electrical characteristics of a dendritic nanotip with additional protein layers was studied by cyclic voltammetry and I-V measurement in deionized (DI) water. When the target bacteria dielectrophoretically captured onto a nanotip were bound with fluorescence antibodies, the electric current through DI water decreased. Measurement results were consistent with fluorescence- and electron microscopy. The sensitivity of the amperometry was 10 cfu/sample volume (10 3 cfu/mL), which was equivalent to the more laborious fluorescence measurement method. The simple configuration of a dendritic nanotip can potentially offer an electrolyte-free detection platform for sensitive and rapid biosensors.

Wireless Instantaneous Neurotransmitter Concentration Sensing System (WINCS) for intraoperative neurochemical monitoring.

PubMed

Kimble, Christopher J; Johnson, David M; Winter, Bruce A; Whitlock, Sidney V; Kressin, Kenneth R; Horne, April E; Robinson, Justin C; Bledsoe, Jonathan M; Tye, Susannah J; Chang, Su-Youne; Agnesi, Filippo; Griessenauer, Christoph J; Covey, Daniel; Shon, Young-Min; Bennet, Kevin E; Garris, Paul A; Lee, Kendall H

2009-01-01

The Wireless Instantaneous Neurotransmitter Concentration Sensing System (WINCS) measures extracellular neurotransmitter concentration in vivo and displays the data graphically in nearly real time. WINCS implements two electroanalytical methods, fast-scan cyclic voltammetry (FSCV) and fixed-potential amperometry (FPA), to measure neurotransmitter concentrations at an electrochemical sensor, typically a carbon-fiber microelectrode. WINCS comprises a battery-powered patient module and a custom software application (WINCSware) running on a nearby personal computer. The patient module impresses upon the electrochemical sensor either a constant potential (for FPA) or a time-varying waveform (for FSCV). A transimpedance amplifier converts the resulting current to a signal that is digitized and transmitted to the base station via a Bluetooth radio link. WINCSware controls the operational parameters for FPA or FSCV, and records the transmitted data stream. Filtered data is displayed in various formats, including a background-subtracted plot of sequential FSCV scans - a representation that enables users to distinguish the signatures of various analytes with considerable specificity. Dopamine, glutamate, adenosine and serotonin were selected as analytes for test trials. Proof-of-principle tests included in vitro flow-injection measurements and in vivo measurements in rat and pig. Further testing demonstrated basic functionality in a 3-Tesla MRI unit. WINCS was designed in compliance with consensus standards for medical electrical device safety, and it is anticipated that its capability for real-time intraoperative monitoring of neurotransmitter release at an implanted sensor will prove useful for advancing functional neurosurgery.

Wireless Instantaneous Neurotransmitter Concentration Sensing System (WINCS) for Intraoperative Neurochemical Monitoring

PubMed Central

Kimble, Christopher J.; Johnson, David M.; Winter, Bruce A.; Whitlock, Sidney V.; Kressin, Kenneth R.; Horne, April E.; Robinson, Justin C.; Bledsoe, Jonathan M.; Tye, Susannah J.; Chang, Su-Youne; Agnesi, Filippo; Griessenauer, Christoph J.; Covey, Daniel; Shon, Young-Min; Bennet, Kevin E.; Garris, Paul A.; Lee, Kendall H.

2010-01-01

The Wireless Instantaneous Neurotransmitter Concentration Sensing System (WINCS) measures extracellular neurotransmitter concentration in vivo and displays the data graphically in nearly real time. WINCS implements two electroanalytical methods, fast-scan cyclic voltammetry (FSCV) and fixed-potential amperometry (FPA), to measure neurotransmitter concentrations at an electrochemical sensor, typically a carbon-fiber microelectrode. WINCS comprises a battery-powered patient module and a custom software application (WINCSware) running on a nearby personal computer. The patient module impresses upon the electrochemical sensor either a constant potential (for FPA) or a time-varying waveform (for FSCV). A transimpedance amplifier converts the resulting current to a signal that is digitized and transmitted to the base station via a Bluetooth® radio link. WINCSware controls the operational parameters for FPA or FSCV, and records the transmitted data stream. Filtered data is displayed in various formats, including a background-subtracted plot of sequential FSCV scans—a representation that enables users to distinguish the signatures of various analytes with considerable specificity. Dopamine, glutamate, adenosine and serotonin were selected as analytes for test trials. Proof-of-principle tests included in vitro flow-injection measurements and in vivo measurements in rat and pig. Further testing demonstrated basic functionality in a 3-Tesla MRI unit. WINCS was designed in compliance with consensus standards for medical electrical device safety, and it is anticipated that its capability for real-time intraoperative monitoring of neurotransmitter release at an implanted sensor will prove useful for advancing functional neurosurgery. PMID:19963865

Fabrication and Characterization of Ultrathin-ring Electrodes for Pseudo-steady-state Amperometric Detection.

PubMed

Kitazumi, Yuki; Hamamoto, Katsumi; Noda, Tatsuo; Shirai, Osamu; Kano, Kenji

2015-01-01

The fabrication of ultrathin-ring electrodes with a diameter of 2 mm and a thickness of 100 nm is established. The ultrathin-ring electrodes provide a large density of pseudo-steady-state currents, and realize pseudo-steady-state amperometry under quiescent conditions without a Faraday cage. Under the limiting current conditions, the current response at the ultrathin-ring electrode can be well explained by the theory of the microband electrode response. Cyclic voltammograms at the ultrathin-ring electrode show sigmoidal characteristics with some hysteresis. Numerical simulation reveals that the hysteresis can be ascribed to the time-dependence of pseudo-steady-state current. The performance of amperometry with the ultrathin-ring electrode has been verified in its application to redox enzyme kinetic measurements.

Surface-modified CMOS IC electrochemical sensor array targeting single chromaffin cells for highly parallel amperometry measurements.

PubMed

Huang, Meng; Delacruz, Joannalyn B; Ruelas, John C; Rathore, Shailendra S; Lindau, Manfred

2018-01-01

Amperometry is a powerful method to record quantal release events from chromaffin cells and is widely used to assess how specific drugs modify quantal size, kinetics of release, and early fusion pore properties. Surface-modified CMOS-based electrochemical sensor arrays allow simultaneous recordings from multiple cells. A reliable, low-cost technique is presented here for efficient targeting of single cells specifically to the electrode sites. An SU-8 microwell structure is patterned on the chip surface to provide insulation for the circuitry as well as cell trapping at the electrode sites. A shifted electrode design is also incorporated to increase the flexibility of the dimension and shape of the microwells. The sensitivity of the electrodes is validated by a dopamine injection experiment. Microwells with dimensions slightly larger than the cells to be trapped ensure excellent single-cell targeting efficiency, increasing the reliability and efficiency for on-chip single-cell amperometry measurements. The surface-modified device was validated with parallel recordings of live chromaffin cells trapped in the microwells. Rapid amperometric spikes with no diffusional broadening were observed, indicating that the trapped and recorded cells were in very close contact with the electrodes. The live cell recording confirms in a single experiment that spike parameters vary significantly from cell to cell but the large number of cells recorded simultaneously provides the statistical significance.

Parsing glucose entry into the brain: novel findings obtained with enzyme-based glucose biosensors.

PubMed

Kiyatkin, Eugene A; Wakabayashi, Ken T

2015-01-21

Extracellular levels of glucose in brain tissue reflect dynamic balance between its gradient-dependent entry from arterial blood and its use for cellular metabolism. In this work, we present several sets of previously published and unpublished data obtained by using enzyme-based glucose biosensors coupled with constant-potential high-speed amperometry in freely moving rats. First, we consider basic methodological issues related to the reliability of electrochemical measurements of extracellular glucose levels in rats under physiologically relevant conditions. Second, we present data on glucose responses induced in the nucleus accumbens (NAc) by salient environmental stimuli and discuss the relationships between local neuronal activation and rapid glucose entry into brain tissue. Third, by presenting data on changes in NAc glucose induced by intravenous and intragastric glucose delivery, we discuss other mechanisms of glucose entry into the extracellular domain following changes in glucose blood concentrations. Lastly, by showing the pattern of NAc glucose fluctuations during glucose-drinking behavior, we discuss the relationships between "active" and "passive" glucose entry to the brain, its connection to behavior-related metabolic activation, and the possible functional significance of these changes in behavioral regulation. These data provide solid experimental support for the "neuronal" hypothesis of neurovascular coupling, which postulates the critical role of neuronal activity in rapid regulation of vascular tone, local blood flow, and entry of glucose and oxygen to brain tissue to maintain active cellular metabolism.

Determination of Phenolic Acids in Sugarcane Vinasse by HPLC with Pulse Amperometry

PubMed Central

Freitas, P. V.; Beluomini, M. A.; da Silva, J. L.; Stradiotto, N. R.

2018-01-01

A reversed-phase liquid chromatographic separation with pulsed amperometric detection of phenolic acids at a glassy carbon electrode is described. Chromatographic separation was carried out in isocratic conditions using 0.20 mol·L−1 acetic acid (pH 5.0)/water (80 : 20, v/v) as mobile phase under constant working potential mode of 0.80 V. Chromatographic peaks presented high resolution and separation. Calibration curves exhibited excellent correlation coefficients, above 0.995. Linear ranges of the analytes, in mg L−1, were of 0.018–18 (gallic acid), 0.146–19 (vanillic acid), 0.13–17 (caffeic acid), 0.016–16 (ferulic acid), and 0.008–17 (p-coumaric acid), respectively. Limits of detection ranged from 1.6 to 97 μg·L−1 and precision varied in 1.73–3.78% interval. Concentrations of 19 ± 0.51 mg·L−1 and 7.8 ± 2.5 mg·L−1 were found for vanillic and caffeic acids, respectively, in a sugarcane vinasse sample. Gallic, ferulic, and p-coumaric acids were not detected. Recovery results demonstrated that the proposed method is accurate, and it can be used to detect and quantify phenolic acids in sugarcane vinasse without any influence of interferents. PMID:29600112

Electrochemical Quantification of the Antioxidant Capacity of Medicinal Plants Using Biosensors

PubMed Central

Rodríguez-Sevilla, Erika; Ramírez-Silva, María-Teresa; Romero-Romo, Mario; Ibarra-Escutia, Pedro; Palomar-Pardavé, Manuel

2014-01-01

The working area of a screen-printed electrode, SPE, was modified with the enzyme tyrosinase (Tyr) using different immobilization methods, namely entrapment with water-soluble polyvinyl alcohol (PVA), cross-linking using glutaraldehyde (GA), and cross-linking using GA and human serum albumin (HSA); the resulting electrodes were termed SPE/Tyr/PVA, SPE/Tyr/GA and SPE/Tyr/HSA/GA, respectively. These biosensors were characterized by means of amperometry and EIS techniques. From amperometric evaluations, the apparent Michaelis-Menten constant, Km′, of each biosensor was evaluated while the respective charge transfer resistance, Rct, was assessed from impedance measurements. It was found that the SPE/Tyr/GA had the smallest Km′ (57 ± 7) μM and Rct values. This electrode also displayed both the lowest detection and quantification limits for catechol quantification. Using the SPE/Tyr/GA, the Trolox Equivalent Antioxidant Capacity (TEAC) was determined from infusions prepared with “mirto” (Salvia microphylla), “hHierba dulce” (Lippia dulcis) and “salve real” (Lippia alba), medicinal plants commonly used in Mexico. PMID:25111237

Electrochemical quantification of the antioxidant capacity of medicinal plants using biosensors.

PubMed

Rodríguez-Sevilla, Erika; Ramírez-Silva, María-Teresa; Romero-Romo, Mario; Ibarra-Escutia, Pedro; Palomar-Pardavé, Manuel

2014-08-08

The working area of a screen-printed electrode, SPE, was modified with the enzyme tyrosinase (Tyr) using different immobilization methods, namely entrapment with water-soluble polyvinyl alcohol (PVA), cross-linking using glutaraldehyde (GA), and cross-linking using GA and human serum albumin (HSA); the resulting electrodes were termed SPE/Tyr/PVA, SPE/Tyr/GA and SPE/Tyr/HSA/GA, respectively. These biosensors were characterized by means of amperometry and EIS techniques. From amperometric evaluations, the apparent Michaelis-Menten constant, Km', of each biosensor was evaluated while the respective charge transfer resistance, Rct, was assessed from impedance measurements. It was found that the SPE/Tyr/GA had the smallest Km' (57 ± 7) µM and Rct values. This electrode also displayed both the lowest detection and quantification limits for catechol quantification. Using the SPE/Tyr/GA, the Trolox Equivalent Antioxidant Capacity (TEAC) was determined from infusions prepared with "mirto" (Salvia microphylla), "hHierba dulce" (Lippia dulcis) and "salve real" (Lippia alba), medicinal plants commonly used in Mexico.

Selective Amperometric Recording of Endogenous Ascorbate Secretion from a Single Rat Adrenal Chromaffin Cell with Pretreated Carbon Fiber Microelectrodes.

PubMed

Wang, Kai; Xiao, Tongfang; Yue, Qingwei; Wu, Fei; Yu, Ping; Mao, Lanqun

2017-09-05

Quantitative description of ascorbate secretion at a single-cell level is of great importance in physiological studies; however, most studies on the ascorbate secretion have so far been performed through analyzing cell extracts with high performance liquid chromatography, which lacks time resolution and analytical performance on a single-cell level. This study demonstrates a single-cell amperometry with carbon fiber microelectrodes (CFEs) to selectively monitor amperometric vesicular secretion of endogenous ascorbate from a single rat adrenal chromaffin cell. The CFEs are electrochemically pretreated in a weakly basic solution (pH 9.5), and such pretreatment essentially enables the oxidation of ascorbate to occur at a relatively low potential (i.e., 0.0 V vs Ag/AgCl), and further a high selectivity for ascorbate measurement over endogenously existing electroactive species such as epinephrine, norepinephrine, and dopamine. The selectivity is ensured by much larger amperometric response at the pretreated CFEs toward ascorbate over those toward other endogenously existing electroactive species added into the solution or ejected to the electrode with a micropuffer pipet, and by the totally suppressed current response by adding ascorbate oxidase into the cell lysate. With the pretreated CFE-based single-cell amperometry developed here, exocytosis of endogenous ascorbate of rat adrenal chromaffin cells is directly observed and ensured with the calcium ion-dependent high K + -induced secretion of endogenous ascorbate from the cells. Moreover, the quantitative information on the exocytosis of endogenous ascorbate is provided.

Insect haptoelectrical stimulation of Venus flytrap triggers exocytosis in gland cells.

PubMed

Scherzer, Sönke; Shabala, Lana; Hedrich, Benjamin; Fromm, Jörg; Bauer, Hubert; Munz, Eberhard; Jakob, Peter; Al-Rascheid, Khaled A S; Kreuzer, Ines; Becker, Dirk; Eiblmeier, Monika; Rennenberg, Heinz; Shabala, Sergey; Bennett, Malcolm; Neher, Erwin; Hedrich, Rainer

2017-05-02

The Venus flytrap Dionaea muscipula captures insects and consumes their flesh. Prey contacting touch-sensitive hairs trigger traveling electrical waves. These action potentials (APs) cause rapid closure of the trap and activate secretory functions of glands, which cover its inner surface. Such prey-induced haptoelectric stimulation activates the touch hormone jasmonate (JA) signaling pathway, which initiates secretion of an acidic hydrolase mixture to decompose the victim and acquire the animal nutrients. Although postulated since Darwin's pioneering studies, these secretory events have not been recorded so far. Using advanced analytical and imaging techniques, such as vibrating ion-selective electrodes, carbon fiber amperometry, and magnetic resonance imaging, we monitored stimulus-coupled glandular secretion into the flytrap. Trigger-hair bending or direct application of JA caused a quantal release of oxidizable material from gland cells monitored as distinct amperometric spikes. Spikes reminiscent of exocytotic events in secretory animal cells progressively increased in frequency, reaching steady state 1 d after stimulation. Our data indicate that trigger-hair mechanical stimulation evokes APs. Gland cells translate APs into touch-inducible JA signaling that promotes the formation of secretory vesicles. Early vesicles loaded with H + and Cl - fuse with the plasma membrane, hyperacidifying the "green stomach"-like digestive organ, whereas subsequent ones carry hydrolases and nutrient transporters, together with a glutathione redox moiety, which is likely to act as the major detected compound in amperometry. Hence, when glands perceive the haptoelectrical stimulation, secretory vesicles are tailored to be released in a sequence that optimizes digestion of the captured animal.

Amperometric IFN-γ immunosensors with commercially fabricated PCB sensing electrodes.

PubMed

Moschou, Despina; Greathead, Louise; Pantelidis, Panagiotis; Kelleher, Peter; Morgan, Hywel; Prodromakis, Themistoklis

2016-12-15

Lab-on-a-Chip (LoC) technology has the potential to revolutionize medical Point-of-Care diagnostics. Currently, considerable research efforts are focused on innovative production technologies that will make commercial upscaling of lab-on-chip products financially viable. Printed circuit board (PCB) manufacturing techniques have several advantages in this field. In this paper we focus on transferring a complete IFN-γ enzyme-linked immune-sorbent assay (ELISA) onto a commercial PCB electrochemical biosensing platform, We adapted a commercially available ELISA to detect the enzyme product TMB/H2O2 using amperometry, successfully reproducing the colorimetry-obtained ELISA standard curve. The results demonstrate the potential for the integration of these components into an automated, disposable, electronic ELISA Lab-on-PCB diagnostic platform. Copyright © 2016 Elsevier B.V. All rights reserved.

Development of a Flow Injection System for Differential Pulse Amperometry and Its Application for Diazepam Determination

PubMed Central

Antunović, Vesna; Tešanović, Slavna; Perušković, Danica; Stevanović, Nikola; Baošić, Rada; Mandić, Snežana

2018-01-01

This work presents the development of a flow injection system for differential pulse amperometry (DPA) for diazepam determination in the presence of oxygen. The thin flow cell consisted of the bare glassy carbon electrode, reference silver/silver chloride, and stainless steel as the auxiliary electrode. Electrochemical reduction of diazepam (DZP) was characterised by cyclic voltammetry. Azomethine reduction peak was used for DZP quantification. The detector response was linear in the range 20–250 µmol/dm3 of diazepam, with a calculated detection limit of 3.83 µg/cm3. Intraday and interday precision were 1.53 and 10.8%, respectively. The method was applied on three beverage samples, energetic drink, and two different beer samples, and obtained recoveries were from 93.65 up to 104.96%. The throughoutput of the method was up to 90 analyses per hour. PMID:29744233

Parsing Glucose Entry into the Brain: Novel Findings Obtained with Enzyme-Based Glucose Biosensors

PubMed Central

2015-01-01

Extracellular levels of glucose in brain tissue reflect dynamic balance between its gradient-dependent entry from arterial blood and its use for cellular metabolism. In this work, we present several sets of previously published and unpublished data obtained by using enzyme-based glucose biosensors coupled with constant-potential high-speed amperometry in freely moving rats. First, we consider basic methodological issues related to the reliability of electrochemical measurements of extracellular glucose levels in rats under physiologically relevant conditions. Second, we present data on glucose responses induced in the nucleus accumbens (NAc) by salient environmental stimuli and discuss the relationships between local neuronal activation and rapid glucose entry into brain tissue. Third, by presenting data on changes in NAc glucose induced by intravenous and intragastric glucose delivery, we discuss other mechanisms of glucose entry into the extracellular domain following changes in glucose blood concentrations. Lastly, by showing the pattern of NAc glucose fluctuations during glucose-drinking behavior, we discuss the relationships between “active” and “passive” glucose entry to the brain, its connection to behavior-related metabolic activation, and the possible functional significance of these changes in behavioral regulation. These data provide solid experimental support for the “neuronal” hypothesis of neurovascular coupling, which postulates the critical role of neuronal activity in rapid regulation of vascular tone, local blood flow, and entry of glucose and oxygen to brain tissue to maintain active cellular metabolism. PMID:25490002

Enhanced Cognition and Hypoglutamatergic Signaling in a Growth Hormone Receptor Knockout Mouse Model of Successful Aging.

PubMed

Hascup, Kevin N; Lynn, Mary K; Fitzgerald, Patrick J; Randall, Shari; Kopchick, John J; Boger, Heather A; Bartke, Andrzej; Hascup, Erin R

2017-03-01

Growth hormone receptor knockout (GHR-KO) mice are long lived with improved health span, making this an excellent model system for understanding biochemical mechanisms important to cognitive reserve. The purpose of the present study was to elucidate differences in cognition and glutamatergic dynamics between aged (20- to 24-month-old) GHR-KO and littermate controls. Glutamate plays a critical role in hippocampal learning and memory and is implicated in several neurodegenerative disorders, including Alzheimer's disease. Spatial learning and memory were assessed using the Morris water maze (MWM), whereas independent dentate gyrus (DG), CA3, and CA1 basal glutamate, release, and uptake measurements were conducted in isoflurane anesthetized mice utilizing an enzyme-based microelectrode array (MEA) coupled with constant potential amperometry. These MEAs have high temporal and low spatial resolution while causing minimal damage to the surrounding parenchyma. Littermate controls performed worse on the memory portion of the MWM behavioral task and had elevated DG, CA3, and CA1 basal glutamate and stimulus-evoked release compared with age-matched GHR-KO mice. CA3 basal glutamate negatively correlated with MWM performance. These results support glutamatergic regulation in learning and memory and may have implications for therapeutic targets to delay the onset of, or reduce cognitive decline, in Alzheimer's disease. © The Author 2016. Published by Oxford University Press on behalf of The Gerontological Society of America. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

Ultrasound Stimulation of Insulin Release from Pancreatic Beta Cells

NASA Astrophysics Data System (ADS)

Suarez Castellanos, Ivan M.

Type 2 diabetes (T2D) mellitus is a complex metabolic disease that has reached epidemic proportions in the United States and around the world. Controlling T2D is often difficult as pharmacological management routinely requires complex therapy with multiple medications, and loses its effectiveness over time. The objective of this dissertation was to explore a novel, non-pharmacological approach that utilizes the application of ultrasound energy to stimulate insulin release. Our experiments have focused on determination of effectiveness and safety of ultrasound application in stimulation of insulin release from the pancreatic beta cells. Our results showed that ultrasound treatment, applied at frequencies of 800 kHz and 1 MHz and intensities of 0.5 W/cm2 and 1 W/cm2, did not produce any significant effects on cell viability compared to sham group as assessed with trypan blue dye exclusion test and MTT cytotoxicity assay. ELISA quantification of insulin release from beta cells resulting from ultrasound treatment showed clinically-significant amounts of released insulin as compared to sham-treated beta cells. Carbon fiber amperometry detection of secretory events from dopamine-loaded beta cells treated with ultrasound showed that release of secretory content could be temporally controlled by careful selection of ultrasound parameters. Both ELISA and amperometry experiments demonstrated that ultrasound-stimulated insulin release is a calcium-dependent process, potentially mediated by the mechanical effects of ultrasound. This study demonstrated that therapeutic ultrasound is a technique capable of stimulating the release of insulin from pancreatic beta cells in a safe, effective and controlled manner.

Insect haptoelectrical stimulation of Venus flytrap triggers exocytosis in gland cells

PubMed Central

Scherzer, Sönke; Shabala, Lana; Hedrich, Benjamin; Fromm, Jörg; Bauer, Hubert; Munz, Eberhard; Jakob, Peter; Al-Rascheid, Khaled A. S.; Kreuzer, Ines; Becker, Dirk; Eiblmeier, Monika; Rennenberg, Heinz; Shabala, Sergey; Neher, Erwin; Hedrich, Rainer

2017-01-01

The Venus flytrap Dionaea muscipula captures insects and consumes their flesh. Prey contacting touch-sensitive hairs trigger traveling electrical waves. These action potentials (APs) cause rapid closure of the trap and activate secretory functions of glands, which cover its inner surface. Such prey-induced haptoelectric stimulation activates the touch hormone jasmonate (JA) signaling pathway, which initiates secretion of an acidic hydrolase mixture to decompose the victim and acquire the animal nutrients. Although postulated since Darwin’s pioneering studies, these secretory events have not been recorded so far. Using advanced analytical and imaging techniques, such as vibrating ion-selective electrodes, carbon fiber amperometry, and magnetic resonance imaging, we monitored stimulus-coupled glandular secretion into the flytrap. Trigger-hair bending or direct application of JA caused a quantal release of oxidizable material from gland cells monitored as distinct amperometric spikes. Spikes reminiscent of exocytotic events in secretory animal cells progressively increased in frequency, reaching steady state 1 d after stimulation. Our data indicate that trigger-hair mechanical stimulation evokes APs. Gland cells translate APs into touch-inducible JA signaling that promotes the formation of secretory vesicles. Early vesicles loaded with H+ and Cl− fuse with the plasma membrane, hyperacidifying the “green stomach”-like digestive organ, whereas subsequent ones carry hydrolases and nutrient transporters, together with a glutathione redox moiety, which is likely to act as the major detected compound in amperometry. Hence, when glands perceive the haptoelectrical stimulation, secretory vesicles are tailored to be released in a sequence that optimizes digestion of the captured animal. PMID:28416693

Advanced Oxygen Systems for Aircraft (Systemes d’Oxygene Avances)

DTIC Science & Technology

1996-04-01

This purge gas sweeps out the nitrogen and at the same time fills the micro- pore structure of the molecular sieve with the product gas. When the...electrochemical (amperometry, voltametry , polarography, coulometry), (c) spectrometry (mass spectrometry, ultraviolet spectrometry), (d) solid-state

Development of intraoperative electrochemical detection: wireless instantaneous neurochemical concentration sensor for deep brain stimulation feedback

PubMed Central

Van Gompel, Jamie J.; Chang, Su-Youne; Goerss, Stephan J.; Kim, In Yong; Kimble, Christopher; Bennet, Kevin E.; Lee, Kendall H.

2010-01-01

Deep brain stimulation (DBS) is effective when there appears to be a distortion in the complex neurochemical circuitry of the brain. Currently, the mechanism of DBS is incompletely understood; however, it has been hypothesized that DBS evokes release of neurochemicals. Well-established chemical detection systems such as microdialysis and mass spectrometry are impractical if one is assessing changes that are happening on a second-to-second time scale or for chronically used implanted recordings, as would be required for DBS feedback. Electrochemical detection techniques such as fast-scan cyclic voltammetry (FSCV) and amperometry have until recently remained in the realm of basic science; however, it is enticing to apply these powerful recording technologies to clinical and translational applications. The Wireless Instantaneous Neurochemical Concentration Sensor (WINCS) currently is a research device designed for human use capable of in vivo FSCV and amperometry, sampling at subsecond time resolution. In this paper, the authors review recent advances in this electrochemical application to DBS technologies. The WINCS can detect dopamine, adenosine, and serotonin by FSCV. For example, FSCV is capable of detecting dopamine in the caudate evoked by stimulation of the subthalamic nucleus/substantia nigra in pig and rat models of DBS. It is further capable of detecting dopamine by amperometry and, when used with enzyme linked sensors, both glutamate and adenosine. In conclusion, WINCS is a highly versatile instrument that allows near real-time (millisecond) detection of neurochemicals important to DBS research. In the future, the neurochemical changes detected using WINCS may be important as surrogate markers for proper DBS placement as well as the sensor component for a “smart” DBS system with electrochemical feedback that allows automatic modulation of stimulation parameters. Current work is under way to establish WINCS use in humans. PMID:20672923

A highly Ca2+-sensitive pool of granules is regulated by glucose and protein kinases in insulin-secreting INS-1 cells.

PubMed

Yang, Yan; Gillis, Kevin D

2004-12-01

We have used membrane capacitance measurements and carbon-fiber amperometry to assay exocytosis triggered by photorelease of caged Ca(2+) to directly measure the Ca(2+) sensitivity of exocytosis from the INS-1 insulin-secreting cell line. We find heterogeneity of the Ca(2+) sensitivity of release in that a small proportion of granules makes up a highly Ca(2+)-sensitive pool (HCSP), whereas the bulk of granules have a lower sensitivity to Ca(2+). A substantial HCSP remains after brief membrane depolarization, suggesting that the majority of granules with high sensitivity to Ca(2+) are not located close to Ca(2+) channels. The HCSP is enhanced in size by glucose, cAMP, and a phorbol ester, whereas the Ca(2+)-sensitive rate constant of exocytosis from the HCSP is unaffected by cAMP and phorbol ester. The effects of cAMP and phorbol ester on the HCSP are mediated by PKA and PKC, respectively, because they can be blocked with specific protein kinase inhibitors. The size of the HCSP can be enhanced by glucose even in the presence of high concentrations of phorbol ester or cAMP, suggesting that glucose can increase granule pool sizes independently of activation of PKA or PKC. The effects of PKA and PKC on the size of the HCSP are not additive, suggesting they converge on a common mechanism. Carbon-fiber amperometry was used to assay quantal exocytosis of serotonin (5-HT) from insulin-containing granules following preincubation of INS-1 cells with 5-HT and a precursor. The amount or kinetics of release of 5-HT from each granule is not significantly different between granules with higher or lower sensitivity to Ca(2+), suggesting that granules in these two pools do not differ in morphology or fusion kinetics. We conclude that glucose and second messengers can modulate insulin release triggered by a high-affinity Ca(2+) sensor that is poised to respond to modest, global elevations of [Ca(2+)](i).

Potentiostatic controlled nucleation and growth modes of electrodeposited cobalt thin films on n-Si(1 1 1)

NASA Astrophysics Data System (ADS)

Mechehoud, Fayçal; Khelil, Abdelbacet; Eddine Hakiki, Nour; Bubendorff, Jean-Luc

2016-08-01

The nucleation and growth of Co electrodeposits on n-Si(1 1 1) substrate have been investigated as a function of the applied potential in a large potential range using electrochemical techniques (voltammetry and chrono-amperometry) and surface imaging by atomic force microscopy (AFM). The surface preparation of the sample is crucial and we achieve a controlled n-Si(1 1 1) surface with mono-atomic steps and flat terraces. Using Scharifker-Hills models for fitting the current-time transients, we show that a transition from an instantaneous nucleation process to a progressive one occurs when the overpotential increases. A good agreement between the nucleation and growth parameters extracted from the models and the AFM data's is observed. The growth is of the Volmer-Weber type with a roughness and a spatial extension in the substrate plane of the deposited islands that increase with thickness.

Optimizing the Temporal Resolution of Fast-Scan Cyclic Voltammetry

PubMed Central

2012-01-01

Electrochemical detection with carbon-fiber microelectrodes has become an established method to monitor directly the release of dopamine from neurons and its uptake by the dopamine transporter. With constant potential amperometry (CPA), the measured current provides a real time view of the rapid concentration changes, but the method lacks chemical identification of the monitored species and markedly increases the difficulty of signal calibration. Monitoring with fast-scan cyclic voltammetry (FSCV) allows species identification and concentration measurements but often exhibits a delayed response time due to the time-dependent adsorption/desorption of electroactive species at the electrode. We sought to improve the temporal resolution of FSCV to make it more comparable to CPA by increasing the waveform repetition rate from 10 to 60 Hz with uncoated carbon-fiber electrodes. The faster acquisition led to diminished time delays of the recordings that tracked more closely with CPA measurements. The measurements reveal that FSCV at 10 Hz underestimates the normal rate of dopamine uptake by about 18%. However, FSCV collection at 10 and 60 Hz provide identical results when a dopamine transporter (DAT) blocker such as cocaine is bath applied. To verify further the utility of this method, we used transgenic mice that overexpress DAT. After accounting for the slight adsorption delay time, FSCV at 60 Hz adequately monitored the increased uptake rate that arose from overexpression of DAT and, again, was similar to CPA results. Furthermore, the utility of collecting data at 60 Hz was verified in an anesthetized rat by using a higher scan rate (2400 V/s) to increase sensitivity and the overall signal. PMID:22708011

Increased cortical extracellular adenosine correlates with seizure termination.

PubMed

Van Gompel, Jamie J; Bower, Mark R; Worrell, Gregory A; Stead, Matt; Chang, Su-Youne; Goerss, Stephan J; Kim, Inyong; Bennet, Kevin E; Meyer, Fredric B; Marsh, W Richard; Blaha, Charles D; Lee, Kendall H

2014-02-01

Seizures are currently defined by their electrographic features. However, neuronal networks are intrinsically dependent on neurotransmitters of which little is known regarding their periictal dynamics. Evidence supports adenosine as having a prominent role in seizure termination, as its administration can terminate and reduce seizures in animal models. Furthermore, microdialysis studies in humans suggest that adenosine is elevated periictally, but the relationship to the seizure is obscured by its temporal measurement limitations. Because electrochemical techniques can provide vastly superior temporal resolution, we test the hypothesis that extracellular adenosine concentrations rise during seizure termination in an animal model and humans using electrochemistry. White farm swine (n = 45) were used in an acute cortical model of epilepsy, and 10 human epilepsy patients were studied during intraoperative electrocorticography (ECoG). Wireless Instantaneous Neurotransmitter Concentration Sensor (WINCS)-based fast scan cyclic voltammetry (FSCV) and fixed potential amperometry were obtained utilizing an adenosine-specific triangular waveform or biosensors, respectively. Simultaneous ECoG and electrochemistry demonstrated an average adenosine increase of 260% compared to baseline, at 7.5 ± 16.9 s with amperometry (n = 75 events) and 2.6 ± 11.2 s with FSCV (n = 15 events) prior to electrographic seizure termination. In agreement with these animal data, adenosine elevation prior to seizure termination in a human patient utilizing FSCV was also seen. Simultaneous ECoG and electrochemical recording supports the hypothesis that adenosine rises prior to seizure termination, suggesting that adenosine itself may be responsible for seizure termination. Future work using intraoperative WINCS-based FSCV recording may help to elucidate the precise relationship between adenosine and seizure termination. Wiley Periodicals, Inc. © 2014 International League Against Epilepsy.

Ketamine Suppresses the Ventral Striatal Response to Reward Anticipation: A Cross-Species Translational Neuroimaging Study

PubMed Central

Francois, Jennifer; Grimm, Oliver; Schwarz, Adam J; Schweiger, Janina; Haller, Leila; Risterucci, Celine; Böhringer, Andreas; Zang, Zhenxiang; Tost, Heike; Gilmour, Gary; Meyer-Lindenberg, Andreas

2016-01-01

Convergent evidence implicates regional neural responses to reward anticipation in the pathogenesis of several psychiatric disorders, such as schizophrenia, where blunted ventral striatal responses to positive reward are observed in patients and at-risk populations. In vivo oxygen amperometry measurements in the ventral striatum in awake, behaving rats reveal reward-related tissue oxygen changes that closely parallel blood oxygen level dependent (BOLD) signal changes observed in human functional magnetic resonance imaging (fMRI), suggesting that a cross-species approach targeting this mechanism might be feasible in psychopharmacology. The present study explored modulatory effects of acute, subanaesthetic doses of ketamine—a pharmacological model widely used in psychopharmacological research, both preclinically and clinically—on ventral striatum activity during performance of a reward anticipation task in both species, using fMRI in humans and in vivo oxygen amperometry in rats. In a region-of-interest analysis conducted following a cross-over placebo and ketamine study in human subjects, an attenuated ventral striatal response during reward anticipation was observed following ketamine relative to placebo during performance of a monetary incentive delay task. In rats, a comparable attenuation of ventral striatal signal was found after ketamine challenge, relative to vehicle, in response to a conditioned stimulus that predicted delivery of reward. This study provides the first data in both species demonstrating an attenuating effect of acute ketamine on reward-related ventral striatal (O2) and fMRI signals. These findings may help elucidate a deeper mechanistic understanding of the potential role of ketamine as a model for psychosis, show that cross-species pharmacological experiments targeting reward signaling are feasible, and suggest this phenotype as a promising translational biomarker for the development of novel compounds, assessment of disease status, and treatment efficacy. PMID:26388147

Electrochemical Selective and Simultaneous Detection of Diclofenac and Ibuprofen in Aqueous Solution Using HKUST-1 Metal-Organic Framework-Carbon Nanofiber Composite Electrode.

PubMed

Motoc, Sorina; Manea, Florica; Iacob, Adriana; Martinez-Joaristi, Alberto; Gascon, Jorge; Pop, Aniela; Schoonman, Joop

2016-10-17

In this study, the detection protocols for the individual, selective, and simultaneous determination of ibuprofen (IBP) and diclofenac (DCF) in aqueous solutions have been developed using HKUST-1 metal-organic framework-carbon nanofiber composite (HKUST-CNF) electrode. The morphological and electrical characterization of modified composite electrode prepared by film casting was studied by scanning electronic microscopy and four-point-probe methods. The electrochemical characterization of the electrode by cyclic voltammetry (CV) was considered the reference basis for the optimization of the operating conditions for chronoamperometry (CA) and multiple-pulsed amperometry (MPA). This electrode exhibited the possibility to selectively detect IBP and DCF by simple switching the detection potential using CA. However, the MPA operated under optimum working conditions of four potential levels selected based on CV shape in relation to the potential value, pulse time, and potential level number, and order allowed the selective/simultaneous detection of IBP and DCF characterized by the enhanced detection performance. For this application, the HKUST-CNF electrode exhibited a good stability and reproducibility of the results was achieved.

Electrochemical Selective and Simultaneous Detection of Diclofenac and Ibuprofen in Aqueous Solution Using HKUST-1 Metal-Organic Framework-Carbon Nanofiber Composite Electrode

PubMed Central

Motoc, Sorina; Manea, Florica; Iacob, Adriana; Martinez-Joaristi, Alberto; Gascon, Jorge; Pop, Aniela; Schoonman, Joop

2016-01-01

In this study, the detection protocols for the individual, selective, and simultaneous determination of ibuprofen (IBP) and diclofenac (DCF) in aqueous solutions have been developed using HKUST-1 metal-organic framework-carbon nanofiber composite (HKUST-CNF) electrode. The morphological and electrical characterization of modified composite electrode prepared by film casting was studied by scanning electronic microscopy and four-point-probe methods. The electrochemical characterization of the electrode by cyclic voltammetry (CV) was considered the reference basis for the optimization of the operating conditions for chronoamperometry (CA) and multiple-pulsed amperometry (MPA). This electrode exhibited the possibility to selectively detect IBP and DCF by simple switching the detection potential using CA. However, the MPA operated under optimum working conditions of four potential levels selected based on CV shape in relation to the potential value, pulse time, and potential level number, and order allowed the selective/simultaneous detection of IBP and DCF characterized by the enhanced detection performance. For this application, the HKUST-CNF electrode exhibited a good stability and reproducibility of the results was achieved. PMID:27763509

Dynamin-related protein-1 controls fusion pore dynamics during platelet granule exocytosis.

PubMed

Koseoglu, Secil; Dilks, James R; Peters, Christian G; Fitch-Tewfik, Jennifer L; Fadel, Nathalie A; Jasuja, Reema; Italiano, Joseph E; Haynes, Christy L; Flaumenhaft, Robert

2013-03-01

Platelet granule exocytosis serves a central role in hemostasis and thrombosis. Recently, single-cell amperometry has shown that platelet membrane fusion during granule exocytosis results in the formation of a fusion pore that subsequently expands to enable the extrusion of granule contents. However, the molecular mechanisms that control platelet fusion pore expansion and collapse are not known. We identified dynamin-related protein-1 (Drp1) in platelets and found that an inhibitor of Drp1, mdivi-1, blocked exocytosis of both platelet dense and α-granules. We used single-cell amperometry to monitor serotonin release from individual dense granules and, thereby, measured the effect of Drp1 inhibition on fusion pore dynamics. Inhibition of Drp1 increased spike width and decreased prespike foot events, indicating that Drp1 influences fusion pore formation and expansion. Platelet-mediated thrombus formation in vivo after laser-induced injury of mouse cremaster arterioles was impaired after infusion of mdivi-1. These results demonstrate that inhibition of Drp1 disrupts platelet fusion pore dynamics and indicate that Drp1 can be targeted to control thrombus formation in vivo.

Tin oxide quantum dots embedded iron oxide composite as efficient lead sensor

NASA Astrophysics Data System (ADS)

Dutta, Dipa; Bahadur, Dhirendra

2018-04-01

SnO2 quantum dots (QDs) embedded iron oxide (IO) nanocomposite is fabricated and explored as a capable sensor for lead detection. Square wave anodic stripping voltammetry (SWASV) and amperometry have been used to explore the proposed sensor's response towards lead detection. The modified electrode shows linear current response for concentration of lead ranging from 99 nM to 6.6 µM with limit of detection 0.42 µM (34 ppb). Amperometry shows a detection limit as low as 0.18 nM (0.015 ppb); which is far below the permissible limit of lead in drinking water by World Health Organization. This proposed sensor shows linear current response (R2 = 0.98) for the lead concentration ranging from 133 × 10-9 to 4.4 × 10-6M. It also exhibits rapid response time of 12 sec with an ultra high sensitivity of 5.5 µA/nM. These detection properties promise the use of SnO2 QDs -IO composite for detection of lead in environmental sample with great ease.

One step preparation and electrochemical analysis of IQS, a cell-cell communication signal in the nosocomial pathogen Pseudomonas aeruginosa.

PubMed

Shang, Fengjun; Muimhneacháin, Eoin Ó; Jerry Reen, F; Buzid, Alyah; O'Gara, Fergal; Luong, John H T; Glennon, Jeremy D; McGlacken, Gerard P

2014-10-01

Pseudomonas aeruginosa uses a hierarchical cell-cell communication system consisting of a number of regulatory elements to coordinate the expression of bacterial virulence genes. Sensitive detection of quorum sensing (QS) molecules has the potential for early identification of P. aeruginosa facilitating early medical intervention. A recently isolated cell-cell communication molecule, a thiazole termed IQS, can bypass the las QS system of P. aeruginosa under times of stress, activating a subset of QS-controlled genes. This compound offers a new target for pathogen detection and has been prepared in a one step protocol. A simple electrochemical strategy was employed for its sensitive detection using boron-doped diamond and glassy carbon electrodes by cyclic voltammetry and amperometry. Copyright © 2014 Elsevier Ltd. All rights reserved.

An electrochemical acetylcholine sensor based on lichen-like nickel oxide nanostructure.

PubMed

Sattarahmady, N; Heli, H; Vais, R Dehdari

2013-10-15

Lichen-like nickel oxide nanostructure was synthesized by a simple method and characterized. The nanostructure was then applied to modify a carbon paste electrode and for the fabrication of a sensor, and the electrocatalytic oxidation of acetylcholine (ACh) on the modified electrode was investigated. The electrocatalytic efficiency of the nickel oxide nanostructure was compared with nickel micro- and nanoparticles, and the lichen-like nickel oxide nanostructure showed the highest efficiency. The mechanism and kinetics of the electrooxidation process were investigated by cyclic voltammetry, steady-state polarization curve and chronoamperometry. The catalytic rate constant and the charge transfer coefficient of ACh electrooxidation by the active nickel species, and the diffusion coefficient of ACh were reported. A sensitive and time-saving hydrodynamic amperometry method was developed for the determination of ACh. ACh was determined with a sensitivity of 392.4 mA M⁻¹ cm⁻² and a limit of detection of 26.7 μM. The sensor had the advantages of simple fabrication method without using any enzyme or reagent and immobilization step, high electrocatalytic activity, very high sensitivity, long-term stability, and antifouling surface property toward ACh and its oxidation product. Copyright © 2013 Elsevier B.V. All rights reserved.

Direct electron transfer of Phanerochaete chrysosporium cellobiose dehydrogenase at platinum and palladium nanoparticles decorated carbon nanotubes modified electrodes.

PubMed

Bozorgzadeh, Somayyeh; Hamidi, Hassan; Ortiz, Roberto; Ludwig, Roland; Gorton, Lo

2015-10-07

In the present work, platinum and palladium nanoparticles (PtNPs and PdNPs) were decorated on the surface of multi-walled carbon nanotubes (MWCNTs) by a simple thermal decomposition method. The prepared nanohybrids, PtNPs-MWCNTs and PdNPs-MWCNTs, were cast on the surface of spectrographic graphite electrodes and then Phanerochaete chrysosporium cellobiose dehydrogenase (PcCDH) was adsorbed on the modified layer. Direct electron transfer between PcCDH and the nanostructured modified electrodes was studied using flow injection amperometry and cyclic voltammetry. The maximum current responses (Imax) and the apparent Michaelis-Menten constants (K) for the different PcCDH modified electrodes were calculated by fitting the data to the Michaelis-Menten equation and compared. The sensitivity towards lactose was 3.07 and 3.28 μA mM(-1) at the PcCDH/PtNPs-MWCNTs/SPGE and PcCDH/PdNPs-MWCNTs/SPGE electrodes, respectively, which were higher than those measured at the PcCDH/MWCNTs/SPGE (2.60 μA mM(-1)) and PcCDH/SPGE (0.92 μA mM(-1)). The modified electrodes were additionally tested as bioanodes for biofuel cell applications.

Electrodeposited nanostructured MnO{sub 2} for non-enzymatic hydrogen peroxide sensing

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

Saha, B., E-mail: barnamala.saha@gmail.com; Jana, S. K.; Banerjee, S.

2015-06-24

Electrodeposited MnO{sub 2} nanostructure was synthesized on indium tin oxide coated glass electrode by cyclic voltammetry. The as obtained samples were subsequently characterized by atomic force microscopy and their electro-catalytic response towards hydrogen peroxide in alkaline medium of 0.1M NaOH was studied using cyclic voltammetry and amperometry.

Improved peroxide biosensor based on Horseradish Peroxidase/Carbon Nanotube on a thiol-modified gold electrode.

PubMed

Kafi, A K M; Naqshabandi, M; Yusoff, Mashitah M; Crossley, Maxwell J

2018-06-01

A new 3-dimensional (3D) network of crosslinked Horseradish Peroxidase/Carbon Nanotube (HRP/CNT) on a thiol-modified Au surface has been described in order to build up the effective electrical wiring of the enzyme units with the electrode. The synthesized 3D HRP/CNT network has been characterized with cyclic voltammetry and amperometry which results the establishment of direct electron transfer between the redox active unit of HRP and the Au surface. Electrochemical measurements reveal that the high biological activity and stability is exhibited by the immobilized HRP and a quasi-reversible redox peak of the redox centre of HRP was observed at about -0.355 and -0.275V vs. Ag/AgCl. The electron transfer rate constant, K S and electron transfer co-efficient α were found as 0.57s -1 and 0.42, respectively. Excellent electrocatalytic activity for the reduction of H 2 O 2 was exhibited by the developed biosensor. The proposed biosensor modified with HRP/CNT 3D network displays a broader linear range and a lower detection limit for H 2 O 2 determination. The linear range is from 1.0×10 -7 to 1.2×10 -4 M with a detection limit of 2.2.0×10 -8 M at 3σ. The Michaelies-Menten constant Kapp M value is estimated to be 0.19mM. Moreover, this biosensor exhibits very high sensitivity, good reproducibility and long-time stability. Copyright © 2017 Elsevier Inc. All rights reserved.

Imidazoline derivative templated synthesis of broccoli-like Bi2S3 and its electrocatalysis towards the direct electrochemistry of hemoglobin.

PubMed

Chen, Xiaoqian; Wang, Qingxiang; Wang, Liheng; Gao, Feng; Wang, Wei; Hu, Zhengshui

2015-04-15

A broccoli-like bismuth sulfide (bBi2S3) was synthesized via a solvothermal method using a self-made imidazoline derivative of 2-undecyl-1-dithioureido-ethyl-imidazoline as the soft template. The morphology and chemical constitution of the product were characterized by scanning electron microscope (SEM), transmission electron microscope (TEM) and X-ray diffraction (XRD). Electrochemical characterization experiments show that the bBi2S3 has the higher specific surface area and standard heterogeneous electron transfer rate constant than the rod-like Bi2S3 (rBi2S3). Hemoglobin (Hb) was then chosen as a protein model to investigate the electrocatalytic property of the synthesized bBi2S3. The results show that Hb entrapped in the composite film of chitosan and bBi2S3 displays an excellent direct electrochemistry, and retains its biocatalytic activity toward the electro-reduction of hydrogen peroxide. The current response in the amperometry shows a linear response to H2O2 concentrations in the range from 0.4 to 4.8µM with high sensitivity (444µAmM(-1)) and low detection limit (0.096µM). The Michaelis-Menten constant (KM(app)) of the fabricated bioelectrode for H2O2 was determined as low as 1µM. These results demonstrate that the synthesized bBi2S3 offers a new path for the immobilization of redox-active protein and the construction of the third-generation biosensors. Copyright © 2014 Elsevier B.V. All rights reserved.

Biosensing hydrogen peroxide utilizing carbon paste electrodes containing peroxidases naturally immobilized on coconut (Cocus nucifera L.) fibers.

PubMed

Kozan, J V B; Silva, R P; Serrano, S H P; Lima, A W O; Angnes, L

2007-05-22

A novel unmediated hydrogen peroxide biosensor based on the incorporation of fibrous tissue of coconut fruit in carbon paste matrix is presented. Cyclic voltammetry and amperometry were utilized to characterize the main electrochemical parameters and the performance of this new biosensor under different preparation and operation conditions. The resulting H2O2-sensitive biosensors respond rapidly (7 s to attain 90% of the signal), was operated at -0.15 V, presented linear response between 2.0x10(-4) and 3.4x10(-3) mol L(-1), the detection limit was estimated as 4.0x10(-5) mol L(-1). Its operation potential was situated between -0.2 and 0.1 V and the best pH was determined as 5.2. Electrodes containing 5% (w/w) of coconut fiber presented the best signal and their lifetime was extended to 3 months. The apparent Michaelis-Menten constant KM(app) and Vmax were estimated to be 8.90 mmol L(-1) and 6.92 mmol L(-1) microA(-1), respectively. The results obtained for determination of hydrogen peroxide in four pharmaceutical products (antiseptic solution, contact lenses cleaning solution, hair coloring cream and antiseptic dental rinse solution) were in agreement with those obtained by the spectrophotometric method. An additional advantage of these biosensors is the capacity to measure hydrogen peroxide even in samples with relatively low pH. To demonstrate the enzymatic activity of the coconut tissue, a very simple way was created during this work. Coconut fibers were immersed in H2O2 solution between two glass slides. Sequential images were taken to show the rapid generation of O2, attesting the high activity of the enzymes.

Characterisation of Weibel-Palade body fusion by amperometry in endothelial cells reveals fusion pore dynamics and the effect of cholesterol on exocytosis.

PubMed

Cookson, Emma A; Conte, Ianina L; Dempster, John; Hannah, Matthew J; Carter, Tom

2013-12-01

Regulated secretion from endothelial cells is mediated by Weibel-Palade body (WPB) exocytosis. Plasma membrane cholesterol is implicated in regulating secretory granule exocytosis and fusion pore dynamics; however, its role in modulating WPB exocytosis is not clear. To address this we combined high-resolution electrochemical analysis of WPB fusion pore dynamics, by amperometry, with high-speed optical imaging of WPB exocytosis following cholesterol depletion or supplementation in human umbilical vein endothelial cells. We identified serotonin (5-HT) immunoreactivity in WPBs, and VMAT1 expression allowing detection of secreted 5-HT as discrete current spikes during exocytosis. A high proportion of spikes (∼75%) had pre-spike foot signals, indicating that WPB fusion proceeds via an initial narrow pore. Cholesterol depletion significantly reduced pre-spike foot signal duration and increased the rate of fusion pore expansion, whereas cholesterol supplementation had broadly the reverse effect. Cholesterol depletion slowed the onset of hormone-evoked WPB exocytosis, whereas its supplementation increased the rate of WPB exocytosis and hormone-evoked proregion secretion. Our results provide the first analysis of WPB fusion pore dynamics and highlight an important role for cholesterol in the regulation of WPB exocytosis.

Preparation of TiO2-Decorated Boron Particles by Wet Ball Milling and their Photoelectrochemical Hydrogen and Oxygen Evolution Reactions

PubMed Central

Jung, Hye Jin; Nam, Kyusuk; Sung, Hong-Gye; Hyun, Hyung Soo; Sohn, Youngku; Shin, Weon Gyu

2016-01-01

TiO2-coated boron particles were prepared by a wet ball milling method, with the particle size distribution and average particle size being easily controlled by varying the milling operation time. Based on the results from X-ray photoelectron spectroscopy, transmission electron microscopy, energy dispersive X-ray analysis, and Fourier transform infrared spectroscopy, it was confirmed that the initial oxide layer on the boron particles surface was removed by the wet milling process, and that a new B–O–Ti bond was formed on the boron surface. The uniform TiO2 layer on the 150 nm boron particles was estimated to be 10 nm thick. Based on linear sweep voltammetry, cyclic voltammetry, current-time amperometry, and electrochemical impedance analyses, the potential for the application of TiO2-coated boron particles as a photoelectrochemical catalyst was demonstrated. A current of 250 μA was obtained at a potential of 0.5 V for hydrogen evolution, with an onset potential near to 0.0 V. Finally, a current of 220 μA was obtained at a potential of 1.0 V for oxygen evolution. PMID:28774132

Bacteria-Templated NiO Nanoparticles/Microstructure for an Enzymeless Glucose Sensor.

PubMed

Vaidyanathan, Settu; Cherng, Jong-Yuh; Sun, An-Cheng; Chen, Chien-Yen

2016-07-11

The bacterial-induced hollow cylinder NiO (HCNiO) nanomaterial was utilized for the enzymeless (without GOx) detection of glucose in basic conditions. The determination of glucose in 0.05 M NaOH solution with high sensitivity was performed using cyclic voltammetry (CV) and amperometry (i-t). The fundamental electrochemical parameters were analyzed and the obtained values of diffusion coefficient (D), heterogeneous rate constant (ks), electroactive surface coverage (Г), and transfer coefficient (alpha-α) are 1.75 × 10(-6) cm²/s, 57.65 M(-1)·s(-1), 1.45 × 10(-10) mol/cm², and 0.52 respectively. The peak current of the i-t method shows two dynamic linear ranges of calibration curves 0.2 to 3.5 µM and 0.5 to 250 µM for the glucose electro-oxidation. The Ni(2+)/Ni(3+) couple with the HCNiO electrode and the electrocatalytic properties were found to be sensitive to the glucose oxidation. The green chemistry of NiO preparation from bacteria and the high catalytic ability of the oxyhydroxide (NiOOH) is the good choice for the development of a glucose sensor. The best obtained sensitivity and limit of detection (LOD) for this sensor were 3978.9 µA mM(-1)·cm(-2) and 0.9 µM, respectively.

Electrochemical Determination of Pentachlorophenol in Water on a Multi-Wall Carbon Nanotubes-Epoxy Composite Electrode

PubMed Central

Remes, Adriana; Pop, Aniela; Manea, Florica; Baciu, Anamaria; Picken, Stephen J.; Schoonman, Joop

2012-01-01

The aim of this study was the preparation, characterization, and application of a multi-wall carbon nanotubes-epoxy composite electrode (MWCNT-EP) with 25%, wt. MWCNTs loading for the voltammetric/amperometric determination of pentachlorophenol (PCP) in aqueous solutions. The structural and morphological aspects of the MWCNT-EP composite electrode were examined by scanning electron microscopy. The electrical properties were characterized by direct-current conductivity measurements in relation with the percolation threshold. The electrochemical behavior of PCP at the MWCNT-EP composite electrode was investigated using cyclic voltammetry in 0.1 M Na2SO4 supporting electrolyte in order to establish the parameters for amperometric/voltammetric determination of PCP. The linear dependence of current vs. PCP concentrations was reached in a wide concentration range from 0.2 to 12 μM PCP using cyclic voltammetry, differential-pulsed voltammetry, square-wave voltammetry, chronoamperometry, and multiple-pulsed amperometry techniques. The best electroanalytical performances of this composite electrode were achieved using a pre-concentration/square-wave voltammetric technique and also multiple-pulsed amperometry techniques envisaging the practical applications. The ease of preparation, high sensitivity, and stability of this composite electrode should open novel avenues and applications for fabricating robust sensors for detection of many important species. PMID:22969335

Assessment of functional changes in nanoparticle-exposed neuroendocrine cells with amperometry: exploring the generalizability of nanoparticle-vesicle matrix interactions.

PubMed

Love, Sara A; Haynes, Christy L

2010-09-01

Using two of the most commonly synthesized noble metal nanoparticle preparations, citrate-reduced Au and Ag, the impacts of short-term accidental nanoparticle exposure are examined in primary culture murine adrenal medullary chromaffin cells. Transmission electron microscopy (TEM), inductively coupled plasma atomic emission spectroscopy (ICP-AES) and Alamar Blue viability studies revealed that nanoparticles are taken up by cells but do not decrease cell viability within 48 hours of exposure. Carbon-fiber microelectrode amperometry (CFMA) examination of exocytosis in nanoparticle-exposed cells revealed that nanoparticle exposure does lead to decreased secretion of chemical messenger molecules, of up to 32.5% at 48 hours of Au exposure. The kinetics of intravesicular species liberation also slows after nanoparticle exposure, between 30 and 50% for Au and Ag, respectively. Repeated stimulation of exocytosis demonstrated that these effects persisted during subsequent stimulations, meaning that nanoparticles do not interfere directly with the vesicle recycling machinery but also that cellular function is unable to recover following vesicle content expulsion. By comparing these trends with parallel studies done using mast cells, it is clear that similar exocytosis perturbations occur across cell types following noble metal nanoparticle exposure, supporting a generalizable effect of nanoparticle-vesicle interactions.

The Effects of Magnetic Exposure on the Nervous System: A study on the effects of low-strength low-frequency magnetic fields on neurotransmitter exocytosis and cell viability through ionic cyclotron resonance frequency

NASA Astrophysics Data System (ADS)

Saveriades, George

This PhD dissertation focuses on the study of the effects of magnetic exposure on biological systems using amperometry techniques and viability assays. In our prior work based on the cyclotron resonance model, chromaffin cells in physiological saline and Ca2+-free media were exposed for 5 minutes to a 2.7 muT magnetic field, with frequency sweeps going from 30-60 Hz (targeting several ions involved in exocytosis) and 44-48 Hz (targeting specifically Ca2+ ions), with noticeable effects on exocytosis. The present study extended the work on chromaffin cells by covering frequency sweeps for different ions, manipulating the time of exposure and the strength of the magnetic field. Furthermore, amperometry was conducted on acute coronal brain slices, to demonstrate that the recorded effects could be measured on neuronal tissue. The viability of chromaffin cells and primary neuronal cultures exposed to magnetic fields was also addressed. The results demonstrate that cellular exocytosis is sensitive to the frequency of the magnetic field it is exposed to, the strength of the magnetic field and the duration of exposure. No significant effects were established with regards to the viability of the cells exposed to magnetic fields.

Preparation and characterization of AuNPs/CNTs-ErGO electrochemical sensors for highly sensitive detection of hydrazine.

PubMed

Zhao, Zhenting; Sun, Yongjiao; Li, Pengwei; Zhang, Wendong; Lian, Kun; Hu, Jie; Chen, Yong

2016-09-01

A highly sensitive electrochemical sensor of hydrazine has been fabricated by Au nanoparticles (AuNPs) coating of carbon nanotubes-electrochemical reduced graphene oxide composite film (CNTs-ErGO) on glassy carbon electrode (GCE). Cyclic voltammetry and potential amperometry have been used to investigate the electrochemical properties of the fabricated sensors for hydrazine detection. The performances of the sensors were optimized by varying the CNTs to ErGO ratio and the quantity of Au nanoparticles. The results show that under optimal conditions, a sensitivity of 9.73μAμM(-1)cm(-2), a short response time of 3s, and a low detection limit of 0.065μM could be achieved with a linear concentration response range from 0.3μM to 319μM. The enhanced electrochemical performances could be attributed to the synergistic effect between AuNPs and CNTs-ErGO film and the outstanding catalytic effect of the Au nanoparticles. Finally, the sensor was successfully used to analyse the tap water, showing high potential for practical applications. Copyright © 2016 Elsevier B.V. All rights reserved.

Electrochemical sensing of total antioxidant capacity and polyphenol content in wine samples using amperometry online-coupled with microdialysis.

PubMed

Jakubec, Petr; Bancirova, Martina; Halouzka, Vladimir; Lojek, Antonin; Ciz, Milan; Denev, Petko; Cibicek, Norbert; Vacek, Jan; Vostalova, Jitka; Ulrichova, Jitka; Hrbac, Jan

2012-08-15

This work describes the method for total antioxidant capacity (TAC) and/or total content of phenolics (TCP) analysis in wines using microdialysis online-coupled with amperometric detection using a carbon microfiber working electrode. The system was tested on 10 selected wine samples, and the results were compared with total reactive antioxidant potential (TRAP), oxygen radical absorbance capacity (ORAC), and chemiluminescent determination of total antioxidant capacity (CL-TAC) methods using Trolox and catechin as standards. Microdialysis online-coupled with amperometric detection gives similar results to the widely used cyclic voltammetry methodology and closely correlates with ORAC and TRAP. The problem of electrode fouling is overcome by the introduction of an electrochemical cleaning step (1-2 min at the potential of 0 V vs Ag/AgCl). Such a procedure is sufficient to fully regenerate the electrode response for both red and white wine samples as well as catechin/Trolox standards. The appropriate size of microdialysis probes enables easy automation of the electrochemical TAC/TCP measurement using 96-well microtitration plates.

Gold-copper bimetallic nanoparticles supported on nano P zeolite modified carbon paste electrode as an efficient electrocatalyst and sensitive sensor for determination of hydrazine.

PubMed

Amiripour, Fatemeh; Azizi, Seyed Naser; Ghasemi, Shahram

2018-06-01

In this report, a facile, efficient and low cost electrochemical sensor based on bimetallic Au-Cu nanoparticles supported on P nanozeolite modified carbon paste electrode (Au-Cu/NPZ/CPE) was constructed and its efficiency for determination of hydrazine in trace level was studied. For this purpose, agro waste material, stem sweep ash (SSA) was employed as the starting material (silica source) for the synthesis of nano P zeolite (NPZ). After characterization of the synthesized NPZ by analytical instruments (scanning electronic microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) spectroscopy), construction of Au-Cu/NPZ/CPE was performed by three steps procedure involving preparation of nano P zeolite modified carbon paste electrode (NPZ/CPE), introducing Cu +2 ions into nano zeolite structure by ion exchange and electrochemical reduction of Cu +2 ions upon applying constant potential. This procedure is followed by partial replacement of Cu by Au due to galvanic replacement reaction (GRR). The electrochemical properties of hydrazine at the surface of Au-Cu/NPZ/CPE was evaluated using cyclic voltammetry (CV), amperometry, and chronoamperometry methods in 0.1 M phosphate buffer solution (PBS). It was found that the prepared sensor has higher electrocatalytic activity at a relatively lower potential compared to other modified electrodes including Au/NPZ/CPE, Cu/NPZ/CPE, Au-Cu/CPE and etc. Moreover, the proposed electrochemical sensor presented the favorable analytical properties for determination of hydrazine such as low detection limit (0.04 µM), rapid response time (3 s), wide linear range (0.01-150 mM), and high sensitivity (99.53 µA mM -1 ) that are related to the synergic effect of bimetallic of Au-Cu, porous structure and enough surface area of NPZ. In addition, capability of Au-Cu/NPZ/CPE sensor was successfully tested in real samples with good accuracy and precision. Copyright © 2018 Elsevier B.V. All rights reserved.

An improved glycerol biosensor with an Au-FeS-NAD-glycerol-dehydrogenase anode.

PubMed

Mahadevan, Aishwarya; Fernando, Sandun

2017-06-15

An improved glycerol biosensor was developed via direct attachment of NAD + -glycerol dehydrogenase coenzyme-apoenzyme complex onto supporting gold electrodes, using novel inorganic iron (II) sulfide (FeS)-based single molecular wires. Sensing performance factors, i.e., sensitivity, a detection limit and response time of the FeS and conventional pyrroloquinoline quinone (PQQ)-based biosensor were evaluated by dynamic constant potential amperometry at 1.3V under non-buffered conditions. For glycerol concentrations ranging from 1 to 25mM, a 77% increase in sensitivity and a 53% decrease in detection limit were observed for the FeS-based biosensor when compared to the conventional PQQ-based counterpart. The electrochemical behavior of the FeS-based glycerol biosensor was analyzed at different concentrations of glycerol, accompanied by an investigation into the effects of applied potential and scan rate on the current response. Effects of enzyme stimulants ((NH 4 ) 2 SO 4 and MnCl 2 ·4H 2 O) concentrations and buffers/pH (potassium phosphate buffer pH 6-8, Tris buffer pH 8-10) on the current responses generated by the FeS-based glycerol biosensor were also studied. The optimal detection conditions were 0.03M (NH 4 ) 2 SO 4 and 0.3µm MnCl 2 ·4H 2 O in non-buffered aqueous electrolyte under stirring whereas under non-stirring, Tris buffer at pH 10 with 0.03M (NH 4 ) 2 SO 4 and 30µm MnCl 2 ·4H 2 O were found to be optimal detection conditions. Interference by glucose, fructose, ethanol, and acetic acid in glycerol detection was studied. The observations indicated a promising enhancement in glycerol detection using the novel FeS-based glycerol sensing electrode compared to the conventional PQQ-based one. These findings support the premise that FeS-based bioanodes are capable of biosensing glycerol successfully and may be applicable for other enzymatic biosensors. Copyright © 2016 Elsevier B.V. All rights reserved.

In vivo monitor oxidative burst induced by Cd2+ stress for the oilseed rape (Brassica napus L.) based on electrochemical microbiosensor.

PubMed

Xu, Qiao; Wei, Fang; Wang, Zhan; Yang, Qin; Zhao, Yuan-Di; Chen, Hong

2010-01-01

Since the mechanism of Cd(2+) stress for plants is not clear, an in vivo method to monitor Cd(2+) stress for plants is necessary. However, oxidative burst (OB) is a signal messenger in the process of Cd(2+) stress for plants. To establish an electrochemical method with poly-o-phenylenediamine and Pt microparticle modified Pt electrode (POPD-Pt-MP-Pt) as a microbiosensor for the in vivo detection of oxidative burst induced by Cd(2+) stress in oilseed rape (Brassica napus L.). The optimal fabrication of POPD-Pt-MP-Pt biosensor was achieved. Electrochemical signal was collected by amperometry. After oilseed rape was exposed to 84.9 mM CdCl(2) stress, three oxidative bursts were observed in oilseed rape by amperometry at 3.3 h, 8.4 h and 13.2 h, respectively. However, there was no obvious signal observed in the controlled assay. This contribution presents the in vivo monitoring of the OB process induced by Cd(2+) stress in oilseed rape by POPD-Pt-MP-Pt microbiosensor in real-time. The novel electrochemical microbiosensor not only facilitates the real-time study in plant self-defence response to the adverse environment such as Cd(2+) stress, but also provides an effective tool for probing the self-defence mechanism in plants.

Bacteria-Templated NiO Nanoparticles/Microstructure for an Enzymeless Glucose Sensor

PubMed Central

Vaidyanathan, Settu; Cherng, Jong-Yuh; Sun, An-Cheng; Chen, Chien-Yen

2016-01-01

The bacterial-induced hollow cylinder NiO (HCNiO) nanomaterial was utilized for the enzymeless (without GOx) detection of glucose in basic conditions. The determination of glucose in 0.05 M NaOH solution with high sensitivity was performed using cyclic voltammetry (CV) and amperometry (i–t). The fundamental electrochemical parameters were analyzed and the obtained values of diffusion coefficient (D), heterogeneous rate constant (ks), electroactive surface coverage (Г), and transfer coefficient (alpha-α) are 1.75 × 10−6 cm2/s, 57.65 M−1·s−1, 1.45 × 10−10 mol/cm2, and 0.52 respectively. The peak current of the i–t method shows two dynamic linear ranges of calibration curves 0.2 to 3.5 µM and 0.5 to 250 µM for the glucose electro-oxidation. The Ni2+/Ni3+ couple with the HCNiO electrode and the electrocatalytic properties were found to be sensitive to the glucose oxidation. The green chemistry of NiO preparation from bacteria and the high catalytic ability of the oxyhydroxide (NiOOH) is the good choice for the development of a glucose sensor. The best obtained sensitivity and limit of detection (LOD) for this sensor were 3978.9 µA mM−1·cm−2 and 0.9 µM, respectively. PMID:27409615

A lactate electrochemical biosensor with a titanate nanotube as direct electron transfer promoter

NASA Astrophysics Data System (ADS)

Yang, Mingli; Wang, Jin; Li, Huaqing; Zheng, Jian-Guo; Wu, Nianqiang Nick

2008-02-01

Hydrogen titanate (H2Ti3O7) nanotubes (TNTs) have been synthesized by a one-step hydrothermal processing. Lactate oxidase (LOx) enzyme has been immobilized on the three-dimensional porous TNT network to make an electrochemical biosensor for lactate detection. Cyclic voltammetry and amperometry tests reveal that the LOx enzyme, which is supported on TNTs, maintains their substrate-specific catalytic activity. The nanotubes offer the pathway for direct electron transfer between the electrode surface and the active redox centers of LOx, which enables the biosensor to operate at a low working potential and to avoid the influence of the presence of O2 on the amperometric current response. The biosensor exhibits a sensitivity of 0.24 µA cm-2 mM-1, a 90% response time of 5 s, and a linear response in the range from 0.5 to 14 mM and the redox center of enzyme obviates the need of redox mediators for electrochemical enzymatic sensors, which is attractive for the development of reagentless biosensors.

Immobilization of Glucose Oxidase on a Carbon Nanotubes/Dendrimer-Ferrocene Modified Electrode for Reagentless Glucose Biosensing.

PubMed

Zhou, Juan; Li, Huan; Yang, Huasong; Cheng, Hui; Lai, Guosong

2017-01-01

Ferrocene-grafted dendrimer was covalently linked to the surface of a carbon nanotubes (CNTs)-chitosan (CS) nanocomposite modified electrode for immobilizing high-content glucose oxidase (GOx), which resulted in the successful development a novel reagentless glucose biosensor. Electrochemical impedance spectroscopy, cyclic voltammetry, and amperometry were used to characterize the preparation process and the enzymatically catalytic response of this biosensor. Due to the excellent electron transfer acceleration of the CNTs and the high-content loading of the GOx biomolecule and ferrocene mediator on the electrode matrix, this biosensor showed excellent analytical performance such as fast response time less than 10 s, wide linear range from 0.02 to 2.91 mM and low detection limit down to 7.5 μM as well as satisfactory stability and reproducibility toward the amperometric glucose determination. In addition, satisfactory result was obtained when it was used for the glucose measurements in human blood samples. Thus this biosensor provides great potentials for practical applications.

Catecholamine exocytosis during low frequency stimulation in mouse adrenal chromaffin cells is primarily asynchronous and controlled by the novel mechanism of Ca2+ syntilla suppression

PubMed Central

Lefkowitz, Jason J; DeCrescenzo, Valerie; Duan, Kailai; Bellve, Karl D; Fogarty, Kevin E; Walsh, John V; ZhuGe, Ronghua

2014-01-01

Adrenal chromaffin cells (ACCs), stimulated by the splanchnic nerve, generate action potentials (APs) at a frequency near 0.5 Hz in the resting physiological state, at times described as ‘rest and digest’. How such low frequency stimulation in turn elicits sufficient catecholamine exocytosis to set basal sympathetic tone is not readily explained by the classical mechanism of stimulus–secretion coupling, where exocytosis is synchronized to AP-induced Ca2+ influx. By using simulated action potentials (sAPs) at 0.5 Hz in isolated patch-clamped mouse ACCs, we show here that less than 10% of all catecholaminergic exocytosis, measured by carbon fibre amperometry, is synchronized to an AP. The asynchronous phase, the dominant phase, of exocytosis does not require Ca2+ influx. Furthermore, increased asynchronous exocytosis is accompanied by an AP-dependent decrease in frequency of Ca2+ syntillas (i.e. transient, focal Ca2+ release from internal stores) and is ryanodine sensitive. We propose a mechanism of disinhibition, wherein APs suppress Ca2+ syntillas, which themselves inhibit exocytosis as they do in the case of spontaneous catecholaminergic exocytosis. PMID:25128575

An electrocatalytic oxidation and voltammetric method using a chemically reduced graphene oxide film for the determination of caffeic acid.

PubMed

Vilian, A T Ezhil; Chen, Shen-Ming; Chen, Ying-Hui; Ali, M Ajmal; Al-Hemaid, Fahad M A

2014-06-01

The present work describes the characterization of a chemically reduced graphene oxide (CRGO) modified glassy carbon electrode (GCE) for electrochemical investigation of caffeic acid (CA). Cyclic voltammetry (CV), differential pulse voltammetry (DPV), amperometry, and electrochemical impedance spectroscopy (EIS) techniques were used to characterize the properties of the electrode. There was an obvious enhancement of the current response and a decreased over potential for the oxidation of CA. The interfacial electron transfer rate of CA was studied by EIS. Under optimal conditions, the CRGO displayed a linear response range of 1×10(-8) to 8×10(-4) M and the detection limit was 2×10(-9) M (S/N=3), with a sensitivity of 192.21 μA mM(-1) cm(-2) at an applied potential of +0.2V (vs. Ag/AgCl reference), which suggests that the CRGO is a promising sensing materials for the electrochemical investigation of CA. The results showed the good sensitivity, selectivity and high reproducibility of the CRGO modified electrode. Moreover, this modified electrode was further applied to investigate the CA in real samples of wine with satisfactory results. Copyright © 2014 Elsevier Inc. All rights reserved.

Sensitive and selective determination of gallic acid in green tea samples based on an electrochemical platform of poly(melamine) film.

PubMed

Su, Ya-Ling; Cheng, Shu-Hua

2015-12-11

In this work, an electrochemical sensor coupled with an effective flow-injection amperometry (FIA) system is developed, targeting the determination of gallic acid (GA) in a mild neutral condition, in contrast to the existing electrochemical methods. The sensor is based on a thin electroactive poly(melamine) film immobilized on a pre-anodized screen-printed carbon electrode (SPCE*/PME). The characteristics of the sensing surface are well-characterized by field emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS) and surface water contact angle experiments. The proposed assay exhibits a wide linear response to GA in both pH 3 and pH 7.0 phosphate buffer solutions (PBS) under the optimized flow-injection amperometry. The detection limit (S/N = 3) is 0.076 μM and 0.21 μM in the pH 3 and pH 7 solutions, respectively. A relative standard deviation (RSD) of 3.9% is obtained for 57 successive measurements of 50 μM GA in pH 7 solutions. Interference studies indicate that some inorganic salts, catechol, caffeine and ascorbic acid do not interfere with the GA assay. The interference effects from some orthodiphenolic compounds are also investigated. The proposed method and a conventional Folin-Ciocalteu method are applied to detect GA in green tea samples using the standard addition method, and satisfactory spiked recoveries are obtained. Copyright © 2015 Elsevier B.V. All rights reserved.

Alpha-Glucosidase Enzyme Biosensor for the Electrochemical Measurement of Antidiabetic Potential of Medicinal Plants

NASA Astrophysics Data System (ADS)

Mohiuddin, M.; Arbain, D.; Islam, A. K. M. Shafiqul; Ahmad, M. S.; Ahmad, M. N.

2016-02-01

A biosensor for measuring the antidiabetic potential of medicinal plants was developed by covalent immobilization of α-glucosidase (AG) enzyme onto amine-functionalized multi-walled carbon nanotubes (MWCNTs-NH2). The immobilized enzyme was entrapped in freeze-thawed polyvinyl alcohol (PVA) together with p-nitrophenyl-α- d-glucopyranoside (PNPG) on the screen-printed carbon electrode at low pH to prevent the premature reaction between PNPG and AG enzyme. The enzymatic reaction within the biosensor is inhibited by bioactive compounds in the medicinal plant extracts. The capability of medicinal plants to inhibit the AG enzyme on the electrode correlates to the potential of the medicinal plants to inhibit the production of glucose from the carbohydrate in the human body. Thus, the inhibition indicates the antidiabetic potential of the medicinal plants. The performance of the biosensor was evaluated to measure the antidiabetic potential of three medicinal plants such as Tebengau ( Ehretis laevis), Cemumar ( Micromelum pubescens), and Kedondong ( Spondias dulcis) and acarbose (commercial antidiabetic drug) via cyclic voltammetry, amperometry, and spectrophotometry. The cyclic voltammetry (CV) response for the inhibition of the AG enzyme activity by Tebengau plant extracts showed a linear relation in the range from 0.423-8.29 μA, and the inhibition detection limit was 0.253 μA. The biosensor exhibited good sensitivity (0.422 μA/mg Tebengau plant extracts) and rapid response (22 s). The biosensor retains approximately 82.16 % of its initial activity even after 30 days of storage at 4 °C.

Fundamentals of electrochemical detection techniques for CE and MCE.

PubMed

Kubán, Pavel; Hauser, Peter C

2009-10-01

The electroanalytical techniques of amperometry, conductometry and potentiometry match well with the instrumental simplicity of CE. Indeed, all three detection approaches have been reported for electrophoretic separations. However, the characteristics of the three methods are quite distinct and these are not related to the optical methods more commonly employed. A detailed discussion of the underlying principles of each is given. The issue of possible effects of the separation voltage on the electrochemical detection techniques is considered in depth, and approaches to the elimination of such interferences are also discussed for each case.

Electrochemistry in hollow-channel paper analytical devices.

PubMed

Renault, Christophe; Anderson, Morgan J; Crooks, Richard M

2014-03-26

In the present article we provide a detailed analysis of fundamental electrochemical processes in a new class of paper-based analytical devices (PADs) having hollow channels (HCs). Voltammetry and amperometry were applied under flow and no flow conditions yielding reproducible electrochemical signals that can be described by classical electrochemical theory as well as finite-element simulations. The results shown here provide new and quantitative insights into the flow within HC-PADs. The interesting new result is that despite their remarkable simplicity these HC-PADs exhibit electrochemical and hydrodynamic behavior similar to that of traditional microelectrochemical devices.

[Application of iodine metabolism analysis methods in thyroid diseases].

PubMed

Han, Jian-hua; Qiu, Ling

2013-08-01

The main physiological role of iodine in the body is to synthesize thyroid hormone. Both iodine deficiency and iodine excess can lead to severe thyroid diseases. While its role in thyroid diseases has increasingly been recognized, few relevant platforms and techniques for iodine detection have been available in China. This paper summarizes the advantages and disadvantages of currently iodine detection methods including direct titration, arsenic cerium catalytic spectrophotometry, chromatography with pulsed amperometry, colorimetry based on automatic biochemistry, inductively coupled plasma mass spectrometry, so as to optimize the iodine nutrition for patients with thyroid diseases.

Redox protein noncovalent functionalization of double-wall carbon nanotubes: electrochemical binder-less glucose biosensor.

PubMed

Pumera, Martin; Smíd, Bretislav

2007-10-01

Double wall carbon nanotubes are noncovalently functionalized with redox protein and such assembly is used for construction of electrochemical binder-less glucose biosensor. Redox protein glucose oxidase performs as biorecognition element and double wall carbon nanotubes act both as immobilization platform for redox enzyme and as signal transducer. The double carbon nanotubes are characterized by cyclic voltammetry and specific surface area measurements; the redox protein noncovalently functionalized double wall carbon nanotubes are characterized in detail by X-ray photoelectron spectroscopy, cyclic voltammetry, amperometry, and transmission electron microscopy.

Biosensors for hepatitis B virus detection.

PubMed

Yao, Chun-Yan; Fu, Wei-Ling

2014-09-21

A biosensor is an analytical device used for the detection of analytes, which combines a biological component with a physicochemical detector. Recently, an increasing number of biosensors have been used in clinical research, for example, the blood glucose biosensor. This review focuses on the current state of biosensor research with respect to efficient, specific and rapid detection of hepatitis B virus (HBV). The biosensors developed based on different techniques, including optical methods (e.g., surface plasmon resonance), acoustic wave technologies (e.g., quartz crystal microbalance), electrochemistry (amperometry, voltammetry and impedance) and novel nanotechnology, are also discussed.

Facile hydrothermal growth graphene/ZnO nanocomposite for development of enhanced biosensor.

PubMed

Low, Sze Shin; Tan, Michelle T T; Loh, Hwei-San; Khiew, Poi Sim; Chiu, Wee Siong

2016-01-15

Graphene/zinc oxide nanocomposite was synthesised via a facile, green and efficient approach consisted of novel liquid phase exfoliation and solvothermal growth for sensing application. Highly pristine graphene was synthesised through mild sonication treatment of graphite in a mixture of ethanol and water at an optimum ratio. The X-ray diffractometry (XRD) affirmed the hydrothermal growth of pure zinc oxide nanoparticles from zinc nitrate hexahydrate precursor. The as-prepared graphene/zinc oxide (G/ZnO) nanocomposite was characterised comprehensively to evaluate its morphology, crystallinity, composition and purity. All results clearly indicate that zinc oxide particles were homogenously distributed on graphene sheets, without any severe aggregation. The electrochemical performance of graphene/zinc oxide nanocomposite-modified screen-printed carbon electrode (SPCE) was evaluated using cyclic voltammetry (CV) and amperometry analysis. The resulting electrode exhibited excellent electrocatalytic activity towards the reduction of hydrogen peroxide (H2O2) in a linear range of 1-15 mM with a correlation coefficient of 0.9977. The sensitivity of the graphene/zinc oxide nanocomposite-modified hydrogen peroxide sensor was 3.2580 μAmM(-1) with a limit of detection of 7.4357 μM. An electrochemical DNA sensor platform was then fabricated for the detection of Avian Influenza H5 gene based on graphene/zinc oxide nanocomposite. The results obtained from amperometry study indicate that the graphene/zinc oxide nanocomposite-enhanced electrochemical DNA biosensor is significantly more sensitive (P < 0.05) and efficient than the conventional agarose gel electrophoresis. Copyright © 2015 Elsevier B.V. All rights reserved.

Novel microfluidic system for online monitoring of biofilm dynamics by electrical impedance spectroscopy and amperometry

NASA Astrophysics Data System (ADS)

Bruchmann, Julia; Sachsenheimer, Kai; Schwartz, Thomas; Rapp, Bastian E.

2016-03-01

Biofilm formation is ubiquitous in nature where microorganisms attach to surfaces and form highly adapted and protected communities. In technical and industrial systems like drinking water supply, food production or shipping industry biofilms are a major cause of product contamination, biofouling, and biocorrosion. Therefore, understanding of biofilm formation and means of preventing biofilm formation is important to develop novel biofilm treatment strategies. A system allowing directly online detection and monitoring biofilm formation is necessary. However, until today, there are little to none technical systems featuring a non-destructive real-time characterization of biofilm formation in a highthroughput manner. This paper presents such a microfluidic system based on electrical impedance spectroscopy (EIS) and amperomertic current measurement. The sensor consists of four modules, each housing 24 independent electrodes within 12 microfluidic channels. Attached biomass on the electrodes is monitored as increased inhibition in charge transfer by EIS and a change in metabolic activity is measured as change in produced electric current by amperometry. This modular sensor system is highly adaptable and suitable for a broad range of microbiological applications. Among others, biofilm formation processes can be characterized online, biofilm manipulation like inactivation or destabilization can be monitored in real-time and gene expression can be analyzed in parallel. The use of different electrode designs allows effective biofilm studies during all biofilm phases. The whole system was recently extended by an integrated pneumatic microfluidic pump which enables easy handling procedures. Further developments of this pumping module will allow a fully- automated computer-controlled valving and pumping.

Miniaturized neural sensing and optogenetic stimulation system for behavioral studies in the rat

NASA Astrophysics Data System (ADS)

Kim, Min Hyuck; Nam, Ilho; Ryu, Youngki; Wellman, Laurie W.; Sanford, Larry D.; Yoon, Hargsoon

2015-04-01

Real time sensing of localized electrophysiological and neurochemical signals associated with spontaneous and evoked neural activity is critically important for understanding neural networks in the brain. Our goal is to enhance the functionality and flexibility of a neural sensing and stimulation system for the observation of brain activity that will enable better understanding from the level of individual cells to that of global structures. We have thus developed a miniaturized electronic system for in-vivo neurotransmitter sensing and optogenetic stimulation amenable to behavioral studies in the rat. The system contains a potentiostat, a data acquisition unit, a control unit, and a wireless data transfer unit. For the potentiostat, we applied embedded op-amps to build single potential amperometry for electrochemical sensing of dopamine. A light emitting diode is controlled by a microcontroller and pulse width modulation utilized to control optogenetic stimulation within a sub-millisecond level. In addition, this proto-typed electronic system contains a Bluetooth module for wireless data communication. In the future, an application-specific integrated circuit (ASIC) will be designed for further miniaturization of the system.

A Facile Electrochemical Preparation of Reduced Graphene Oxide@Polydopamine Composite: A Novel Electrochemical Sensing Platform for Amperometric Detection of Chlorpromazine

NASA Astrophysics Data System (ADS)

Palanisamy, Selvakumar; Thirumalraj, Balamurugan; Chen, Shen-Ming; Wang, Yi-Ting; Velusamy, Vijayalakshmi; Ramaraj, Sayee Kannan

2016-09-01

We report a novel and sensitive amperometric sensor for chlorpromazine (CPZ) based on reduced graphene oxide (RGO) and polydopamine (PDA) composite modified glassy carbon electrode. The RGO@PDA composite was prepared by electrochemical reduction of graphene oxide (GO) with PDA. The RGO@PDA composite modified electrode shows an excellent electro-oxidation behavior to CPZ when compared with other modified electrodes such as GO, RGO and GO@PDA. Amperometric i-t method was used for the determination of CPZ. Amperometry result shows that the RGO@PDA composite detects CPZ in a linear range from 0.03 to 967.6 μM. The sensor exhibits a low detection limit of 0.0018 μM with the analytical sensitivity of 3.63 ± 0.3 μAμM-1 cm-2. The RGO@PDA composite shows its high selectivity towards CPZ in the presence of potentially interfering drugs such as metronidazole, phenobarbital, chlorpheniramine maleate, pyridoxine and riboflavin. In addition, the fabricated RGO@PDA modified electrode showed an appropriate recovery towards CPZ in the pharmaceutical tablets.

Alpha-Glucosidase Enzyme Biosensor for the Electrochemical Measurement of Antidiabetic Potential of Medicinal Plants.

PubMed

Mohiuddin, M; Arbain, D; Islam, A K M Shafiqul; Ahmad, M S; Ahmad, M N

2016-12-01

A biosensor for measuring the antidiabetic potential of medicinal plants was developed by covalent immobilization of α-glucosidase (AG) enzyme onto amine-functionalized multi-walled carbon nanotubes (MWCNTs-NH2). The immobilized enzyme was entrapped in freeze-thawed polyvinyl alcohol (PVA) together with p-nitrophenyl-α-D-glucopyranoside (PNPG) on the screen-printed carbon electrode at low pH to prevent the premature reaction between PNPG and AG enzyme. The enzymatic reaction within the biosensor is inhibited by bioactive compounds in the medicinal plant extracts. The capability of medicinal plants to inhibit the AG enzyme on the electrode correlates to the potential of the medicinal plants to inhibit the production of glucose from the carbohydrate in the human body. Thus, the inhibition indicates the antidiabetic potential of the medicinal plants. The performance of the biosensor was evaluated to measure the antidiabetic potential of three medicinal plants such as Tebengau (Ehretis laevis), Cemumar (Micromelum pubescens), and Kedondong (Spondias dulcis) and acarbose (commercial antidiabetic drug) via cyclic voltammetry, amperometry, and spectrophotometry. The cyclic voltammetry (CV) response for the inhibition of the AG enzyme activity by Tebengau plant extracts showed a linear relation in the range from 0.423-8.29 μA, and the inhibition detection limit was 0.253 μA. The biosensor exhibited good sensitivity (0.422 μA/mg Tebengau plant extracts) and rapid response (22 s). The biosensor retains approximately 82.16 % of its initial activity even after 30 days of storage at 4 °C.

Acetylcholinesterase Immobilized on Magnetic Beads for Pesticides Detection: Application to Olive Oil Analysis

PubMed Central

Ben Oujji, Najwa; Bakas, Idriss; Istamboulié, Georges; Ait-Ichou, Ihya; Ait-Addi, Elhabib; Rouillon, Régis; Noguer, Thierry

2012-01-01

This work presents the development of bioassays and biosensors for the detection of insecticides widely used in the treatment of olive trees. The systems are based on the covalent immobilisation of acetylcholinesterase on magnetic microbeads using either colorimetry or amperometry as detection technique. The magnetic beads were immobilised on screen-printed electrodes or microtitration plates and tested using standard solutions and real samples. The developed devices showed good analytical performances with limits of detection much lower than the maximum residue limit tolerated by international regulations, as well as a good reproducibility and stability. PMID:22969377

D-Amino acid oxidase bio-functionalized platforms: Toward an enhanced enzymatic bio-activity

NASA Astrophysics Data System (ADS)

Herrera, Elisa; Valdez Taubas, Javier; Giacomelli, Carla E.

2015-11-01

The purpose of this work is to study the adsorption process and surface bio-activity of His-tagged D-amino acid oxidase (DAAO) from Rhodotorula gracilis (His6-RgDAAO) as the first step for the development of an electrochemical bio-functionalized platform. With such a purpose this work comprises: (a) the His6-RgDAAO bio-activity in solution determined by amperometry, (b) the adsorption mechanism of His6-RgDAAO on bare gold and carboxylated modified substrates in the absence (substrate/COO-) and presence of Ni(II) (substrate/COO- + Ni(II)) determined by reflectometry, and (c) the bio-activity of the His6-RgDAAO bio-functionalized platforms determined by amperometry. Comparing the adsorption behavior and bio-activity of His6-RgDAAO on these different solid substrates allows understanding the contribution of the diverse interactions responsible for the platform performance. His6-RgDAAO enzymatic performance in solution is highly improved when compared to the previously used pig kidney (pk) DAAO. His6-RgDAAO exhibits an amperometrically detectable bio-activity at concentrations as low as those expected on a bio-functional platform; hence, it is a viable bio-recognition element of D-amino acids to be coupled to electrochemical platforms. Moreover, His6-RgDAAO bio-functionalized platforms exhibit a higher surface activity than pkDAAO physically adsorbed on gold. The platform built on Ni(II) modified substrates present enhanced bio-activity because the surface complexes histidine-Ni(II) provide with site-oriented, native-like enzymes. The adsorption mechanism responsible of the excellent performance of the bio-functionalized platform takes place in two steps involving electrostatic and bio-affinity interactions whose prevalence depends on the degree of surface coverage.

A novel third generation uric acid biosensor using uricase electro-activated with ferrocene on a Nafion coated glassy carbon electrode.

PubMed

Ghosh, Tanushree; Sarkar, Priyabrata; Turner, Anthony P F

2015-04-01

A new uric acid biosensor was constructed using ferrocene (Fc) induced electro-activated uricase (UOx) deposited within Nafion (Naf) on glassy carbon electrode (GCE). Electro-activation of UOx was successfully achieved by cyclic voltammetry through the electrostatic interaction of Fc with Trp residues within the hydrophobic pockets in UOx. The Naf/UOx/Fc composite was characterised by AFM, FTIR and EDX to ensure proper immobilisation. The interaction of Fc with the enzyme was analysed by Trp fluorescence spectroscopy and the α-helicity of the protein was measured by CD spectropolarimetry. The charge transfer resistance (Rct), calculated from electrochemical impedance spectroscopy, for the modified sensor was lowered (1.39 kΩ) and the enzyme efficiency was enhanced by more than two fold as a result of Fc incorporation. Cyclic voltammetry, differential pulse voltammetry and amperometry all demonstrated the excellent response of the Naf/UOx/Fc/GCE biosensor to uric acid. The sensor system generated a linear response over a range of 500 nM to 600 μM UA, with a sensitivity and limit of detection of 1.78 μA μM(-1) and 230 nM, respectively. The heterogeneous rate constant (ks) for UA oxidation was much higher for Naf/UOx/Fc/GCE (1.0 × 10(-4) cm s(-1)) than for Naf/UOx/GCE (8.2 × 10(-5) cm s(-1)). Real samples, i.e. human blood, were tested for serum UA and the sensor yielded accurate results at a 95% confidence limit. Copyright © 2014 Elsevier B.V. All rights reserved.

Effect of anode polarization on biofilm formation and electron transfer in Shewanella oneidensis/graphite felt microbial fuel cells.

PubMed

Pinto, David; Coradin, Thibaud; Laberty-Robert, Christel

2018-04-01

In microbial fuel cells, electricity generation is assumed by bacterial degradation of low-grade organics generating electrons that are transferred to an electrode. The nature and efficiency of the electron transfer from the bacteria to the electrodes are determined by several chemical, physical and biological parameters. Specifically, the application of a specific potential at the bioanode has been shown to stimulate the formation of an electro-active biofilm, but the underlying mechanisms remain poorly understood. In this study, we have investigated the effect of an applied potential on the formation and electroactivity of biofilms established by Shewanella oneidensis bacteria on graphite felt electrodes in single- and double-chamber reactor configurations in oxic conditions. Using amperometry, cyclic voltammetry, and OCP/Power/Polarization curves techniques, we showed that a potential ranging between -0.3V and +0.5V (vs. Ag/AgCl/KCl sat.) and its converse application to a couple of electrodes leads to different electrochemical behaviors, anodic currents and biofilm architectures. For example, when the bacteria were confined in the anodic compartment of a double-chamber cell, a negative applied potential (-0.3V) at the bioanode favors a mediated electron transfer correlated with the progressive formation of a biofilm that fills the felt porosity and bridges the graphite fibers. In contrast, a positive applied potential (+0.3V) at the bioanode stimulates a direct electron transfer resulting in the fast-bacterial colonization of the fibers only. These results provide significant insight for the understanding of the complex bacteria-electrode interactions in microbial fuel cells. Copyright © 2017 Elsevier B.V. All rights reserved.

A Facile Electrochemical Preparation of Reduced Graphene Oxide@Polydopamine Composite: A Novel Electrochemical Sensing Platform for Amperometric Detection of Chlorpromazine

PubMed Central

Palanisamy, Selvakumar; Thirumalraj, Balamurugan; Chen, Shen-Ming; Wang, Yi-Ting; Velusamy, Vijayalakshmi; Ramaraj, Sayee Kannan

2016-01-01

We report a novel and sensitive amperometric sensor for chlorpromazine (CPZ) based on reduced graphene oxide (RGO) and polydopamine (PDA) composite modified glassy carbon electrode. The RGO@PDA composite was prepared by electrochemical reduction of graphene oxide (GO) with PDA. The RGO@PDA composite modified electrode shows an excellent electro-oxidation behavior to CPZ when compared with other modified electrodes such as GO, RGO and GO@PDA. Amperometric i-t method was used for the determination of CPZ. Amperometry result shows that the RGO@PDA composite detects CPZ in a linear range from 0.03 to 967.6 μM. The sensor exhibits a low detection limit of 0.0018 μM with the analytical sensitivity of 3.63 ± 0.3 μAμM–1 cm–2. The RGO@PDA composite shows its high selectivity towards CPZ in the presence of potentially interfering drugs such as metronidazole, phenobarbital, chlorpheniramine maleate, pyridoxine and riboflavin. In addition, the fabricated RGO@PDA modified electrode showed an appropriate recovery towards CPZ in the pharmaceutical tablets. PMID:27650697

Non-enzymatic electrochemical glucose sensor based on NiMoO4 nanorods

NASA Astrophysics Data System (ADS)

Wang, Dandan; Cai, Daoping; Huang, Hui; Liu, Bin; Wang, Lingling; Liu, Yuan; Li, Han; Wang, Yanrong; Li, Qiuhong; Wang, Taihong

2015-04-01

A non-enzymatic glucose sensor based on the NiMoO4 nanorods has been fabricated for the first time. The electrocatalytic performance of the NiMoO4 nanorods’ modified electrode toward glucose oxidation was evaluated by cyclic voltammetry and amperometry. The NiMoO4 nanorods’ modified electrode showed a greatly enhanced electrocatalytic property toward glucose oxidation, as well as an excellent anti-interference and a good stability. Impressively, good accuracy and high precision for detecting glucose concentration in human serum samples were obtained. These excellent sensing properties, combined with good reproducibility and low cost, indicate that NiMoO4 nanorods are a promising candidate for non-enzymatic glucose sensors.

Direct electron transfer of glucose oxidase-boron doped diamond interface: a new solution for a classical problem.

PubMed

Bai, Yan-Feng; Xu, Tai-Bin; Luong, John H T; Cui, Hui-Fang

2014-05-20

A planar boron-doped diamond (BDD) electrode was treated with KOH and functionalized with 3-aminopropyltriethoxysilane (APTES) to serve as a biosensing platform for biomolecule immobilization with glucose oxidase (GOx) as a test model. The free amino groups of GOx and APTES were cross-linked by glutaraldehyde (X), a bifunctional chemical to form a stable enzyme layer (GOx-X-APTES) on BDD. Micrographs obtained by scanning electron microscopy revealed that a mesoporous structure uniformly covered the BDD surface. Cyclic voltammetry of GOx immobilized showed a pair of well-defined redox peaks in neutral phosphate buffer solution, corresponding to the direct electron transfer of GOx. The apparent heterogeneous electron transfer rate constant of the immobilized GOx was estimated to be 8.85 ± 0.47 s(-1), considerably higher than the literature reported values. The determination of glucose was carried out by amperometry at -0.40 V, and the developed biosensor showed good reproducibility and stability with a detection limit of 20 μM. Both ascorbic and uric acids at normal physiological conditions did not provoke any signals. The dynamic range of glucose detection was further extended by covering the enzyme electrode with a thin Nafion layer. The Nafion/GOx-X-APTES/BDD biosensor showed excellent stability, a detection limit of 30 μM, a linear range between 35 μM and 8 mM, and a dynamic range up to 14 mM. Such analytical performances were compared favorably with other complicated sensing schemes using nanomaterials, redox polymers, and nanowires. The APTES-functionalized BDD could be easily extended to immobilize other redox enzymes or proteins of interests.

Self-assembly of glucose oxidase on reduced graphene oxide-magnetic nanoparticles nanocomposite-based direct electrochemistry for reagentless glucose biosensor.

PubMed

Pakapongpan, Saithip; Poo-Arporn, Rungtiva P

2017-07-01

A novel approach of the immobilization of a highly selective and stable glucose biosensor based on direct electrochemistry was fabricated by a self-assembly of glucose oxidase (GOD) on reduced graphene oxide (RGO) covalently conjugated to magnetic nanoparticles (Fe 3 O 4 NPs) modified on a magnetic screen-printed electrode (MSPE). The RGO-Fe 3 O 4 nanocomposite has remarkable enhancement in large surface areas, is favorable environment for enzyme immobilization, facilitates electron transfer between enzymes and electrode surfaces and possesses superparamagnetism property. The morphology and electrochemical properties of RGO-Fe 3 O 4 /GOD were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, cyclic voltammetry (CV) and amperometry. The modified electrode was a fast, direct electron transfer with an apparent electron transfer rate constant (k s ) of 13.78s -1 . The proposed biosensor showed fast amperometric response (3s) to glucose with a wide linear range from 0.05 to 1mM, a low detection limit of 0.1μM at a signal to noise ratio of 3 (S/N=3) and good sensitivity (5.9μA/mM). The resulting biosensor has high stability, good reproducibility, excellent selectivity and successfully applied detection potential at -0.45V. This mediatorless glucose sensing used the advantages of covalent bonding and self-assembly as a new approach for immobilizing enzymes without any binder. It would be worth noting that it opens a new avenue for fabricating excellent electrochemical biosensors. This is a new approach that reporting the immobilization of glucose oxidase on reduced graphene oxide (RGO) covalently conjugated to magnetic nanoparticles (Fe 3 O 4 NPs) by electrostatic interaction and modified screen printed electrode. We propose the reagentless with fabrication method without binder and adhesive agents for immobilized enzyme. Fe 3 O 4 NPs increasing surface area to enhance the immobilization and prevent the leaching of enzymes at electrode surfaces by magnetic stickers which is improve the stability of the biosensor. Based on this synthesis technique, it is a good new strategy and simple used to fabrication of third-generation glucose biosensor and this nanocomposite could be used as a platform for disposable biosensor and biofuel cell applications. Copyright © 2017 Elsevier B.V. All rights reserved.

Mechanism for optimization of signal-to-noise ratio of dopamine release based on short-term bidirectional plasticity.

PubMed

Da Cunha, Claudio; McKimm, Eric; Da Cunha, Rafael M; Boschen, Suelen L; Redgrave, Peter; Blaha, Charles D

2017-07-15

Repeated electrical stimulation of dopamine (dopamine) fibers can cause variable effects on further dopamine release; sometimes there are short-term decreases while in other cases short-term increases have been reported. Previous studies have failed to discover what factors determine in which way dopamine neurons will respond to repeated stimulation. The aim of the present study was therefore to investigate what determines the direction and magnitude of this particular form of short-term plasticity. Fixed potential amperometry was used to measure dopamine release in the nucleus accumbens in response to two trains of electrical pulses administered to the ventral tegmental area of anesthetized mice. When the pulse trains were of equal magnitude we found that low magnitude stimulation was associated with short-term suppression and high magnitude stimulation with short-term facilitation of dopamine release. Secondly, we found that the magnitude of the second pulse train was critical for determining the sign of the plasticity (suppression or facilitation), while the magnitude of the first pulse train determined the extent to which the response to the second train was suppressed or facilitated. This form of bidirectional plasticity might provide a mechanism to enhance signal-to-noise ratio of dopamine neurotransmission. Copyright © 2017 Elsevier B.V. All rights reserved.

A microchip-based flow injection-amperometry system with mercaptopropionic acid modified electroless gold microelectrode for the selective determination of dopamine.

PubMed

Wang, Yi; Luo, Jie; Chen, Hengwu; He, Qiaohong; Gan, Nin; Li, Tianhua

2008-09-12

A novel chip-based flow injection analysis (FIA) system has been developed for automatic, rapid and selective determination of dopamine (DA) in the presence of ascorbic acid (AA). The system is composed of a polycarbonate (PC) microfluidic chip with an electrochemical detector (ED), a gravity pump, and an automatic sample loading and injection unit. The selectivity of the ED was improved by modification of the gold working microelectrode, which was fabricated on the PC chip by UV-directed electroless gold plating, with a self-assembled monolayer (SAM) of 3-mercaptopropionic acid (MPA). Postplating treatment methods for cleaning the surface of electroless gold microelectrodes were investigated to ensure the formation of high quality SAMs. The effects of detection potential, flow rate, and sampling volume on the performance of the chip-based FIA system were studied. Under optimum conditions, a detection limit of 74 nmol L(-1) for DA was achieved at the sample throughput rate of 180 h(-1). A RSD of 0.9% for peak heights was observed for 19 runs of a 100 micromol L(-1) DA solution. Interference-free determination of DA could be conducted if the concentration ratio of AA-DA was no more than 10.

Electrocatalytic oxidation of hydrazine and hydroxylamine by graphene oxide-Pd nanoparticle-modified glassy carbon electrode.

PubMed

Lee, Eunhee; Kim, Daekun; You, Jung-Min; Kim, Seul Ki; Yun, Mira; Jeon, Seungwon

2012-12-01

Pd nanoparticle catalysts supported by thiolated graphene oxide (tGO) on a glassy carbon electrode (GCE), and denoted as tGO-Pd/GCE, are used in this study for the electrochemical determination of hydroxylamine and hydrazine. The physicochemical properties of tGO-Pd were characterized by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS). They showed strong catalytic activity toward the oxidation of hydroxylamine and hydrazine. Cyclic voltammetry (CV) and amperometry were used to characterize the sensors' performances. The detection limits of hydroxylamine and hydrazine by tGO-Pd/GCE were 0.31 and 0.25 microM (s/n = 3), respectively. The sensors' sensitivity, selectivity, and stability were also investigated.

Toxicity assessment using different bioassays and microbial biosensors.

PubMed

Hassan, Sedky H A; Van Ginkel, Steven W; Hussein, Mohamed A M; Abskharon, Romany; Oh, Sang-Eun

2016-01-01

Toxicity assessment of water streams, wastewater, and contaminated sediments, is a very important part of environmental pollution monitoring. Evaluation of biological effects using a rapid, sensitive and cost effective method can indicate specific information on ecotoxicity assessment. Recently, different biological assays for toxicity assessment based on higher and lower organisms such as fish, invertebrates, plants and algal cells, and microbial bioassays have been used. This review focuses on microbial biosensors as an analytical device for environmental, food, and biomedical applications. Different techniques which are commonly used in microbial biosensing include amperometry, potentiometry, conductometry, voltammetry, microbial fuel cells, fluorescence, bioluminescence, and colorimetry. Examples of the use of different microbial biosensors in assessing a variety of environments are summarized. Copyright © 2016 Elsevier Ltd. All rights reserved.

Fast BIA-amperometric determination of isoniazid in tablets.

PubMed

Quintino, Maria S M; Angnes, Lúcio

2006-09-26

This paper proposes a new, fast and precise method to analyze isoniazid based on the electrochemical oxidation of the analyte at a glassy carbon electrode in 0.1M NaOH. The quantification was performed utilizing amperometry associated with batch injection analysis (BIA) technique. Fast sequential analysis (60 determinations h(-1)) in an unusually wide linear dynamic range (from 2.5 x 10(-8) to 1.0 x 10(-3)M), with high sensitivity and low limits of detection (4.1 x 10(-9)M) and quantification (1.4 x 10(-8)M), was achieved. Such characteristics allied to a good repeatability of the current responses (relative standard deviation of 0.79% for 30 measurements), were explored for the specific determination of isoniazid in isoniazid-rifampin tablet.

Higher success rate with transcranial electrical stimulation of motor-evoked potentials using constant-voltage stimulation compared with constant-current stimulation in patients undergoing spinal surgery.

PubMed

Shigematsu, Hideki; Kawaguchi, Masahiko; Hayashi, Hironobu; Takatani, Tsunenori; Iwata, Eiichiro; Tanaka, Masato; Okuda, Akinori; Morimoto, Yasuhiko; Masuda, Keisuke; Tanaka, Yuu; Tanaka, Yasuhito

2017-10-01

During spine surgery, the spinal cord is electrophysiologically monitored via transcranial electrical stimulation of motor-evoked potentials (TES-MEPs) to prevent injury. Transcranial electrical stimulation of motor-evoked potential involves the use of either constant-current or constant-voltage stimulation; however, there are few comparative data available regarding their ability to adequately elicit compound motor action potentials. We hypothesized that the success rates of TES-MEP recordings would be similar between constant-current and constant-voltage stimulations in patients undergoing spine surgery. The objective of this study was to compare the success rates of TES-MEP recordings between constant-current and constant-voltage stimulation. This is a prospective, within-subject study. Data from 100 patients undergoing spinal surgery at the cervical, thoracic, or lumbar level were analyzed. The success rates of the TES-MEP recordings from each muscle were examined. Transcranial electrical stimulation with constant-current and constant-voltage stimulations at the C3 and C4 electrode positions (international "10-20" system) was applied to each patient. Compound muscle action potentials were bilaterally recorded from the abductor pollicis brevis (APB), deltoid (Del), abductor hallucis (AH), tibialis anterior (TA), gastrocnemius (GC), and quadriceps (Quad) muscles. The success rates of the TES-MEP recordings from the right Del, right APB, bilateral Quad, right TA, right GC, and bilateral AH muscles were significantly higher using constant-voltage stimulation than those using constant-current stimulation. The overall success rates with constant-voltage and constant-current stimulations were 86.3% and 68.8%, respectively (risk ratio 1.25 [95% confidence interval: 1.20-1.31]). The success rates of TES-MEP recordings were higher using constant-voltage stimulation compared with constant-current stimulation in patients undergoing spinal surgery. Copyright © 2017 Elsevier Inc. All rights reserved.

Milestone report on MD potential development for uranium silicide

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

Yu, Jianguo; Zhang, Yongfeng; Hales, Jason Dean

2016-03-01

This report summarizes the progress on the interatomic potential development of triuranium-disilicide (U 3Si 2) for molecular dynamics (MD) simulations. The development is based on the Tersoff type potentials for single element U and Si. The Si potential is taken from the literature and a Tersoff type U potential is developed in this project. With the primary focus on the U 3Si 2 phase, some other U-Si systems such as U 3Si are also included as a test of the transferability of the potentials for binary U-Si phases. Based on the potentials for unary U and Si, two sets ofmore » parameters for the binary U-Si system are developed using the Tersoff mixing rules and the cross-term fitting, respectively. The cross-term potential is found to give better results on the enthalpy of formation, lattice constants and elastic constants than those produced by the Tersoff mixing potential, with the reference data taken from either experiments or density functional theory (DFT) calculations. In particular, the results on the formation enthalpy and lattice constants for the U 3Si 2 phase and lattice constants for the high temperature U 3Si (h-U 3Si) phase generated by the cross-term potential agree well with experimental data. Reasonable agreements are also reached on the elastic constants of U 3Si 2, on the formation enthalpy for the low temperature U 3Si (m-U 3Si) and h-U 3Si phases, and on the lattice constants of m-U 3Si phase. All these phases are predicted to be mechanically stable. The unary U potential is tested for three metallic U phases (α, β, γ). The potential is found capable to predict the cohesive energies well against experimental data for all three phases. It matches reasonably with previous experiments on the lattice constants and elastic constants of αU.« less

Physiological stimuli evoke two forms of endocytosis in bovine chromaffin cells.

PubMed

Chan, S A; Smith, C

2001-12-15

1. Exocytosis and endocytosis were measured following single, or trains of, simulated action potentials (sAP) in bovine adrenal chromaffin cells. Catecholamine secretion was measured by oxidative amperometry and cell membrane turnover was measured by voltage clamp cell capacitance measurements. 2. The sAPs evoked inward Na(+) and Ca(2+) currents that were statistically identical to those evoked by native action potential waveforms. On average, a single secretory granule underwent fusion following sAP stimulation. An equivalent amount of membrane was then quickly internalised (tau = 560 ms). 3. Stimulation with sAP trains revealed a biphasic relationship between cell firing rate and endocytic activity. At basal stimulus frequencies (single to 0.5 Hz) cells exhibited a robust membrane internalisation that then diminished as firing increased to intermediate levels (1.9 and 6 Hz). However at the higher stimulation rates (10 and 16 Hz) endocytic activity rebounded and was again able to effectively maintain cell surface near pre-stimulus levels. 4. Treatment with cyclosporin A and FK506, inhibitors of the phosphatase calcineurin, left endocytosis characteristics unaltered at the lower basal stimulus levels, but blocked the resurgence in endocytosis seen in control cells at higher sAP frequencies. 5. Based on these findings we propose that, under physiological electrical stimulation, chromaffin cells internalise membrane via two distinct pathways that are separable. One is prevalent at basal stimulus frequencies, is lessened with increased firing, and is insensitive to cyclosporin A and FK506. A second endocytic form is activated by increased firing frequencies, and is selectively blocked by cyclosporin A and FK506.

Physiological stimuli evoke two forms of endocytosis in bovine chromaffin cells

PubMed Central

Chan, Shyue-An; Smith, Corey

2001-01-01

Exocytosis and endocytosis were measured following single, or trains of, simulated action potentials (sAP) in bovine adrenal chromaffin cells. Catecholamine secretion was measured by oxidative amperometry and cell membrane turnover was measured by voltage clamp cell capacitance measurements. The sAPs evoked inward Na+ and Ca2+ currents that were statistically identical to those evoked by native action potential waveforms. On average, a single secretory granule underwent fusion following sAP stimulation. An equivalent amount of membrane was then quickly internalised (τ = 560 ms). Stimulation with sAP trains revealed a biphasic relationship between cell firing rate and endocytic activity. At basal stimulus frequencies (single to 0.5 Hz) cells exhibited a robust membrane internalisation that then diminished as firing increased to intermediate levels (1.9 and 6 Hz). However at the higher stimulation rates (10 and 16 Hz) endocytic activity rebounded and was again able to effectively maintain cell surface near pre-stimulus levels. Treatment with cyclosporin A and FK506, inhibitors of the phosphatase calcineurin, left endocytosis characteristics unaltered at the lower basal stimulus levels, but blocked the resurgence in endocytosis seen in control cells at higher sAP frequencies. Based on these findings we propose that, under physiological electrical stimulation, chromaffin cells internalise membrane via two distinct pathways that are separable. One is prevalent at basal stimulus frequencies, is lessened with increased firing, and is insensitive to cyclosporin A and FK506. A second endocytic form is activated by increased firing frequencies, and is selectively blocked by cyclosporin A and FK506. PMID:11744761

Potentiostatic pulse-deposition of calcium phosphate on magnesium alloy for temporary implant applications--an in vitro corrosion study.

PubMed

Kannan, M Bobby; Wallipa, O

2013-03-01

In this study, a magnesium alloy (AZ91) was coated with calcium phosphate using potentiostatic pulse-potential and constant-potential methods and the in vitro corrosion behaviour of the coated samples was compared with the bare metal. In vitro corrosion studies were carried out using electrochemical impedance spectroscopy and potentiodynamic polarization in simulated body fluid (SBF) at 37 °C. Calcium phosphate coatings enhanced the corrosion resistance of the alloy, however, the pulse-potential coating performed better than the constant-potential coating. The pulse-potential coating exhibited ~3 times higher polarization resistance than that of the constant-potential coating. The corrosion current density obtained from the potentiodynamic polarization curves was significantly less (~60%) for the pulse-deposition coating as compared to the constant-potential coating. Post-corrosion analysis revealed only slight corrosion on the pulse-potential coating, whereas the constant-potential coating exhibited a large number of corrosion particles attached to the coating. The better in vitro corrosion performance of the pulse-potential coating can be attributed to the closely packed calcium phosphate particles. Copyright © 2012 Elsevier B.V. All rights reserved.

Low cost microfluidic device based on cotton threads for electroanalytical application.

PubMed

Agustini, Deonir; Bergamini, Márcio F; Marcolino-Junior, Luiz Humberto

2016-01-21

Microfluidic devices are an interesting alternative for performing analytical assays, due to the speed of analyses, reduced sample, reagent and solvent consumption and less waste generation. However, the high manufacturing costs still prevent the massive use of these devices worldwide. Here, we present the construction of a low cost microfluidic thread-based electroanalytical device (μTED), employing extremely cheap materials and a manufacturing process free of equipment. The microfluidic channels were built with cotton threads and the estimated cost per device was only $0.39. The flow of solutions (1.12 μL s(-1)) is generated spontaneously due to the capillary forces, eliminating the use of any pumping system. To demonstrate the analytical performance of the μTED, a simultaneous determination of acetaminophen (ACT) and diclofenac (DCF) was performed by multiple pulse amperometry (MPA). A linear dynamic range (LDR) of 10 to 320 μmol L(-1) for both species, a limit of detection (LOD) and a limit of quantitation (LOQ) of 1.4 and 4.7 μmol L(-1) and 2.5 and 8.3 μmol L(-1) for ACT and DCF, respectively, as well as an analytical frequency of 45 injections per hour were reached. Thus, the proposed device has shown potential to extend the use of microfluidic analytical devices, due to its simplicity, low cost and good analytical performance.

Electrocatalytic oxidation and determination of insulin at nickel oxide nanoparticles-multiwalled carbon nanotube modified screen printed electrode.

PubMed

Rafiee, Banafsheh; Fakhari, Ali Reza

2013-08-15

Nickel oxide nanoparticles modified nafion-multiwalled carbon nanotubes screen printed electrode (NiONPs/Nafion-MWCNTs/SPE) were prepared using pulsed electrodeposition of NiONPs on the MWCNTs/SPE surface. The size, distribution and structure of the NiONPs/Nafion-MWCNTs were characterized by transmission electron microscopy (TEM) and x-ray diffraction (XRD) and also the results show that NiO nanoparticles were homogeneously electrodeposited on the surfaces of MWCNTs. Also, the electrochemical behavior of NiONPs/Nafion-MWCNTs composites in aqueous alkaline solutions of insulin was studied by cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy (EIS). It was found that the prepared nanoparticles have excellent electrocatalytic activity towards insulin oxidation due to special properties of NiO nanoparticles. Cyclic voltammetric studies showed that the NiONPs/Nafion-MWCNTs film modified SPE, lowers the overpotentials and improves electrochemical behavior of insulin oxidation, as compared to the bare SPE. Amperometry was also used to evaluate the analytical performance of modified electrode in the quantitation of insulin. Excellent analytical features, including high sensitivity (1.83 μA/μM), low detection limit (6.1 nM) and satisfactory dynamic range (20.0-260.0 nM), were achieved under optimized conditions. Moreover, these sensors show good repeatability and a high stability after a while or successive potential cycling. Copyright © 2013 Elsevier B.V. All rights reserved.

Sleep/wake dependent changes in cortical glucose concentrations.

PubMed

Dash, Michael B; Bellesi, Michele; Tononi, Giulio; Cirelli, Chiara

2013-01-01

Most of the energy in the brain comes from glucose and supports glutamatergic activity. The firing rate of cortical glutamatergic neurons, as well as cortical extracellular glutamate levels, increase with time spent awake and decline throughout non rapid eye movement sleep, raising the question whether glucose levels reflect behavioral state and sleep/wake history. Here chronic (2-3 days) electroencephalographic recordings in the rat cerebral cortex were coupled with fixed-potential amperometry to monitor the extracellular concentration of glucose ([gluc]) on a second-by-second basis across the spontaneous sleep-wake cycle and in response to 3 h of sleep deprivation. [Gluc] progressively increased during non rapid eye movement sleep and declined during rapid eye movement sleep, while during wake an early decline in [gluc] was followed by an increase 8-15 min after awakening. There was a significant time of day effect during the dark phase, when rats are mostly awake, with [gluc] being significantly lower during the last 3-4 h of the night relative to the first 3-4 h. Moreover, the duration of the early phase of [gluc] decline during wake was longer after prolonged wake than after consolidated sleep. Thus, the sleep/wake history may affect the levels of glucose available to the brain upon awakening. © 2012 The Authors Journal of Neurochemistry © 2012 International Society for Neurochemistry.

Regulation of striatal nitric oxide synthesis by local dopamine and glutamate interactions

PubMed Central

Park, Diana J.; West, Anthony R.

2009-01-01

Nitric oxide (NO) is a key neuromodulator of corticostriatal synaptic transmission. We have shown previously that dopamine (DA) D1/5 receptor stimulation facilitates neuronal NO synthase (nNOS) activity in the intact striatum. To study the impact of local manipulations of D1/5 and glutamatergic NMDA receptors on striatal nNOS activity, we combined the techniques of in vivo amperometry and reverse microdialysis. Striatal NO efflux was monitored proximal to the microdialysis probe in urethane anesthetized rats during local infusion of vehicle or drug. NO efflux elicited by systemic administration of SKF-81297 was blocked following intrastriatal infusion of: 1) the D1/5 receptor antagonist SCH-23390, 2) the nNOS inhibitor 7-nitroindazole, 3) the nonspecific ionotropic glutamate receptor antagonist kynurenic acid, and 4) the selective NMDA receptor antagonist 3-phosphonopropyl-piperazine-2-carboxylic acid. Glycine coperfusion did not affect SKF-81297-induced NO efflux. Furthermore, intrastriatal infusion of SKF-81297 potentiated NO efflux evoked during electrical stimulation of the motor cortex. The facilitatory effects of cortical stimulation and SKF-81297 were both blocked by intrastriatal infusion of SCH-23390, indicating that striatal D1/5 receptor activation is necessary for the activation of nNOS by corticostriatal afferents. These studies demonstrate for the first time that reciprocal DA-glutamate interactions play a critical role in stimulating striatal nNOS activity. PMID:19799710

Electrocatalytic oxidation of dopamine based on non-covalent functionalization of manganese tetraphenylporphyrin/reduced graphene oxide nanocomposite.

PubMed

Sakthinathan, Subramanian; Lee, Hsin Fang; Chen, Shen-Ming; Tamizhdurai, P

2016-04-15

In the present work, a reduced graphene oxide (RGO) supported manganese tetraphenylporphyrin (Mn-TPP) nanocomposite was electrochemically synthesized and used for the highly selective and sensitive detection of dopamine (DA). The nuclear magnetic resonance, scanning electron microscopy and elemental analysis were confirmed the successful formation of RGO/Mn-TPP nanocomposite. The prepared RGO/Mn-TPP nanocomposite modified electrode exhibited an enhanced electrochemical response to DA with less oxidation potential and enhanced response current. The electrochemical studies revealed that the oxidation of the DA at the composite electrode is a surface controlled process. The cyclic voltammetry, differential pulse voltammetry and amperometry methods were enable to detect DA. The working linear range of the electrode was observed from 0.3 to 188.8 μM, limit of detection was 8 nM and the sensitivity was 2.606 μA μM(-1) cm(-2). Here, the positively charged DA and negatively charged porphyrin modified RGO can accelerate the electrocatalysis of DA via electrostatic attraction, while the negatively charged ascorbic acid (AA) repulsed by the negatively charged electrode surface which supported for good selectivity. The good recovery results obtained for the determination of DA present in DA injection samples and human pathological sample further revealed the good practicality of RGO/Mn-TPP nanocomposite film modified electrode. Copyright © 2016 Elsevier Inc. All rights reserved.

Heroin Contaminated with Fentanyl Dramatically Enhances Brain Hypoxia and Induces Brain Hypothermia.

PubMed

Solis, Ernesto; Cameron-Burr, Keaton T; Kiyatkin, Eugene A

2017-01-01

While opioid abuse is an established medical and public health issue, the increased availability of highly potent synthetic opioids, such as fentanyl, has given rise to acute health complications, including a comatose state and death during drug overdose. Since respiratory depression that leads to acute hypoxia is the most dangerous complication of opioid drug use, we examined the effects of intravenous heroin and heroin contaminated with 10% fentanyl on oxygen levels in the nucleus accumbens (NAc) monitored using high-speed amperometry in freely moving rats. Additionally, we examined the effects of heroin, fentanyl, and their mixture on locomotion and temperatures in the NAc, temporal muscle, and skin. Both fentanyl and heroin at human-relevant doses (400 and 40 μg/kg, respectively) induced rapid, strong and transient decreases in NAc oxygen, indicative of brain hypoxia. When the heroin-fentanyl mixture was injected, the NAc hypoxic response was greatly potentiated in its duration, suggesting sustained hypoxia. In contrast to modest, monophasic brain temperature increases caused by heroin alone, the heroin-fentanyl mixture induced a biphasic temperature response, with a prominent postinjection decrease resulting from peripheral vasodilation. This hypothermic effect, albeit much smaller and more transient, was typical of fentanyl injected alone. Our findings indicate that accidental use of fentanyl instead of heroin, or even a relatively minor contamination of "street heroin" with fentanyl, poses great danger for acute health complications, including a comatose state and death.

Implementation of a new integrated d-lactic acid biosensor in a semiautomatic FIA system for the simultaneous determination of lactic acid enantiomers. Application to the analysis of beer samples.

PubMed

Vargas, E; Ruiz, M A; Campuzano, S; González de Rivera, G; López-Colino, F; Reviejo, A J; Pingarrón, J M

2016-05-15

An integrated amperometric d-lactic acid biosensor involving a gold film deposited by sputtering on a stainless steel disk electrode where the enzymes D-lactic acid dehydrogenase (DLDH) and diaphorase (DP) as well as the redox mediator tetrathiafulvalene (TTF) are coimmobilized by using a dialysis membrane, is reported in this work. Amperometry in stirred solutions at a detection potential of +0.15 V (vs Ag/AgCl reference electrode) provided a linear calibration plot for D-lactic acid over the 1.0×10(-4) to 3.8×10(-3) g L(-1) concentration range, with a limit of detection of 3.1×10(-5) g L(-1). The usefulness of the biosensor was demonstrated by determining D-lactic acid in beer samples with good results. Additionally, the biosensor was implemented together with a commercial L-lactic amperometric biosensor in a semiautomatic flow-injection analysis (FIA) system able to perform a rapid and simple stereo-specific determination of D- and D-lactic without a previous separation step. The operational characteristics of the biosensors under flow conditions were evaluated and its applicability was demonstrated through the simultaneous determination of both enantiomers in beer samples. Copyright © 2016 Elsevier B.V. All rights reserved.

Enzymes immobilized on amine-terminated ionic liquid-functionalized carbon nanotube for hydrogen peroxide determination.

PubMed

Liu, Xiuhui; Bu, Caihong; Nan, Zhihan; Zheng, Lichun; Qiu, Yu; Lu, Xiaoquan

2013-02-15

We report on a new approach for the electrochemical detection of hydrogen peroxide (H2O2) based on Cytochrome C (Cyt c) immobilized ionic liquid (IL)-functionalized multi-walled carbon nanotubes (MWCNTs) modified glass carbon electrode (GCE). Functionalization of multi-walled carbon nanotube with amine-terminated ionic liquid materials was characterized using fourier transform infrared spectroscopy (FTIR), UV-vis spectra, and electrochemical impedance spectroscopy (EIS), and the results showed that the covalent modification of MWCNTs with ILs exhibited a high surface area for enzyme immobilization and provided a good microenvironment for Cyt c to retain its bioelectrocatalytic activity toward H2O2. Amperometry was used to evaluate the catalytic activity of the cyt c towards H2O2. The proposed biosensor exhibited a wide linear response range nearly 4 orders of magnitude of H2O2 (4.0 × 10(-8)M-1.0 × 10(-4)M) with a good linearity (0.9980) and a low detection limit of 1.3 × 10(-8)M (based on S/N=3). Furthermore, the biosensor also displays some other excellent characteristics such as high selectivity, good reproducibility and long-term stability. Thus, the biosensor constructed in this study has great potential for detecting H2O2 in the complex biosystems. Copyright © 2012 Elsevier B.V. All rights reserved.

In situ optimization of pH for parts-per-billion electrochemical detection of dissolved hydrogen sulfide using boron doped diamond flow electrodes.

PubMed

Bitziou, Eleni; Joseph, Maxim B; Read, Tania L; Palmer, Nicola; Mollart, Tim; Newton, Mark E; Macpherson, Julie V

2014-11-04

A novel electrochemical approach to the direct detection of hydrogen sulfide (H2S), in aqueous solutions, covering a wide pH range (acid to alkali), is described. In brief, a dual band electrode device is employed, in a hydrodynamic flow cell, where the upstream electrode is used to controllably generate hydroxide ions (OH(-)), which flood the downstream detector electrode and provide the correct pH environment for complete conversion of H2S to the electrochemically detectable, sulfide (HS(-)) ion. All-diamond, coplanar conducting diamond band electrodes, insulated in diamond, were used due to their exceptional stability and robustness when applying extreme potentials, essential attributes for both local OH(-) generation via the reduction of water, and for in situ cleaning of the electrode, post oxidation of sulfide. Using a galvanostatic approach, it was demonstrated the pH locally could be modified by over five pH units, depending on the initial pH of the mobile phase and the applied current. Electrochemical detection limits of 13.6 ppb sulfide were achieved using flow injection amperometry. This approach which offers local control of the pH of the detector electrode in a solution, which is far from ideal for optimized detection of the analyte of interest, enhances the capabilities of online electrochemical detection systems.

Distinguishing mechanisms for alternans in cardiac cells using constant-diastolic-interval pacing

NASA Astrophysics Data System (ADS)

Cherry, Elizabeth M.

2017-09-01

Alternans, a proarrhythmic dynamical state in which cardiac action potentials alternate between long and short durations despite a constant pacing period, traditionally has been explained at the cellular level using nonlinear dynamics principles under the assumption that the action potential duration (APD) is determined solely by the time elapsed since the end of the previous action potential, called the diastolic interval (DI). In this scenario, APDs at a steady state should be the same provided that the preceding DIs are the same. Nevertheless, experiments attempting to eliminate alternans by dynamically adjusting the timing of pacing stimuli to keep the DI constant showed that alternans persisted, contradicting the traditional theory. It is now widely known that alternans also can arise from a different mechanism associated with intracellular calcium cycling. Our goal is to determine whether intracellular calcium dynamics can explain the experimental findings regarding the persistence of alternans despite a constant DI. For this, we use mathematical models capable of producing alternans through both voltage- and calcium-mediated mechanisms. We show that for voltage-driven alternans, action potentials elicited from a constant-DI protocol are always the same. However, in the case of calcium-driven alternans, the constant-DI protocol can result in alternans. Reducing the strength of the calcium instability progressively reduces and finally eliminates constant-DI alternans. Our findings suggest that screening for the presence of alternans using a constant-DI protocol has the potential for differentiating between voltage-driven and calcium-driven alternans.

Nonenzymetic glucose sensing using carbon functionalized carbon doped ZnO nanorod arrays

NASA Astrophysics Data System (ADS)

Chakraborty, Pinak; Majumder, Tanmoy; Dhar, Saurab; Mondal, Suvra Prakash

2018-04-01

Fabrication of highly sensitive, long stability and low cost glucose sensors are attractive for biomedical applications and food industries. Most of the commercial glucose sensors are based on enzymatic detection which suffers from problems underlying in enzyme activities. Development of high sensitive, enzyme free sensors is a great challenge for next generation glucose sensing applications. In our study Zinc oxide nanorod sensing electrodes have been grown using low cost hydrothermal route and their nonenzymatic glucose sensing properties have been demonstrated with carbon functionalized, carbon doped ZnO nanorods (C-ZnO NRs) in neutral medium (0.1M PBS, pH 7.4) using cyclic voltammetry and amperometry measurements. The C-ZnO NRs electrodes demonstrated glucose sensitivity˜ 13.66 µAmM-1cm-2 in the concentration range 0.7 - 14 mM.

Highly sensitive and selective electrochemical dopamine sensing properties of multilayer graphene nanobelts

NASA Astrophysics Data System (ADS)

Karthick Kannan, Padmanathan; Moshkalev, Stanislav A.; Sekhar Rout, Chandra

2016-02-01

In the present study, we report the electrochemical sensing property of multi-layer graphene nanobelts (GNBs) towards dopamine (DA). GNBs are synthesized from natural graphite and characterized by using techniques like field-emission scanning electron microscopy, atomic force microscopy and Raman spectroscopy. An electrochemical sensor based on GNBs is developed for the detection of DA. From the cyclic voltammetry and amperometry studies, it is found that GNBs possess excellent electrocatalytic activity towards DA molecules. The developed DA sensor showed a sensitivity value of 0.95 μA μM-1 cm-2 with a linear range of 2 μM to 0.2 mM. The interference data exhibited that GNB is highly selective to DA even in the presence of common interfering species like ascorbic acid, uric acid, glucose and lactic acid.

Highly sensitive and selective electrochemical dopamine sensing properties of multilayer graphene nanobelts.

PubMed

Kannan, Padmanathan Karthick; Moshkalev, Stanislav A; Rout, Chandra Sekhar

2016-02-19

In the present study, we report the electrochemical sensing property of multi-layer graphene nanobelts (GNBs) towards dopamine (DA). GNBs are synthesized from natural graphite and characterized by using techniques like field-emission scanning electron microscopy, atomic force microscopy and Raman spectroscopy. An electrochemical sensor based on GNBs is developed for the detection of DA. From the cyclic voltammetry and amperometry studies, it is found that GNBs possess excellent electrocatalytic activity towards DA molecules. The developed DA sensor showed a sensitivity value of 0.95 μA μM(-1) cm(-2) with a linear range of 2 μM to 0.2 mM. The interference data exhibited that GNB is highly selective to DA even in the presence of common interfering species like ascorbic acid, uric acid, glucose and lactic acid.

Electroreduction of CO{sub 2} using copper-deposited on boron-doped diamond (BDD)

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

Panglipur, Hanum Sekar; Ivandini, Tribidasari A., E-mail: ivandini.tri@sci.ui.ac.id; Einaga, Yasuaki

Electroreduction of CO{sub 2} was studied at copper-modified boron-doped diamond (Cu-BDD) electrodes as the working electrode. The Cu-BDD electrodes were prepared by electrochemical reduction with various concentrations of CuSO{sub 4} solutions. FE-SEM was utilized to characterize the electrodes. At Cu-BDD electrodes, a reduction peak at around -1.2 V (vs Ag/AgCl) attributtable to CO{sub 2} reductions could be observed by cyclic voltammetry technique of CO{sub 2} bubbled in water containing 0.1M NaCl. Accordingly, electroreduction of CO{sub 2} was conducted at -1.2 V (vs Ag/AgCl) using amperometry technique. The chemical products of the electroreduction analyzed by using HPLC showed the formation of formaldehyde, formicmore » acid, and acetic acid at Cu-BDD electrodes.« less

Constant potential pulse polarography

USGS Publications Warehouse

Christie, J.H.; Jackson, L.L.; Osteryoung, R.A.

1976-01-01

The new technique of constant potential pulse polarography, In which all pulses are to be the same potential, is presented theoretically and evaluated experimentally. The response obtained is in the form of a faradaic current wave superimposed on a constant capacitative component. Results obtained with a computer-controlled system exhibit a capillary response current similar to that observed In normal pulse polarography. Calibration curves for Pb obtained using a modified commercial pulse polarographic instrument are in good accord with theoretical predictions.

Electrochemical characterization and control of triple-layer muscles

NASA Astrophysics Data System (ADS)

Otero, Toribio F.; Cortes, Maria T.

2000-06-01

The electrochemical characterization of triple-layers formed by a EPA (Electroactive Polymer)/double-sided tape/EPA, like artificial muscles is described. Those muscles were characterized working under constant potential or under constant current. Due to the electrochemical nature of the electrochemomechanical property, muscles working under constant current produce constant movements, consuming increasing energies at decreasing temperatures, decreasing concentrations of electrolytes or trailing increasing masses. Muscles working at constant potential response with a faster movement if the temperature or the concentration of the electrolyte increase, or if the trailed weight decreases. Specific charges and specific energies were determined for every experimental condition.

PdNi- and Pd-coated electrodes prepared by electrodeposition from ionic liquid for nonenzymatic electrochemical determination of ethanol and glucose in alkaline media.

PubMed

Huang, Hsin-Yi; Chen, Po-Yu

2010-12-15

Nonenzymatic electrochemical determination of ethanol and glucose was respectively achieved using PdNi- and Pd-coated electrodes prepared by electrodeposition from the novel metal-free ionic liquid (IL); N-butyl-N-methylpyrrolidinium dicyanamide (BMP-DCA). BMP-DCA provided an excellent environment and wide cathodic limit for electrodeposition of metals and alloys because many metal chlorides could dissolve in this IL where the reduction potentials of Pd(II) and Ni(II) indeed overlapped, leading to the convenience of potentiostatic codeposition. In aqueous solutions, the reduction potentials of Pd(II) and Ni(II) are considerably separated. The bimetallic PdNi coatings with atomic ratios of ∼ 80/20 showed the highest current for ethanol oxidation reaction (EOR). Ethanol was detected by either cyclic voltammetry (CV) or hydrodynamic amperometry (HA). Using CV, the dependence of EOR peak current on concentration was linear from 4.92 to 962 μM with a detection limit of 2.26 μM (σ=3), and a linearity was observed from 4.92 to 988 μM using HA (detection limit 0.83 μM (σ=3)). The Pd-coated electrodes prepared by electrodeposition from BMP-DCA showed electrocatalytic activity to glucose oxidation and CV, HA, and square-wave voltammetry (SWV) were employed to determine glucose. SWV showed the best sensitivity and linearity was observed from 2.86 μM to 107 μM, and from 2.99 mM to 10.88 mM with detection limits of 0.78 μM and 25.9 μM (σ=3), respectively. For glucose detection, the interference produced from ascorbic acid, uric acid, and acetaminophen was significantly suppressed, compared with a regular Pt disk electrode. Copyright © 2010 Elsevier B.V. All rights reserved.

Improving carbon dioxide yields and cell efficiencies for ethanol oxidation by potential scanning

NASA Astrophysics Data System (ADS)

Majidi, Pasha; Pickup, Peter G.

2014-12-01

An ethanol electrolysis cell with aqueous ethanol supplied to the anode and nitrogen at the cathode has been operated under potential cycling conditions in order to increase the yield of carbon dioxide and thereby increase cell efficiency relative to operation at a fixed potential. At ambient temperature, faradaic yields of CO2 as high as 26% have been achieved, while only transient CO2 production was observed at constant potential. Yields increased substantially at higher temperatures, with maximum values at Pt anodes reaching 45% at constant potential and 65% under potential cycling conditions. Use of a PtRu anode increased the cell efficiency by decreasing the anode potential, but this was offset by decreased CO2 yields. Nonetheless, cycling increased the efficiency relative to constant potential. The maximum yields at PtRu and 80 °C were 13% at constant potential and 32% under potential cycling. The increased yields under cycling conditions have been attributed to periodic oxidative stripping of adsorbed CO, which occurs at lower potentials on PtRu than on Pt. These results will be important in the optimization of operating conditions for direct ethanol fuel cells and for the electrolysis of ethanol to produce clean hydrogen.

Hydroxylation increases the neurotoxic potential of BDE-47 to affect exocytosis and calcium homeostasis in PC12 cells.

PubMed

Dingemans, Milou M L; de Groot, Aart; van Kleef, Regina G D M; Bergman, Ake; van den Berg, Martin; Vijverberg, Henk P M; Westerink, Remco H S

2008-05-01

Oxidative metabolism, resulting in the formation of hydroxylated polybrominated diphenyl ether (PBDE) metabolites, may enhance the neurotoxic potential of brominated flame retardants. Our objective was to investigate the effects of a hydroxylated metabolite of 2,2',4,4'-tetra-bromodiphenyl ether (BDE-47; 6-OH-BDE-47) on changes in the intracellular Ca2+ concentration ([Ca2+]i) and vesicular catecholamine release in PC12 cells. We measured vesicular catecholamine release and [Ca2+]i using amperometry and imaging of the fluorescent Ca2+-sensitive dye Fura-2, respectively. Acute exposure of PC12 cells to 6-OH-BDE-47 (5 microM) induced vesicular catecholamine release. Catecholamine release coincided with a transient increase in [Ca2+]i, which was observed shortly after the onset of exposure to 6-OH-BDE-47 (120 microM). An additional late increase in [Ca2+]i was often observed at > or =1 microM 6-OH-BDE-47. The initial transient increase was absent in cells exposed to the parent compound BDE-47, whereas the late increase was observed only at 20 microM. Using the mitochondrial uncoupler carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone (FCCP) and thapsigargin to empty intracellular Ca2+ stores, we found that the initial increase originates from emptying of the endoplasmic reticulum and consequent influx of extracellular Ca2+, whereas the late increase originates primarily from mitochondria. The hydroxylated metabolite 6-OH-BDE-47 is more potent in disturbing Ca2+ homeostasis and neurotransmitter release than the parent compound BDE-47. The present findings indicate that bioactivation by oxidative metabolism adds considerably to the neurotoxic potential of PBDEs. Additionally, based on the observed mechanism of action, a cumulative neurotoxic effect of PBDEs and ortho-substituted polychlorinated biphenyls on [Ca2+]i cannot be ruled out.

Pulse electrodeposited nickel-indium tin oxide nanocomposite as an electrocatalyst for non-enzymatic glucose sensing.

PubMed

Sivasakthi, P; Ramesh Bapu, G N K; Chandrasekaran, Maruthai

2016-01-01

Nickel and nickel-ITO nanocomposite on mild steel substrate were prepared by pulse electrodeposition method from nickel sulphamate electrolyte and were examined as electrocatalysts for non-enzymatic glucose sensing. The surface morphology, chemical composition, preferred orientation and oxidation states of the nickel metal ion in the deposits were characterized by SEM, EDAX, XRD and XPS. Electrochemical sensing of glucose was studied by cyclic voltammetry and amperometry. The modified Ni-ITO nanocomposite electrode showed higher electrocatalytic activity for the oxidation of glucose in alkaline medium and exhibited a linear range from 0.02 to 3.00 mM with a limit of detection 3.74 μM at a signal-to-noise ratio of 3. The higher selectivity, longer stability and better reproducibility of this electrode compared to nickel in the sensing of glucose are pointers for exploitation in practical clinical applications. Copyright © 2015 Elsevier B.V. All rights reserved.

Stabilization of glucose-oxidase in the graphene paste for screen-printed glucose biosensor

NASA Astrophysics Data System (ADS)

Pepłowski, Andrzej; Janczak, Daniel; Jakubowska, Małgorzata

2015-09-01

Various methods and materials for enzyme stabilization within screen-printed graphene sensor were analyzed. Main goal was to develop technology allowing immediate printing of the biosensors in single printing process. Factors being considered were: toxicity of the materials used, ability of the material to be screen-printed (squeezed through the printing mesh) and temperatures required in the fabrication process. Performance of the examined sensors was measured using chemical amperometry method, then appropriate analysis of the measurements was conducted. The analysis results were then compared with the medical requirements. Parameters calculated were: correlation coefficient between concentration of the analyte and the measured electrical current (0.986) and variation coefficient for the particular concentrations of the analyte used as the calibration points. Variation of the measured values was significant only in ranges close to 0, decreasing for the concentrations of clinical importance. These outcomes justify further development of the graphene-based biosensors fabricated through printing techniques.

Decreased subcortical cholinergic arousal in focal seizures

PubMed Central

Motelow, Joshua E.; Li, Wei; Zhan, Qiong; Mishra, Asht M.; Sachdev, Robert N. S.; Liu, Geoffrey; Gummadavelli, Abhijeet; Zayyad, Zaina; Lee, Hyun Seung; Chu, Victoria; Andrews, John P.; Englot, Dario J.; Herman, Peter; Sanganahalli, Basavaraju G.; Hyder, Fahmeed; Blumenfeld, Hal

2015-01-01

SUMMARY Impaired consciousness in temporal lobe seizures has a major negative impact on quality of life. The prevailing view holds that this disorder impairs consciousness by seizure spread to the bilateral temporal lobes. We propose instead that seizures invade subcortical regions and depress arousal, causing impairment through decreases rather than through increases in activity. Using functional magnetic resonance imaging in a rodent model, we found increased activity in regions known to depress cortical function including lateral septum and anterior hypothalamus. Importantly, we found suppression of intralaminar thalamic and brainstem arousal systems and suppression of the cortex. At a cellular level, we found reduced firing of identified cholinergic neurons in the brainstem pedunculopontine tegmental nucleus and basal forebrain. Finally, we used enzyme-based amperometry to demonstrate reduced cholinergic neurotransmission in both cortex and thalamus. Decreased subcortical arousal is a novel mechanism for loss of consciousness in focal temporal lobe seizures. PMID:25654258

Simple flow injection analysis system for simultaneous determination of phenolic antioxidants with multiple pulse amperometric detection at a boron-doped diamond electrode.

PubMed

Medeiros, Roberta Antigo; Lourenção, Bruna Cláudia; Rocha-Filho, Romeu Cardozo; Fatibello-Filho, Orlando

2010-10-15

A method for simultaneous determination of butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) in food was developed that uses multiple pulse amperometry (MPA) with flow injection analysis (FIA). Determination of these phenolic antioxidants was carried out with a cathodically pretreated boron-doped diamond electrode and an aqueous ethanolic (30% ethanol, v/v) 10 mmol L⁻¹ KNO₃ solution (pH(cond) = 1.5) as supporting electrolyte. A dual-potential waveform, at E(det1) = 850 mV/200 ms and E(det2) = 1150 mV/200 ms versus Ag/AgCl (3.0 mol L⁻¹ KCl), was employed. The use of E(det1) or E(det2) caused the oxidation of BHA or of BHA and BHT, respectively; hence, concentration subtraction could be used to determine both species. The respective analytical curves presented good linearity in the investigated concentration range (0.050-3.0 μmol L⁻¹ for BHA and 0.70-70 μmol L⁻¹ for BHT), and the detection limits were 0.030 μmol L⁻¹ for BHA and 0.40 μmol L⁻¹ for BHT. The proposed method, which is simple, quick, and presents good precision and accuracy, was successfully applied in the simultaneous determination of BHA and BHT in commercial mayonnaise samples, with results similar to those obtained by HPLC, at a 95% confidence level.

Graphene: The Missing Piece for Cancer Diagnosis?

PubMed Central

Cruz, Sandra M. A.; Girão, André F.; Gonçalves, Gil; Marques, Paula A. A. P.

2016-01-01

This paper reviews recent advances in graphene-based biosensors development in order to obtain smaller and more portable devices with better performance for earlier cancer detection. In fact, the potential of Graphene for sensitive detection and chemical/biological free-label applications results from its exceptional physicochemical properties such as high electrical and thermal conductivity, aspect-ratio, optical transparency and remarkable mechanical and chemical stability. Herein we start by providing a general overview of the types of graphene and its derivatives, briefly describing the synthesis procedure and main properties. It follows the reference to different routes to engineer the graphene surface for sensing applications with organic biomolecules and nanoparticles for the development of advanced biosensing platforms able to detect/quantify the characteristic cancer biomolecules in biological fluids or overexpressed on cancerous cells surface with elevated sensitivity, selectivity and stability. We then describe the application of graphene in optical imaging methods such as photoluminescence and Raman imaging, electrochemical sensors for enzymatic biosensing, DNA sensing, and immunosensing. The bioquantification of cancer biomarkers and cells is finally discussed, particularly electrochemical methods such as voltammetry and amperometry which are generally adopted transducing techniques for the development of graphene based sensors for biosensing due to their simplicity, high sensitivity and low-cost. To close, we discuss the major challenges that graphene based biosensors must overcome in order to reach the necessary standards for the early detection of cancer biomarkers by providing reliable information about the patient disease stage. PMID:26805845

Examining changes in cellular communication in neuroendocrine cells after noble metal nanoparticle exposure.

PubMed

Love, Sara A; Liu, Zhen; Haynes, Christy L

2012-07-07

As nanoparticles enjoy increasingly widespread use in commercial applications, the potential for unintentional exposure has become much more likely during any given day. Researchers in the field of nanotoxicity are working to determine the physicochemical nanoparticle properties that lead to toxicity in an effort to establish safe design rules. This work explores the effects of noble metal nanoparticle exposure in murine chromaffin cells, focusing on examining the effects of size and surface functionality (coating) in silver and gold, respectively. Carbon-fibre microelectrode amperometry was utilized to examine the effect of exposure on exocytosis function, at the single cell level, and provided new insights into the compromised functions of cells. Silver nanoparticles of varied size, between 15 and 60 nm diameter, were exposed to cells and found to alter the release kinetics of exocytosis for those cells exposed to the smallest examined size. Effects of gold were examined after modification with two commonly used 'bio-friendly' polymers, either heparin or poly (ethylene glycol), and gold nanoparticles were found to induce altered cellular adhesion or the number of chemical messenger molecules released, respectively. These results support the body of work suggesting that noble metal nanoparticles perturb exocytosis, typically altering the number of molecules and kinetics of release, and supports a direct disruption of the vesicle matrix by the nanoparticle. Overall, it is clear that various nanoparticle physicochemical properties, including size and surface coating, do modulate changes in cellular communication via exocytosis.

Enterochromaffin cells of the human gut: sensors for spices and odorants.

PubMed

Braun, Thomas; Voland, Petra; Kunz, Lars; Prinz, Christian; Gratzl, Manfred

2007-05-01

Release of serotonin from mucosal enterochromaffin cells triggered by luminal substances is the key event in the regulation of gut motility and secretion. We were interested to know whether nasal olfactory receptors are also expressed in the human gut mucosa by enterochromaffin cells and whether their ligands and odorants present in spices, fragrances, detergents, and cosmetics cause serotonin release. Receptor expression was studied by the reverse-transcription polymerase chain reaction method in human mucosal enterochromaffin cells isolated by laser microdissection and in a cell line derived from human enterochromaffin cells. Activation of the cells by odorants was investigated by digital fluorescence imaging using the fluorescent Ca(2+) indicator Fluo-4. Serotonin release was measured in culture supernatants by a serotonin enzyme immunoassay and amperometry using carbon fiber microelectrodes placed on single cells. We found expression of 4 olfactory receptors in microdissected human mucosal enterochromaffin cells and in a cell line derived from human enterochromaffin cells. Ca(2+) imaging studies revealed that odorant ligands of the identified olfactory receptors cause Ca(2+) influx, elevation of intracellular free Ca(2+) levels, and, consequently, serotonin release. Our results show that odorants present in the luminal environment of the gut may stimulate serotonin release via olfactory receptors present in human enterochromaffin cells. Serotonin controls both gut motility and secretion and is implicated in pathologic conditions such as vomiting, diarrhea, and irritable bowel syndrome. Thus, olfactory receptors are potential novel targets for the treatment of gastrointestinal diseases and motility disorders.

Vibrational properties of TaW alloy using modified embedded atom method potential

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

Chand, Manesh, E-mail: maneshchand@gmail.com; Uniyal, Shweta; Joshi, Subodh

2016-05-06

Force-constants up to second neighbours of pure transition metal Ta and TaW alloy are determined using the modified embedded atom method (MEAM) potential. The obtained force-constants are used to calculate the phonon dispersion of pure Ta and TaW alloy. As a further application of MEAM potential, the force-constants are used to calculate the local vibrational density of states and mean square thermal displacements of pure Ta and W impurity atoms with Green’s function method. The calculated results are found to be in agreement with the experimental measurements.

Phonons in random alloys: The itinerant coherent-potential approximation

NASA Astrophysics Data System (ADS)

Ghosh, Subhradip; Leath, P. L.; Cohen, Morrel H.

2002-12-01

We present the itinerant coherent-potential approximation (ICPA), an analytic, translationally invariant, and tractable form of augmented-space-based multiple-scattering theory18 in a single-site approximation for harmonic phonons in realistic random binary alloys with mass and force-constant disorder. We provide expressions for quantities needed for comparison with experimental structure factors such as partial and average spectral functions and derive the sum rules associated with them. Numerical results are presented for Ni55Pd45 and Ni50Pt50 alloys which serve as test cases, the former for weak force-constant disorder and the latter for strong. We present results on dispersion curves and disorder-induced widths. Direct comparisons with the single-site coherent potential approximation (CPA) and experiment are made which provide insight into the physics of force-constant changes in random alloys. The CPA accounts well for the weak force-constant disorder case but fails for strong force-constant disorder where the ICPA succeeds.

Centrifugal distortion and the ring puckering vibration in the microwave spectrum of 2,3-dihydrofuran

NASA Astrophysics Data System (ADS)

Cervellati, R.; Degli Esposti, A.; Lister, D. G.; Lopez, J. C.; Alonso, J. L.

1986-10-01

The microwave spectrum of 2,3-dihydrofuran has been reinvestigated and measurements for the ground and first five excited states of the ring puckering vibration have been extended to higher frequencies and rotational quantum numbers in order to study the vibrational dependence of the rotational and centrifugal distortion constants. The ring puckering potential function derived by Green from the far infrared spectrum does not reproduce the vibrational dependence of the rotational constants well. A slightly different potential function is derived which gives a reasonable fit both to the far infrared spectrum and the rotational constants. This changes the barrier to ring inversion from 1.00 kJ mol -1 to 1.12 kJ mol -1. The vibrational dependence of the centrifugal distortion constants is accounted for satisfactorily by the theory developed by Creswell and Mills. An attempt to reproduce the vibrational dependence of the rotational and centrifugal distortion constants using the ring puckering potential function and a simple model for this vibration has very limited success.

Inflation with a constant rate of roll

NASA Astrophysics Data System (ADS)

Motohashi, Hayato; Starobinsky, Alexei A.; Yokoyama, Jun'ichi

2015-09-01

We consider an inflationary scenario where the rate of inflaton roll defined by ̈phi/H dot phi remains constant. The rate of roll is small for slow-roll inflation, while a generic rate of roll leads to the interesting case of 'constant-roll' inflation. We find a general exact solution for the inflaton potential required for such inflaton behaviour. In this model, due to non-slow evolution of background, the would-be decaying mode of linear scalar (curvature) perturbations may not be neglected. It can even grow for some values of the model parameter, while the other mode always remains constant. However, this always occurs for unstable solutions which are not attractors for the given potential. The most interesting particular cases of constant-roll inflation remaining viable with the most recent observational data are quadratic hilltop inflation (with cutoff) and natural inflation (with an additional negative cosmological constant). In these cases even-order slow-roll parameters approach non-negligible constants while the odd ones are asymptotically vanishing in the quasi-de Sitter regime.

Graviton fluctuations erase the cosmological constant

NASA Astrophysics Data System (ADS)

Wetterich, C.

2017-10-01

Graviton fluctuations induce strong non-perturbative infrared renormalization effects for the cosmological constant. The functional renormalization flow drives a positive cosmological constant towards zero, solving the cosmological constant problem without the need to tune parameters. We propose a simple computation of the graviton contribution to the flow of the effective potential for scalar fields. Within variable gravity, with effective Planck mass proportional to the scalar field, we find that the potential increases asymptotically at most quadratically with the scalar field. The solutions of the derived cosmological equations lead to an asymptotically vanishing cosmological "constant" in the infinite future, providing for dynamical dark energy in the present cosmological epoch. Beyond a solution of the cosmological constant problem, our simplified computation also entails a sizeable positive graviton-induced anomalous dimension for the quartic Higgs coupling in the ultraviolet regime, substantiating the successful prediction of the Higgs boson mass within the asymptotic safety scenario for quantum gravity.

Electric Double-Layer Interaction between Dissimilar Charge-Conserved Conducting Plates.

PubMed

Chan, Derek Y C

2015-09-15

Small metallic particles used in forming nanostructured to impart novel optical, catalytic, or tribo-rheological can be modeled as conducting particles with equipotential surfaces that carry a net surface charge. The value of the surface potential will vary with the separation between interacting particles, and in the absence of charge-transfer or electrochemical reactions across the particle surface, the total charge of each particle must also remain constant. These two physical conditions require the electrostatic boundary condition for metallic nanoparticles to satisfy an equipotential whole-of-particle charge conservation constraint that has not been studied previously. This constraint gives rise to a global charge conserved constant potential boundary condition that results in multibody effects in the electric double-layer interaction that are either absent or are very small in the familiar constant potential or constant charge or surface electrochemical equilibrium condition.

Determination of Acid Dissociation Constants (pKa) of Bicyclic Thiohydantoin-Pyrrolidine Compounds in 20% Ethanol-Water Hydroorganic Solvent

PubMed Central

Nural, Yahya; Döndaş, H. Ali; Sarı, Hayati; Atabey, Hasan; Belveren, Samet; Gemili, Müge

2014-01-01

The acid dissociation constants of potential bioactive fused ring thiohydantoin-pyrrolidine compounds were determined by potentiometric titration in 20% (v/v) ethanol-water mixed at 25 ± 0.1°C, at an ionic background of 0.1 mol/L of NaCl using the HYPERQUAD computer program. Proton affinities of potential donor atoms of the ligands were calculated by AM1 and PM3 semiempiric methods. We found, potentiometrically, three different acid dissociation constants for 1a–f. We suggest that these acid dissociation constants are related to the carboxyl, enol, and amino groups. PMID:24799905

Differential Mobility Spectrometry: Preliminary Findings on Determination of Fundamental Constants

NASA Technical Reports Server (NTRS)

Limero, Thomas; Cheng, Patti; Boyd, John

2007-01-01

The electron capture detector (ECD) has been used for 40+ years (1) to derive fundamental constants such as a compound's electron affinity. Given this historical perspective, it is not surprising that differential mobility spectrometry (DMS) might be used in a like manner. This paper will present data from a gas chromatography (GC)-DMS instrument that illustrates the potential capability of this device to derive fundamental constants for electron-capturing compounds. Potential energy curves will be used to provide possible explanation of the data.

Constant-intensity waves and their modulation instability in non-Hermitian potentials

NASA Astrophysics Data System (ADS)

Makris, K. G.; Musslimani, Z. H.; Christodoulides, D. N.; Rotter, S.

2015-07-01

In all of the diverse areas of science where waves play an important role, one of the most fundamental solutions of the corresponding wave equation is a stationary wave with constant intensity. The most familiar example is that of a plane wave propagating in free space. In the presence of any Hermitian potential, a wave's constant intensity is, however, immediately destroyed due to scattering. Here we show that this fundamental restriction is conveniently lifted when working with non-Hermitian potentials. In particular, we present a whole class of waves that have constant intensity in the presence of linear as well as of nonlinear inhomogeneous media with gain and loss. These solutions allow us to study the fundamental phenomenon of modulation instability in an inhomogeneous environment. Our results pose a new challenge for the experiments on non-Hermitian scattering that have recently been put forward.

Inflation with a constant rate of roll

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

Motohashi, Hayato; Starobinsky, Alexei A.; Yokoyama, Jun'ichi, E-mail: motohashi@kicp.uchicago.edu, E-mail: alstar@landau.ac.ru, E-mail: yokoyama@resceu.s.u-tokyo.ac.jp

2015-09-01

We consider an inflationary scenario where the rate of inflaton roll defined by {sup ··}φ/H φ-dot remains constant. The rate of roll is small for slow-roll inflation, while a generic rate of roll leads to the interesting case of 'constant-roll' inflation. We find a general exact solution for the inflaton potential required for such inflaton behaviour. In this model, due to non-slow evolution of background, the would-be decaying mode of linear scalar (curvature) perturbations may not be neglected. It can even grow for some values of the model parameter, while the other mode always remains constant. However, this always occurs formore » unstable solutions which are not attractors for the given potential. The most interesting particular cases of constant-roll inflation remaining viable with the most recent observational data are quadratic hilltop inflation (with cutoff) and natural inflation (with an additional negative cosmological constant). In these cases even-order slow-roll parameters approach non-negligible constants while the odd ones are asymptotically vanishing in the quasi-de Sitter regime.« less

Simulation of electric double-layer capacitors: evaluation of constant potential method

NASA Astrophysics Data System (ADS)

Wang, Zhenxing; Laird, Brian; Yang, Yang; Olmsted, David; Asta, Mark

2014-03-01

Atomistic simulations can play an important role in understanding electric double-layer capacitors (EDLCs) at a molecular level. In such simulations, typically the electrode surface is modeled using fixed surface charges, which ignores the charge fluctuation induced by local fluctuations in the electrolyte solution. In this work we evaluate an explicit treatment of charges, namely constant potential method (CPM)[1], in which the electrode charges are dynamically updated to maintain constant electrode potential. We employ a model system with a graphite electrode and a LiClO4/acetonitrile electrolyte, examined as a function of electrode potential differences. Using various molecular and macroscopic properties as metrics, we compare CPM simulations on this system to results using fixed surface charges. Specifically, results for predicted capacity, electric potential gradient and solvent density profile are identical between the two methods; However, ion density profiles and solvation structure yield significantly different results.

A relativistic coupled-cluster interaction potential and rovibrational constants for the xenon dimer

NASA Astrophysics Data System (ADS)

Jerabek, Paul; Smits, Odile; Pahl, Elke; Schwerdtfeger, Peter

2018-01-01

An accurate potential energy curve has been derived for the xenon dimer using state-of-the-art relativistic coupled-cluster theory up to quadruple excitations accounting for both basis set superposition and incompleteness errors. The data obtained is fitted to a computationally efficient extended Lennard-Jones potential form and to a modified Tang-Toennies potential function treating the short- and long-range part separately. The vibrational spectrum of Xe2 obtained from a numerical solution of the rovibrational Schrödinger equation and subsequently derived spectroscopic constants are in excellent agreement with experimental values. We further present solid-state calculations for xenon using a static many-body expansion up to fourth-order in the xenon interaction potential including dynamic effects within the Einstein approximation. Again we find very good agreement with the experimental (face-centred cubic) lattice constant and cohesive energy.

Constant fields and constant gradients in open ionic channels.

PubMed Central

Chen, D P; Barcilon, V; Eisenberg, R S

1992-01-01

Ions enter cells through pores in proteins that are holes in dielectrics. The energy of interaction between ion and charge induced on the dielectric is many kT, and so the dielectric properties of channel and pore are important. We describe ionic movement by (three-dimensional) Nemst-Planck equations (including flux and net charge). Potential is described by Poisson's equation in the pore and Laplace's equation in the channel wall, allowing induced but not permanent charge. Asymptotic expansions are constructed exploiting the long narrow shape of the pore and the relatively high dielectric constant of the pore's contents. The resulting one-dimensional equations can be integrated numerically; they can be analyzed when channels are short or long (compared with the Debye length). Traditional constant field equations are derived if the induced charge is small, e.g., if the channel is short or if the total concentration gradient is zero. A constant gradient of concentration is derived if the channel is long. Plots directly comparable to experiments are given of current vs voltage, reversal potential vs. concentration, and slope conductance vs. concentration. This dielectric theory can easily be tested: its parameters can be determined by traditional constant field measurements. The dielectric theory then predicts current-voltage relations quite different from constant field, usually more linear, when gradients of total concentration are imposed. Numerical analysis shows that the interaction of ion and channel can be described by a mean potential if, but only if, the induced charge is negligible, that is to say, the electric field is spatially constant. Images FIGURE 1 PMID:1376159

Catalytic hydrodeoxygenation of methyl-substituted phenols: correlations of kinetic parameters with molecular properties.

PubMed

Massoth, F E; Politzer, P; Concha, M C; Murray, J S; Jakowski, J; Simons, Jack

2006-07-27

The hydrodeoxygenation of methyl-substituted phenols was carried out in a flow microreactor at 300 degrees C and 2.85 MPa hydrogen pressure over a sulfided CoMo/Al(2)O(3) catalyst. The primary reaction products were methyl-substituted benzene, cyclohexene, cyclohexane, and H(2)O. Analysis of the results suggests that two independent reaction paths are operative, one leading to aromatics and the other to partially or completely hydrogenated cyclohexanes. The reaction data were analyzed using Langmuir-Hinshelwood kinetics to extract the values of the reactant-to-catalyst adsorption constant and of the rate constants characterizing the two reaction paths. The adsorption constant was found to be the same for both reactions, suggesting that a single catalytic site center is operative in both reactions. Ab initio electronic structure calculations were used to evaluate the electrostatic potentials and valence orbital ionization potentials for all of the substituted phenol reactants. Correlations were observed between (a) the adsorption constant and the two reaction rate constants measured for various methyl-substitutions and (b) certain moments of the electrostatic potentials and certain orbitals' ionization potentials of the isolated phenol molecules. On the basis of these correlations to intrinsic reactant-molecule properties, a reaction mechanism is proposed for each pathway, and it is suggested that the dependencies of adsorption and reaction rates upon methyl-group substitution are a result of the substituents' effects on the electrostatic potential and orbitals rather than geometric (steric) effects.

Extracellular levels of lactate, but not oxygen, reflect sleep homeostasis in the rat cerebral cortex.

PubMed

Dash, Michael B; Tononi, Giulio; Cirelli, Chiara

2012-07-01

It is well established that brain metabolism is higher during wake and rapid eye movement (REM) sleep than in nonrapid eye movement (NREM) sleep. Most of the brain's energy is used to maintain neuronal firing and glutamatergic transmission. Recent evidence shows that cortical firing rates, extracellular glutamate levels, and markers of excitatory synaptic strength increase with time spent awake and decline throughout NREM sleep. These data imply that the metabolic cost of each behavioral state is not fixed but may reflect sleep-wake history, a possibility that is investigated in the current report. Chronic (4d) electroencephalographic (EEG) recordings in the rat cerebral cortex were coupled with fixed-potential amperometry to monitor the extracellular concentration of oxygen ([oxy]) and lactate ([lac]) on a second-by-second basis across the spontaneous sleep-wake cycle and in response to sleep deprivation. Basic sleep research laboratory. Wistar Kyoto (WKY) adult male rats. N/A. Within 30-60 sec [lac] and [oxy] progressively increased during wake and REM sleep and declined during NREM sleep (n = 10 rats/metabolite), but with several differences. [Oxy], but not [lac], increased more during wake with high motor activity and/or elevated EEG high-frequency power. Meanwhile, only the NREM decline of [lac] reflected sleep pressure as measured by slow-wave activity, mirroring previous results for cortical glutamate. The observed state-dependent changes in cortical [lac] and [oxy] are consistent with higher brain metabolism during waking and REM sleep in comparison with NREM sleep. Moreover, these data suggest that glycolytic activity, most likely through its link with glutamatergic transmission, reflects sleep homeostasis.

Cerebellar modulation of frontal cortex dopamine efflux in mice: relevance to autism and schizophrenia.

PubMed

Mittleman, Guy; Goldowitz, Daniel; Heck, Detlef H; Blaha, Charles D

2008-07-01

Cerebellar and frontal cortical pathologies have been commonly reported in schizophrenia, autism, and other developmental disorders. Whether there is a relationship between prefrontal and cerebellar pathologies is unknown. Using fixed potential amperometry, dopamine (DA) efflux evoked by cerebellar or, dentate nucleus electrical stimulation (50 Hz, 200 muA) was recorded in prefrontal cortex of urethane anesthetized lurcher (Lc/+) mice with 100% loss of cerebellar Purkinje cells and wildtype (+/+) control mice. Cerebellar stimulation with 25 and 100 pulses evoked prefrontal cortex DA efflux in +/+ mice that persisted for 12 and 25 s poststimulation, respectively. In contrast, 25 pulse cerebellar stimulation failed to evoke prefrontal cortex DA efflux in Lc/+ mice indicating a dependency on cerebellar Purkinje cell outputs. Dentate nucleus stimulation (25 pulses) evoked a comparable but briefer (baseline recovery within 7 s) increase in prefrontal cortex DA efflux compared to similar cerebellar stimulation in +/+ mice. However, in Lc/+ mice 25 pulse dentate nucleus evoked prefrontal cortex DA efflux was attenuated by 60% with baseline recovery within 4 s suggesting that dentate nucleus outputs to prefrontal cortex remain partially functional. DA reuptake blockade enhanced 100 pulse stimulation evoked prefrontal cortex responses, while serotonin or norepinephrine reuptake blockade were without effect indicating the specificity of the amperometric recordings to DA. Results provide neurochemical evidence that the cerebellum can modulate DA efflux in the prefrontal cortex. Together, these findings may explain why cerebellar and frontal cortical pathologies co-occur, and may provide a mechanism that accounts for the diversity of symptoms common to multiple developmental disorders.

Cerebellar Modulation of Frontal Cortex Dopamine Efflux in Mice: Relevance to Autism and Schizophrenia

PubMed Central

MITTLEMAN, GUY; GOLDOWITZ, DANIEL; HECK, DETLEF H.; BLAHA, CHARLES D.

2013-01-01

Cerebellar and frontal cortical pathologies have been commonly reported in schizophrenia, autism, and other developmental disorders. Whether there is a relationship between prefrontal and cerebellar pathologies is unknown. Using fixed potential amperometry, dopamine (DA) efflux evoked by cerebellar or, dentate nucleus electrical stimulation (50 Hz, 200 μA) was recorded in prefrontal cortex of urethane anesthetized lurcher (Lc/+) mice with 100% loss of cerebellar Purkinje cells and wildtype (+/+) control mice. Cerebellar stimulation with 25 and 100 pulses evoked prefrontal cortex DA efflux in +/+ mice that persisted for 12 and 25 s poststimulation, respectively. In contrast, 25 pulse cerebellar stimulation failed to evoke prefrontal cortex DA efflux in Lc/+ mice indicating a dependency on cerebellar Purkinje cell outputs. Dentate nucleus stimulation (25 pulses) evoked a comparable but briefer (baseline recovery within 7 s) increase in prefrontal cortex DA efflux compared to similar cerebellar stimulation in +/+ mice. However, in Lc/+ mice 25 pulse dentate nucleus evoked prefrontal cortex DA efflux was attenuated by 60% with baseline recovery within 4 s suggesting that dentate nucleus outputs to prefrontal cortex remain partially functional. DA reuptake blockade enhanced 100 pulse stimulation evoked pre-frontal cortex responses, while serotonin or norepinephrine reuptake blockade were without effect indicating the specificity of the amperometric recordings to DA. Results provide neurochemical evidence that the cerebellum can modulate DA efflux in the prefrontal cortex. Together, these findings may explain why cerebellar and frontal cortical pathologies co-occur, and may provide a mechanism that accounts for the diversity of symptoms common to multiple developmental disorders. PMID:18435424

Fabrication of potato-like silver molybdate microstructures for photocatalytic degradation of chronic toxicity ciprofloxacin and highly selective electrochemical detection of H2O2

NASA Astrophysics Data System (ADS)

Kumar, J. Vinoth; Karthik, R.; Chen, Shen-Ming; Muthuraj, V.; Karuppiah, Chelladurai

2016-09-01

In the present work, potato-like silver molybdate (Ag2MoO4) microstructures were synthesized through a simple hydrothermal method. The microstructures of Ag2MoO4 were characterized by various analytical and spectroscopic techniques such as XRD, FTIR, Raman, SEM, EDX and XPS. Interestingly, the as-prepared Ag2MoO4 showed excellent photocatalytic and electrocatalytic activity for the degradation of ciprofloxacin (CIP) and electrochemical detection of hydrogen peroxide (H2O2), respectively. The ultraviolet-visible (UV-Vis) spectroscopy results revealed that the potato-like Ag2MoO4 microstructures could offer a high photocatalytic activity towards the degradation of CIP under UV-light illumination, leads to rapid degradation within 40 min with a degradation rate of above 98%. In addition, the cyclic voltammetry (CV) and amperometry studies were realized that the electrochemical performance of Ag2MoO4 modified electrode toward H2O2 detection. Our H2O2 sensor shows a wide linear range and lower detection limit of 0.04-240 μM and 0.03 μM, respectively. The Ag2MoO4 modified electrode exhibits a high selectivity towards the detection of H2O2 in the presence of different biological interferences. These results suggested that the development of potato-like Ag2MoO4 microstructure could be an efficient photocatalyst as well as electrocatalyst in the potential application of environmental, biomedical and pharmaceutical samples.

A novel carbon tipped single micro-optrode for combined optogenetics and electrophysiology

PubMed Central

Vizvári, Attila D.; Bali, Zsolt K.; Márki, Balázs; Nagy, Lili V.; Kónya, Zoltán; Madarász, Dániel; Henn-Mike, Nóra; Varga, Csaba; Hernádi, István

2018-01-01

Optical microelectrodes (optrodes) are used in neuroscience to transmit light into the brain of a genetically modified animal to evoke and record electrical activity from light-sensitive neurons. Our novel micro-optrode solution integrates a light-transmitting 125 micrometer optical fiber and a 9 micrometer carbon monofilament to form an electrical lead element, which is contained in a borosilicate glass sheathing coaxial arrangement ending with a micrometer-sized carbon tip. This novel unit design is stiff and slender enough to be used for targeting deep brain areas, and may cause less tissue damage compared with previous models. The center-positioned carbon fiber is less prone to light-induced artifacts than side-lit metal microelectrodes previously presented. The carbon tip is capable of not only recording electrical signals of neuronal origin but can also provide valuable surface area for electron transfer, which is essential in electrochemical (voltammetry, amperometry) or microbiosensor applications. We present details of design and manufacture as well as operational examples of the newly developed single micro-optrode, which includes assessments of 1) carbon tip length–impedance relationship, 2) light transmission capabilities, 3) photoelectric artifacts in carbon fibers, 4) responses to dopamine using fast-scan cyclic voltammetry in vivo, and 5) optogenetic stimulation and spike or local field potential recording from the rat brain transfected with channelrhodopsin-2. With this work, we demonstrate that our novel carbon tipped single micro-optrode may open up new avenues for use in optogenetic stimulation when needing to be combined with extracellular recording, electrochemical, or microbiosensor measurements performed on a millisecond basis. PMID:29513711

Simulating Supercapacitors: Can We Model Electrodes As Constant Charge Surfaces?

PubMed

Merlet, Céline; Péan, Clarisse; Rotenberg, Benjamin; Madden, Paul A; Simon, Patrice; Salanne, Mathieu

2013-01-17

Supercapacitors based on an ionic liquid electrolyte and graphite or nanoporous carbon electrodes are simulated using molecular dynamics. We compare a simplified electrode model in which a constant, uniform charge is assigned to each carbon atom with a realistic model in which a constant potential is applied between the electrodes (the carbon charges are allowed to fluctuate). We show that the simulations performed with the simplified model do not provide a correct description of the properties of the system. First, the structure of the adsorbed electrolyte is partly modified. Second, dramatic differences are observed for the dynamics of the system during transient regimes. In particular, upon application of a constant applied potential difference, the increase in the temperature, due to the Joule effect, associated with the creation of an electric current across the cell follows Ohm's law, while unphysically high temperatures are rapidly observed when constant charges are assigned to each carbon atom.

Rapid Prototyping of a High Sensitivity Graphene Based Glucose Sensor Strip.

PubMed

Tehrani, Farshad; Reiner, Lisa; Bavarian, Behzad

2015-01-01

A rapid prototyping of an inexpensive, disposable graphene and copper nanocomposite sensor strip using polymeric flexible substrate for highly sensitive and selective nonenzymatic glucose detection has been developed and tested for direct oxidization of glucose. The CuNPs were electrochemically deposited on to the graphene sheets to improve electron transfer rates and to enhance electrocatalytic activity toward glucose. The graphene based electrode with CuNPs demonstrated a high degree of sensitivity (1101.3 ± 56 μA/mM.cm2), excellent selectivity (without an interference with Ascorbic Acid, Uric Acid, Dopamine, and Acetaminophen), good stability with a linear response to glucose ranging from 0.1 mM to 0.6 mM concentration, and detection limits of 0.025 mM to 0.9 mM. Characterization of the electrodes was performed by scanning electron microscopy (FESEM and SEM). The electrochemical properties of the modified graphene electrodes were inspected by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and amperometry.

Sensors and Biosensors for C-Reactive Protein, Temperature and pH, and Their Applications for Monitoring Wound Healing: A Review

PubMed Central

Dini, Valentina; Kirchhain, Arno; Janowska, Agata; Oranges, Teresa; Di Francesco, Fabio

2017-01-01

Wound assessment is usually performed in hospitals or specialized labs. However, since patients spend most of their time at home, a remote real time wound monitoring would help providing a better care and improving the healing rate. This review describes the advances in sensors and biosensors for monitoring the concentration of C-reactive protein (CRP), temperature and pH in wounds. These three parameters can be used as qualitative biomarkers to assess the wound status and the effectiveness of therapy. CRP biosensors can be classified in: (a) field effect transistors, (b) optical immunosensors based on surface plasmon resonance, total internal reflection, fluorescence and chemiluminescence, (c) electrochemical sensors based on potentiometry, amperometry, and electrochemical impedance, and (d) piezoresistive sensors, such as quartz crystal microbalances and microcantilevers. The last section reports the most recent developments for wearable non-invasive temperature and pH sensors suitable for wound monitoring. PMID:29257113

Rapid Prototyping of a High Sensitivity Graphene Based Glucose Sensor Strip

PubMed Central

Tehrani, Farshad; Reiner, Lisa; Bavarian, Behzad

2015-01-01

A rapid prototyping of an inexpensive, disposable graphene and copper nanocomposite sensor strip using polymeric flexible substrate for highly sensitive and selective nonenzymatic glucose detection has been developed and tested for direct oxidization of glucose. The CuNPs were electrochemically deposited on to the graphene sheets to improve electron transfer rates and to enhance electrocatalytic activity toward glucose. The graphene based electrode with CuNPs demonstrated a high degree of sensitivity (1101.3±56 μA/mM.cm2), excellent selectivity (without an interference with Ascorbic Acid, Uric Acid, Dopamine, and Acetaminophen), good stability with a linear response to glucose ranging from 0.1 mM to 0.6 mM concentration, and detection limits of 0.025 mM to 0.9 mM. Characterization of the electrodes was performed by scanning electron microscopy (FESEM and SEM). The electrochemical properties of the modified graphene electrodes were inspected by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and amperometry. PMID:26678700

Electrochemical Enzyme Biosensors Revisited: Old Solutions for New Problems.

PubMed

Monteiro, Tiago; Almeida, Maria Gabriela

2018-05-14

Worldwide legislation is driving the development of novel and highly efficient analytical tools for assessing the composition of every material that interacts with Consumers or Nature. The biosensor technology is one of the most active R&D domains of Analytical Sciences focused on the challenge of taking analytical chemistry to the field. Electrochemical biosensors based on redox enzymes, in particular, are highly appealing due to their usual quick response, high selectivity and sensitivity, low cost and portable dimensions. This review paper aims to provide an overview of the most important advances made in the field since the proposal of the first biosensor, the well-known hand-held glucose meter. The first section addresses the current needs and challenges for novel analytical tools, followed by a brief description of the different components and configurations of biosensing devices, and the fundamentals of enzyme kinetics and amperometry. The following sections emphasize on enzyme-based amperometric biosensors and the different stages of their development.

Mesoporous silica (MCM-41)-Fe2O3 as a novel magnetic nanosensor for determination of trace amounts of amino acids.

PubMed

Hasanzadeh, Mohammad; Shadjou, Nasrin; Omidinia, Eskandar

2013-08-01

Magnetic (Fe2O3) mobile crystalline material-41 (MCM-41) was prepared and characterized using transmission electron microscopy (TEM) and nitrogen adsorption-desorption techniques. Due to the large surface area (1213 m(2)g(-1)) and remarkable electrocatalytic properties of MCM-41-Fe2O3, the MCM-41-Fe2O3 modified glassy carbon electrode (MCM-41-Fe2O3/GCE) exhibits potent electrocatalytic activity toward the electro-oxidation of amino acids. MCM-41-Fe2O3/GCE brings new capabilities for electrochemical sensing by combining the advantages of Fe2O3 magnetic nanoparticles and MCM-41 with very large surface area. Cyclic voltammetry, hydrodynamic amperometry and flow injection analysis used to determination of amino acids at higher concentration range. Fast response time, excellent catalytic activity, and ease of preparation are the advantages of the proposed amino acid sensor. Copyright © 2013 Elsevier B.V. All rights reserved.

Comparative study of label-free electrochemical immunoassay on various gold nanostructures

NASA Astrophysics Data System (ADS)

Rafique, S.; Gao, C.; Li, C. M.; Bhatti, A. S.

2013-10-01

Electrochemical methods such as amperometry and impedance spectroscopy provide the feasibility of label-free immunoassay. However, the performance of electrochemical interfaces varies with the shape of gold nanostructures. In the present work three types of gold nanostructures including pyramid, spherical, and rod-like nanostructures were electrochemically synthesized on the gold electrode and were further transformed into immunosensor by covalent binding of antibodies. As a model protein, a cancer biomarker, Carcinoembryonic Antigen (CEA) was detected using amperometric and impedimetric techniques on three nanostructured electrodes, which enabled to evaluate and compare the immunoassay's performance. It was found that all three immunosensors showed improved linear electrochemical response to the concentration of CEA compared to bare Au electrode. Among all the spherical gold nanostructure based immunosensors displayed superior performance. Under optimal condition, the immunosensors exhibited a limit of detection of 4.1 pg ml-1 over a concentration range of five orders of magnitude. This paper emphasizes that fine control over the geometry of nanostructures is essentially important for high-performance electrochemical immunoassay.

Constant-roll tachyon inflation and observational constraints

NASA Astrophysics Data System (ADS)

Gao, Qing; Gong, Yungui; Fei, Qin

2018-05-01

For the constant-roll tachyon inflation, we derive the analytical expressions for the scalar and tensor power spectra, the scalar and tensor spectral tilts and the tensor to scalar ratio to the first order of epsilon1 by using the method of Bessel function approximation. The derived ns-r results are compared with the observations, we find that only the constant-roll inflation with ηH being a constant is consistent with the observations and observations constrain the constant-roll inflation to be slow-roll inflation. The tachyon potential is also reconstructed for the constant-roll inflation which is consistent with the observations.

Solubility of methane in water: the significance of the methane-water interaction potential.

PubMed

Konrad, Oliver; Lankau, Timm

2005-12-15

The influence of the methane-water interaction potential on the value of the Henry constant obtained from molecular dynamics simulations was investigated. The SPC, SPC/E, MSPC/E, and TIP3P potentials were used to describe water and the OPLS-UA and TraPPE potentials for methane. Nonbonding interactions between unlike atoms were calculated both with one of four mixing rules and with our new methane-water interaction potential. The Henry constants obtained from simulations using any of the mixing rules differed significantly from the experimental ones. Good agreement between simulation and experiment was achieved with the new potential over the whole temperature range.

Ventral tegmental ionotropic glutamate receptor stimulation of nucleus accumbens tonic dopamine efflux blunts hindbrain-evoked phasic neurotransmission: implications for dopamine dysregulation disorders.

PubMed

Tye, S J; Miller, A D; Blaha, C D

2013-11-12

Activation of glutamate receptors within the ventral tegmental area (VTA) stimulates extrasynaptic (basal) dopamine release in terminal regions, including the nucleus accumbens (NAc). Hindbrain inputs from the laterodorsal tegmental nucleus (LDT) are critical for elicitation of phasic VTA dopamine cell activity and consequent transient dopamine release. This study investigated the role of VTA ionotropic glutamate receptor (iGluR) stimulation on both basal and LDT electrical stimulation-evoked dopamine efflux in the NAc using in vivo chronoamperometry and fixed potential amperometry in combination with stearate-graphite paste and carbon fiber electrodes, respectively. Intra-VTA infusion of the iGluR agonists (±)-α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA; 1 μg/μl) or N-methyl-d-aspartic acid (NMDA; 2 μg/μl) enhanced basal NAc dopamine efflux. This iGluR-mediated potentiation of basal dopamine efflux was paralleled by an attenuation of LDT-evoked transient NAc dopamine efflux, suggesting that excitation of basal activity effectively inhibited the capacity of hindbrain afferents to elicit transient dopamine efflux. In line with this, post-NMDA infusion of the dopamine D2 autoreceptor (D2R) agonist quinpirole (1 μg/μl; intra-VTA) partially recovered NMDA-mediated attenuation of LDT-evoked NAc dopamine, while concurrently attenuating NMDA-mediated potentiation of basal dopamine efflux. Post-NMDA infusion of quinpirole (1 μg/μl) alone attenuated basal and LDT-evoked dopamine efflux. Taken together, these data reveal that hyperstimulation of basal dopamine transmission can stunt hindbrain burst-like stimulation-evoked dopamine efflux. Inhibitory autoreceptor mechanisms within the VTA help to partially recover the magnitude of phasic dopamine efflux, highlighting the importance of both iGluRs and D2 autoreceptors in maintaining the functional balance of tonic and phasic dopamine neurotransmission. Dysregulation of this balance may have important implications for disorders of dopamine dysregulation such as attention deficit hyperactivity disorder. Copyright © 2013 IBRO. Published by Elsevier Ltd. All rights reserved.

Calcium ion binding to a soil fulvic acid using a donnan potential model

USGS Publications Warehouse

Marinsky, J.A.; Mathuthu, A.; Ephraim, J.H.; Reddy, M.M.

1999-01-01

Calcium ion binding to a soil fulvic acid (Armadale Bh Horizon) was evaluated over a range of calcium ion concentrations, from pH 3.8 to 7.3, using potentiometric titrations and calcium ion electrode measurements. Fulvic acid concentration was constant (100 milligrams per liter) and calcium ion concentration varied up to 8 X 10-4 moles per liter. Experiments discussed here included: (1) titrations of fulvic acid-calcium ion containing solutions with sodium hydroxide; and (2) titrations of fully neutralized fulvic acid with calcium chloride solutions. Apparent binding constants (expressed as the logarithm of the value, log ??app) vary with solution pH, calcium ion concentration, degree of acid dissociation, and ionic strength (from log ??app = 2.5 to 3.9) and are similar to those reported by others. Fulvic acid charge, and the associated Donnan Potential, influences calcium ion-fulvic acid ion pair formation. A Donnan Potential corrrection term allowed calculation of intrinsic calcium ion-fulvic acid binding constants. Intrinsic binding constants vary from 1.2 to 2.5 (the average value is about log??= 1.6) and are similar to, but somewhat higher than, stability constants for calcium ion-carboxylic acid monodentate complexes. ?? by Oldenbourg Wissenschaftsverlag, Mu??nchen.

Hydration effects on the electrostatic potential around tuftsin.

PubMed

Valdeavella, C V; Blatt, H D; Yang, L; Pettitt, B M

1999-08-01

The electrostatic potential and component dielectric constants from molecular dynamics (MD) trajectories of tuftsin, a tetrapeptide with the amino acid sequence Thr-Lys-Pro-Arg in water and in saline solution are presented. The results obtained from the analysis of the MD trajectories for the total electrostatic potential at points on a grid using the Ewald technique are compared with the solution to the Poisson-Boltzmann (PB) equation. The latter was solved using several sets of dielectric constant parameters. The effects of structural averaging on the PB results were also considered. Solute conformational mobility in simulations gives rise to an electrostatic potential map around the solute dominated by the solute monopole (or lowest order multipole). The detailed spatial variation of the electrostatic potential on the molecular surface brought about by the compounded effects of the distribution of water and ions close to the peptide, solvent mobility, and solute conformational mobility are not qualitatively reproducible from a reparametrization of the input solute and solvent dielectric constants to the PB equation for a single structure or for structurally averaged PB calculations. Nevertheless, by fitting the PB to the MD electrostatic potential surfaces with the dielectric constants as fitting parameters, we found that the values that give the best fit are the values calculated from the MD trajectories. Implications of using such field calculations on the design of tuftsin peptide analogues are discussed.

Development of a nanowire based titanium needle probe sensor for glucose monitoring

NASA Astrophysics Data System (ADS)

Deshpande, Devesh C.

The need for continuous monitoring of various physiological functions such as blood glucose levels, neural functions and cholesterol levels has fostered the research and development of various schemes of biosensors to sense and help control the respective function. The needs of patients for sensors with minimal discomfort, longer life and better performance have necessitated the development towards smaller and more efficient sensors. In addition, the need for higher functionality from smaller sensors has led to the development of sensors with multiple electrodes, each electrode capable of sensing a different body function. Such multi-electrode sensors need to be fabricated using micro-fabrication processes in order to achieve precise control over the size, shape and placement of the electrodes. Multielectrode sensors fabricated using silicon and polymers have been demonstrated. One physiological function that attracts widespread interest is continuous glucose monitoring in our blood, since Diabetes affects millions of people all over the world. Significant deviations of blood glucose levels from the normal levels of 4-8 mM can cause fainting, coma and damage to the eyes, kidneys, nerves and blood vessels. For chronic patients, continuous monitoring of glucose levels is essential for accurate and timely treatment. A few continuous monitoring sensors are available in the market, but they have problems and cannot replace the strip type one-time glucose monitoring systems as yet. To address this need, large scale research efforts have been targeted towards continuous monitoring. The demand for higher accuracy and sensitivity has motivated researchers to evaluate the use of nanostructures in sensing. The large surface area-to-volume ratio of such structures could enable further miniaturization and push the detection limits, potentially enabling even single molecule detection. This research involved the development of a biocompatible titanium needle probe sensor for glucose monitoring. The working electrode of the sensor comprised of vertically aligned, free standing Au nanowires to utilize the advantages of nanostructures. The sensor was fabricated on biocompatible titanium substrate using Micro/Nano fabrication processes such as Plasma Enhanced Chemical Vapor Deposition (PECVD), Electron Beam Evaporation, Lithography, aligned nanowire growth and wet and plasma etching. Arrays of free-standing nanowires were grown at room temperature and pressure using a novel template based growth process. After fabrication of the sensor, immobilization of an enzyme was carried out on the sensing electrode to ensure selectivity of the sensor to glucose. This was achieved by using self-assembled thiol monolayers and entrapment in a conducting polymer matrix. Glucose oxidase was used for this purpose, which catalyzed the conversion of glucose to gluconic acid, producing hydrogen peroxide in the process. Amperometry was used for glucose detection, in which a constant voltage was applied to the sensor. This potential oxidized the hydrogen peroxide and produced changes in the current which were correlated to the glucose concentration. This dissertation will address the importance of continuous glucose monitoring, current technology and problems faced, the design and fabrication of the sensor and electrochemical sensing to detect glucose levels in solution. Finally, the problems encountered during the process will be discussed and the future work will be detailed.

Theory of relativistic Brownian motion in the presence of electromagnetic field in (1+1) dimension

NASA Astrophysics Data System (ADS)

Mukhopadhyay, Annesh; Bandyopadhyay, M.; Bhamidipati, C.

2018-04-01

In this work, we consider the relativistic generalization of the theory of Brownian motion for the (1+1) dimensional case, which is again consistent with Einstein's special theory of relativity and reduces to standard Brownian motion in the Newtonian limit. All the generalizations are made considering Special theory of relativity into account. The particle under consideration has a velocity close to the speed of light and is a free Brownian particle suspended in a heat bath. With this generalization the velocity probability density functions are also obtained using Ito, Stratonovich and Hanggi-Klimontovich approach of pre-point, mid-point and post-point discretization rule. Subsequently, in our work, we have obtained the relativistic Langevin equations in the presence of an electromagnetic field. Finally, taking a special case of a constant vector potential and a constant electric field into account the Langevin equations are solved for the momentum and subsequently the velocity of the particle. Using a similar approach to the Fokker-planck equations of motion, the velocity distributions are also obtained in the presence of a constant vector potential and are plotted, which shows essential deviations from the one obtained without a potential. Our constant potential model can be realized in an optical potential.

Microclimate, Water Potential, Transpiration, and Bole Dielectric Constant of Coniferous and Deciduous Tree Species in the Continental Boreal Ecotone of Central Alaska

NASA Technical Reports Server (NTRS)

Zimmermann, R.; McDonald, K.; Way, J.; Oren, R.

1994-01-01

Tree canopy microclimate, xylem water flux and xylem dielectric constant have been monitored in situ since June 1993 in two adjacent natural forest stands in central Alaska. The deciduous stand represents a mature balsam poplar site on the Tanana River floodplain, while the coniferous stand consists of mature white spruce with some black spruce mixed in. During solstice in June and later in summer, diurnal changes of xylem water potential were measured to investigate the occurrence and magnitude of tree transpiration and dielectric constant changes in stems.

A constant current charge technique for low Earth orbit life testing

NASA Technical Reports Server (NTRS)

Glueck, Peter

1991-01-01

A constant current charge technique for low earth orbit testing of nickel cadmium cells is presented. The method mimics the familiar taper charge of the constant potential technique while maintaining cell independence for statistical analysis. A detailed example application is provided and the advantages and disadvantages of this technique are discussed.

Classical calculation of the equilibrium constants for true bound dimers using complete potential energy surface.

PubMed

Buryak, Ilya; Vigasin, Andrey A

2015-12-21

The present paper aims at deriving classical expressions which permit calculation of the equilibrium constant for weakly interacting molecular pairs using a complete multidimensional potential energy surface. The latter is often available nowadays as a result of the more and more sophisticated and accurate ab initio calculations. The water dimer formation is considered as an example. It is shown that even in case of a rather strongly bound dimer the suggested expression permits obtaining quite reliable estimate for the equilibrium constant. The reliability of our obtained water dimer equilibrium constant is briefly discussed by comparison with the available data based on experimental observations, quantum calculations, and the use of RRHO approximation, provided the latter is restricted to formation of true bound states only.

Classical calculation of the equilibrium constants for true bound dimers using complete potential energy surface

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

Buryak, Ilya; Vigasin, Andrey A., E-mail: vigasin@ifaran.ru

The present paper aims at deriving classical expressions which permit calculation of the equilibrium constant for weakly interacting molecular pairs using a complete multidimensional potential energy surface. The latter is often available nowadays as a result of the more and more sophisticated and accurate ab initio calculations. The water dimer formation is considered as an example. It is shown that even in case of a rather strongly bound dimer the suggested expression permits obtaining quite reliable estimate for the equilibrium constant. The reliability of our obtained water dimer equilibrium constant is briefly discussed by comparison with the available data basedmore » on experimental observations, quantum calculations, and the use of RRHO approximation, provided the latter is restricted to formation of true bound states only.« less

Dielectric studies on PEG-LTMS based polymer composites

NASA Astrophysics Data System (ADS)

Patil, Ravikumar V.; Praveen, D.; Damle, R.

2018-02-01

PEG LTMS based polymer composites were prepared and studied for dielectric constant variation with frequency and temperature as a potential candidate with better dielectric properties. Solution cast technique is used for the preparation of polymer composite with five different compositions. Samples show variation in dielectric constant with frequency and temperature. Dielectric constant is large at low frequencies and higher temperatures. Samples with larger space charges have shown larger dielectric constant. The highest dielectric constant observed was about 29244 for PEG25LTMS sample at 100Hz and 312 K.

Internal Forced Convection to Low Prandtl Number Gas Mixtures.

DTIC Science & Technology

1984-07-15

heating; v iV 0" ..- . --- NCX~ENCLATURE (continued) Greek Symbols -/K Force constant in Lennard - Jones potential ; y Ratio of specific heats, c p/cV...Absolute viscosity; V Kinematic viscosity; P Density; C Force constant in Lennard - Jones potential ; Nondimensional Parameters 2 f Friction factor, g P DAp...Reynolds and Perkins, 1968] id= c = (T - Tref)and (9) C VyRT= v(5/3)RT The Lennard - Jones (6-12) potential can be employed in the Chapman- Enskog kinetic

Brane-world black hole solutions via a confining potential

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

Heydari-Fard, M.; Sepangi, H. R.; Razmi, H.

2007-09-15

Using a confining potential, we consider spherically symmetric vacuum (static black hole) solutions in a brane-world scenario. Working with a constant curvature bulk, two interesting cases/solutions are studied. A Schwarzschild-de Sitter black hole solution similar to the standard solution in the presence of a cosmological constant is obtained which confirms the idea that an extra term in the field equations on the brane can play the role of a positive cosmological constant and may be used to account for the accelerated expansion of the universe. The other solution is one in which we can have a proper potential to explainmore » the galaxy rotation curves without assuming the existence of dark matter and without working with new modified theories (modified Newtonian dynamics)« less

Nonlocal conservation laws of the constant astigmatism equation

NASA Astrophysics Data System (ADS)

Hlaváč, Adam; Marvan, Michal

2017-03-01

For the constant astigmatism equation, we construct a system of nonlocal conservation laws (an abelian covering) closed under the reciprocal transformations. The corresponding potentials are functionally independent modulo a Wronskian type relation.

Constant-roll (quasi-)linear inflation

NASA Astrophysics Data System (ADS)

Karam, A.; Marzola, L.; Pappas, T.; Racioppi, A.; Tamvakis, K.

2018-05-01

In constant-roll inflation, the scalar field that drives the accelerated expansion of the Universe is rolling down its potential at a constant rate. Within this framework, we highlight the relations between the Hubble slow-roll parameters and the potential ones, studying in detail the case of a single-field Coleman-Weinberg model characterised by a non-minimal coupling of the inflaton to gravity. With respect to the exact constant-roll predictions, we find that assuming an approximate slow-roll behaviour yields a difference of Δ r = 0.001 in the tensor-to-scalar ratio prediction. Such a discrepancy is in principle testable by future satellite missions. As for the scalar spectral index ns, we find that the existing 2-σ bound constrains the value of the non-minimal coupling to ξphi ~ 0.29–0.31 in the model under consideration.

The observational constraint on constant-roll inflation

NASA Astrophysics Data System (ADS)

Gao, Qing

2018-07-01

We discuss the constant-roll inflation with constant ɛ2 and constant \\bar η . By using the method of Bessel function approximation, the analytical expressions for the scalar and tensor power spectra, the scalar and tensor spectral tilts, and the tensor to scalar ratio are derived up to the first order of ɛ1. The model with constant ɛ2 is ruled out by the observations at the 3σ confidence level, and the model with constant \\bar η is consistent with the observations at the 1σ confidence level. The potential for the model with constant \\bar η is also obtained from the Hamilton-Jacobi equation. Although the observations constrain the constant-roll inflation to be the slow-roll inflation, the n s- r results from the constant-roll inflation are not the same as those from the slow-roll inflation even when \\bar η 0.01.

Adsorption of surfactant ions and binding of their counterions at an air/water interface.

PubMed

Tagashira, Hiroaki; Takata, Youichi; Hyono, Atsushi; Ohshima, Hiroyuki

2009-01-01

An expression for the surface tension of an aqueous mixed solution of surfactants and electrolyte ions in the presence of the common ions was derived from the Helmholtz free energy of an air/water surface. By applying the equation to experimental data for the surface tension, the adsorption constant of surfactant ions onto the air/water interface, the binding constant of counterions on the surfactants, and the surface potential and surface charge density of the interface were estimated. The adsorption constant and binding constant were dependent on the species of surfactant ion and counterion, respectively. Taking account of the dependence of surface potential and surface charge density on the concentration of electrolyte, it was suggested that the addition of electrolyte to the aqueous surfactant solution brings about the decrease in the surface potential, the increase in the surface density of surfactant ions, and consequently, the decrease in the surface tension. Furthermore, it was found that the configurational entropy plays a predominant role for the surface tension, compared to the electrical work.

Estimated Viscosities and Thermal Conductivities of Gases at High Temperatures

NASA Technical Reports Server (NTRS)

Svehla, Roger A.

1962-01-01

Viscosities and thermal conductivities, suitable for heat-transfer calculations, were estimated for about 200 gases in the ground state from 100 to 5000 K and 1-atmosphere pressure. Free radicals were included, but excited states and ions were not. Calculations for the transport coefficients were based upon the Lennard-Jones (12-6) potential for all gases. This potential was selected because: (1) It is one of the most realistic models available and (2) intermolecular force constants can be estimated from physical properties or by other techniques when experimental data are not available; such methods for estimating force constants are not as readily available for other potentials. When experimental viscosity data were available, they were used to obtain the force constants; otherwise the constants were estimated. These constants were then used to calculate both the viscosities and thermal conductivities tabulated in this report. For thermal conductivities of polyatomic gases an Eucken-type correction was made to correct for exchange between internal and translational energies. Though this correction may be rather poor at low temperatures, it becomes more satisfactory with increasing temperature. It was not possible to obtain force constants from experimental thermal conductivity data except for the inert atoms, because most conductivity data are available at low temperatures only (200 to 400 K), the temperature range where the Eucken correction is probably most in error. However, if the same set of force constants is used for both viscosity and thermal conductivity, there is a large degree of cancellation of error when these properties are used in heat-transfer equations such as the Dittus-Boelter equation. It is therefore concluded that the properties tabulated in this report are suitable for heat-transfer calculations of gaseous systems.

Strongly nonlinear composite dielectrics: A perturbation method for finding the potential field and bulk effective properties

NASA Astrophysics Data System (ADS)

Blumenfeld, Raphael; Bergman, David J.

1991-10-01

A class of strongly nonlinear composite dielectrics is studied. We develop a general method to reduce the scalar-potential-field problem to the solution of a set of linear Poisson-type equations in rescaled coordinates. The method is applicable for a large variety of nonlinear materials. For a power-law relation between the displacement and the electric fields, it is used to solve explicitly for the value of the bulk effective dielectric constant ɛe to second order in the fluctuations of its local value. A simlar procedure for the vector potential, whose curl is the displacement field, yields a quantity analogous to the inverse dielectric constant in linear dielectrics. The bulk effective dielectric constant is given by a set of linear integral expressions in the rescaled coordinates and exact bounds for it are derived.

Numerical calculation of the decay widths, the decay constants, and the decay energy spectra of the resonances of the delta-shell potential

NASA Astrophysics Data System (ADS)

de la Madrid, Rafael

2017-06-01

We express the resonant energies of the delta-shell potential in terms of the Lambert W function, and we calculate their decay widths and decay constants. The ensuing numerical results strengthen the interpretation of such decay widths and constants as a way to quantify the coupling between a resonance and the continuum. We calculate explicitly the decay energy spectrum of the resonances of the delta-shell potential, and we show numerically that the lineshape of such spectrum is not the same as, and can be very different from, the Breit-Wigner (Lorentzian) distribution. We argue that the standard Golden Rule cannot describe the interference of two resonances, and we show how to describe such interference by way of the decay energy spectrum of two resonant states.

USSR Report, Physics and Mathematics

DTIC Science & Technology

1985-08-20

TEKHNICHESKIY FIZIKI, No 6(148), Nov-Dec 84) 80 Thermodynamic Potential of Quark -Antiquark Plasma in Constant Chromomagnetic Field CSh. S. Agayev... QUARK -ANTIQUARK PLASMA IN CONSTANT CHROMOMAGNETIC FIELD Tomsk IZVESTIYA VYSSHIKH UCHEBNYKH ZAVEDENIY: FIZIKA in Russian Vol 28, No 1, Jan 85...Automation Institute; Moscow State University imeni M. V. Lomonosov [Abstract] Light-neutral quark -antiquark plasma in a constant optical magnetic

Carter constant and angular momentum

NASA Astrophysics Data System (ADS)

Mukherjee, Sajal; Nayak, K. Rajesh

We investigate the Carter-like constant in the case of a particle moving in a nonrelativistic dipolar potential. This special case is a missing link between the Carter constant in stationary and axially symmetric spacetimes (SASS) such as Kerr solution and its possible Newtonian counterpart. We use this system to carry over the definition of angular momentum from the Newtonian mechanics to the relativistic SASS.

Interatomic potential at small internuclear distances. A simple formula for the screening constant

NASA Astrophysics Data System (ADS)

Zinoviev, A. N.

2017-09-01

A simple formula for estimating the screening constant has been proposed. This formula fits well experimental data on the interaction potentials. Quantitative description of the experiment for the effect of electronic screening on the nuclear synthesis reaction cross-section for the D+-D system has been obtained. A conclusion has been made that the differences between the measured cross-sections and their theoretically predicted values, which take place in more complicated cases nuclear synthesis reactions, are not caused by uncertainties in the knowledge of potentials.

Loop corrections in double field theory: non-trivial dilaton potentials

NASA Astrophysics Data System (ADS)

Lv, Songlin; Wu, Houwen; Yang, Haitang

2014-10-01

It is believed that the invariance of the generalised diffeomorphisms prevents any non-trivial dilaton potential from double field theory. It is therefore difficult to include loop corrections in the formalism. We show that by redefining a non-local dilaton field, under strong constraint which is necessary to preserve the gauge invariance of double field theory, the theory does permit non-constant dilaton potentials and loop corrections. If the fields have dependence on only one single coordinate, the non-local dilaton is identical to the ordinary one with an additive constant.

Stresses and elastic constants of crystalline sodium, from molecular dynamics

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

Schiferl, S.K.

1985-02-01

The stresses and the elastic constants of bcc sodium are calculated by molecular dynamics (MD) for temperatures to T = 340K. The total adiabatic potential of a system of sodium atoms is represented by pseudopotential model. The resulting expression has two terms: a large, strictly volume-dependent potential, plus a sum over ion pairs of a small, volume-dependent two-body potential. The stresses and the elastic constants are given as strain derivatives of the Helmholtz free energy. The resulting expressions involve canonical ensemble averages (and fluctuation averages) of the position and volume derivatives of the potential. An ensemble correction relates the resultsmore » to MD equilibrium averages. Evaluation of the potential and its derivatives requires the calculation of integrals with infinite upper limits of integration, and integrand singularities. Methods for calculating these integrals and estimating the effects of integration errors are developed. A method is given for choosing initial conditions that relax quickly to a desired equilibrium state. Statistical methods developed earlier for MD data are extended to evaluate uncertainties in fluctuation averages, and to test for symmetry. 45 refs., 10 figs., 4 tabs.« less

Direct growth of metal-organic frameworks thin film arrays on glassy carbon electrode based on rapid conversion step mediated by copper clusters and hydroxide nanotubes for fabrication of a high performance non-enzymatic glucose sensing platform.

PubMed

Shahrokhian, Saeed; Khaki Sanati, Elnaz; Hosseini, Hadi

2018-07-30

The direct growth of self-supported metal-organic frameworks (MOFs) thin film can be considered as an effective strategy for fabrication of the advanced modified electrodes in sensors and biosensor applications. However, most of the fabricated MOFs-based sensors suffer from some drawbacks such as time consuming for synthesis of MOF and electrode making, need of a binder or an additive layer, need of expensive equipment and use of hazardous solvents. Here, a novel free-standing MOFs-based modified electrode was fabricated by the rapid direct growth of MOFs on the surface of the glassy carbon electrode (GCE). In this method, direct growth of MOFs was occurred by the formation of vertically aligned arrays of Cu clusters and Cu(OH) 2 nanotubes, which can act as both mediator and positioning fixing factor for the rapid formation of self-supported MOFs on GCE surface. The effect of both chemically and electrochemically formed Cu(OH) 2 nanotubes on the morphological and electrochemical performance of the prepared MOFs were investigated. Due to the unique properties of the prepared MOFs thin film electrode such as uniform and vertically aligned structure, excellent stability, high electroactive surface area, and good availability to analyte and electrolyte diffusion, it was directly used as the electrode material for non-enzymatic electrocatalytic oxidation of glucose. Moreover, the potential utility of this sensing platform for the analytical determination of glucose concentration was evaluated by the amperometry technique. The results proved that the self-supported MOFs thin film on GCE is a promising electrode material for fabricating and designing non-enzymatic glucose sensors. Copyright © 2018 Elsevier B.V. All rights reserved.

Spontaneous Water Oxidation at Hematite (α-Fe2O3) Crystal Faces

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

Chatman, Shawn ME; Zarzycki, Piotr P.; Rosso, Kevin M.

2015-01-28

Hematite (α-Fe2O3) persists as a promising candidate for photoelectrochemical water splitting but a slow oxygen evolution reaction (OER) at its surfaces remains a limitation. Here we extend a series of studies that examine pH-dependent surface potentials and electron transfer properties of effectively perfect low-index crystal faces of hematite in contact with simple electrolyte. Zero resistance amperometry was performed in a two electrode configuration to quantify spontaneous dark current between hematite crystal face pairs (001)/(012), (001)/(113), and (012)/(113) at pH 3. Exponentially decaying currents initially of up to 200 nA were reported between faces over four minute experiments. Fourth order ZRAmore » kinetics indicated rate limitation by the OER for current that flows between (001)/(012) and (001)/(113) face pairs, with the (012) and (113) faces serving as the anodes when paired with (001). The cathodic partner reaction is reductive dissolution of the (001) face, converting surface Fe3+ to solubilized aqueous Fe2+, at a rate maintained by the OER at the anode. In contrast, OER rate limitation does not manifest for the (012)/(113) pair. The uniqueness of the (001) face is established in terms of a faster intrinsic ability to accept the protons required for the reductive dissolution reaction. OER rate limitation inversely may thus arise from sluggish kinetics of hematite surfaces to dispense with the protons that accompany the four-electron OER. The results are explained in terms of semi-quantitative energy band diagrams. The finding may be useful as a consideration for tailoring the design of polycrystalline hematite photoanodes that present multiple terminations to the interface with electrolyte.« less

Reorganization of circuits underlying cerebellar modulation of prefrontal cortical dopamine in mouse models of autism spectrum disorder

PubMed Central

Rogers, Tiffany D.; Dickson, Price E.; McKimm, Eric; Heck, Detlef H.; Goldowitz, Dan; Blaha, Charles D.; Mittleman, Guy

2013-01-01

Imaging, clinical and pre-clinical studies have provided ample evidence for a cerebellar involvement in cognitive brain function including cognitive brain disorders, such as autism and schizophrenia. We previously reported that cerebellar activity modulates dopamine release in the mouse medial prefrontal cortex (mPFC) via two distinct pathways: (1) cerebellum to mPFC via dopaminergic projections from the ventral tegmental area [VTA] and (2) cerebellum to mPFC via glutamatergic projections from the mediodorsal and ventrolateral thalamus (ThN md and vl). The present study compared functional adaptations of cerebello-cortical circuitry following developmental cerebellar pathology in a mouse model of developmental loss of Purkinje cells (Lurcher) and a mouse model of fragile X syndrome (Fmr1 KO mice). Fixed potential amperometry was used to measure mPFC dopamine release in response to cerebellar electrical stimulation. Mutant mice of both strains showed an attenuation in cerebellar-evoked mPFC dopamine release compared to respective wildtype mice. This was accompanied by a functional reorganization of the VTA and thalamic pathways mediating cerebellar modulation of mPFC dopamine release. Inactivation of the VTA pathway by intra-VTA lidocaine or kynurenate infusions decreased dopamine release by 50% in wildtype and 20-30% in mutant mice of both strains. Intra-ThN vl infusions of either drug decreased dopamine release by 15% in wildtype and 40% in mutant mice of both strains, while dopamine release remained relatively unchanged following intra-ThN md drug infusions. These results indicate a shift in strength towards the thalamic vl projection, away from the VTA. Thus, cerebellar neuropathologies associated with autism spectrum disorders may cause a reduction in cerebellar modulation of mPFC dopamine release that is related to a reorganization of the mediating neuronal pathways. PMID:23436049

Reorganization of circuits underlying cerebellar modulation of prefrontal cortical dopamine in mouse models of autism spectrum disorder.

PubMed

Rogers, Tiffany D; Dickson, Price E; McKimm, Eric; Heck, Detlef H; Goldowitz, Dan; Blaha, Charles D; Mittleman, Guy

2013-08-01

Imaging, clinical, and pre-clinical studies have provided ample evidence for a cerebellar involvement in cognitive brain function including cognitive brain disorders, such as autism and schizophrenia. We previously reported that cerebellar activity modulates dopamine release in the mouse medial prefrontal cortex (mPFC) via two distinct pathways: (1) cerebellum to mPFC via dopaminergic projections from the ventral tegmental area (VTA) and (2) cerebellum to mPFC via glutamatergic projections from the mediodorsal and ventrolateral thalamus (ThN md and vl). The present study compared functional adaptations of cerebello-cortical circuitry following developmental cerebellar pathology in a mouse model of developmental loss of Purkinje cells (Lurcher) and a mouse model of fragile X syndrome (Fmr1 KO mice). Fixed potential amperometry was used to measure mPFC dopamine release in response to cerebellar electrical stimulation. Mutant mice of both strains showed an attenuation in cerebellar-evoked mPFC dopamine release compared to respective wildtype mice. This was accompanied by a functional reorganization of the VTA and thalamic pathways mediating cerebellar modulation of mPFC dopamine release. Inactivation of the VTA pathway by intra-VTA lidocaine or kynurenate infusions decreased dopamine release by 50 % in wildtype and 20-30 % in mutant mice of both strains. Intra-ThN vl infusions of either drug decreased dopamine release by 15 % in wildtype and 40 % in mutant mice of both strains, while dopamine release remained relatively unchanged following intra-ThN md drug infusions. These results indicate a shift in strength towards the thalamic vl projection, away from the VTA. Thus, cerebellar neuropathologies associated with autism spectrum disorders may cause a reduction in cerebellar modulation of mPFC dopamine release that is related to a reorganization of the mediating neuronal pathways.

Electrochemical estimation of the polyphenol index in wines using a laccase biosensor.

PubMed

Gamella, M; Campuzano, S; Reviejo, A J; Pingarrón, J M

2006-10-18

The use of a laccase biosensor, under both batch and flow injection (FI) conditions, for a rapid and reliable amperometric estimation of the total content of polyphenolic compounds in wines is reported. The enzyme was immobilized by cross-linking with glutaraldehyde onto a glassy carbon electrode. Caffeic acid and gallic acid were selected as standard compounds to carry out such estimation. Experimental variables such as the enzyme loading, the applied potential, and the pH value were optimized, and different aspects regarding the operational stability of the laccase biosensor were evaluated. Using batch amperometry at -200 mV, the detection limits obtained were 2.6 x 10(-3) and 7.2 x 10(-4) mg L(-1) gallic acid and caffeic acid, respectively, which compares advantageously with previous biosensor designs. An extremely simple sample treatment consisting only of an appropriate dilution of wine sample with the supporting electrolyte solution (0.1 mol L(-1) citrate buffer of pH 5.0) was needed for the amperometric analysis of red, rosé, and white wines. Good correlations were found when the polyphenol indices obtained with the biosensor (in both the batch and FI modes) for different wine samples were plotted versus the results achieved with the classic Folin-Ciocalteu method. Application of the calibration transfer chemometric model (multiplicative fitting) allowed that the confidence intervals (for a significance level of 0.05) for the slope and intercept values of the amperometric index versus Folin-Ciocalteu index plots (r = 0.997) included the unit and zero values, respectively. This indicates that the laccase biosensor can be successfully used for the estimation of the polyphenol index in wines when compared with the Folin-Ciocalteu reference method.

Nonenzymatic electrochemical detection of glucose using well-distributed nickel nanoparticles on straight multi-walled carbon nanotubes.

PubMed

Nie, Huagui; Yao, Zhen; Zhou, Xuemei; Yang, Zhi; Huang, Shaoming

2011-12-15

A nonenzymatic electrochemical sensor device was fabricated for glucose detection based on nickel nanoparticles (NiNPs)/straight multi-walled carbon nanotubes (SMWNTs) nanohybrids, which were synthesized through in situ precipitation procedure. SMWNTs can be easily dispersed in solution after mild sonication pretreatment, which facilitates the precursor of NiNPs binding to their surface and results in the homogeneous distribution of NiNPs on the surface of SMWNTs. The morphology and component of the nanohybrids were characterized by scanning electron microscopy (SEM) and X-ray powder diffraction (XRD), respectively. Cyclic voltammetry (CV) and amperometry were used to evaluate the catalytic activity of the NiNPs/SMWNTs nanohybrids modified electrode towards glucose. It was found that the nanohybrids modified electrode showed remarkably enhanced electrocatalytic activity towards the oxidation of glucose in alkaline solution compared to that of the bare glass carbon electrode (GCE), the NiNPs and the SMWNTs modified electrode, attributing to the synergistic effect of SMWNTs and Ni(2+)/Ni(3+) redox couple. Under the optimal detection conditions, the as-prepared sensors exhibited linear behavior in the concentration range from 1 μM to 1 mM for the quantification of glucose with a limit of detection of 500 nM (3σ). Moreover, the NiNPs/SMWNTs modified electrode was also relatively insensitive to commonly interfering species such as ascorbic acid (AA), uric acid (UA), dopamine (DA), galactose (GA), and xylose (XY). The robust selectivities, sensitivities, and stabilities determined experimentally indicated the great potential of NiNPs/SMWNTs nanohybrids for construction of a variety of electrochemical sensors. Copyright © 2011 Elsevier B.V. All rights reserved.

Impedance biosensor for the rapid detection of Listeria spp. based on aptamer functionalized Pt-interdigitated microelectrodes array

NASA Astrophysics Data System (ADS)

Sidhu, R.; Rong, Y.; Vanegas, D. C.; Claussen, J.; McLamore, E. S.; Gomes, C.

2016-05-01

Listeria monocytogenes is one of the most common causes of food illness deaths worldwide, with multiple outbreaks in the United States alone. Current methods to detect foodborne pathogens are laborious and can take several hours to days to produce results. Thus, faster techniques are needed to detect bacteria within the same reliability level as traditional techniques. This study reports on a rapid, accurate, and sensitive aptamer biosensor device for Listeria spp. detection based on platinum interdigitated array microelectrodes (Pt-IDEs). Pt-IDEs with different geometric electrode gaps were fabricated by lithographic techniques and characterized by cyclic voltammetric (CV), electrochemical impedance spectroscopy (EIS), and potential amperometry (DCPA) measurements of reversible redox species. Based on these results, 50 μm Pt-IDE was chosen to further functionalize with a Listeria monocytogenes DNA aptamer selective to the cell surface protein internalin A, via metal-thiol self-assembly at the 5' end of the 47-mer's. EIS analysis was used to detect Listeria spp. without the need for label amplification and pre-concentration steps. The optimized aptamer concentration of 800 nM was selected to capture the bacteria through internalin A binding and the aptamer hairpin structure near the 3' end. The aptasensor was capable of detecting a wide range of bacteria concentration from 10 to 106 CFU/mL at lower detection limit of 5.39 +/- 0.21 CFU/mL with sensitivity of 268.1 +/- 25.40 (Ohms/log [CFU/mL]) in 17 min. The aptamer based biosensor offers a portable, rapid and sensitive alternative for food safety applications with one of the lowest detection limits reported to date.

Amperometric immunoassay for the obesity biomarker amylin using a screen printed carbon electrode functionalized with an electropolymerized carboxylated polypyrrole.

PubMed

Martínez-García, Gonzalo; Sánchez-Tirado, Esther; González-Cortés, Araceli; Yáñez-Sedeño, Paloma; Pingarrón, José M

2018-06-09

Amylin (the islet amyloid polypeptide) is a hormone related to adiposity, hunger and satiety. It is co-secreted with insulin from pancreatic B-cells. An amperometric immunosensor is presented here for the determination of amylin. It is making use of a screen printed carbon electrode (SPCE) functionalized with electropolymerized poly(pyrrole propionic acid) (pPPA) with abundant carboxyl groups that facilitate covalent binding of antibody against amylin. A competitive immunoassay was implemented using biotinylated amylin and streptavidin labeled with horse radish peroxidase (HRP-Strept) as the enzymatic tracer. The amperometric detection of H 2 O 2 mediated by hydroquinone was employed as an electrochemical probe to monitor the affinity reaction. The variables involved in the preparation and function of the immunosensor were optimized and the electrodes were characterized by electrochemical impedance spectroscopy and cyclic voltammetry. The calibration graph for amylin, obtained by amperometry at -200 mV vs Ag pseudo-reference electrode, showed a range of linearity extending from 1.0 fg∙mL -1 to 50 pg∙mL -1 , with a detection limit of 0.92 fg∙mL -1 . This is approximately 7000 times lower than the minimum detectable concentration reported for the ELISA immunoassays available for amylin. The assay has excellent reproducibility and good selectivity over potential interferents. Graphical abstract Schematic of an amperometric competitive immunoassay for the obesity biomarker amylin using a poly(pyrrole propionic acid)-modified screen-printed electrode. The detection limit is 0.92 fg∙mL-1 amylin. The method provides excellent reproducibility for the measurements, good selectivity and successful applicability to human urine and serum samples.

Replica Exchange Gaussian Accelerated Molecular Dynamics: Improved Enhanced Sampling and Free Energy Calculation.

PubMed

Huang, Yu-Ming M; McCammon, J Andrew; Miao, Yinglong

2018-04-10

Through adding a harmonic boost potential to smooth the system potential energy surface, Gaussian accelerated molecular dynamics (GaMD) provides enhanced sampling and free energy calculation of biomolecules without the need of predefined reaction coordinates. This work continues to improve the acceleration power and energy reweighting of the GaMD by combining the GaMD with replica exchange algorithms. Two versions of replica exchange GaMD (rex-GaMD) are presented: force constant rex-GaMD and threshold energy rex-GaMD. During simulations of force constant rex-GaMD, the boost potential can be exchanged between replicas of different harmonic force constants with fixed threshold energy. However, the algorithm of threshold energy rex-GaMD tends to switch the threshold energy between lower and upper bounds for generating different levels of boost potential. Testing simulations on three model systems, including the alanine dipeptide, chignolin, and HIV protease, demonstrate that through continuous exchanges of the boost potential, the rex-GaMD simulations not only enhance the conformational transitions of the systems but also narrow down the distribution width of the applied boost potential for accurate energetic reweighting to recover biomolecular free energy profiles.

NVU dynamics. I. Geodesic motion on the constant-potential-energy hypersurface.

PubMed

Ingebrigtsen, Trond S; Toxvaerd, Søren; Heilmann, Ole J; Schrøder, Thomas B; Dyre, Jeppe C

2011-09-14

An algorithm is derived for computer simulation of geodesics on the constant-potential-energy hypersurface of a system of N classical particles. First, a basic time-reversible geodesic algorithm is derived by discretizing the geodesic stationarity condition and implementing the constant-potential-energy constraint via standard Lagrangian multipliers. The basic NVU algorithm is tested by single-precision computer simulations of the Lennard-Jones liquid. Excellent numerical stability is obtained if the force cutoff is smoothed and the two initial configurations have identical potential energy within machine precision. Nevertheless, just as for NVE algorithms, stabilizers are needed for very long runs in order to compensate for the accumulation of numerical errors that eventually lead to "entropic drift" of the potential energy towards higher values. A modification of the basic NVU algorithm is introduced that ensures potential-energy and step-length conservation; center-of-mass drift is also eliminated. Analytical arguments confirmed by simulations demonstrate that the modified NVU algorithm is absolutely stable. Finally, we present simulations showing that the NVU algorithm and the standard leap-frog NVE algorithm have identical radial distribution functions for the Lennard-Jones liquid. © 2011 American Institute of Physics

Lattice model calculation of elastic and thermodynamic properties at high pressure and temperature. [for alkali halides in NaCl lattice

NASA Technical Reports Server (NTRS)

Demarest, H. H., Jr.

1972-01-01

The elastic constants and the entire frequency spectrum were calculated up to high pressure for the alkali halides in the NaCl lattice, based on an assumed functional form of the inter-atomic potential. The quasiharmonic approximation is used to calculate the vibrational contribution to the pressure and the elastic constants at arbitrary temperature. By explicitly accounting for the effect of thermal and zero point motion, the adjustable parameters in the potential are determined to a high degree of accuracy from the elastic constants and their pressure derivatives measured at zero pressure. The calculated Gruneisen parameter, the elastic constants and their pressure derivatives are in good agreement with experimental results up to about 600 K. The model predicts that for some alkali halides the Grunesen parameter may decrease monotonically with pressure, while for others it may increase with pressure, after an initial decrease.

On Thermodiffusion and Gauge Transformations for Thermodynamic Fluxes and Driving Forces

NASA Astrophysics Data System (ADS)

Goldobin, D. S.

2017-12-01

We discuss the molecular diffusion transport in infinitely dilute liquid solutions under nonisothermal conditions. This discussion is motivated by an occurring misinterpretation of thermodynamic transport equations written in terms of chemical potential in the presence of temperature gradient. The transport equations contain the contributions owned by a gauge transformation related to the fact that chemical potential is determined up to the summand of form ( AT + B) with arbitrary constants A and B, where constant A is owned by the entropy invariance with respect to shifts by a constant value and B is owned by the potential energy invariance with respect to shifts by a constant value. The coefficients of the cross-effect terms in thermodynamic fluxes are contributed by this gauge transformation and, generally, are not the actual cross-effect physical transport coefficients. Our treatment is based on consideration of the entropy balance and suggests a promising hint for attempts of evaluation of the thermal diffusion constant from the first principles. We also discuss the impossibility of the "barodiffusion" for dilute solutions, understood in a sense of diffusion flux driven by the pressure gradient itself. When one speaks of "barodiffusion" terms in literature, these terms typically represent the drift in external potential force field (e.g., electric or gravitational fields), where in the final equations the specific force on molecules is substituted with an expression with the hydrostatic pressure gradient this external force field produces. Obviously, the interpretation of the latter as barodiffusion is fragile and may hinder the accounting for the diffusion fluxes produced by the pressure gradient itself.

Cosmological perturbations of axion with a dynamical decay constant

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

Kobayashi, Takeshi; INFN, Sezione di Trieste,Via Bonomea 265, 34136 Trieste; Takahashi, Fuminobu

2016-08-25

A QCD axion with a time-dependent decay constant has been known to be able to accommodate high-scale inflation without producing topological defects or too large isocurvature perturbations on CMB scales. We point out that a dynamical decay constant also has the effect of enhancing the small-scale axion isocurvature perturbations. The enhanced axion perturbations can even exceed the periodicity of the axion potential, and thus lead to the formation of axionic domain walls. Unlike the well-studied axionic walls, the walls produced from the enhanced perturbations are not bounded by cosmic strings, and thus would overclose the universe independently of the numbermore » of degenerate vacua along the axion potential.« less

Self-diffusion in a system of interacting Langevin particles

NASA Astrophysics Data System (ADS)

Dean, D. S.; Lefèvre, A.

2004-06-01

The behavior of the self-diffusion constant of Langevin particles interacting via a pairwise interaction is considered. The diffusion constant is calculated approximately within a perturbation theory in the potential strength about the bare diffusion constant. It is shown how this expansion leads to a systematic double expansion in the inverse temperature β and the particle density ρ . The one-loop diagrams in this expansion can be summed exactly and we show that this result is exact in the limit of small β and ρβ constants. The one-loop result can also be resummed using a semiphenomenological renormalization group method which has proved useful in the study of diffusion in random media. In certain cases the renormalization group calculation predicts the existence of a diverging relaxation time signaled by the vanishing of the diffusion constant, possible forms of divergence coming from this approximation are discussed. Finally, at a more quantitative level, the results are compared with numerical simulations, in two dimensions, of particles interacting via a soft potential recently used to model the interaction between coiled polymers.

Assessing the performance of the Tran-Blaha modified Becke-Johnson exchange potential for optical constants of semiconductors in the ultraviolet-visible light region

NASA Astrophysics Data System (ADS)

Nakano, Kousuke; Sakai, Tomohiro

2018-01-01

We report on the performance of density functional theory (DFT) with the Tran-Blaha modified Becke-Johnson exchange potential and the random phase approximation dielectric function for optical constants of semiconductors in the ultraviolet-visible (UV-Vis) light region. We calculate optical bandgaps Eg, refractive indices n, and extinction coefficients k of 70 semiconductors listed in the Handbook of Optical Constants of Solids [(Academic Press, 1985), Vol. 1; (Academic Press, 1991), Vol. 2; and (Academic Press, 1998), Vol. 3] and compare the results with experimental values. The results show that the calculated bandgaps and optical constants agree well with the experimental values to within 0.440 eV for Eg, 0.246-0.299 for n, and 0.207-0.598 for k in root mean squared error (RMSE). The small values of the RMSEs indicate that the optical constants of semiconductors in the UV-Vis region can be quantitatively predicted even by a low-cost DFT calculation of this type.

Constraining possible variations of the fine structure constant in strong gravitational fields with the Kα iron line

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

Bambi, Cosimo, E-mail: bambi@fudan.edu.cn

2014-03-01

In extensions of general relativity and in theories aiming at unifying gravity with the forces of the Standard Model, the value of the ''fundamental constants'' is often determined by the vacuum expectation value of new fields, which may thus change in different backgrounds. Variations of fundamental constants with respect to the values measured today in laboratories on Earth are expected to be more evident on cosmological timescales and/or in strong gravitational fields. In this paper, I show that the analysis of the Kα iron line observed in the X-ray spectrum of black holes can potentially be used to probe themore » fine structure constant α in gravitational potentials relative to Earth of Δφ ≈ 0.1. At present, systematic effects not fully under control prevent to get robust and stringent bounds on possible variations of the value of α with this technique, but the fact that current data can be fitted with models based on standard physics already rules out variations of the fine structure constant larger than some percent.« less

Relativistic problems on astronomical constants.

NASA Astrophysics Data System (ADS)

Tao, Jinhe; Huang, Tianyi

1999-06-01

The fact that modern astronomical observational technique has made rapid progress and the 1PN approximation of general relativity has been extensively applied in celestial mechanics and astrometry, makes it is necessary to investigate and examine the system of astronomical constants carefully and rigorously in the relativistic framework. The mass of a celestial body in the solar system should be defined as its BD mass that changes relatively in an amount less than 10-19 and could be considered as a constant. The equations satisfied by the gravitational potentials are not Poisson equations anymore but depend on the choice of the coordinate gauge. Therefore the gravitational potentials cannot be expanded in the traditional harmonics. It is neccessary to choose the coordinate gauge and take BD multipole moments as astronomical constants. The obliquity of the ecliptic has been determined in high precision and it would be neccessary to give a conventional definition of the 1PN ecliptic. A relativistic definition of the geoid is important and left to be discussed. The astronomical constants that relate the units of time and length have been clearly defined but need to be clarified to avoid their misuse.

Estimation of the zeta potential and the dielectric constant using velocity measurements in the electroosmotic flows.

PubMed

Park, H M; Hong, S M

2006-12-15

In this paper we develop a method for the determination of the zeta potential zeta and the dielectric constant epsilon by exploiting velocity measurements of the electroosmotic flow in microchannels. The inverse problem is solved through the minimization of a performance function utilizing the conjugate gradient method. The present method is found to estimate zeta and epsilon with reasonable accuracy even with noisy velocity measurements.

Pion properties at finite isospin chemical potential with isospin symmetry breaking

NASA Astrophysics Data System (ADS)

Wu, Zuqing; Ping, Jialun; Zong, Hongshi

2017-12-01

Pion properties at finite temperature, finite isospin and baryon chemical potentials are investigated within the SU(2) NJL model. In the mean field approximation for quarks and random phase approximation fpr mesons, we calculate the pion mass, the decay constant and the phase diagram with different quark masses for the u quark and d quark, related to QCD corrections, for the first time. Our results show an asymmetry between μI <0 and μI >0 in the phase diagram, and different values for the charged pion mass (or decay constant) and neutral pion mass (or decay constant) at finite temperature and finite isospin chemical potential. This is caused by the effect of isospin symmetry breaking, which is from different quark masses. Supported by National Natural Science Foundation of China (11175088, 11475085, 11535005, 11690030) and the Fundamental Research Funds for the Central Universities (020414380074)

Monte Carlo Study of Melting of a Model Bulk Ice.

NASA Astrophysics Data System (ADS)

Han, Kyu-Kwang

The methods of NVT (constant number, volume and temperature) and NPT (constant number, pressure and temperature) Monte Carlo computer simulations are used to examine the melting of a periodic hexagonal ice (ice Ih) sample with a unit cell of 192 (rigid) water molecules interacting via the revised central force potentials of Stillinger and Rahman (RSL2). In NVT Monte Carlo simulation of P-T plot for a constant density (0.904g/cm^3) is used to locate onset of the liquid-solid coexistence region (where the slope of the pressure changes sign) and estimate the (constant density) melting point. The slope reversal is a natural consequence of the constant density condition for substances which expand upon freezing and it is pointed out that this analysis is extremely useful for substances such as water. In this study, a sign reversal of the pressure slope is observed near 280 K, indicating that the RSL2 potentials reproduce the freezing expansion expected for water and support a bulk ice Ih system which melts <280 K. The internal energy, specific heat, and two dimensional structure factors for the constant density H_2O system are also examined at a range of temperatures between 100 and 370 K and support the P-T analysis for location of the melting point. This P-T analysis might likewise be useful for determining a (constant density) freezing point, or, with multiple simulations at appropriate densities, the triple point. For NPT Monte Carlo simulations preliminary results are presented. In this study the density, enthalpy, specific heat, and structure factor dependences on temperature are monitored during a sequential heating of the system from 100 to 370 K at a constant pressure (1 atm.). A jump in density upon melting is observed and indicates that the RSL2 potentials reproduce the melting contraction of ice. From the dependences of monitored physical properties on temperature an upper bound on the melting temperature is estimated. In this study we made the first analysis and calculation of the P-T curve for ice Ih melting at constant volume and the first NPT study of ice and of ice melting. In the NVT simulation we found for rho = 0.904g/cm^3 T_ {rm m} ~eq 280 K which is much closer to physical T_ {rm m} than any other published NVT simulation of ice. Finally it is shown that RSL2 potentials do a credible job of describing the thermodynamic properties of ice Ih near its melting point.

Interaction potential for indium phosphide: a molecular dynamics and first-principles study of the elastic constants, generalized stacking fault and surface energies.

PubMed

Branicio, Paulo Sergio; Rino, José Pedro; Gan, Chee Kwan; Tsuzuki, Hélio

2009-03-04

Indium phosphide is investigated using molecular dynamics (MD) simulations and density-functional theory calculations. MD simulations use a proposed effective interaction potential for InP fitted to a selected experimental dataset of properties. The potential consists of two- and three-body terms that represent atomic-size effects, charge-charge, charge-dipole and dipole-dipole interactions as well as covalent bond bending and stretching. Predictions are made for the elastic constants as a function of density and temperature, the generalized stacking fault energy and the low-index surface energies.

Phosphate determination in seawater: toward an autonomous electrochemical method.

PubMed

Jońca, Justyna; León Fernández, Violeta; Thouron, Danièle; Paulmier, Aurélien; Graco, Michelle; Garçon, Véronique

2011-12-15

Initial steps to create an autonomous in situ electrochemical sensor for orthophosphate determination in seawater are presented. First, the optimal conditions to form the molybdophosphate complex in artificial seawater medium were determined by addition of sulphuric acid and sodium molybdate to the solution containing orthophosphate. Secondly, the anodic oxidation of molybdenum to form molybdate ions and protons was used to create the molybdophosphate complex without addition of any liquid reagents. The molybdophosphate complex is detectable by amperometry with an average precision of 2.2% for the concentration range found in the open ocean and the detection limit is 0.12 μM. Three solutions are proposed to address the silicate interferences issue and one of these methods is used for the natural samples collected in the coastal waters offshore Peru during the Pelagico 1011-12-BIC OLAYA cruise in November-December 2010. Results showed a good precision with an average of 2.5% and a reasonable deviation of the amperometric analysis as compared with colorimetric measurements (4.9%). Copyright © 2011 Elsevier B.V. All rights reserved.

MWCNT-ruthenium oxide composite paste electrode as non-enzymatic glucose sensor.

PubMed

Tehrani, Ramin M A; Ab Ghani, Sulaiman

2012-01-01

A non-enzymatic glucose sensor of multi-walled carbon nanotube-ruthenium oxide/composite paste electrode (MWCNT-RuO(2)/CPE) was developed. The electrode was characterized by using XRD, SEM, TEM and EIS. Meanwhile, cyclic voltammetry and amperometry were used to check on the performances of the MWCNT-RuO(2)/CPE towards glucose. The proposed electrode has displayed a synergistic effect of RuO(2) and MWCNT on the electrocatalytic oxidation of glucose in 3M NaOH. This was possible via the formation of transitions of two redox pairs, viz. Ru(VI)/Ru(IV) and Ru(VII)/Ru(VI). A linear range of 0.5-50mM glucose and a limit of detection of 33 μM glucose (S/N=3) were observed. There was no significant interference observable from the traditional interferences, viz. ascorbic acid and uric acid. Indeed, results so obtained have indicated that the developed MWCNT-RuO(2)/CPE would pave the way for a better future to glucose sensor development as its fabrication was without the use of any enzyme. Copyright © 2012 Elsevier B.V. All rights reserved.

Simultaneous electrochemical determination of dopamine and paracetamol on multiwalled carbon nanotubes/graphene oxide nanocomposite-modified glassy carbon electrode.

PubMed

Cheemalapati, Srikanth; Palanisamy, Selvakumar; Mani, Veerappan; Chen, Shen-Ming

2013-12-15

In the present study, multiwalled carbon nanotubes (MWCNT)/graphene oxide (GO) nanocomposite was prepared by homogenous dispersion of MWCNT and GO and used for the simultaneous voltammetric determination of dopamine (DA) and paracetamol (PA). The TEM results confirmed that MWCNT walls were wrapped well with GO sheets. The MWCNT/GO nanocomposite showed superior electrocatalytic activity towards the oxidation of DA and PA, when compared with either pristine MWCNT or GO. The major reason for the efficient simultaneous detection of DA and PA at nanocomposite was the synergistic effect between MWCNT and GO. The electrochemical oxidation of DA and PA was investigated by cyclic voltammetry, differential pulse voltammetry and amperometry. The nanocomposite modified electrode showed electrocatalytic oxidation of DA and PA in the linear response range from 0.2 to 400 µmol L(-1) and 0.5 to 400 µmol L(-1) with the detection limit of 22 nmol L(-1) and 47 nmol L(-1) respectively. The proposed sensor displayed good selectivity, sensitivity, stability with appreciable consistency and precision. © 2013 Elsevier B.V. All rights reserved.

Electrochemical processing of lead-containing waste ballistics

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

Huber, C.O.; Olsen, G.P.

1995-12-31

Literature review indicates that propellant ingredients in NOSIH-AA2 have been investigated electrochemical separation. Papers on related electroanalytical chemistry offer help in indicating which electrolytic separation systems to investigate. These included copper and nickel electrodes in alkaline solution. Voltammetry studies in 0.1 M NaOH showed that lead metal can be readily collected at a copper cathode and that lead dioxide can be deposited at a nickel anode. Cathodic and anodic deposition reactions begin at less than minus or plus 0.5 V. resp. Other species present in the propellant are also reactive at the anode. Deposits with good mechanical properties resulted, evenmore » with 40 mA/cm{sup 2} current density. Lead concentrations in alkaline solutions can readily be monitored using anodic amperometry with the nickel electrode. Separations from actual propellant solutions in 3 M NaOH were demonstrated using nickel as anode and cathode. Gravimetric monitoring of both anode and cathode showed accumulations suggesting the exhaustive lead collection. Associated voltammetry data showed decreasing amounts of other electroactive species at the anode as well as lead.« less

Determination of monosaccharides and sugar alcohols in tissues from diabetic rats by high-performance liquid chromatography with pulsed amperometric detection.

PubMed

Tomiya, N; Suzuki, T; Awaya, J; Mizuno, K; Matsubara, A; Nakano, K; Kurono, M

1992-10-01

A sensitive and simple high-performance liquid chromatographic method has been developed to determine the concentration of monosaccharides and sugar alcohols in animal tissues. Five neutral monosaccharides (D-glucose, D-galactose, D-mannose, D-fructose, and D-ribose) and three neutral sugar alcohols (myo-inositol, glycerol, and D-sorbitol) predominate in the renal cortices and sciatic nerves of rats. These monosaccharides and sugar alcohols were extracted with distilled water, purified by deproteinization with ethanol, a Sep-Pak C18 cartridge, and columns of Dowex 50W-X8 and Amberlite CG-400, then separated on Ca2+ and Pb2+ cation-exchange columns, eluted with deionized distilled water at 80 degrees C, and detected using integrated pulsed amperometry. About 10 pmol of each sugar was detectable with a signal-to-noise ratio of 10:1. D-Glucose, D-fructose, D-sorbitol, and D-mannose were higher in both the renal and sciatic tissues of diabetic rats than in those of normal animals. D-Ribose and glycerol were higher in the renal cortex of diabetic animals.

Evaluating the diffusion coefficient of dopamine at the cell surface during amperometric detection: disk vs ring microelectrodes.

PubMed

Trouillon, Raphaël; Lin, Yuqing; Mellander, Lisa J; Keighron, Jacqueline D; Ewing, Andrew G

2013-07-02

During exocytosis, small quantities of neurotransmitters are released by the cell. These neurotransmitters can be detected quantitatively using electrochemical methods, principally with disk carbon fiber microelectrode amperometry. An exocytotic event then results in the recording of a current peak whose characteristic features are directly related to the mechanisms of exocytosis. We have compared two exocytotic peak populations obtained from PC12 cells with a disk carbon fiber microelectrode and with a pyrolyzed carbon ring microelectrode array, with a 500 nm ring thickness. The specific shape of the ring electrode allows for precise analysis of diffusion processes at the vicinity of the cell membrane. Peaks obtained with a ring microelectrode array show a distorted average shape, owing to increased diffusion pathways. This result has been used to evaluate the diffusion coefficient of dopamine at the surface of a cell, which is up to an order of magnitude smaller than that measured in free buffer. The lower rate of diffusion is discussed as resulting from interactions with the glycocalyx.

Water Relations, Gas Exchange, and Nutrient Response to a Long Term Constant Water Deficit

NASA Technical Reports Server (NTRS)

Berry, Wade L.; Goldstein, Guillermo; Dreschel, Thomas W.; Wheeler, Raymond M.; Sager, John C.; Knott, William M.

1992-01-01

Wheat plants (Triticum aestivum) were grown for 43 days in a micro-porous tube nutrient delivery system. Roots were unable to penetrate the microporous tube, but grew on the surface and maintained capillary contact with the nutrient solution on the inside of the tube through the 5-microns pores of the porous tube. Water potential in the system was controlled at -0.4, -0.8, and -3.0 kPa by adjusting the applied pressure (hydrostatic head) to the nutrient solution flowing through the microporous tubes. A relatively small decrease in applied water potential from -0.4 to -3.0 kPa resulted in a 34% reduction of shoot growth but only a moderate reduction in the mid-day leaf water potential from - 1.3 to - 1.7 MPa. Carbon dioxide assimilation decreased and water use efficiency increased with the more negative applied water Potentials, while intercellular C02 concentration remained constant. The physiological responses observed in this study in response to small constant differences in applied water potentials were much greater than expected from either the applied water potential or the observed plant water potential. Even though the micro-porous tube may not represent natural conditions and could possibly introduce morphological and physiological artifacts , it enables a high degree of control of water potential that facilitates the investigation of many aspects of water relations not practical with other experimental systems.

Role of constant value of surface diffuseness in alpha decay half-lives of superheavy nuclei

NASA Astrophysics Data System (ADS)

Dehghani, V.; Alavi, S. A.; Benam, Kh.

2018-05-01

By using WKB method and considering deformed Woods-Saxon nuclear potential, deformed Coulomb potential, and centrifugal potential, the alpha decay half-lives of 68 superheavy alpha emitters have been calculated. The effect of the constant value of surface diffuseness parameter in the range of 0.1 ≤ a ≤ 0.9 (fm) on the potential barrier, tunneling probability, assault frequency, and alpha decay half-lives has been investigated. Significant differences were observed for alpha decay half-lives and decay quantities in this range of surface diffuseness. Good agreement between calculated half-lives with fitted surface diffuseness parameter a = 0.54 (fm) and experiment was observed.

Application of an Artificial Neural Network to the Prediction of OH Radical Reaction Rate Constants for Evaluating Global Warming Potential.

PubMed

Allison, Thomas C

2016-03-03

Rate constants for reactions of chemical compounds with hydroxyl radical are a key quantity used in evaluating the global warming potential of a substance. Experimental determination of these rate constants is essential, but it can also be difficult and time-consuming to produce. High-level quantum chemistry predictions of the rate constant can suffer from the same issues. Therefore, it is valuable to devise estimation schemes that can give reasonable results on a variety of chemical compounds. In this article, the construction and training of an artificial neural network (ANN) for the prediction of rate constants at 298 K for reactions of hydroxyl radical with a diverse set of molecules is described. Input to the ANN consists of counts of the chemical bonds and bends present in the target molecule. The ANN is trained using 792 (•)OH reaction rate constants taken from the NIST Chemical Kinetics Database. The mean unsigned percent error (MUPE) for the training set is 12%, and the MUPE of the testing set is 51%. It is shown that the present methodology yields rate constants of reasonable accuracy for a diverse set of inputs. The results are compared to high-quality literature values and to another estimation scheme. This ANN methodology is expected to be of use in a wide range of applications for which (•)OH reaction rate constants are required. The model uses only information that can be gathered from a 2D representation of the molecule, making the present approach particularly appealing, especially for screening applications.

A combining rule calculation of the ground-state van der Waals potentials of the magnesium rare-gas complexes

NASA Astrophysics Data System (ADS)

Saidi, Samah; Alharzali, Nissrin; Berriche, Hamid

2017-04-01

The potential energy curves and spectroscopic constants of the ground-state of the Mg-Rg (Rg = He, Ne, Ar, Kr, and Xe) van der Waals complexes are generated by the Tang-Toennies potential model and a set of derived combining rules. The parameters of the model are calculated from the potentials of the homonuclear magnesium and rare-gas dimers. The predicted spectroscopic constants are comparable to other available theoretical and experimental results, except in the case of Mg-He, we note that there are large differences between various determinations. Moreover, in order to reveal relative differences between species more obviously we calculated the reduced potential of these five systems. The curves are clumped closely together, but at intermediate range the Mg-He reduced potential is clearly very different from the others.

Rate constant for the fraction of atomic chlorine with formaldehyde from 200 to 500K

NASA Technical Reports Server (NTRS)

Michael, J. V.; Nava, D. F.; Payne, W. A.; Stief, L. J.

1978-01-01

A flash photolysis - resonance fluorescence technique was used to measure rate constant. The results were independent of substantial variations in H2CO, total pressure (Ar), and flash intensity (i.e., initial Cl). The rate constant was shown to be invariant with temperature, the best representation for this temperature range being K = (7.48 + or - 0.50) x 10 to the minus 11 power cu cm molecule-1 s-1 where the error is one standard deviation. The rate constant is theoretically discussed and the potential importance of the reaction in stratospheric chemistry is considered.

Redox properties of the nitronyl nitroxide antioxidants studied via their reactions with nitroxyl and ferrocyanide.

PubMed

Bobko, A A; Khramtsov, V V

2015-01-01

Nitronyl nitroxides (NNs) are the paramagnetic probes that are capable of scavenging physiologically relevant reactive oxygen (ROS) and nitrogen (RNS) species, namely superoxide, nitric oxide (NO), and nitroxyl (HNO). NNs are increasingly considered as potent antioxidants and potential therapeutic agents. Understanding redox chemistry of the NNs is important for their use as antioxidants and as paramagnetic probes for discriminative detection of NO and HNO by electron paramagnetic resonance (EPR) spectroscopy. Here we investigated the redox properties of the two most commonly used NNs, including determination of the equilibrium and rate constants of their reduction by HNO and ferrocyanide, and reduction potential of the couple NN/hydroxylamine of nitronyl nitroxide (hNN). The rate constants of the reaction of the NNs with HNO were found to be equal to (1-2) × 10(4) M(-1)s(- 1) being close to the rate constants of scavenging superoxide and NO by NNs. The reduction potential of the NNs and iminonitroxides (INs, product of NNs reaction with NO) were calculated based on their reaction constants with ferrocyanide. The obtained values of the reduction potential for NN/hNN (E'0 ≈ 285 mV) and IN/hIN (E' ≈ 495 mV) are close to the corresponding values for vitamin C and vitamin E, correspondingly. The "balanced" scavenging rates of the NNs towards superoxide, NO, and HNO, and their low reduction potential being thermodynamically close to the bottom of the pecking order of oxidizing radicals, might be important factors contributing into their antioxidant activity.

Development of a direct experimental test for any violation of the equivalence principle by the weak interaction

NASA Technical Reports Server (NTRS)

Parker, P. D. M.

1981-01-01

Violation of the equivalence principle by the weak interaction is tested. Any variation of the weak interaction coupling constant with gravitational potential, i.e., a spatial variation of the fundamental constants is investigated. The level of sensitivity required for such a measurement is estimated on the basis of the size of a change in the gravitational potential which is accessible. The alpha particle spectrum is analyzed, and the counting rate was improved by a factor of approximately 100.

Concentration Dependent Physical Properties of Ge1-xSnx Solid Solution

NASA Astrophysics Data System (ADS)

Jivani, A. R.; Jani, A. R.

2011-12-01

Our own proposed potential is used to investigate few physical properties like total energy, bulk modulus, pressure derivative of bulk modulus, elastic constants, pressure derivative of elastic constants, Poisson's ratio and Young's modulus of Ge1-xSnx solid solution with x is atomic concentration of α-Sn. The potential combines linear plus quadratic types of electron-ion interaction. First time screening function proposed by Sarkar et al is used to investigate the properties of the Ge-Sn solid solution system.

Independence of the effective dielectric constant of an electrolytic solution on the ionic distribution in the linear Poisson-Nernst-Planck model.

PubMed

Alexe-Ionescu, A L; Barbero, G; Lelidis, I

2014-08-28

We consider the influence of the spatial dependence of the ions distribution on the effective dielectric constant of an electrolytic solution. We show that in the linear version of the Poisson-Nernst-Planck model, the effective dielectric constant of the solution has to be considered independent of any ionic distribution induced by the external field. This result follows from the fact that, in the linear approximation of the Poisson-Nernst-Planck model, the redistribution of the ions in the solvent due to the external field gives rise to a variation of the dielectric constant that is of the first order in the effective potential, and therefore it has to be neglected in the Poisson's equation that relates the actual electric potential across the electrolytic cell to the bulk density of ions. The analysis is performed in the case where the electrodes are perfectly blocking and the adsorption at the electrodes is negligible, and in the absence of any ion dissociation-recombination effect.

FAST TRACK COMMUNICATION: Necessary conditions for classical super-integrability of a certain family of potentials in constant curvature spaces

NASA Astrophysics Data System (ADS)

Maciejewski, Andrzej J.; Przybylska, Maria; Yoshida, Haruo

2010-09-01

We formulate the necessary conditions for the maximal super-integrability of a certain family of classical potentials defined in the constant curvature two-dimensional spaces. We give examples of homogeneous potentials of degree -2 on {\\bb E}^2 as well as their equivalents on {\\bb S}^2 and {\\bb H}^2 for which these necessary conditions are also sufficient. We show explicit forms of the additional first integrals which can always be chosen as a polynomial with respect to the momenta and which can be of an arbitrary high degree with respect to the momenta.

Oxygen potentials, oxygen diffusion coefficients and defect equilibria of nonstoichiometric (U,Pu)O2±x

NASA Astrophysics Data System (ADS)

Kato, Masato; Watanabe, Masashi; Matsumoto, Taku; Hirooka, Shun; Akashi, Masatoshi

2017-04-01

Oxygen potential of (U,Pu)O2±x was evaluated based on defect chemistry using an updated experimental data set. The relationship between oxygen partial pressure and deviation x in (U,Pu)O2±x was analyzed, and equilibrium constants of defect formation were determined as functions of Pu content and temperature. Brouwer's diagrams were constructed using the determined equilibrium constants, and a relational equation to determine O/M ratio was derived as functions of O/M ratio, Pu content and temperature. In addition, relationship between oxygen potential and oxygen diffusion coefficients were described.

Constant-current corona triode adapted and optimized for the characterization of thin dielectric films

NASA Astrophysics Data System (ADS)

Giacometti, José A.

2018-05-01

This work describes an enhanced corona triode with constant current adapted to characterize the electrical properties of thin dielectric films used in organic electronic devices. A metallic grid with a high ionic transparency is employed to charge thin films (100 s of nm thick) with a large enough charging current. The determination of the surface potential is based on the grid voltage measurement, but using a more sophisticated procedure than the previous corona triode. Controlling the charging current to zero, which is the open-circuit condition, the potential decay can be measured without using a vibrating grid. In addition, the electric capacitance and the characteristic curves of current versus the stationary surface potential can also be determined. To demonstrate the use of the constant current corona triode, we have characterized poly(methyl methacrylate) thin films with films with thicknesses in the range from 300 to 500 nm, frequently used as gate dielectric in organic field-effect transistors.

Photochemical parameters of atmospheric source gases: accurate determination of OH reaction rate constants over atmospheric temperatures, UV and IR absorption spectra

NASA Astrophysics Data System (ADS)

Orkin, V. L.; Khamaganov, V. G.; Martynova, L. E.; Kurylo, M. J.

2012-12-01

The emissions of halogenated (Cl, Br containing) organics of both natural and anthropogenic origin contribute to the balance of and changes in the stratospheric ozone concentration. The associated chemical cycles are initiated by the photochemical decomposition of the portion of source gases that reaches the stratosphere. Reactions with hydroxyl radicals and photolysis are the main processes dictating the compound lifetime in the troposphere and release of active halogen in the stratosphere for a majority of halogen source gases. Therefore, the accuracy of photochemical data is of primary importance for the purpose of comprehensive atmospheric modeling and for simplified kinetic estimations of global impacts on the atmosphere, such as in ozone depletion (i.e., the Ozone Depletion Potential, ODP) and climate change (i.e., the Global Warming Potential, GWP). The sources of critically evaluated photochemical data for atmospheric modeling, NASA/JPL Publications and IUPAC Publications, recommend uncertainties within 10%-60% for the majority of OH reaction rate constants with only a few cases where uncertainties lie at the low end of this range. These uncertainties can be somewhat conservative because evaluations are based on the data from various laboratories obtained during the last few decades. Nevertheless, even the authors of the original experimental works rarely estimate the total combined uncertainties of the published OH reaction rate constants to be less than ca. 10%. Thus, uncertainties in the photochemical properties of potential and current atmospheric trace gases obtained under controlled laboratory conditions still may constitute a major source of uncertainty in estimating the compound's environmental impact. One of the purposes of the presentation is to illustrate the potential for obtaining accurate laboratory measurements of the OH reaction rate constant over the temperature range of atmospheric interest. A detailed inventory of accountable sources of instrumental uncertainties related to our FP-RF experiment proves a total uncertainty of the OH reaction rate constant to be as small as ca. 2-3%. The high precision of kinetic measurements allows reliable determination of weak temperature dependences of the rate constants and clear resolution of the curvature of the Arrhenius plots for the OH reaction rate constants of various compounds. The results of OH reaction rate constant determinations between 220 K and 370 K will be presented. Similarly, the accuracy of UV and IR absorption measurements will be highlighted to provide an improved basis for atmospheric modeling.

Anharmonic Potential Constants and Their Dependence Upon Bond Length

DOE R&D Accomplishments Database

Herschbach, D. R.; Laurie, V. W.

1961-01-01

Empirical study of cubic and quartic vibrational force constants for diatomic molecules shows them to be approximately exponential functions of internuclear distance. A family of curves is obtained, determined by the location of the bonded atoms in rows of the periodic table. Displacements between successive curves correspond closely to those in Badger's rule for quadratic force constants (for which the parameters are redetermined to accord with all data now available). Constants for excited electronic and ionic states appear on practically the same curves as those for the ground states. Predictions based on the diatomic correlations agree with the available cubic constants for bond stretching in polyatomic molecules, regardless of the type of bonding involved. Implications of these regularities are discussed. (auth)

Constant DI pacing suppresses cardiac alternans formation in numerical cable models

NASA Astrophysics Data System (ADS)

Zlochiver, S.; Johnson, C.; Tolkacheva, E. G.

2017-09-01

Cardiac repolarization alternans describe the sequential alternation of the action potential duration (APD) and can develop during rapid pacing. In the ventricles, such alternans may rapidly turn into life risking arrhythmias under conditions of spatial heterogeneity. Thus, suppression of alternans by artificial pacing protocols, or alternans control, has been the subject of numerous theoretical, numerical, and experimental studies. Yet, previous attempts that were inspired by chaos control theories were successful only for a short spatial extent (<2 cm) from the pacing electrode. Previously, we demonstrated in a single cell model that pacing with a constant diastolic interval (DI) can suppress the formation of alternans at high rates of activation. We attributed this effect to the elimination of feedback between the pacing cycle length and the last APD, effectively preventing restitution-dependent alternans from developing. Here, we extend this idea into cable models to study the extent by which constant DI pacing can control alternans during wave propagation conditions. Constant DI pacing was applied to ventricular cable models of up to 5 cm, using human kinetics. Our results show that constant DI pacing significantly shifts the onset of both cardiac alternans and conduction blocks to higher pacing rates in comparison to pacing with constant cycle length. We also demonstrate that constant DI pacing reduces the propensity of spatially discordant alternans, a precursor of wavebreaks. We finally found that the protective effect of constant DI pacing is stronger for increased electrotonic coupling along the fiber in the sense that the onset of alternans is further shifted to higher activation rates. Overall, these results support the potential clinical applicability of such type of pacing in improving protocols of implanted pacemakers, in order to reduce the risk of life-threatening arrhythmias. Future research should be conducted in order to experimentally validate these promising results.

The mathematical formulation of a generalized Hooke's law for blood vessels.

PubMed

Zhang, Wei; Wang, Chong; Kassab, Ghassan S

2007-08-01

It is well known that the stress-strain relationship of blood vessels is highly nonlinear. To linearize the relationship, the Hencky strain tensor is generalized to a logarithmic-exponential (log-exp) strain tensor to absorb the nonlinearity. A quadratic nominal strain potential is proposed to derive the second Piola-Kirchhoff stresses by differentiating the potential with respect to the log-exp strains. The resulting constitutive equation is a generalized Hooke's law. Ten material constants are needed for the three-dimensional orthotropic model. The nondimensional constant used in the log-exp strain definition is interpreted as a nonlinearity parameter. The other nine constants are the elastic moduli with respect to the log-exp strains. In this paper, the proposed linear stress-strain relation is shown to represent the pseudoelastic Fung model very well.

Lattice constant changes leading to significant changes of the spin-gapless features and physical nature in a inverse Heusler compound Zr2MnGa

NASA Astrophysics Data System (ADS)

Wang, Xiaotian; Cheng, Zhenxiang; Khenata, Rabah; Wu, Yang; Wang, Liying; Liu, Guodong

2017-12-01

The spin-gapless semiconductors with parabolic energy dispersions [1-3] have been recently proposed as a new class of materials for potential applications in spintronic devices. In this work, according to the Slater-Pauling rule, we report the fully-compensated ferrimagnetic (FCF) behavior and spin-gapless semiconducting (SGS) properties for a new inverse Heusler compound Zr2MnGa by means of the plane-wave pseudo-potential method based on density functional theory. With the help of GGA-PBE, the electronic structures and the magnetism of Zr2MnGa compound at its equilibrium and strained lattice constants are systematically studied. The calculated results show that the Zr2MnGa is a new SGS at its equilibrium lattice constant: there is an energy gap between the conduction and valence bands for both the majority and minority electrons, while there is no gap between the majority electrons in the valence band and the minority electrons in the conduction band. Remarkably, not only a diverse physical nature transition, but also different types of spin-gapless features can be observed with the change of the lattice constants. Our calculated results of Zr2MnGa compound indicate that this material has great application potential in spintronic devices.

Challenges for semilocal density functionals with asymptotically nonvanishing potentials

NASA Astrophysics Data System (ADS)

Aschebrock, Thilo; Armiento, Rickard; Kümmel, Stephan

2017-08-01

The Becke-Johnson model potential [A. D. Becke and E. R. Johnson, J. Chem. Phys. 124, 221101 (2006), 10.1063/1.2213970] and the potential of the AK13 functional [R. Armiento and S. Kümmel, Phys. Rev. Lett. 111, 036402 (2013), 10.1103/PhysRevLett.111.036402] have been shown to mimic features of the exact Kohn-Sham exchange potential, such as step structures that are associated with shell closings and particle-number changes. A key element in the construction of these functionals is that the potential has a limiting value far outside a finite system that is a system-dependent constant rather than zero. We discuss a set of anomalous features in these functionals that are closely connected to the nonvanishing asymptotic potential. The findings constitute a formidable challenge for the future development of semilocal functionals based on the concept of a nonvanishing asymptotic constant.

Corrosion of 310 stainless steel in H2-H2O-H2S gas mixtures: Studies at constant temperature and fixed oxygen potential

NASA Technical Reports Server (NTRS)

Rao, D. B.; Jacob, K. T.; Nelson, H. G.

1981-01-01

Corrosion of SAE 310 stainless steel in H2-H2O-H2S gas mixtures was studied at a constant temperature of 1150 K. Reactive gas mixtures were chosen to yield a constant oxygen potential of approximately 6 x 10 to the minus 13th power/cu Nm and sulfur potentials ranging from 0.19 x 10 to the minus 2nd power/cu Nm to 33 x 10 to the minus 2nd power/cu Nm. The kinetics of corrosion were determined using a thermobalance, and the scales were analyzed using metallography, scanning electron microscopy, and energy dispersive X-ray analysis. Two corrosion regimes, which were dependent on sulfur potential, were identified. At high sulfur potentials (p sub S sub 2 less than or equal to 2.7 x 10 to the minus 2nd power/cu Nm) the corrosion rates were high, the kinetics obeyed a linear rate equation, and the scales consisted mainly of sulfide phases similar to those observed from pure sulfication. At low sulfur potentials (P sub S sub 2 less than or equal to 0.19 x 10 to the minus 2nd power/cu Nm) the corrosion rates were low, the kinetics obeyed a parabolic rate equation, and scales consisted mainly of oxide phases.

Vibration-rotation spectrum of BH X1Σ+ by Fourier transform emission spectroscopy

NASA Astrophysics Data System (ADS)

Pianalto, F. S.; O'Brien, L. C.; Keller, P. C.; Bernath, P. F.

1988-06-01

The vibration-rotation emission spectrum of the BH X1Σ+ state was observed with the McMath Fourier transform spectrometer at Kitt Peak. The 1-0, 2-1, and 3-2 bands were observed in a microwave discharge of B2H6 in He. Spectroscopic constants of the individual vibrational levels and equilibrium molecular constants were determined. An RKR potential curve was calculated from the equilibrium constants. Alfred P. Sloan Fellow; Camille and Henry Dreyfus Teacher-Scholar.

Nuclear shielding constants by density functional theory with gauge including atomic orbitals

NASA Astrophysics Data System (ADS)

Helgaker, Trygve; Wilson, Philip J.; Amos, Roger D.; Handy, Nicholas C.

2000-08-01

Recently, we introduced a new density-functional theory (DFT) approach for the calculation of NMR shielding constants. First, a hybrid DFT calculation (using 5% exact exchange) is performed on the molecule to determine Kohn-Sham orbitals and their energies; second, the constants are determined as in nonhybrid DFT theory, that is, the paramagnetic contribution to the constants is calculated from a noniterative, uncoupled sum-over-states expression. The initial results suggested that this semiempirical DFT approach gives shielding constants in good agreement with the best ab initio and experimental data; in this paper, we further validate this procedure, using London orbitals in the theory, having implemented DFT into the ab initio code DALTON. Calculations on a number of small and medium-sized molecules confirm that our approach produces shieldings in excellent agreement with experiment and the best ab initio results available, demonstrating its potential for the study of shielding constants of large systems.

On the interpretation of quantitative structure–function activity relationship data for lactate oxidase

PubMed Central

Yorita, Kazuko; Misaki, Hideo; Palfey, Bruce A.; Massey, Vincent

2000-01-01

The native flavin, FMN, has been removed from the l-lactate oxidase of Aerococcus viridans, and the apoprotein reconstituted with 12 FMN derivatives with various substituents at the flavin 6- and 8-positions. Impressive linear relationships are exhibited between the sum of the Hammett σpara and σortho parameters and the redox potentials of the free flavins, and between the redox potentials of the free and enzyme-bound flavins. Rapid reaction kinetics studies of the reconstituted enzymes with the substrates l-lactate and l-mandelate show an increase in the reduction rate constant with increasing redox potential, except that, with lactate, a limiting rate constant of ≈700 s−1 is obtained with flavins of high potential. Similar breakpoints are found in plots of the rate constants for flavin N5-sulfite adduct formation and for the reaction of the reduced enzymes with molecular oxygen. These results are interpreted in terms of a two-step equilibrium preceding the chemical reaction step, in which the second equilibrium step provides an upper limit to the rate with which the particular substrate or ligand is positioned with the flavin in the correct fashion for the observed chemical reaction to occur. The relationship of rate constants for flavin reduction and N5-sulfite adduct formation with flavin redox potential below the observed breakpoint indicate development of significant negative charge in the transition states of the reactions. In the case of reduction by substrate, the results are consistent either with a hydride transfer mechanism or with the so called “carbanion” mechanism, in which the substrate α-proton is abstracted by an enzyme base protected from exchange with solvent. These conclusions are supported by substrate α-deuterium isotope effects and by solvent viscosity effects on sulfite binding. PMID:10706608

Inflation with a smooth constant-roll to constant-roll era transition

NASA Astrophysics Data System (ADS)

Odintsov, S. D.; Oikonomou, V. K.

2017-07-01

In this paper, we study canonical scalar field models, with a varying second slow-roll parameter, that allow transitions between constant-roll eras. In the models with two constant-roll eras, it is possible to avoid fine-tunings in the initial conditions of the scalar field. We mainly focus on the stability of the resulting solutions, and we also investigate if these solutions are attractors of the cosmological system. We shall calculate the resulting scalar potential and, by using a numerical approach, we examine the stability and attractor properties of the solutions. As we show, the first constant-roll era is dynamically unstable towards linear perturbations, and the cosmological system is driven by the attractor solution to the final constant-roll era. As we demonstrate, it is possible to have a nearly scale-invariant power spectrum of primordial curvature perturbations in some cases; however, this is strongly model dependent and depends on the rate of the final constant-roll era. Finally, we present, in brief, the essential features of a model that allows oscillations between constant-roll eras.

The influence of polarizability and charge transfer on specific ion effects in the dynamics of aqueous salt solutions

NASA Astrophysics Data System (ADS)

Nguyen, Mary; Rick, Steven W.

2018-06-01

The diffusion rates for water molecules in salt solutions depend on the identity of the ions, as well as their concentration. Among the alkali metal ions, cesium and potassium increase and sodium strongly decreases the diffusion constant of water. The origin of the difference can be understood by examining the simulation results using different potential models. In this work, aqueous solutions of salts are simulated with a variety of models. Commonly used non-polarizable models, which otherwise reproduce many experimental properties, do not capture the trend in the diffusion constant, while models which include polarization and/or charge transfer interactions do. For the non-polarizable models, the diffusion constant decreases too strongly with salt concentration. The changes in the water diffusion constant with increasing salt concentration match the diffusion constant of the ion. The ion diffusion constant is dependent on the residence time for water in the ion solvation shell. The non-polarizable models over-estimate the residence time, relative to the translational diffusion constant and so tend to under-estimate the ion and water diffusion constants.

Colloidal Dynamics Simulations of Rheology and Stability of Concentrated Fuel Slurries.

DTIC Science & Technology

1987-04-10

Weals potential as the adsorbed polymer concentration and Hamaker con- stant are changed. These calculations provide quantitative evidence for the...derived by Hamaker : 3 6 U (r) A d 2 2 +2Ln( 2- d2(3 A T2 2 2 2 2 A value of 5.0 x 10" 2 0 j was used for the Hamaker constant, A. A plot of Eq. (31) is...parameter controlling the strength of the repulsive steric potential. The Hamaker constant A (Eq. (33)) is the nat- ural choice for the attractive

Thermophysical properties of liquid rare earth metals

NASA Astrophysics Data System (ADS)

Thakor, P. B.; Sonvane, Y. A.; Patel, H. P.; Jani, A. R.

2013-06-01

The thermodynamical properties like long wavelength limit S(0), iso-thermal compressibility (χT), thermal expansion coefficient (αV), thermal pressure coefficient (γV), specific heat at constant volume (CV) and specific heat at constant pressure (CP) are calculated for liquid rare earth metals. Our newly constructed parameter free model potential is used to describe the electron ion interaction due to Sarkar et al (S) local field correction function. Lastly, we conclude that our newly constructed model potential is capable to explain the thermophysical properties of liquid rare earth metals.

Phase Diagrams and the Non-Linear Dielectric Constant in the Landau-Type Potential Including the Linear-Quadratic Coupling between Order Parameters

NASA Astrophysics Data System (ADS)

Iwata, Makoto; Orihara, Hiroshi; Ishibashi, Yoshihiro

1997-04-01

The phase diagrams in the Landau-type thermodynamic potential including the linear-quadratic coupling between order parameters p and q, i.e., qp2, which is applicable to the phase transition in the benzil, phospholipid bilayers, and the isotropic-nematic phase transition in liquid crystals, are studied. It was found that the phase diagram in the extreme case has one tricritical point c1, one critical end point e1, and two triple points t1 and t2. The linear and nonlinear dielectric constants in the potential are discussed in the case that the order parameter p is the polarization.

Fast Shepard interpolation on graphics processing units: potential energy surfaces and dynamics for H + CH4 → H2 + CH3.

PubMed

Welsch, Ralph; Manthe, Uwe

2013-04-28

A strategy for the fast evaluation of Shepard interpolated potential energy surfaces (PESs) utilizing graphics processing units (GPUs) is presented. Speed ups of several orders of magnitude are gained for the title reaction on the ZFWCZ PES [Y. Zhou, B. Fu, C. Wang, M. A. Collins, and D. H. Zhang, J. Chem. Phys. 134, 064323 (2011)]. Thermal rate constants are calculated employing the quantum transition state concept and the multi-layer multi-configurational time-dependent Hartree approach. Results for the ZFWCZ PES are compared to rate constants obtained for other ab initio PESs and problems are discussed. A revised PES is presented. Thermal rate constants obtained for the revised PES indicate that an accurate description of the anharmonicity around the transition state is crucial.

Combined valence bond-molecular mechanics potential-energy surface and direct dynamics study of rate constants and kinetic isotope effects for the H + C2H6 reaction.

PubMed

Chakraborty, Arindam; Zhao, Yan; Lin, Hai; Truhlar, Donald G

2006-01-28

This article presents a multifaceted study of the reaction H+C(2)H(6)-->H(2)+C(2)H(5) and three of its deuterium-substituted isotopologs. First we present high-level electronic structure calculations by the W1, G3SX, MCG3-MPWB, CBS-APNO, and MC-QCISD/3 methods that lead to a best estimate of the barrier height of 11.8+/-0.5 kcal/mol. Then we obtain a specific reaction parameter for the MPW density functional in order that it reproduces the best estimate of the barrier height; this yields the MPW54 functional. The MPW54 functional, as well as the MPW60 functional that was previously parametrized for the H+CH(4) reaction, is used with canonical variational theory with small-curvature tunneling to calculate the rate constants for all four ethane reactions from 200 to 2000 K. The final MPW54 calculations are based on curvilinear-coordinate generalized-normal-mode analysis along the reaction path, and they include scaled frequencies and an anharmonic C-C bond torsion. They agree with experiment within 31% for 467-826 K except for a 38% deviation at 748 K; the results for the isotopologs are predictions since these rate constants have never been measured. The kinetic isotope effects (KIEs) are analyzed to reveal the contributions from subsets of vibrational partition functions and from tunneling, which conspire to yield a nonmonotonic temperature dependence for one of the KIEs. The stationary points and reaction-path potential of the MPW54 potential-energy surface are then used to parametrize a new kind of analytical potential-energy surface that combines a semiempirical valence bond formalism for the reactive part of the molecule with a standard molecular mechanics force field for the rest; this may be considered to be either an extension of molecular mechanics to treat a reactive potential-energy surface or a new kind of combined quantum-mechanical/molecular mechanical (QM/MM) method in which the QM part is semiempirical valence bond theory; that is, the new potential-energy surface is a combined valence bond molecular mechanics (CVBMM) surface. Rate constants calculated with the CVBMM surface agree with the MPW54 rate constants within 12% for 534-2000 K and within 23% for 200-491 K. The full CVBMM potential-energy surface is now available for use in variety of dynamics calculations, and it provides a prototype for developing CVBMM potential-energy surfaces for other reactions.

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

AlHallak, M.; Chamoun, N.; Physikalisches Institut der Universität Bonn,Nußalle 12, D-53115 Bonn

We present a model of power law inflation generated by variation of the strong coupling constant. We then extend the model to two varying coupling constants which leads to a potential consisting of a linear combination of exponential terms. Some variants of the latter may be self-consistent and can accommodate the experimental data of the Planck 2015 and other recent experiments.

A novel pressure variation study on electronic structure, mechanical stability and thermodynamic properties of potassium based fluoroperovskite

NASA Astrophysics Data System (ADS)

Erum, Nazia; Azhar Iqbal, Muhammad

2017-09-01

The effect of pressure variation on stability, structural parameters, elastic constants, mechanical, electronic and thermodynamic properties of cubic SrKF3 fluoroperovskite have been investigated by using the full-potential linearized augmented plane wave (FP-LAPW) method combined with Quasi-harmonic Debye model in which the phonon effects are considered. The calculated lattice parameters show a prominent decrease in lattice constant and bonds length with the increase in pressure. The application of pressure from 0 to 25 GPa reveals a predominant characteristic associated with widening of bandgap with GGA and GGA plus Tran-Blaha modified Becke-Johnson (TB-mBJ) potential. The influence of pressure on elastic constants and their related mechanical parameters have been discussed in detail. Apart of linear dependence of elastic coefficients, transition from brittle to ductile behavior is also observed at elevated pressure ranges. We have successfully computed variation of lattice constant, volume expansion, bulk modulus, Debye temperature and specific heat capacities at pressure and temperature in the range of 0-25 GPa and 0-600 K.

Fundamental Physics from Observations of White Dwarf Stars

NASA Astrophysics Data System (ADS)

Bainbridge, M. B.; Barstow, M. A.; Reindl, N.; Barrow, J. D.; Webb, J. K.; Hu, J.; Preval, S. P.; Holberg, J. B.; Nave, G.; Tchang-Brillet, L.; Ayres, T. R.

2017-03-01

Variation in fundamental constants provide an important test of theories of grand unification. Potentially, white dwarf spectra allow us to directly observe variation in fundamental constants at locations of high gravitational potential. We study hot, metal polluted white dwarf stars, combining far-UV spectroscopic observations, atomic physics, atmospheric modelling and fundamental physics, in the search for variation in the fine structure constant. This registers as small but measurable shifts in the observed wavelengths of highly ionized Fe and Ni lines when compared to laboratory wavelengths. Measurements of these shifts were performed by Berengut et al (2013) using high-resolution STIS spectra of G191-B2B, demonstrating the validity of the method. We have extended this work by; (a) using new (high precision) laboratory wavelengths, (b) refining the analysis methodology (incorporating robust techniques from previous studies towards quasars), and (c) enlarging the sample of white dwarf spectra. A successful detection would be the first direct measurement of a gravitational field effect on a bare constant of nature. We describe our approach and present preliminary results.

Cosmological dynamics with non-minimally coupled scalar field and a constant potential function

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

Hrycyna, Orest; Szydłowski, Marek, E-mail: orest.hrycyna@ncbj.gov.pl, E-mail: marek.szydlowski@uj.edu.pl

2015-11-01

Dynamical systems methods are used to investigate global behaviour of the spatially flat Friedmann-Robertson-Walker cosmological model in gravitational theory with a non-minimally coupled scalar field and a constant potential function. We show that the system can be reduced to an autonomous three-dimensional dynamical system and additionally is equipped with an invariant manifold corresponding to an accelerated expansion of the universe. Using this invariant manifold we find an exact solution of the reduced dynamics. We investigate all solutions for all admissible initial conditions using theory of dynamical systems to obtain a classification of all evolutional paths. The right-hand sides of themore » dynamical system depend crucially on the value of the non-minimal coupling constant therefore we study bifurcation values of this parameter under which the structure of the phase space changes qualitatively. We found a special bifurcation value of the non-minimal coupling constant which is distinguished by dynamics of the model and may suggest some additional symmetry in matter sector of the theory.« less

A simple method relating specific rate constants k(E,J) and Thermally averaged rate constants k(infinity)(T) of unimolecular bond fission and the reverse barrierless association reactions.

PubMed

Troe, J; Ushakov, V G

2006-06-01

This work describes a simple method linking specific rate constants k(E,J) of bond fission reactions AB --> A + B with thermally averaged capture rate constants k(cap)(T) of the reverse barrierless combination reactions A + B --> AB (or the corresponding high-pressure dissociation or recombination rate constants k(infinity)(T)). Practical applications are given for ionic and neutral reaction systems. The method, in the first stage, requires a phase-space theoretical treatment with the most realistic minimum energy path potential available, either from reduced dimensionality ab initio or from model calculations of the potential, providing the centrifugal barriers E(0)(J). The effects of the anisotropy of the potential afterward are expressed in terms of specific and thermal rigidity factors f(rigid)(E,J) and f(rigid)(T), respectively. Simple relationships provide a link between f(rigid)(E,J) and f(rigid)(T) where J is an average value of J related to J(max)(E), i.e., the maximum J value compatible with E > or = E0(J), and f(rigid)(E,J) applies to the transitional modes. Methods for constructing f(rigid)(E,J) from f(rigid)(E,J) are also described. The derived relationships are adaptable and can be used on that level of information which is available either from more detailed theoretical calculations or from limited experimental information on specific or thermally averaged rate constants. The examples used for illustration are the systems C6H6+ <==> C6H5+ + H, C8H10+ --> C7H7+ + CH3, n-C9H12+ <==> C7H7+ + C2H5, n-C10H14+ <==> C7H7+ + C3H7, HO2 <==> H + O2, HO2 <==> HO + O, and H2O2 <==> 2HO.

Compilation of Henry's law constants (version 4.0) for water as solvent

NASA Astrophysics Data System (ADS)

Sander, R.

2015-04-01

Many atmospheric chemicals occur in the gas phase as well as in liquid cloud droplets and aerosol particles. Therefore, it is necessary to understand the distribution between the phases. According to Henry's law, the equilibrium ratio between the abundances in the gas phase and in the aqueous phase is constant for a dilute solution. Henry's law constants of trace gases of potential importance in environmental chemistry have been collected and converted into a uniform format. The compilation contains 17 350 values of Henry's law constants for 4632 species, collected from 689 references. It is also available at http://www.henrys-law.org.

Compilation of Henry's law constants, version 3.99

NASA Astrophysics Data System (ADS)

Sander, R.

2014-11-01

Many atmospheric chemicals occur in the gas phase as well as in liquid cloud droplets and aerosol particles. Therefore, it is necessary to understand the distribution between the phases. According to Henry's law, the equilibrium ratio between the abundances in the gas phase and in the aqueous phase is constant for a dilute solution. Henry's law constants of trace gases of potential importance in environmental chemistry have been collected and converted into a uniform format. The compilation contains 14775 values of Henry's law constants for 3214 species, collected from 639 references. It is also available on the internet at http://www.henrys-law.org.

Leaching risk of N-nitrosodimethylamine (NDMA) in soil receiving reclaimed wastewater.

PubMed

Haruta, Shinsuke; Chen, Weiping; Gan, Jay; Simůnek, Jirka; Chang, Andrew C; Wu, Laosheng

2008-03-01

N-nitrosodimethylamine (NDMA) is a potential carcinogen frequently found in treated wastewater as a byproduct of chlorination. The potential for NDMA to contaminate the groundwater is a significant concern. A solute fate and transport model, Hydrus-1D, was used to evaluate the leaching potential of NDMA under different irrigation practices and soil properties. The results indicate that the risk of NDMA to reach the ground water is slim, when the reclaimed wastewater is applied under the customary conditions for landscape irrigation. The NDMA disappears in the reclaimed wastewater receiving soils rapidly through the microbial degradation and the volatilization processes. The factors that enhance the leaching risk are the soil hydraulic conductivity, the NDMA adsorption constants, and the irrigation intensity. When the hydraulic conductivity of soil is high, the NDMA adsorption constant of soil is low and/or the irrigation intensity is high, the NDMA leaching risk may dramatically increase. To reduce the NDMA leaching risk, it is imperative that the fields be irrigated at the proper volume and frequency and attention be paid to fields with soils having high-hydraulic conductivities and/or low-NDMA adsorption constants.

Superintegrability on N-dimensional spaces of constant curvature from so( N + 1) and its contractions

NASA Astrophysics Data System (ADS)

Herranz, F. J.; Ballesteros, Á.

2008-05-01

The Lie—Poisson algebra so( N + 1) and some of its contractions are used to construct a family of superintegrable Hamiltonians on the N-dimensional spherical, Euclidean, hyperbolic, Minkowskian, and (anti-)de Sitter spaces. We firstly present a Hamiltonian which is a superposition of an arbitrary central potential with N arbitrary centrifugal terms. Such a system is quasi-maximally superintegrable since this is endowed with 2 N — 3 functionally independent constants of motion (plus the Hamiltonian). Secondly, we identify two maximally superintegrable Hamiltonians by choosing a specific central potential and finding at the same time the remaining integral. The former is the generalization of the Smorodinsky—Winternitz system to the above six spaces, while the latter is a generalization of the Kepler—Coulomb potential, for which the Laplace—Runge—Lenz N vector is also given. All the systems and constants of motion are explicitly expressed in a unified form in terms of ambient and polar coordinates as they are parametrized by two contraction parameters (curvature and signature of the metric).

Critical cracking potentials of 26Cr-1 Mo ferritic stainless steels in boiling 42% LiCl solution

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

Kwon, H.S.; Troiano, A.R.; Hehemann, R.F.

This paper reports that the critical cracking potentials (E[sub cc] for 26Cr-1Mo ferritic stainless steels (UNS S44627), above which stress corrosion cracking (SCC) does occur, have been measured at constant load in a hot chloride solution. Various factors affecting E[sub cc] for the low interstitial 26Cr-1Mo alloy (E-Brite) is shown to be a potential for crack initiation and is determined by the competing rates of generation of new surface by slip-induced film breakdown and repassivation. E[sub cc] for E-Brite is very sensitive to the microstructural conditions developed by prior thermal and mechanical treatments; varying in the range of -485 mVmore » for the mill annealed to -625 mV for the grain coarsened. On the other hand, the minimum potential permitting crack growth is insensitive to these treatments and corresponds to the most active value of E[sub cc] -625 mV. When strained at a constant strain rate (2.5 [times] 10[sup [minus]6]/S), the critical potential above which E-Brite is susceptible to SCC corresponds to the most active value of E[sub cc] measured at constant load. Thus, it appears that the most active value of E[sub cc](-625 mV) is a repassivation potential for growing cracks, and E[sub cc] approaches that for crack propagation as a limiting condition.« less

Effect of Red Blood Cell Storage on Cardiac Performance. Improved Myocardial Oxygen Delivery and Function during Constant Flow Coronary Perfusion with Low Oxy-Hemoglobin Affinity Human Red Blood Cells in Normothermic and Hypothermic Rabbit Hearts.

DTIC Science & Technology

1983-02-01

with an isovolumic left ven- tricular balloon. Coronary flow was held constant to simulate the physiolog of coronary atherosclerosis and other...erythrocyte DPG content can potentially benefit patients with coronary atherosclerosis , or other states with a limited coronary vasodilator reserve, who...Coronary flow was held constant to simulate the physiology of coronary atherosclerosis and other conditions of limited coronary vasodilator reserve

The Influence of Uncompensated Solution Resistance on the Determination and Standard Electrochemical Rate Constants Using Cyclic Voltammetry, and Some Comparisons with AC Voltammetry.

DTIC Science & Technology

1987-09-25

rate constants, k2r using cyclic voltametry . The res tss are expressed in terms of systematic deviations oP sapparent measured" rate constants, k~b(app...concentration was taken to be lum unless otherwise noted. The voltammetric sweep rate was set at 20 V sŕ unless specified otherwise. The general procedure...peaks for the negative- and positive-going potential sweeps have opposite signs, the measured cathodic-anodic peak separation, AEp, will clearly be

Communication: Prediction of the rate constant of bimolecular hydrogen exchange in the water dimer using an ab initio potential energy surface.

PubMed

Wang, Yimin; Bowman, Joel M; Huang, Xinchuan

2010-09-21

We report the properties of two novel transition states of the bimolecular hydrogen exchange reaction in the water dimer, based on an ab initio water dimer potential [A. Shank et al., J. Chem. Phys. 130, 144314 (2009)]. The realism of the two transition states is assessed by comparing structures, energies, and harmonic frequencies obtained from the potential energy surface and new high-level ab initio calculations. The rate constant for the exchange is obtained using conventional transition state theory with a tunneling correction. We employ a one-dimensional approach for the tunneling calculations using a relaxed potential from the full-dimensional potential in the imaginary-frequency normal mode of the saddle point, Q(im). The accuracy of this one-dimensional approach has been shown for the ground-state tunneling splittings for H and D-transfer in malonaldehyde and for the D+H(2) reaction [Y. Wang and J. M. Bowman, J. Chem. Phys. 129, 121103 (2008)]. This approach is applied to calculate the rate constant for the H(2)O+H(2)O exchange and also for H(2)O+D(2)O→2HOD. The local zero-point energy is also obtained using diffusion Monte Carlo calculations in the space of real-frequency-saddle-point normal modes, as a function of Q(im).

Dynamics of electrical double layer formation in room-temperature ionic liquids under constant-current charging conditions

NASA Astrophysics Data System (ADS)

Jiang, Xikai; Huang, Jingsong; Zhao, Hui; Sumpter, Bobby G.; Qiao, Rui

2014-07-01

We report detailed simulation results on the formation dynamics of an electrical double layer (EDL) inside an electrochemical cell featuring room-temperature ionic liquids (RTILs) enclosed between two planar electrodes. Under relatively small charging currents, the evolution of cell potential from molecular dynamics (MD) simulations during charging can be suitably predicted by the Landau-Ginzburg-type continuum model proposed recently (Bazant et al 2011 Phys. Rev. Lett. 106 046102). Under very large charging currents, the cell potential from MD simulations shows pronounced oscillation during the initial stage of charging, a feature not captured by the continuum model. Such oscillation originates from the sequential growth of the ionic space charge layers near the electrode surface. This allows the evolution of EDLs in RTILs with time, an atomistic process difficult to visualize experimentally, to be studied by analyzing the cell potential under constant-current charging conditions. While the continuum model cannot predict the potential oscillation under such far-from-equilibrium charging conditions, it can nevertheless qualitatively capture the growth of cell potential during the later stage of charging. Improving the continuum model by introducing frequency-dependent dielectric constant and density-dependent ion diffusion coefficients may help to further extend the applicability of the model. The evolution of ion density profiles is also compared between the MD and the continuum model, showing good agreement.

Dynamics of electrical double layer formation in room-temperature ionic liquids under constant-current charging conditions.

PubMed

Jiang, Xikai; Huang, Jingsong; Zhao, Hui; Sumpter, Bobby G; Qiao, Rui

2014-07-16

We report detailed simulation results on the formation dynamics of an electrical double layer (EDL) inside an electrochemical cell featuring room-temperature ionic liquids (RTILs) enclosed between two planar electrodes. Under relatively small charging currents, the evolution of cell potential from molecular dynamics (MD) simulations during charging can be suitably predicted by the Landau-Ginzburg-type continuum model proposed recently (Bazant et al 2011 Phys. Rev. Lett. 106 046102). Under very large charging currents, the cell potential from MD simulations shows pronounced oscillation during the initial stage of charging, a feature not captured by the continuum model. Such oscillation originates from the sequential growth of the ionic space charge layers near the electrode surface. This allows the evolution of EDLs in RTILs with time, an atomistic process difficult to visualize experimentally, to be studied by analyzing the cell potential under constant-current charging conditions. While the continuum model cannot predict the potential oscillation under such far-from-equilibrium charging conditions, it can nevertheless qualitatively capture the growth of cell potential during the later stage of charging. Improving the continuum model by introducing frequency-dependent dielectric constant and density-dependent ion diffusion coefficients may help to further extend the applicability of the model. The evolution of ion density profiles is also compared between the MD and the continuum model, showing good agreement.

CE microchips: an opened gate to food analysis.

PubMed

Escarpa, Alberto; González, María Cristina; Crevillén, Agustín González; Blasco, Antonio Javier

2007-03-01

CE microchips are the first generation of micrototal analysis systems (-TAS) emerging in the miniaturization scene of food analysis. CE microchips for food analysis are fabricated in both glass and polymer materials, such as PDMS and poly(methyl methacrylate) (PMMA), and use simple layouts of simple and double T crosses. Nowadays, the detection route preferred is electrochemical in both, amperometry and conductivity modes, using end-channel and contactless configurations, respectively. Food applications using CE microchips are now emerging since food samples present complex matrices, the selectivity being a very important challenge because the total integration of analytical steps into microchip format is very difficult. As a consequence, the first contributions that have recently appeared in the relevant literature are based primarily on fast separations of analytes of high food significance. These protocols are combined with different strategies to achieve selectivity using a suitable nonextensive sample preparation and/or strategically choosing detection routes. Polyphenolic compounds, amino acids, preservatives, and organic and inorganic ions have been studied using CE microchips. Thus, new and exciting future expectations arise in the domain of food analysis. However, several drawbacks could easily be found and assumed within the miniaturization map.

Electrochemical MIP-Sensors for Drugs.

PubMed

Yarman, Aysu; Kurbanoglu, Sevinc; Jetzschmann, Katharina J; Ozkan, Sibel A; Wollenberger, Ulla; Scheller, Frieder

2017-10-05

In order to replace bio-macromolecules by stable synthetic materials in separation techniques and bioanalysis biomimetic receptors and catalysts have been developed: Functional monomers are polymerized together with the target analyte and after template removal cavities are formed in the "molecularly imprinted polymer" (MIP) which resemble the active sites of antibodies and enzymes. Staring almost 80 years ago, around 1,100 papers on MIPs were published in 2016. Electropolymerization allows to deposit MIPs directly on voltammetric electrodes or chips for quartz crystal microbalance (QCM) and surface plasmon resonance (SPR). For the readout of MIPs for drugs amperometry, differential pulse voltammetry (DPV) and impedance spectroscopy (EIS) offer higher sensitivity as compared with QCM or SPR. Application of simple electrochemical devices allows both the reproducible preparation of MIP sensors, but also the sensitive signal generation. Electrochemical MIP-sensors for the whole arsenal of drugs, e.g. the most frequently used analgesics, antibiotics and anticancer drugs have been presented in literature and tested under laboratory conditions. These biomimetic sensors typically have measuring ranges covering the lower nano- up to millimolar concentration range and they are stable under extreme pH and in organic solvents like non-aqueous extracts. Copyright© Bentham Science Publishers; For any queries, please email at epub@benthamscience.org.

In vivo voltammetry: from wire to wireless measurements.

PubMed

Crespi, Francesco; Dalessandro, Davide; Annovazzi-Lodi, Valerio; Heidbreder, Christian; Norgia, Michele

2004-12-30

A novel telemetric system based on either differential pulse voltammetry (DPV) or direct current amperometry (DCA) by using a diffused infrared transmission channel is presented. Unlike similar pre-existing instruments based on infrared transmission, the present system works on a single-way communication, thus avoiding problems related to cross-talking between two-way channels. The infrared channel is also immune from electromagnetic interferences from the surrounding environment. Further advancement is the development of an original miniaturised system (dimension 1cm x 1.2 cm x 0.5 cm) with reduced weight (5-6 g), suitable for affixing to the rat head and allowing real time telemetric monitoring using DCA sampling of neurotransmitters such as dopamine or serotonin every 100 ms. The set-up is based on a transmitter (TX) circuit mounted on the animal's head and connected to the electrodes inserted into its brain. The TX circuit generates the proper electrical signals for DPV or DCA, collects the electrical response of the brain and transmits it, via an infrared channel, to a receiving station (RX) interfaced with a personal computer. The PC performs the sampling and elaboration of polarographic traces in a flexible and programmable way.

The application of graphene for in vitro and in vivo electrochemical biosensing.

PubMed

Janegitz, Bruno Campos; Silva, Tiago Almeida; Wong, Ademar; Ribovski, Laís; Vicentini, Fernando Campanhã; Taboada Sotomayor, Maria Del Pilar; Fatibello-Filho, Orlando

2017-03-15

Advances in analysis are required for rapid and reliable clinical diagnosis. Graphene is a 2D material that has been extensively used in the development of devices for the medical proposes due to properties such as an elevated surface area and excellent electrical conductivity. On the other hand, architectures have been designed with the incorporation of different biological recognition elements such as antibodies/antigens and DNA probes for the proposition of immunosensors and genosensors. This field presents a great progress in the last few years, which have opened up a wide range of applications. Here, we highlight a rather comprehensive overview of the interesting properties of graphene for in vitro, in vivo, and point-of-care electrochemical biosensing. In the course of the paper, we first introduce graphene, electroanalytical methods (potentiometry, voltammetry, amperometry and electrochemical impedance spectroscopy) followed by an overview of the prospects and possible applications of this material in electrochemical biosensors. In this context, we discuss some relevant trends including the monitoring of multiple biomarkers for cancer diagnostic, implantable devices for in vivo sensing and, development of point-of-care devices to real-time diagnostics. Copyright © 2016 Elsevier B.V. All rights reserved.

The Differential Organization of F-Actin Alters the Distribution of Organelles in Cultured When Compared to Native Chromaffin Cells

PubMed Central

Gimenez-Molina, Yolanda; Villanueva, José; Nanclares, Carmen; Lopez-Font, Inmaculada; Viniegra, Salvador; Francés, Maria del Mar; Gandia, Luis; Gil, Amparo; Gutiérrez, Luis M.

2017-01-01

Cultured bovine chromaffin cells have been used extensively as a neuroendocrine model to study regulated secretion. In order to extend such experimental findings to the physiological situation, it is necessary to study mayor cellular structures affecting secretion in cultured cells with their counterparts present in the adrenomedullary tissue. F-actin concentrates in a peripheral ring in cultured cells, as witnessed by phalloidin–rodhamine labeling, while extends throughout the cytoplasm in native cells. This result is also confirmed when studying the localization of α-fodrin, a F-actin-associated protein. Furthermore, as a consequence of this redistribution of F-actin, we observed that chromaffin granules and mitochondria located into two different cortical and internal populations in cultured cells, whereas they are homogeneously distributed throughout the cytoplasm in the adrenomedullary tissue. Nevertheless, secretion from isolated cells and adrenal gland pieces is remarkably similar when measured by amperometry. Finally, we generate mathematical models to consider how the distribution of organelles affects the secretory kinetics of intact and cultured cells. Our results imply that we have to consider F-actin structural changes to interpret functional data obtained in cultured neuroendocrine cells. PMID:28522964

Exact Electromagnetic Fields Produced by a Finite Wire with Constant Current

ERIC Educational Resources Information Center

Jimenez, J. L.; Campos, I.; Aquino, N.

2008-01-01

We solve exactly the problem of calculating the electromagnetic fields produced by a finite wire with a constant current, by using two methods: retarded potentials and Jefimenko's formalism. One result in this particular case is that the usual Biot-Savart law of magnetostatics gives the correct magnetic field of the problem. We also show…

Small field axion inflation with sub-Planckian decay constant

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

Kadota, Kenji; Kobayashi, Tatsuo; Oikawa, Akane

2016-10-10

We study an axion inflation model recently proposed within the framework of type IIB superstring theory, where we pay a particular attention to a sub-Planckian axion decay constant. Our axion potential can lead to the small field inflation with a small tensor-to-scalar ratio, and a typical reheating temperature can be as low as GeV.

Real Space Imaging of the Microscopic Origins of the Ultrahigh Dielectric Constant in Polycrystalline CaCu 3Ti 4O 12

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

Kalinin, Sergei V; Shin, Junsoo; Veith, Gabriel M

2005-01-01

The origins of an ultrahigh dielectric constant in polycrystalline CaCu{sub 3}Ti{sub 4}O{sub 12} (CCTO) were studied using the combination of impedance spectroscopy, electron microscopy, and scanning probe microscopy (SPM). Impedance spectra indicate that the transport properties in the 0.1 Hz-1 MHz frequency range are dominated by a single parallel resistive-capacitive (RC) element with a characteristic relaxation frequency of 16 Hz. dc potential distributions measurements by SPM illustrate that significant potential drops occur at the grain boundaries, which thus can be unambiguously identified as the dominant RC element. High frequency ac amplitude and phase distributions illustrate very weak grain boundary contrastmore » in SPM, indicative of strong capacitive coupling across the interfaces. These results demonstrate that the ultrahigh dielectric constant reported for polycrystalline CCTO materials is related to grain-boundary behavior.« less

Chemical equilibrium. [maximizing entropy of gas system to derive relations between thermodynamic variables

NASA Technical Reports Server (NTRS)

1976-01-01

The entropy of a gas system with the number of particles subject to external control is maximized to derive relations between the thermodynamic variables that obtain at equilibrium. These relations are described in terms of the chemical potential, defined as equivalent partial derivatives of entropy, energy, enthalpy, free energy, or free enthalpy. At equilibrium, the change in total chemical potential must vanish. This fact is used to derive the equilibrium constants for chemical reactions in terms of the partition functions of the species involved in the reaction. Thus the equilibrium constants can be determined accurately, just as other thermodynamic properties, from a knowledge of the energy levels and degeneracies for the gas species involved. These equilibrium constants permit one to calculate the equilibrium concentrations or partial pressures of chemically reacting species that occur in gas mixtures at any given condition of pressure and temperature or volume and temperature.

Nonminimal kinetic coupled gravity: Inflation on the warped DGP brane

NASA Astrophysics Data System (ADS)

Darabi, F.; Parsiya, A.; Atazadeh, K.

2016-03-01

We consider the nonminimally kinetic coupled version of DGP brane model, where the kinetic term of the scalar field is coupled to the metric and Einstein tensor on the brane by a coupling constant ζ. We obtain the corresponding field equations, using the Friedmann-Robertson-Walker metric and the perfect fluid, and study the inflationary scenario to confront the numerical analysis of six typical scalar field potentials with the current observational results. We find that among the suggested potentials and coupling constants, subject to the e-folding N = 60, the potentials V (ϕ) = σϕ, V (ϕ) = σϕ2 and V (ϕ) = σϕ3 provide the best fits with both Planck+WP+highL data and Planck+WP+highL+BICEP2 data.

Instanton rate constant calculations close to and above the crossover temperature.

PubMed

McConnell, Sean; Kästner, Johannes

2017-11-15

Canonical instanton theory is known to overestimate the rate constant close to a system-dependent crossover temperature and is inapplicable above that temperature. We compare the accuracy of the reaction rate constants calculated using recent semi-classical rate expressions to those from canonical instanton theory. We show that rate constants calculated purely from solving the stability matrix for the action in degrees of freedom orthogonal to the instanton path is not applicable at arbitrarily low temperatures and use two methods to overcome this. Furthermore, as a by-product of the developed methods, we derive a simple correction to canonical instanton theory that can alleviate this known overestimation of rate constants close to the crossover temperature. The combined methods accurately reproduce the rate constants of the canonical theory along the whole temperature range without the spurious overestimation near the crossover temperature. We calculate and compare rate constants on three different reactions: H in the Müller-Brown potential, methylhydroxycarbene → acetaldehyde and H 2  + OH → H + H 2 O. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

Elastic constants and pressure derivative of elastic constants of Si1-xGex solid solution

NASA Astrophysics Data System (ADS)

Jivani, A. R.; Baria, J. K.; Vyas, P. S.; Jani, A. R.

2013-02-01

Elastic properties of Si1-xGex solid solution with arbitrary (atomic) concentration (x) are studied using the pseudo-alloy atom model based on the pseudopotential theory and on the higher-order perturbation scheme with the application of our own proposed model potential. We have used local-field correction function proposed by Sarkar et al to study Si-Ge system. The Elastic constants and pressure derivatives of elastic constants of the solid solution is investigated with different concentration x of Ge. It is found in the present study that the calculated numerical values of the aforesaid physical properties of Si-Ge system are function of x. The elastic constants (C11, C12 and C44) decrease linearly with increase in concentration x and pressure derivative of elastic constants (C11, C12 and C44) increase with the concentration x of Ge. This study provides better set of theoretical results for such solid solution for further comparison either with theoretical or experimental results.

Evaluation of the constant potential method in simulating electric double-layer capacitors

NASA Astrophysics Data System (ADS)

Wang, Zhenxing; Yang, Yang; Olmsted, David L.; Asta, Mark; Laird, Brian B.

2014-11-01

A major challenge in the molecular simulation of electric double layer capacitors (EDLCs) is the choice of an appropriate model for the electrode. Typically, in such simulations the electrode surface is modeled using a uniform fixed charge on each of the electrode atoms, which ignores the electrode response to local charge fluctuations in the electrolyte solution. In this work, we evaluate and compare this Fixed Charge Method (FCM) with the more realistic Constant Potential Method (CPM), [S. K. Reed et al., J. Chem. Phys. 126, 084704 (2007)], in which the electrode charges fluctuate in order to maintain constant electric potential in each electrode. For this comparison, we utilize a simplified LiClO4-acetonitrile/graphite EDLC. At low potential difference (ΔΨ ⩽ 2 V), the two methods yield essentially identical results for ion and solvent density profiles; however, significant differences appear at higher ΔΨ. At ΔΨ ⩾ 4 V, the CPM ion density profiles show significant enhancement (over FCM) of "inner-sphere adsorbed" Li+ ions very close to the electrode surface. The ability of the CPM electrode to respond to local charge fluctuations in the electrolyte is seen to significantly lower the energy (and barrier) for the approach of Li+ ions to the electrode surface.

Correlation potential of a test ion near a strongly charged plate.

PubMed

Lu, Bing-Sui; Xing, Xiangjun

2014-03-01

We analytically calculate the correlation potential of a test ion near a strongly charged plate inside a dilute m:-n electrolyte. We do this by calculating the electrostatic Green's function in the presence of a nonlinear background potential, the latter having been obtained using the nonlinear Poisson-Boltzmann theory. We consider the general case where the dielectric constants of the plate and the electrolyte are distinct. The following generic results emerge from our analyses: (1) If the distance to the plate Δz is much larger than a Gouy-Chapman length, the plate surface will behave effectively as an infinitely charged surface, and the dielectric constant of the plate effectively plays no role. (2) If Δz is larger than a Gouy-Chapman length but shorter than a Debye length, the correlation potential can be interpreted in terms of an image charge that is three times larger than the source charge. This behavior is independent of the valences of the ions. (3) The Green's function vanishes inside the plate if the surface charge density is infinitely large; hence the electrostatic potential is constant there. In this respect, a strongly charged plate behaves like a conductor plate. (4) If Δz is smaller than a Gouy-Chapman length, the correlation potential is dominated by the conventional image charge due to the dielectric discontinuity at the interface. (5) If Δz is larger than a Debye length, the leading order behavior of the correlation potential will depend on the valences of the ions in the electrolyte. Furthermore, inside an asymmetric electrolyte, the correlation potential is singly screened, i.e., it undergoes exponential decay with a decay width equal to the Debye length.

Quantum dynamics in phase space: Moyal trajectories 2

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

Braunss, G.

Continuing a previous paper [G. Braunss, J. Phys. A: Math. Theor. 43, 025302 (2010)] where we had calculated Planck-Constant-Over-Two-Pi {sup 2}-approximations of quantum phase space viz. Moyal trajectories of examples with one and two degrees of freedom, we present in this paper the calculation of Planck-Constant-Over-Two-Pi {sup 2}-approximations for four examples: a two-dimensional Toda chain, the radially symmetric Schwarzschild field, and two examples with three degrees of freedom, the latter being the nonrelativistic spherically Coulomb potential and the relativistic cylinder symmetrical Coulomb potential with a magnetic field H. We show in particular that an Planck-Constant-Over-Two-Pi {sup 2}-approximation of the nonrelativisticmore » Coulomb field has no singularity at the origin (r= 0) whereas the classical trajectories are singular at r= 0. In the third example, we show in particular that for an arbitrary function {gamma}(H, z) the expression {beta}{identical_to}p{sub z}+{gamma}(H, z) is classically ( Planck-Constant-Over-Two-Pi = 0) a constant of motion, whereas for Planck-Constant-Over-Two-Pi {ne} 0 this holds only if {gamma}(H, z) is an arbitrary polynomial of second order in z. This statement is shown to extend correspondingly to a cylinder symmetrical Schwarzschild field with a magnetic field. We exhibit in detail a number of properties of the radially symmetric Schwarzschild field. We exhibit finally the problems of the nonintegrable Henon-Heiles Hamiltonian and give a short review of the regular Hilbert space representation of Moyal operators.« less

The vibrational dependence of dissociative recombination: Rate constants for N{sub 2}{sup +}

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

Guberman, Steven L., E-mail: slg@sci.org

Dissociative recombination rate constants are reported with electron temperature dependent uncertainties for the lowest 5 vibrational levels of the N{sub 2}{sup +} ground state. The rate constants are determined from ab initio calculations of potential curves, electronic widths, quantum defects, and cross sections. At 100 K electron temperature, the rate constants overlap with the exception of the third vibrational level. At and above 300 K, the rate constants for excited vibrational levels are significantly smaller than that for the ground level. It is shown that any experimentally determined total rate constant at 300 K electron temperature that is smaller thanmore » 2.0 × 10{sup −7} cm{sup 3}/s is likely to be for ions that have a substantially excited vibrational population. Using the vibrational level specific rate constants, the total rate constant is in very good agreement with that for an excited vibrational distribution found in a storage ring experiment. It is also shown that a prior analysis of a laser induced fluorescence experiment is quantitatively flawed due to the need to account for reactions with unknown rate constants. Two prior calculations of the dissociative recombination rate constant are shown to be inconsistent with the cross sections upon which they are based. The rate constants calculated here contribute to the resolution of a 30 year old disagreement between modeled and observed N{sub 2}{sup +} ionospheric densities.« less

Partial compilation and revision of basic data in the WATEQ programs

USGS Publications Warehouse

Nordstrom, D. Kirk; Valentine, S.D.; Ball, J.W.; Plummer, Niel; Jones, B.F.

1984-01-01

Several portions of the basic data in the WATEQ series of computer programs (WATEQ, WATEQF, WATEQ2, WATEQ3, and PHREEQE) are compiled. The density and dielectric constant of water and their temperature dependence are evaluated for the purpose of updating the Debye-Huckel solvent parameters in the activity coefficient equations. The standard state thermodynamic properties of the Fe2+ and Fe3+ aqueous ions are refined. The main portion of this report is a comprehensive listing of aluminum hydrolysis constants, aluminum fluoride, aluminum sulfate, calcium chloride, magnesium chloride, potassium sulfate and sodium sulfate stability constants, solubility product constants for gibbsite and amorphous aluminum hydroxide, and the standard electrode potentials for Fe (s)/Fe2+(aq) and Fe2 +(aq)/Fe3+(aq). (USGS)

Cosmological constant is a conserved charge

NASA Astrophysics Data System (ADS)

Chernyavsky, Dmitry; Hajian, Kamal

2018-06-01

Cosmological constant can always be considered as the on-shell value of a top form in gravitational theories. The top form is the field strength of a gauge field, and the theory enjoys a gauge symmetry. We show that cosmological constant is the charge of the global part of the gauge symmetry, and is conserved irrespective of the dynamics of the metric and other fields. In addition, we introduce its conjugate chemical potential, and prove the generalized first law of thermodynamics which includes variation of cosmological constant as a conserved charge. We discuss how our new term in the first law is related to the volume–pressure term. In parallel with the seminal Wald entropy, this analysis suggests that pressure can also be considered as a conserved charge.

Functionality of bismuth sulfide quantum dots/wires-glass nanocomposite as an optical current sensor with enhanced Verdet constant

NASA Astrophysics Data System (ADS)

Panmand, Rajendra P.; Kumar, Ganapathy; Mahajan, Satish M.; Kulkarni, Milind V.; Amalnerkar, D. P.; Kale, Bharat B.; Gosavi, Suresh. W.

2011-02-01

We report optical studies with magneto-optic properties of Bi2S3 quantum dot/wires-glass nanocomposite. The size of the Q-dot was observed to be in the range 3-15 nm along with 11 nm Q-wires. Optical study clearly demonstrated the size quantization effect with drastic band gap variation with size. Faraday rotation tests on the glass nanocomposites show variation in Verdet constant with Q-dot size. Bi2S3 Q-dot/wires glass nanocomposite demonstrated 190 times enhanced Verdet constant compared to the host glass. Prima facie observations exemplify the significant enhancement in Verdet constant of Q-dot glass nanocomposites and will have potential application in magneto-optical devices.

Scalar field and time varying cosmological constant in f(R,T) gravity for Bianchi type-I universe

NASA Astrophysics Data System (ADS)

Singh, G. P.; Bishi, Binaya K.; Sahoo, P. K.

2016-04-01

In this article, we have analysed the behaviour of scalar field and cosmological constant in $f(R,T)$ theory of gravity. Here, we have considered the simplest form of $f(R,T)$ i.e. $f(R,T)=R+2f(T)$, where $R$ is the Ricci scalar and $T$ is the trace of the energy momentum tensor and explored the spatially homogeneous and anisotropic Locally Rotationally Symmetric (LRS) Bianchi type-I cosmological model. It is assumed that the Universe is filled with two non-interacting matter sources namely scalar field (normal or phantom) with scalar potential and matter contribution due to $f(R,T)$ action. We have discussed two cosmological models according to power law and exponential law of the volume expansion along with constant and exponential scalar potential as sub models. Power law models are compatible with normal (quintessence) and phantom scalar field whereas exponential volume expansion models are compatible with only normal (quintessence) scalar field. The values of cosmological constant in our models are in agreement with the observational results. Finally, we have discussed some physical and kinematical properties of both the models.

Reduced-Dimensionality Semiclassical Transition State Theory: Application to Hydrogen Atom Abstraction and Exchange Reactions of Hydrocarbons.

PubMed

Greene, Samuel M; Shan, Xiao; Clary, David C

2015-12-17

Quantum mechanical methods for calculating rate constants are often intractable for reactions involving many atoms. Semiclassical transition state theory (SCTST) offers computational advantages over these methods but nonetheless scales exponentially with the number of degrees of freedom (DOFs) of the system. Here we present a method with more favorable scaling, reduced-dimensionality SCTST (RD SCTST), that treats only a subset of DOFs of the system explicitly. We apply it to three H abstraction and exchange reactions for which two-dimensional potential energy surfaces (PESs) have previously been constructed and evaluated using RD quantum scattering calculations. We differentiated these PESs to calculate harmonic frequencies and anharmonic constants, which were then used to calculate cumulative reaction probabilities and rate constants by RD SCTST. This method yielded rate constants in good agreement with quantum scattering results. Notably, it performed well for a heavy-light-heavy reaction, even though it does not explicitly account for corner-cutting effects. Recent extensions to SCTST that improve its treatment of deep tunneling were also evaluated within the reduced-dimensionality framework. The success of RD SCTST in this study suggests its potential applicability to larger systems.

Direct measurements of forces between different charged colloidal particles and their prediction by the theory of Derjaguin, Landau, Verwey, and Overbeek (DLVO)

NASA Astrophysics Data System (ADS)

Ruiz-Cabello, F. Javier Montes; Maroni, Plinio; Borkovec, Michal

2013-06-01

Force measurements between three types of latex particles of diameters down to 1 μm with sulfate and carboxyl surface functionalities were carried out with the multi-particle colloidal probe technique. The experiments were performed in monovalent electrolyte up to concentrations of about 5 mM. The force profiles could be quantified with the theory of Derjaguin, Landau, Verwey, and Overbeek (DLVO) by invoking non-retarded van der Waals forces and the Poisson-Boltzmann description of double layer forces within the constant regulation approximation. The forces measured in the symmetric systems were used to extract particle and surface properties, namely, the Hamaker constant, surface potentials, and regulation parameters. The regulation parameter is found to be independent of solution composition. With these values at hand, the DLVO theory is capable to accurately predict the measured forces in the asymmetric systems down to distances of 2-3 nm without adjustable parameters. This success indicates that DLVO theory is highly reliable to quantify interaction forces in such systems. However, charge regulation effects are found to be important, and they must be considered to obtain correct description of the forces. The use of the classical constant charge or constant potential boundary conditions may lead to erroneous results. To make reliable predictions of the force profiles, the surface potentials must be extracted from direct force measurements too. For highly charged surfaces, the commonly used electrophoresis techniques are found to yield incorrect estimates of this quantity.

Direct measurements of forces between different charged colloidal particles and their prediction by the theory of Derjaguin, Landau, Verwey, and Overbeek (DLVO).

PubMed

Montes Ruiz-Cabello, F Javier; Maroni, Plinio; Borkovec, Michal

2013-06-21

Force measurements between three types of latex particles of diameters down to 1 μm with sulfate and carboxyl surface functionalities were carried out with the multi-particle colloidal probe technique. The experiments were performed in monovalent electrolyte up to concentrations of about 5 mM. The force profiles could be quantified with the theory of Derjaguin, Landau, Verwey, and Overbeek (DLVO) by invoking non-retarded van der Waals forces and the Poisson-Boltzmann description of double layer forces within the constant regulation approximation. The forces measured in the symmetric systems were used to extract particle and surface properties, namely, the Hamaker constant, surface potentials, and regulation parameters. The regulation parameter is found to be independent of solution composition. With these values at hand, the DLVO theory is capable to accurately predict the measured forces in the asymmetric systems down to distances of 2-3 nm without adjustable parameters. This success indicates that DLVO theory is highly reliable to quantify interaction forces in such systems. However, charge regulation effects are found to be important, and they must be considered to obtain correct description of the forces. The use of the classical constant charge or constant potential boundary conditions may lead to erroneous results. To make reliable predictions of the force profiles, the surface potentials must be extracted from direct force measurements too. For highly charged surfaces, the commonly used electrophoresis techniques are found to yield incorrect estimates of this quantity.

Fate of global symmetries in the Universe: QCD axion, quintessential axion and trans-Planckian inflaton decay constant

NASA Astrophysics Data System (ADS)

Kim, Jihn E.; Nam, Soonkeon; Semetzidis, Yannis K.

2018-01-01

Pseudoscalars appearing in particle physics are reviewed systematically. From the fundamental point of view at an ultraviolet completed theory, they can be light if they are realized as pseudo-Goldstone bosons of some spontaneously broken global symmetries. The spontaneous breaking scale is parametrized by the decay constant f. The global symmetry is defined by the lowest order terms allowed in the effective theory consistent with the gauge symmetry in question. Since any global symmetry is known to be broken at least by quantum gravitational effects, all pseudoscalars should be massive. The mass scale is determined by f and the explicit breaking terms ΔV in the effective potential and also anomaly terms ΔΛG4 for some non-Abelian gauge groups G. The well-known example by non-Abelian gauge group breaking is the potential for the “invisible” QCD axion, via the Peccei-Quinn symmetry, which constitutes a major part of this review. Even if there is no breaking terms from gauge anomalies, there can be explicit breaking terms ΔV in the potential in which case the leading term suppressed by f determines the pseudoscalar mass scale. If the breaking term is extremely small and the decay constant is trans-Planckian, the corresponding pseudoscalar can be a candidate for a “quintessential axion.” In general, (ΔV )1/4 is considered to be smaller than f, and hence the pseudo-Goldstone boson mass scales are considered to be smaller than the decay constants. In such a case, the potential of the pseudo-Goldstone boson at the grand unification scale is sufficiently flat near the top of the potential that it can be a good candidate for an inflationary model, which is known as “natural inflation.” We review all these ideas in the bosonic collective motion framework.

Elongational flow of polymer melts at constant strain rate, constant stress and constant force

NASA Astrophysics Data System (ADS)

Wagner, Manfred H.; Rolón-Garrido, Víctor H.

2013-04-01

Characterization of polymer melts in elongational flow is typically performed at constant elongational rate or rarely at constant tensile stress conditions. One of the disadvantages of these deformation modes is that they are hampered by the onset of "necking" instabilities according to the Considère criterion. Experiments at constant tensile force have been performed even more rarely, in spite of the fact that this deformation mode is free from necking instabilities and is of considerable industrial relevance as it is the correct analogue of steady fiber spinning. It is the objective of the present contribution to present for the first time a full experimental characterization of a long-chain branched polyethylene melt in elongational flow. Experiments were performed at constant elongation rate, constant tensile stress and constant tensile force by use of a Sentmanat Extensional Rheometer (SER) in combination with an Anton Paar MCR301 rotational rheometer. The accessible experimental window and experimental limitations are discussed. The experimental data are modelled by using the Wagner I model. Predictions of the steady-start elongational viscosity in constant strain rate and creep experiments are found to be identical, albeit only by extrapolation of the experimental data to Hencky strains of the order of 6. For constant stress experiments, a minimum in the strain rate and a corresponding maximum in the elongational viscosity is found at a Hencky strain of the order of 3, which, although larger than the steady-state value, follows roughly the general trend of the steady-state elongational viscosity. The constitutive analysis also reveals that constant tensile force experiments indicate a larger strain hardening potential than seen in constant elongation rate or constant tensile stress experiments. This may be indicative of the effect of necking under constant elongation rate or constant tensile stress conditions according to the Considère criterion.

Enhanced effect of temporal variation of the fine structure constant and the strong interaction in 229Th.

PubMed

Flambaum, V V

2006-09-01

The relative effects of the variation of the fine structure constant alpha = e2/variant Planck's over 2pi c and the dimensionless strong interaction parameter m(q)/LambdaQCD are enhanced by 5-6 orders of magnitude in a very narrow ultraviolet transition between the ground and the first excited states in the 229Th nucleus. It may be possible to investigate this transition with laser spectroscopy. Such an experiment would have the potential of improving the sensitivity to temporal variation of the fundamental constants by many orders of magnitude.

A Conditionally Integrable Bi-confluent Heun Potential Involving Inverse Square Root and Centrifugal Barrier Terms

NASA Astrophysics Data System (ADS)

Ishkhanyan, Tigran A.; Krainov, Vladimir P.; Ishkhanyan, Artur M.

2018-05-01

We present a conditionally integrable potential, belonging to the bi-confluent Heun class, for which the Schrödinger equation is solved in terms of the confluent hypergeometric functions. The potential involves an attractive inverse square root term x-1/2 with arbitrary strength and a repulsive centrifugal barrier core x-2 with the strength fixed to a constant. This is a potential well defined on the half-axis. Each of the fundamental solutions composing the general solution of the Schrödinger equation is written as an irreducible linear combination, with non-constant coefficients, of two confluent hypergeometric functions. We present the explicit solution in terms of the non-integer order Hermite functions of scaled and shifted argument and discuss the bound states supported by the potential. We derive the exact equation for the energy spectrum and approximate that by a highly accurate transcendental equation involving trigonometric functions. Finally, we construct an accurate approximation for the bound-state energy levels.

New Ways of Treating Data for Diatomic Molecule 'shelf' and Double-Minimum States

NASA Astrophysics Data System (ADS)

Le Roy, Robert J.; Tao, Jason; Khanna, Shirin; Pashov, Asen; Tellinghuisen, Joel

2017-06-01

Electronic states whose potential energy functions have 'shelf' or double-minimum shapes have always presented special challenges because, as functions of vibrational quantum number, the vibrational energies/spacings and inertial rotational constants either have an abrupt change of character with discontinuous slope, or past a given point, become completely chaotic. The present work shows that a `traditional' methodology developed for deep `regular' single-well potentials can also provide accurate `parameter-fit' descriptions of the v-dependence of the vibrational energies and rotational constants of shelf-state potentials that allow a conventional RKR calculation of their Potential energy functions. It is also shown that a merging of Pashov's uniquely flexible 'spline point-wise' potential function representation with Le Roy's `Morse/Long-Range' (MLR) analytic functional form which automatically incorporates the correct theoretically known long-range form, yields an analytic function that incorporates most of the advantages of both approaches. An illustrative application of this method to data to a double-minimum state of Na_2 will be described.

Interatomic potential to study plastic deformation in tungsten-rhenium alloys

NASA Astrophysics Data System (ADS)

Bonny, G.; Bakaev, A.; Terentyev, D.; Mastrikov, Yu. A.

2017-04-01

In this work, an interatomic potential for the W-Re system is fitted and benchmarked against experimental and density functional theory (DFT) data, of which part are generated in this work. Having in mind studies related to the plasticity of W-Re alloys under irradiation, emphasis is put on fitting point-defect properties, elastic constants, and dislocation properties. The developed potential can reproduce the mechanisms responsible for the experimentally observed softening, i.e., decreasing shear moduli, decreasing Peierls barrier, and asymmetric screw dislocation core structure with increasing Re content in W-Re solid solutions. In addition, the potential predicts elastic constants in reasonable agreement with DFT data for the phases forming non-coherent precipitates (σ- and χ-phases) in W-Re alloys. In addition, the mechanical stability of the different experimentally observed phases is verified in the temperature range of interest (700-1500 K). As a conclusion, the presented potential provides an excellent tool to study plasticity in W-Re alloys at the atomic level.

Rate dependency of delayed rectifier currents during the guinea-pig ventricular action potential

PubMed Central

Rocchetti, Marcella; Besana, Alessandra; Gurrola, Georgina B; Possani, Lourival D; Zaza, Antonio

2001-01-01

The action potential clamp technique was exploited to evaluate the rate dependency of delayed rectifier currents (IKr and IKs) during physiological electrical activity. IKr and IKs were measured in guinea-pig ventricular myocytes at pacing cycle lengths (CL) of 1000 and 250 ms.A shorter CL, with the attendant changes in action potential shape, was associated with earlier activation and increased magnitude of both IKr and IKs. Nonetheless, the relative contributions of IKr and IKs to total transmembrane current were independent of CL.Shortening of diastolic interval only (constant action potential shape) enhanced IKs, but not IKr.IKr was increased by a change in the action potential shape only (constant diastolic interval).In ramp clamp experiments, IKr amplitude was directly proportional to repolarization rate at values within the low physiological range (< 1.0 V s−1); at higher repolarization rates proportionality became shallower and finally reversed.When action potential duration (APD) was modulated by constant current injection (I-clamp), repolarization rates > 1.0 V s−1 were associated with a reduced effect of IKr block on APD. The effect of changes in repolarization rate was independent of CL and occurred in the presence of IKs blockade.In spite of its complexity, the behaviour of IKr was accurately predicted by a numerical model based entirely on known kinetic properties of the current.Both IKr and IKs may be increased at fast heart rates, but this may occur through completely different mechanisms. The mechanisms identified are such as to contribute to abnormal rate dependency of repolarization in prolonged repolarization syndromes. PMID:11483703

Lifespan metabolic potential of the unicellular organisms expressed by Boltzmann constant, absolute temperature and proton mass

NASA Astrophysics Data System (ADS)

Atanasov, Atanas Todorov

2016-12-01

The unicellular organisms and phages are the first appeared fundamental living organisms on the Earth. The total metabolic energy (Els, J) of these organisms can be expressed by their lifespan metabolic potential (Als, J/kg) and body mass (M, kg): Els =Als M. In this study we found a different expression - by Boltzmann's constant (k, J/K), nucleon mass (mp+, kg) of protons (and neutrons), body mass (M, kg) of organism or mass (Ms) of biomolecules (proteins, nucleotides, polysaccharides and lipids) building organism, and the absolute temperature (T, K). The found equations are: Els= (M/mp+)kT for phages and Els=(Ms/mp+)kT for the unicellular organisms. From these equations the lifespan metabolic potential can be expressed as: Als=Els/M= (k/mp+)T for phages and Als=Els/M= (k/3.3mp+)T for unicellular organisms. The temperature-normated lifespan metabolic potential (Als/T, J/K.kg) is equals to the ratio between Boltzmann's constant and nucleon mass: Als/T=k/mp+ for phages and Als/T=k/3.3mp+ for unicellular organisms. The numerical value of the k/mp+ ratio is equals to 8.254×103 J/K.kg, and the numerical value of k/3.3mp+ ratio is equal to 2.497×103 J/K.kg. These values of temperature-normated lifespan metabolic potential could be considered fundamental for the unicellular organisms.

Phonon dispersion relation of Mg-Cu-Gd bulk metallic glasses

NASA Astrophysics Data System (ADS)

Suthar, P. H.

2016-05-01

Collective dynamics and elastic constants of bulk metallic glasses Mg65Cu25Gd10 and Mg60Cu25Gd15 are computed using the Hubbard -Beeby approach and our well recognized model potential. The important ingredients in the present study are the pair potential and local field correction functions (LFCF). The local field correction functions due to Hartree (H), Farid et al (F) and Sarkar Sen et al (S) are employed to investigation the influence of the screening effects on the longitudinal and traversed of phonon modes of glassy system. The results for the elastic constants are found to be in good agreement with experimental data.

Analytical solution of the Poisson-Nernst-Planck equations for an electrochemical system close to electroneutrality

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

Pabst, M., E-mail: M.Pabst@fz-juelich.de

2014-06-14

Single charge densities and the potential are used to describe models of electrochemical systems. These quantities can be calculated by solving a system of time dependent nonlinear coupled partial differential equations, the Poisson-Nernst-Planck equations. Assuming small deviations from the electroneutral equilibrium, the linearized and decoupled equations are solved for a radial symmetric geometry, which represents the interface between a cell and a sensor device. The densities and the potential are expressed by Fourier-Bessels series. The system considered has a ratio between the Debye-length and its geometric dimension on the order of 10{sup −4} so the Fourier-Bessel series can be approximatedmore » by elementary functions. The time development of the system is characterized by two time constants, τ{sub c} and τ{sub g}. The constant τ{sub c} describes the approach to the stationary state of the total charge and the potential. τ{sub c} is several orders of magnitude smaller than the geometry-dependent constant τ{sub g}, which is on the order of 10 ms characterizing the transition to the stationary state of the single ion densities.« less

Screening Protocol for the Electrochemical Characterization of Potential Supercapacitor Materials

DTIC Science & Technology

2009-11-01

Felix Wong; DRDC Atlantic TM 2009-279; R & D pour la défense Canada – Atlantique; Novembre 2009. Introduction ou contexte : Les forces armées ont... 13 Figure 10: The effect of active material... 13 : Typical Constant Current Charge-Discharge Curve for a 1.34 mg Electrode of PAni-2NSA/MWNT at a Constant Current of 0.2 mA

Anisotropic strange star with Tolman V potential

NASA Astrophysics Data System (ADS)

Shee, Dibyendu; Deb, Debabrata; Ghosh, Shounak; Ray, Saibal; Guha, B. K.

In this paper, we present a strange stellar model using Tolman V-type metric potential employing simplest form of the MIT bag equation of state (EOS) for the quark matter. We consider that the stellar system is spherically symmetric, compact and made of an anisotropic fluid. Choosing different values of n we obtain exact solutions of the Einstein field equations and finally conclude that for a specific value of the parameter n = 1/2, we find physically acceptable features of the stellar object. Further, we conduct different physical tests, viz., the energy condition, generalized Tolman-Oppeheimer-Volkoff (TOV) equation, Herrera’s cracking concept, etc., to confirm the physical validity of the presented model. Matching conditions provide expressions for different constants whereas maximization of the anisotropy parameter provides bag constant. By using the observed data of several compact stars, we derive exact values of some of the physical parameters and exhibit their features in tabular form. It is to note that our predicted value of the bag constant satisfies the report of CERN-SPS and RHIC.

Barrierless association of CF2 and dissociation of C2F4 by variational transition-state theory and system-specific quantum Rice–Ramsperger–Kassel theory

PubMed Central

Bao, Junwei Lucas; Zhang, Xin

2016-01-01

Bond dissociation is a fundamental chemical reaction, and the first principles modeling of the kinetics of dissociation reactions with a monotonically increasing potential energy along the dissociation coordinate presents a challenge not only for modern electronic structure methods but also for kinetics theory. In this work, we use multifaceted variable-reaction-coordinate variational transition-state theory (VRC-VTST) to compute the high-pressure limit dissociation rate constant of tetrafluoroethylene (C2F4), in which the potential energies are computed by direct dynamics with the M08-HX exchange correlation functional. To treat the pressure dependence of the unimolecular rate constants, we use the recently developed system-specific quantum Rice–Ramsperger–Kassel theory. The calculations are carried out by direct dynamics using an exchange correlation functional validated against calculations that go beyond coupled-cluster theory with single, double, and triple excitations. Our computed dissociation rate constants agree well with the recent experimental measurements. PMID:27834727

Barrierless association of CF2 and dissociation of C2F4 by variational transition-state theory and system-specific quantum Rice-Ramsperger-Kassel theory.

PubMed

Bao, Junwei Lucas; Zhang, Xin; Truhlar, Donald G

2016-11-29

Bond dissociation is a fundamental chemical reaction, and the first principles modeling of the kinetics of dissociation reactions with a monotonically increasing potential energy along the dissociation coordinate presents a challenge not only for modern electronic structure methods but also for kinetics theory. In this work, we use multifaceted variable-reaction-coordinate variational transition-state theory (VRC-VTST) to compute the high-pressure limit dissociation rate constant of tetrafluoroethylene (C 2 F 4 ), in which the potential energies are computed by direct dynamics with the M08-HX exchange correlation functional. To treat the pressure dependence of the unimolecular rate constants, we use the recently developed system-specific quantum Rice-Ramsperger-Kassel theory. The calculations are carried out by direct dynamics using an exchange correlation functional validated against calculations that go beyond coupled-cluster theory with single, double, and triple excitations. Our computed dissociation rate constants agree well with the recent experimental measurements.

Evaluating Henry's law constant of N-nitrosodimethylamine (NDMA).

PubMed

Haruta, Shinsuke; Jiao, Wentao; Chen, Weiping; Chang, Andrew C; Gan, Jay

2011-01-01

N-Nitrosodimethylamine (NDMA), a potential carcinogen, may contaminate the groundwater when the reclaimed wastewater is used for irrigation and groundwater recharge. Henry's law constant is a critical parameter to assess the fate and transport of reclaimed wastewater-borne NDMA in the soil profile. We conducted a laboratory experiment in which the change of NDMA concentration in water exposed to the atmosphere was measured with respect to time and, based on the data, obtained the dimensionless Henry's law constant (K(H)') of NDMA, at 1.0 x 10(-4). The K(H)' suggests that NDMA has a relatively high potential to volatilize in the field where NDMA-containing wastewater is used for irrigation and the volatilization loss may be a significant pathway of NDMA transport. The experiment was based on the two boundary-layer approach of mass transfer at the atmosphere-water interface. It is an expedient method to delineate K(H)' for volatile or semi-volatile compounds present in water at low concentrations.

A procedure to find thermodynamic equilibrium constants for CO2 and CH4 adsorption on activated carbon.

PubMed

Trinh, T T; van Erp, T S; Bedeaux, D; Kjelstrup, S; Grande, C A

2015-03-28

Thermodynamic equilibrium for adsorption means that the chemical potential of gas and adsorbed phase are equal. A precise knowledge of the chemical potential is, however, often lacking, because the activity coefficient of the adsorbate is not known. Adsorption isotherms are therefore commonly fitted to ideal models such as the Langmuir, Sips or Henry models. We propose here a new procedure to find the activity coefficient and the equilibrium constant for adsorption which uses the thermodynamic factor. Instead of fitting the data to a model, we calculate the thermodynamic factor and use this to find first the activity coefficient. We show, using published molecular simulation data, how this procedure gives the thermodynamic equilibrium constant and enthalpies of adsorption for CO2(g) on graphite. We also use published experimental data to find similar thermodynamic properties of CO2(g) and of CH4(g) adsorbed on activated carbon. The procedure gives a higher accuracy in the determination of enthalpies of adsorption than ideal models do.

Vibrational stark effects to identify ion pairing and determine reduction potentials in electrolyte-free environments

DOE PAGES

Mani, Tomoyasu; Grills, David C.; Miller, John R.

2015-01-02

A recently-developed instrument for time-resolved infrared detection following pulse radiolysis has been used to measure the ν(C≡N) IR band of the radical anion of a CN-substituted fluorene in tetrahydrofuran. Specific vibrational frequencies can exhibit distinct frequency shifts due to ion-pairing, which can be explained in the framework of the vibrational Stark effect. Measurements of the ratio of free ions and ion-pairs in different electrolyte concentrations allowed us to obtain an association constant and free energy change for ion-pairing. As a result, this new method has the potential to probe the geometry of ion-pairing and allows the reduction potentials of moleculesmore » to be determined in the absence of electrolyte in an environment of low dielectric constant.« less

On Electron-Positron Pair Production by a Spatially Inhomogeneous Electric Field

NASA Astrophysics Data System (ADS)

Chervyakov, A.; Kleinert, H.

2018-05-01

A detailed analysis of electron-positron pair creation induced by a spatially non-uniform and static electric field from vacuum is presented. A typical example is provided by the Sauter potential. For this potential, we derive the analytic expressions for vacuum decay and pair production rate accounted for the entire range of spatial variations. In the limit of a sharp step, we recover the divergent result due to the singular electric field at the origin. The limit of a constant field reproduces the classical result of Euler, Heisenberg and Schwinger, if the latter is properly averaged over the width of a spatial variation. The pair production by the Sauter potential is described for different regimes from weak to strong fields. For all these regimes, the locally constant-field rate is shown to be the upper limit.

Calculation of the acid-base equilibrium constants at the alumina/electrolyte interface from the ph dependence of the adsorption of singly charged ions (Na+, Cl-)

NASA Astrophysics Data System (ADS)

Gololobova, E. G.; Gorichev, I. G.; Lainer, Yu. A.; Skvortsova, I. V.

2011-05-01

A procedure was proposed for the calculation of the acid-base equilibrium constants at an alumina/electrolyte interface from experimental data on the adsorption of singly charged ions (Na+, Cl-) at various pH values. The calculated constants (p K {1/0}= 4.1, p K {2/0}= 11.9, p K {3/0}= 8.3, and p K {4/0}= 7.7) are shown to agree with the values obtained from an experimental pH dependence of the electrokinetic potential and the results of potentiometric titration of Al2O3 suspensions.

Deflation of the cosmological constant associated with inflation and dark energy

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

Geng, Chao-Qiang; Lee, Chung-Chi, E-mail: geng@phys.nthu.edu.tw, E-mail: chungchi@mx.nthu.edu.tw

2016-06-01

In order to solve the fine-tuning problem of the cosmological constant, we propose a simple model with the vacuum energy non-minimally coupled to the inflaton field. In this model, the vacuum energy decays to the inflaton during pre-inflation and inflation eras, so that the cosmological constant effectively deflates from the Planck mass scale to a much smaller one after inflation and plays the role of dark energy in the late-time of the universe. We show that our deflationary scenario is applicable to arbitrary slow-roll inflation models. We also take two specific inflation potentials to illustrate our results.

Ionic Current Measurements in the Squid Giant Axon Membrane

PubMed Central

Cole, Kenneth S.; Moore, John W.

1960-01-01

The concepts, experiments, and interpretations of ionic current measurements after a step change of the squid axon membrane potential require the potential to be constant for the duration and the membrane area measured. An experimental approach to this ideal has been developed. Electrometer, operational, and control amplifiers produce the step potential between internal micropipette and external potential electrodes within 40 microseconds and a few millivolts. With an internal current electrode effective resistance of 2 ohm cm.2, the membrane potential and current may be constant within a few millivolts and 10 per cent out to near the electrode ends. The maximum membrane current patterns of the best axons are several times larger but of the type described by Cole and analyzed by Hodgkin and Huxley when the change of potential is adequately controlled. The occasional obvious distortions are attributed to the marginal adequacy of potential control to be expected from the characteristics of the current electrodes and the axon. Improvements are expected only to increase stability and accuracy. No reason has been found either to question the qualitative characteristics of the early measurements or to so discredit the analyses made of them. PMID:13694548

Water Relations, Gas Exchange, and Nutrient Response to a Long Term Constant Water Deficit

NASA Technical Reports Server (NTRS)

Berry, Wade L.; Goldstein, Guillermo; Dreschel, Thomas W.; Wheeler, Raymond M.; Sager, John C.; Knott, William M.

1992-01-01

Wheat plants (Triticum aestivum) were grown for 43 days in a micro-porous tube nutrient delivery system. Roots were unable to penetrate the microporous tube, but grew on the surface and maintained capillary contact with the nutrient solution on the inside of the tube through the 5-micron pores of the porous tube. Water potential in the system was controlled at -0.4, -0.8, and -3.0 kPa by adjusting the applied pressure (hydrostatic head) to the nutrient solution flowing through the microporous tubes. A relatively small decrease in applied water potential from -0.4 to -3.0 kPa resulted in a 34% reduction of shoot growth but only a moderate reduction in the midday leaf water potential from -1.3 to -1.7 MPa. Carbon dioxide assimilation decreased and water use efficiency increased with the more negative applied water potentials, while intercellular CO2 concentration remained constant. This was associated with a decrease in stomatal conductance to water vapor from 1.90 to 0.98 mol/(sq m sec) and a decrease in total apparent hydraulic conductance from 47 to 12 (micro)mol/(sec MPa). Although the applied water potentials were in the -0.4 to -3.0 kPa range, the actual water potential perceived by the plant roots appeared to be in the range of -0.26 to -0.38 MPa as estimated by the leaf water potential of bagged plants. The amount of K, Ca, Mg, Zn, Cu, and B accumulated with each unit of transpired water increased as the applied water potential became less negative. The increase in accumulation ranged from 1.4-fold for K to 2.2-fold for B. The physiological responses observed in this study in response to small constant differences in applied water potentials were much greater than expected from either the applied water potential or the observed plant water potential. Even though the micro-porous tube may not represent natural conditions and could possibly introduce morphological and physiological artifacts, it enables a high degree of control of water potential that facilitates the investigation of many aspects of water relations not practical with other experimental systems.

Empirical Estimation of Local Dielectric Constants: Toward Atomistic Design of Collagen Mimetic Peptides

PubMed Central

Pike, Douglas H.; Nanda, Vikas

2017-01-01

One of the key challenges in modeling protein energetics is the treatment of solvent interactions. This is particularly important in the case of peptides, where much of the molecule is highly exposed to solvent due to its small size. In this study, we develop an empirical method for estimating the local dielectric constant based on an additive model of atomic polarizabilities. Calculated values match reported apparent dielectric constants for a series of Staphylococcus aureus nuclease mutants. Calculated constants are used to determine screening effects on Coulombic interactions and to determine solvation contributions based on a modified Generalized Born model. These terms are incorporated into the protein modeling platform protCAD, and benchmarked on a data set of collagen mimetic peptides for which experimentally determined stabilities are available. Computing local dielectric constants using atomistic protein models and the assumption of additive atomic polarizabilities is a rapid and potentially useful method for improving electrostatics and solvation calculations that can be applied in the computational design of peptides. PMID:25784456

Determination of the force constant of a single-beam gradient trap by measurement of backscattered light

NASA Astrophysics Data System (ADS)

Friese, M. E. J.; Rubinsztein-Dunlop, H.; Heckenberg, N. R.; Dearden, E. W.

1996-12-01

A single-beam gradient trap could potentially be used to hold a stylus for scanning force microscopy. With a view to development of this technique, we modeled the optical trap as a harmonic oscillator and therefore characterized it by its force constant. We measured force constants and resonant frequencies for 1 4- m-diameter polystyrene spheres in a single-beam gradient trap using measurements of backscattered light. Force constants were determined with both Gaussian and doughnut laser modes, with powers of 3 and 1 mW, respectively. Typical values for spring constants were measured to be between 10 6 and 4 10 6 N m. The resonant frequencies of trapped particles were measured to be between 1 and 10 kHz, and the rms amplitudes of oscillations were estimated to be around 40 nm. Our results confirm that the use of the doughnut mode for single-beam trapping is more efficient in the axial direction.

Microscopic theoretical study of frequency dependent dielectric constant of heavy fermion systems

NASA Astrophysics Data System (ADS)

Shadangi, Keshab Chandra; Rout, G. C.

2017-05-01

The dielectric polarization and the dielectric constant plays a vital role in the deciding the properties of the Heavy Fermion Systems. In the present communication we consider the periodic Anderson's Model which consists of conduction electron kinetic energy, localized f-electron kinetic energy and the hybridization between the conduction and localized electrons, besides the Coulomb correlation energy. We calculate dielectric polarization which involves two particle Green's functions which are calculated by using Zubarev's Green's function technique. Using the equations of motion of the fermion electron operators. Finally, the temperature and frequency dependent dielectric constant is calculated from the dielectric polarization function. The charge susceptibility and dielectric constant are computed numerically for different physical parameters like the position (Ef) of the f-electron level with respect to fermi level, the strength of the hybridization (V) between the conduction and localized f-electrons, Coulomb correlation potential temperature and optical phonon wave vector (q). The results will be discussed in a reference to the experimental observations of the dielectric constants.

Ro-vibrational averaging of the isotropic hyperfine coupling constant for the methyl radical

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

Adam, Ahmad Y.; Jensen, Per, E-mail: jensen@uni-wuppertal.de; Yachmenev, Andrey

2015-12-28

We present the first variational calculation of the isotropic hyperfine coupling constant of the carbon-13 atom in the CH{sub 3} radical for temperatures T = 0, 96, and 300 K. It is based on a newly calculated high level ab initio potential energy surface and hyperfine coupling constant surface of CH{sub 3} in the ground electronic state. The ro-vibrational energy levels, expectation values for the coupling constant, and its temperature dependence were calculated variationally by using the methods implemented in the computer program TROVE. Vibrational energies and vibrational and temperature effects for coupling constant are found to be in verymore » good agreement with the available experimental data. We found, in agreement with previous studies, that the vibrational effects constitute about 44% of the constant’s equilibrium value, originating mainly from the large amplitude out-of-plane bending motion and that the temperature effects play a minor role.« less

Simulation of action potential propagation in plants.

PubMed

Sukhov, Vladimir; Nerush, Vladimir; Orlova, Lyubov; Vodeneev, Vladimir

2011-12-21

Action potential is considered to be one of the primary responses of a plant to action of various environmental factors. Understanding plant action potential propagation mechanisms requires experimental investigation and simulation; however, a detailed mathematical model of plant electrical signal transmission is absent. Here, the mathematical model of action potential propagation in plants has been worked out. The model is a two-dimensional system of excitable cells; each of them is electrically coupled with four neighboring ones. Ion diffusion between excitable cell apoplast areas is also taken into account. The action potential generation in a single cell has been described on the basis of our previous model. The model simulates active and passive signal transmission well enough. It has been used to analyze theoretically the influence of cell to cell electrical conductivity and H(+)-ATPase activity on the signal transmission in plants. An increase in cell to cell electrical conductivity has been shown to stimulate an increase in the length constant, the action potential propagation velocity and the temperature threshold, while the membrane potential threshold being weakly changed. The growth of H(+)-ATPase activity has been found to induce the increase of temperature and membrane potential thresholds and the reduction of the length constant and the action potential propagation velocity. Copyright © 2011 Elsevier Ltd. All rights reserved.

Possible evolution of a bouncing universe in cosmological models with non-minimally coupled scalar fields

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

Pozdeeva, Ekaterina O.; Vernov, Sergey Yu.; Skugoreva, Maria A.

2016-12-01

We explore dynamics of cosmological models with bounce solutions evolving on a spatially flat Friedmann-Lemaître-Robertson-Walker background. We consider cosmological models that contain the Hilbert-Einstein curvature term, the induced gravity term with a negative coupled constant, and even polynomial potentials of the scalar field. Bounce solutions with non-monotonic Hubble parameters have been obtained and analyzed. The case when the scalar field has the conformal coupling and the Higgs-like potential with an opposite sign is studied in detail. In this model the evolution of the Hubble parameter of the bounce solution essentially depends on the sign of the cosmological constant.

Linear frictional forces cause orbits to neither circularize nor precess

NASA Astrophysics Data System (ADS)

Hamilton, B.; Crescimanno, M.

2008-06-01

For the undamped Kepler potential the lack of precession has historically been understood in terms of the Runge-Lenz symmetry. For the damped Kepler problem this result may be understood in terms of the generalization of Poisson structure to damped systems suggested recently by Tarasov (2005 J. Phys. A: Math. Gen. 38 2145). In this generalized algebraic structure the orbit-averaged Runge-Lenz vector remains a constant in the linearly damped Kepler problem to leading order in the damping coefficient. Beyond Kepler, we prove that, for any potential proportional to a power of the radius, the orbit shape and precession angle remain constant to leading order in the linear friction coefficient.

Dynamical approach to the cosmological constant.

PubMed

Mukohyama, Shinji; Randall, Lisa

2004-05-28

We consider a dynamical approach to the cosmological constant. There is a scalar field with a potential whose minimum occurs at a generic, but negative, value for the vacuum energy, and it has a nonstandard kinetic term whose coefficient diverges at zero curvature as well as the standard kinetic term. Because of the divergent coefficient of the kinetic term, the lowest energy state is never achieved. Instead, the cosmological constant automatically stalls at or near zero. The merit of this model is that it is stable under radiative corrections and leads to stable dynamics, despite the singular kinetic term. The model is not complete, however, in that some reheating is required. Nonetheless, our approach can at the very least reduce fine-tuning by 60 orders of magnitude or provide a new mechanism for sampling possible cosmological constants and implementing the anthropic principle.

Theoretical Discussion of Electron Transport Rate Constant at TCNQ / Ge and TiO2 System

NASA Astrophysics Data System (ADS)

Al-agealy, Hadi J. M.; Alshafaay, B.; Hassooni, Mohsin A.; Ashwiekh, Ahmed M.; Sadoon, Abbas K.; Majeed, Raad H.; Ghadhban, Rawnaq Q.; Mahdi, Shatha H.

2018-05-01

We have been studying and estimation the electronic transport constant at TCNQ / Ge and Tio2 interface by means of tunneling potential (TP), transport energy reorientation (TER), driving transition energy DTE and coupling coefficient constant. A simple quantum model for the transition processes was adapted to estimation and analysis depending on the quantum state for donor state |α D > and acceptor stated |α A > and assuming continuum levels of the system. Evaluation results were performed for the surfaces of Ge and Tio2 as best as for multilayer TCNQ. The results show an electronic transfer feature for electronic TCNQ density of states and a semiconductor behavior. The electronic rate constant result for both systems shows a good tool to election system in applied devices. All these results indicate the

New Signal Readout Principle for Solid-Contact Ion-Selective Electrodes.

PubMed

Vanamo, Ulriika; Hupa, Elisa; Yrjänä, Ville; Bobacka, Johan

2016-04-19

A novel approach to signal transduction concerning solid-contact ion-selective electrodes (SC-ISE) with a conducting polymer (CP) as the solid contact is investigated. The method presented here is based on constant potential coulometry, where the potential of the SC-ISE vs the reference electrode is kept constant using a potentiostat. The change in the potential at the interface between the ion-selective membrane (ISM) and the sample solution, due to the change in the activity of the primary ion, is compensated with a corresponding but opposite change in the potential of the CP solid contact. This enforced change in the potential of the solid contact results in a transient reducing/oxidizing current flow through the SC-ISE. By measuring and integrating the current needed to transfer the CP to a new state of equilibrium, the total cumulated charge that is linearly proportional to the change of the logarithm of the primary ion activity is obtained. In this work, different thicknesses of poly(3,4-ethylenedioxythiophene) (PEDOT) doped with poly(styrenesulfonate) (PSS) were used as solid contact. Also, coated wire electrodes (CWEs) were included in the study to show the general validity of the new approach. The ISM employed was selective for K(+) ions, and the selectivity of the membrane under implementation of the presented transduction mechanism was confirmed by measurements performed with a constant background concentration of Na(+) ions. A unique feature of this signal readout principle is that it allows amplification of the analytical signal by increasing the capacitance (film thickness) of the solid contact of the SC-ISE.

Atomistic modeling of high temperature uranium-zirconium alloy structure and thermodynamics

NASA Astrophysics Data System (ADS)

Moore, A. P.; Beeler, B.; Deo, C.; Baskes, M. I.; Okuniewski, M. A.

2015-12-01

A semi-empirical Modified Embedded Atom Method (MEAM) potential is developed for application to the high temperature body-centered-cubic uranium-zirconium alloy (γ-U-Zr) phase and employed with molecular dynamics (MD) simulations to investigate the high temperature thermo-physical properties of U-Zr alloys. Uranium-rich U-Zr alloys (e.g. U-10Zr) have been tested and qualified for use as metallic nuclear fuel in U.S. fast reactors such as the Integral Fast Reactor and the Experimental Breeder Reactors, and are a common sub-system of ternary metallic alloys like U-Pu-Zr and U-Zr-Nb. The potential was constructed to ensure that basic properties (e.g., elastic constants, bulk modulus, and formation energies) were in agreement with first principles calculations and experimental results. After which, slight adjustments were made to the potential to fit the known thermal properties and thermodynamics of the system. The potentials successfully reproduce the experimental melting point, enthalpy of fusion, volume change upon melting, thermal expansion, and the heat capacity of pure U and Zr. Simulations of the U-Zr system are found to be in good agreement with experimental thermal expansion values, Vegard's law for the lattice constants, and the experimental enthalpy of mixing. This is the first simulation to reproduce the experimental thermodynamics of the high temperature γ-U-Zr metallic alloy system. The MEAM potential is then used to explore thermodynamics properties of the high temperature U-Zr system including the constant volume heat capacity, isothermal compressibility, adiabatic index, and the Grüneisen parameters.

Iso-chemical potential trajectories in the P-T plane for He II

NASA Technical Reports Server (NTRS)

Maytal, B.; Nissen, J. A.; Van Sciver, S. W.

1990-01-01

Trajectories of constant chemical potential in the P-T plane serve as an integral formulation of London's equation. The trajectories are useful for analysis and synthesis of fountain effect pump performance. A family of trajectories is generated from available numerical codes.

Methane steam reforming rates over Pt, Rh and Ni(111) accounting for H tunneling and for metal lattice vibrations

NASA Astrophysics Data System (ADS)

German, Ernst D.; Sheintuch, Moshe

2017-02-01

Microkinetic models of methane steam reforming (MSR) over bare platinum and rhodium (111) surfaces are analyzed in present work using calculated rate constants. The individual rate constants are classified into three different sets: (i) rate constants of adsorption and desorption steps of CH4, H2O, CO and of H2; (ii) rate constants of dissociation and formation of A-H bonds (A = C, O, and H), and (iii) rate constants of dissociation and formation of C-O bond. The rate constants of sets (i) and (iii) are calculated using transition state theory and published thermochemical data. The rate constants of H-dissociation reactions (set (ii)) are calculated in terms of a previously-developed approach that accounts for thermal metal lattice vibrations and for H tunneling through a potential barrier of height which depends on distance of AH from a surface. Pre-exponential factors of several group (ii) steps were calculated to be usually lower than the traditional kBT/h due to tunneling effect. Surface composition and overall MSR rates over platinum and rhodium surfaces are compared with those over nickel surface showing that operating conditions strongly affect on the activity order of the catalysts.

Bicanonical ab Initio Molecular Dynamics for Open Systems.

PubMed

Frenzel, Johannes; Meyer, Bernd; Marx, Dominik

2017-08-08

Performing ab initio molecular dynamics simulations of open systems, where the chemical potential rather than the number of both nuclei and electrons is fixed, still is a challenge. Here, drawing on bicanonical sampling ideas introduced two decades ago by Swope and Andersen [ J. Chem. Phys. 1995 , 102 , 2851 - 2863 ] to calculate chemical potentials of liquids and solids, an ab initio simulation technique is devised, which introduces a fictitious dynamics of two superimposed but otherwise independent periodic systems including full electronic structure, such that either the chemical potential or the average fractional particle number of a specific chemical species can be kept constant. As proof of concept, we demonstrate that solvation free energies can be computed from these bicanonical ab initio simulations upon directly superimposing pure bulk water and the respective aqueous solution being the two limiting systems. The method is useful in many circumstances, for instance for studying heterogeneous catalytic processes taking place on surfaces where the chemical potential of reactants rather than their number is controlled and opens a pathway toward ab initio simulations at constant electrochemical potential.

Bimolecular Rate Constants for FAD-Dependent Glucose Dehydrogenase from Aspergillus terreus and Organic Electron Acceptors.

PubMed

Tsuruoka, Nozomu; Sadakane, Takuya; Hayashi, Rika; Tsujimura, Seiya

2017-03-10

The flavin adenine dinucleotide-dependent glucose dehydrogenase (FAD-GDH) from Aspergillus species require suitable redox mediators to transfer electrons from the enzyme to the electrode surface for the application of bioelectrical devices. Although several mediators for FAD-GDH are already in use, they are still far from optimum in view of potential, kinetics, sustainability, and cost-effectiveness. Herein, we investigated the efficiency of various phenothiazines and quinones in the electrochemical oxidation of FAD-GDH from Aspergillus terreus . At pH 7.0, the logarithm of the bimolecular oxidation rate constants appeared to depend on the redox potentials of all the mediators tested. Notably, the rate constant of each molecule for FAD-GDH was approximately 2.5 orders of magnitude higher than that for glucose oxidase from Aspergillus sp. The results suggest that the electron transfer kinetics is mainly determined by the formal potential of the mediator, the driving force of electron transfer, and the electron transfer distance between the redox active site of the mediator and the FAD, affected by the steric or chemical interactions. Higher k ₂ values were found for ortho-quinones than for para-quinones in the reactions with FAD-GDH and glucose oxidase, which was likely due to less steric hindrance in the active site in the case of the ortho-quinones.

Voltage dependence of acetylcholine receptor channel gating in rat myoballs

PubMed Central

1992-01-01

Whole-cell currents from nicotinic acetylcholine receptor (AChR) channels were studied in rat myoballs using a light-activated agonist to determine the voltage dependence of the macroscopic opening and closing rate constants. Myoballs were bathed in a solution containing a low concentration of the inactive isomer of the photoisomerizable azobenzene derivative, cis-Bis-Q. A light flash was then presented to produce a known concentration jump of agonist, trans-Bis-Q, across a wide range of membrane potentials in symmetrical solutions (NaCl or CsCl on both sides) or asymmetrical solutions (NaCl in the bath and CsCl in the pipette). At the low agonist concentration used in this study, the reciprocal of the macroscopic time constants gives an unambiguous measure of the effective closing rate. It showed an exponential decrease with membrane hyperpolarization between +20 and - 100 mV, but tended to level off at more depolarized and at more hyperpolarized membrane potentials. The relative effective opening rate was derived from the steady-state conductance, the single-channel conductance, and the apparent closing rate; it decreased sharply in the depolarizing region and tended to level off and then turn up in the hyperpolarizing region. The two effective rate constants were shown to depend on the first, second, and third power of membrane potential. PMID:1460456

An interference-free glucose biosensor based on an anionic redox polymer-mediated enzymatic oxidation of glucose.

PubMed

Deng, Huimin; Shen, Wei; Gao, Zhiqiang

2013-07-22

Herein a novel strategy for the construction of an amperometric biosensor for highly sensitive and selective determination of glucose is described. The biosensor is made of a biocomposite membrane of glucose oxidase (GOx) and an Os(bpy)2 (bpy=2,2'-bipyridine)-based anionic redox polymer (Os-RP) mediator. The biosensor is fabricated through the co-immobilization of GOx and the Os-RP on the surface of a glassy carbon electrode by a simple one-step chemical crosslinking process. The crosslinked Os-RP/GOx composite membrane shows excellent catalytic activity toward the oxidation of glucose. Under optimal experimental conditions, a linear correlation between the oxidation current of glucose in amperometry at 0.25 V (vs. Ag/AgCl) and glucose concentration up to 10 mM with a sensitivity of 16.5 μA mM(-1) cm(-2) and a response time <5 s. Due to the presence of anionic sulfonic acid groups in the backbone of the redox polymer, the biosensor exhibits excellent selectivity to glucose in the presence of ascorbic acid and uric acid. The low hydrophobicity of the composite membrane also effectively retards the transport of molecular oxygen within the membrane. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Finding out egyptian gods' secret using analytical chemistry: biomedical properties of egyptian black makeup revealed by amperometry at single cells.

PubMed

Tapsoba, Issa; Arbault, Stéphane; Walter, Philippe; Amatore, Christian

2010-01-15

Lead-based compounds were used during antiquity as both pigments and medicines in the formulation of makeup materials. Chemical analysis of cosmetics samples found in Egyptians tombs and the reconstitution of ancient recipes as reported by Greco-Roman authors have shown that two non-natural lead chlorides (laurionite Pb(OH)Cl and phosgenite Pb(2)Cl(2)CO(3)) were purposely synthesized and were used as fine powders in makeup and eye lotions. According to ancient Egyptian manuscripts, these were essential remedies for treating eye illness and skin ailments. This conclusion seems amazing because today we focus only on the well-recognized toxicity of lead salts. Here, using ultramicroelectrodes, we obtain new insights into the biochemical interactions between lead(II) ions and cells, which support the ancient medical use of sparingly soluble lead compounds. Submicromolar concentrations of Pb(2+) ions are shown to be sufficient for eliciting specific oxidative stress responses of keratinocytes. These consist essentially of an overproduction of nitrogen monoxide (NO degrees ). Owing to the biological role of NO degrees in stimulating nonspecific immunological defenses, one may argue that these lead compounds were deliberately manufactured and used in ancient Egyptian formulations to prevent and treat eye illnesses by promoting the action of immune cells.

Flavohemoglobin and nitric oxide detoxification in the human protozoan parasite Giardia intestinalis.

PubMed

Mastronicola, Daniela; Testa, Fabrizio; Forte, Elena; Bordi, Eugenio; Pucillo, Leopoldo Paolo; Sarti, Paolo; Giuffrè, Alessandro

2010-09-03

Flavohemoglobins (flavoHbs), commonly found in bacteria and fungi, afford protection from nitrosative stress by degrading nitric oxide (NO) to nitrate. Giardia intestinalis, a microaerophilic parasite causing one of the most common intestinal human infectious diseases worldwide, is the only pathogenic protozoon as yet identified coding for a flavoHb. By NO amperometry we show that, in the presence of NADH, the recombinant Giardia flavoHb metabolizes NO with high efficacy under aerobic conditions (TN=116+/-10s(-1) at 1microM NO, T=37 degrees C). The activity is [O(2)]-dependent and characterized by an apparent K(M,O2)=22+/-7microM. Immunoblotting analysis shows that the protein is expressed at low levels in the vegetative trophozoites of Giardia; accordingly, these cells aerobically metabolize NO with low efficacy. Interestingly, in response to nitrosative stress (24-h incubation with 5mM nitrite) flavoHb expression is enhanced and the trophozoites thereby become able to metabolize NO efficiently, the activity being sensitive to both cyanide and carbon monoxide. The NO-donors S-nitrosoglutathione (GSNO) and DETA-NONOate mimicked the effect of nitrite on flavoHb expression. We propose that physiologically flavoHb contributes to NO detoxification in G. intestinalis. Copyright 2010 Elsevier Inc. All rights reserved.

A new electrochemical sensor for highly sensitive and selective detection of nitrite in food samples based on sonochemical synthesized Calcium Ferrite (CaFe2O4) clusters modified screen printed carbon electrode.

PubMed

Balasubramanian, Paramasivam; Settu, Ramki; Chen, Shen-Ming; Chen, Tse-Wei; Sharmila, Ganapathi

2018-08-15

Herein, we report a novel, disposable electrochemical sensor for the detection of nitrite ions in food samples based on the sonochemical synthesized orthorhombic CaFe 2 O 4 (CFO) clusters modified screen printed electrode. As synthesized CFO clusters were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transformer infrared spectroscopy (FT-IR), Thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and amperometry (i-t). Under optimal condition, the CFO modified electrode displayed a rapid current response to nitrite, a linear response range from 0.016 to 1921 µM associated with a low detection limit 6.6 nM. The suggested sensor also showed the excellent sensitivity of 3.712 μA μM -1  cm -2 . Furthermore, a good reproducibility, long-term stability and excellent selectivity were also attained on the proposed sensor. In addition, the practical applicability of the sensor was investigated via meat samples, tap water and drinking water, and showed desirable recovery rate, representing its possibilities for practical application. Copyright © 2018 Elsevier Inc. All rights reserved.

Co-immobilization of gold nanoparticles with glucose oxidase to improve bioelectrocatalytic glucose oxidation

NASA Astrophysics Data System (ADS)

Aquino Neto, Sidney; Milton, Ross D.; Crepaldi, Laís B.; Hickey, David P.; de Andrade, Adalgisa R.; Minteer, Shelley D.

2015-07-01

Recently, there has been much effort in developing metal nanoparticle catalysts for fuel oxidation, as well as the development of enzymatic bioelectrocatalysts for fuel oxidation. However, there has been little study of the synergy of hybrid electrocatalytic systems. We report the preparation of hybrid bioanodes based on Au nanoparticles supported on multi-walled carbon nanotubes (MWCNTs) co-immobilized with glucose oxidase (GOx). Mediated electron transfer was achieved by two strategies: ferrocene entrapped within polypyrrole and a ferrocene-modified linear poly(ethylenimine) (Fc-LPEI) redox polymer. Electrochemical characterization of the Au nanoparticles supported on MWCNTs indicate that this catalyst exhibits an electrocatalytic response for glucose even in acidic conditions. Using the redox polymer Fc-LPEI as the mediator, voltammetric and amperometric data demonstrated that these bioanodes can efficiently achieve mediated electron transfer and also indicated higher catalytic currents with the hybrid bioelectrode. From the amperometry, the maximum current density (Jmax) achieved with the hybrid bioelectrode was 615 ± 39 μA cm-2, whereas the bioanode employing GOx only achieved a Jmax of 409 ± 26 μA cm-2. Biofuel cell tests are consistent with the electrochemical characterization, thus confirming that the addition of the metallic species into the bioanode structure can improve fuel oxidation and consequently, improve the power generated by the system.

A highly sensitive NADH sensor based on a mycelium-like nanocomposite using graphene oxide and multi-walled carbon nanotubes to co-immobilize poly(luminol) and poly(neutral red) hybrid films.

PubMed

Chiang Lin, Kuo; Yu Lai, Szu; Ming Chen, Shen

2014-08-21

Hybridization of poly(luminol) (PLM) and poly(neutral red) (PNR) has been successfully performed and further enhanced by a conductive and steric hybrid nanotemplate using graphene oxide (GO) and multi-walled carbon nanotubes (MWCNTs). The morphology of the PLM-PNR-MWCNT-GO mycelium-like nanocomposite is studied by SEM and AFM and it is found to be electroactive, pH-dependent, and stable in the electrochemical system. It shows electrocatalytic activity towards NADH with a high current response and low overpotential. Using amperometry, it has been shown to have a high sensitivity of 288.9 μA mM(-1) cm(-2) to NADH (Eapp. = +0.1 V). Linearity is estimated in a concentration range of 1.33 × 10(-8) to 1.95 × 10(-4) M with a detection limit of 1.33 × 10(-8) M (S/N = 3). Particularly, it also shows another linear range of 2.08 × 10(-4) to 5.81 × 10(-4) M with a sensitivity of 151.3 μA mM(-1) cm(-2). The hybridization and activity of PLM and PNR can be effectively enhanced by MWCNTs and GO, resulting in an active hybrid nanocomposite for determination of NADH.

Fabrication of Highly Sensitive Nonenzymatic Electrochemical H₂O₂ Sensor Based on Pt Nanoparticles Anchored Reduced Graphene Oxide.

PubMed

Dhara, Keerthy; Ramachandran, T; Nair, Bipin G; Babu, T G Satheesh

2018-06-01

A highly sensitive nonenzymatic hydrogen peroxide (H2O2) sensor was fabricated using platinum nanoparticles decorated reduced graphene oxide (Pt/rGO) nanocomposite. The Pt/rGO nanocomposite was prepared by single-step chemical reduction method. Nanocomposite was characterized by various analytical techniques including Raman spectroscopy, X-ray diffraction, field emission scanning electron microscope and high-resolution transmission electron microscopy. Screen printed electrodes (SPEs) were fabricated and the nanocomposite was cast on the working area of the SPE. Cyclic voltammetry and amperometry demonstrated that the Pt/rGO/SPE displayed much higher electrocatalytic activity towards the reduction of H2O2 than the other modified electrodes. The sensor exhibited wide linear detection range (from 10 μM to 8 mM), very high sensitivity of 1848 μA mM-1 cm-2 and a lower limit of detection of 0.06 μM. The excellent performance of Pt/rGO/SPE sensor were attributed to the reduced graphene oxide being used as an effective matrix to load a number of Pt nanoparticles and the synergistic amplification effect of the two kinds of nanomaterials. Moreover, the sensor showed remarkable features such as good reproducibility, repeatability, long-term stability, and selectivity.

N-(4-Trifluoromethylphenyl)amide group of the synthetic histamine receptor agonist inhibits nicotinic acetylcholine receptor-mediated catecholamine secretion.

PubMed

Kim, Dong-Chan; Park, Yong-Soo; Jun, Dong-Jae; Hur, Eun-Mi; Kim, Sun-Hee; Choi, Bo-Hwa; Kim, Kyong-Tai

2006-02-28

The therapeutic targeting of nicotinic receptors requires the identification of drugs that selectively activate or inhibit a limited range of nicotine acetylcholine receptors (nAChRs). In this study, we identified N-(4-trifluoromethylphenyl)amide group of the synthetic histamine receptor ligands, histamine-trifluoromethyltoluide, that act as potent inhibitors of nAChRs in bovine adrenal chromaffin cells. Catecholamine secretion induced by the nAChRs agonist, 1,1-dimethyl-4-phenylpiperazinium iodide (DMPP), was significantly inhibited by histamine-trifluoromethyltoluide. Real time carbon-fiber amperometry confirmed the ability of histamine-trifluoromethyltoluide to inhibit DMPP-induced exocytosis in single chromaffin cells. We also found that histamine-trifluoromethyltoluide inhibited DMPP-induced [Ca(2+)](i) and [Na(+)](i) increases, as well as DMPP-induced inward currents in the absence of extracellular calcium. Histamine-trifluoromethyltoluide had no effect on [(3)H]nicotine binding or on calcium increases induced by high K(+), bradykinin, veratridine, histamine, and benzoylbenzoyl ATP. Among the synthetic histamine receptor ligands, clobenpropit exhibited similarity. In addition, 4'-nitroacetanilide also significantly attenuated nAChR-mediated catecholamine secretion. In conclusion, the N-(4-trifluoromethylphenyl)amide group of the histamine-trifluoromethyltoluide might be the critical moiety in the inhibition of nAChR-mediated CA secretion.

Investigation of sulfonated polysulfone membranes as electrolyte in a passive-mode direct methanol fuel cell mini-stack

NASA Astrophysics Data System (ADS)

Lufrano, F.; Baglio, V.; Staiti, P.; Stassi, A.; Aricò, A. S.; Antonucci, V.

This paper reports on the development of polymer electrolyte membranes (PEMs) based on sulfonated polysulfone for application in a DMFC mini-stack operating at room temperature in passive mode. The sulfonated polysulfone (SPSf) with two degrees of sulfonation (57 and 66%) was synthesized by a well-known sulfonation process. SPSf membranes with different thicknesses were prepared and investigated. These membranes were characterized in terms of methanol/water uptake, proton conductivity, and fuel cell performance in a DMFC single cell and mini-stack operating at room temperature. The study addressed (a) control of the synthesis of sulfonated polysulfone, (b) optimization of the assembling procedure, (c) a short lifetime investigation and (d) a comparison of DMFC performance in active-mode operation vs. passive-mode operation. The best passive DMFC performance was 220 mW (average cell power density of about 19 mW cm -2), obtained with a thin SPSf membrane (70 μm) at room temperature, whereas the performance of the same membrane-based DMFC in active mode was 38 mW cm -2. The conductivity of this membrane, SPSf (IEC = 1.34 mequiv. g -1) was 2.8 × 10 -2 S cm -1. A preliminary short-term test (200 min) showed good stability during chrono-amperometry measurements.

Graphene oxide electrocatalyst on MnO2 air cathode as an efficient electron pump for enhanced oxygen reduction in alkaline solution

NASA Astrophysics Data System (ADS)

Basirun, Wan Jeffrey; Sookhakian, Mehran; Baradaran, Saeid; Endut, Zulkarnain; Mahmoudian, Mohammad Reza; Ebadi, Mehdi; Yousefi, Ramin; Ghadimi, Hanieh; Ahmed, Sohail

2015-03-01

Graphene oxide (GO) was deposited on the surface of a MnO2 air cathode by thermal evaporation at 50°C from a GO colloidal suspension. Fourier transformed infrared spectroscopy and field emission scanning electron microscopy confirmed the presence of GO on the MnO2 air cathode (GO-MnO2). Voltammetry and chrono-amperometry showed increased currents for the oxygen reduction reaction (ORR) in 6 M KOH solution for GO-MnO2 compared to the MnO2 cathode. The GO-MnO2 was used as an air cathode in an alkaline tin-air cell and produced a maximum power density of 13 mW cm-2, in contrast to MnO2, which produced a maximum power density of 9.2 mW cm-2. The electrochemical impedance spectroscopy results suggest that the chemical step for the ORR is the rate determining step, as proposed earlier by different researchers. It is suggested that the presence of GO and electrochemically reduced graphene oxide (ERGO) on the MnO2 surface are responsible for the increased rate of this step, whereby GO and ERGO accelerate the process of electron donation to the MnO2 and to adsorbed oxygen atoms.

Enzymatically enhanced collisions on ultramicroelectrodes for specific and rapid detection of individual viruses

PubMed Central

Dick, Jeffrey E.; Hilterbrand, Adam T.; Strawsine, Lauren M.; Upton, Jason W.; Bard, Allen J.

2016-01-01

We report the specific collision of a single murine cytomegalovirus (MCMV) on a platinum ultramicroelectrode (UME, radius of 1 μm). Antibody directed against the viral surface protein glycoprotein B functionalized with glucose oxidase (GOx) allowed for specific detection of the virus in solution and a biological sample (urine). The oxidation of ferrocene methanol to ferrocenium methanol was carried out at the electrode surface, and the ferrocenium methanol acted as the cosubstrate to GOx to catalyze the oxidation of glucose to gluconolactone. In the presence of glucose, the incident collision of a GOx-covered virus onto the UME while ferrocene methanol was being oxidized produced stepwise increases in current as observed by amperometry. These current increases were observed due to the feedback loop of ferrocene methanol to the surface of the electrode after GOx reduces ferrocenium methanol back to ferrocene. Negative controls (i) without glucose, (ii) with an irrelevant virus (murine gammaherpesvirus 68), and (iii) without either virus do not display these current increases. Stepwise current decreases were observed for the prior two negative controls and no discrete events were observed for the latter. We further apply this method to the detection of MCMV in urine of infected mice. The method provides for a selective, rapid, and sensitive detection technique based on electrochemical collisions. PMID:27217569

Simultaneous detection of antibacterial sulfonamides in a microfluidic device with amperometry.

PubMed

Won, So-Young; Chandra, Pranjal; Hee, Tak Seong; Shim, Yoon-Bo

2013-01-15

A highly sensitive and robust method for simultaneous detection of five sulfonamide drugs is developed by integrating the preconcentration and separation steps in a microfluidic device. An ampetrometry is performed for the selective detection of sulfonamides using an aluminum oxide-gold nanoparticle (Al(2)O(3)-AuNPs) modified carbon paste (CP) electrode at the end of separation channel. The preconcentration capacity of the channel is enhanced by using the field amplified sample stacking and the field amplified sample injection techniques. The experimental parameters affecting the analytical performances, such as pH, % of Al(2)O(3), volume of AuNPs, buffer concentration, and water plug length are optimized. A reproducible response is observed during the multiple injections of samples with RSDs<4%. The calibration plots are linear with the correlation coefficient between 0.991 and 0.997 over the range between 0.01 and 2025pM. The detection limits of five drugs are determined to be between 0.91 (±0.03) and 2.21 (±0.09)fM. The interference effects of common biological compounds are also investigated and the applicability of the method to the direct analysis of sulfonamides in real meat samples is successfully demonstrated. Long term stability of the modified electrode was also investigated. Copyright © 2012 Elsevier B.V. All rights reserved.

Eco-synthesis of graphene and its use in dihydronicotinamide adenine dinucleotide sensing.

PubMed

Amouzadeh Tabrizi, Mahmoud; Jalilzadeh Azar, Somayeh; Nadali Varkani, Javad

2014-09-01

In this paper, we report a green and eco-friendly approach to synthesize reduced graphene oxide (rGO) via a mild hydrothermal process using malt as a reduced agent. The proposed method is based on the reduction of graphene oxide (GO) in malt solution by making use of the reducing capability of phenolic compounds contained in malt solution. The obtained rGO was characterized by atomic force microscopy (AFM), ultraviolet-visible (UV-vis) absorption spectroscopy, X-ray diffraction spectroscopy (XRD), Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Electrochemical impedance spectroscopy analysis revealed that the charge transfer resistance of rGO modified glassy carbon (GC) electrode was much lower than that of the GC electrode. The electrochemical behavior of dihydronicotinamide adenine dinucleotide (NADH) on rGO modified GC electrode was investigated by cyclic voltammetry and amperometry. Electrochemical experiments indicated that rGO/GC electrode exhibited excellent electrocatalytic activity toward the NADH, which can be attributed to excellent electrical conductivity and high specific surface area of the rGO composite. The resulting biosensor showed highly sensitive amperometric response to NADH with a low detection limit (0.33μM). Copyright © 2014 Elsevier Inc. All rights reserved.

Homogeneous anisotropic solutions of topologically massive gravity with a cosmological constant and their homogeneous deformations

NASA Astrophysics Data System (ADS)

Moutsopoulos, George

2013-06-01

We solve the equations of topologically massive gravity (TMG) with a potentially non-vanishing cosmological constant for homogeneous metrics without isotropy. We only reproduce known solutions. We also discuss their homogeneous deformations, possibly with isotropy. We show that de Sitter space and hyperbolic space cannot be infinitesimally homogeneously deformed in TMG. We clarify some of their Segre-Petrov types and discuss the warped de Sitter spacetime.

Observational constraints on holographic tachyonic dark energy in interaction with dark matter

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

Micheletti, Sandro M. R., E-mail: smrm@fma.if.usp.br

2010-05-01

We discuss an interacting tachyonic dark energy model in the context of the holographic principle. The potential of the holographic tachyon field in interaction with dark matter is constructed. The model results are compared with CMB shift parameter, baryonic acoustic oscilations, lookback time and the Constitution supernovae sample. The coupling constant of the model is compatible with zero, but dark energy is not given by a cosmological constant.

Eight-dimensional quantum reaction rate calculations for the H+CH{sub 4} and H{sub 2}+CH{sub 3} reactions on recent potential energy surfaces

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

Zhou, Yong; Zhang, Dong H., E-mail: zhangdh@dicp.ac.cn

2014-11-21

Eight-dimensional (8D) transition-state wave packet simulations have been performed on two latest potential energy surfaces (PES), the Zhou-Fu-Wang-Collins-Zhang (ZFWCZ) PES [Y. Zhou, B. Fu, C. Wang, M. A. Collins, and D. H. Zhang, J. Chem. Phys. 134, 064323 (2011)] and the Xu-Chen-Zhang (XCZ)-neural networks (NN) PES [X. Xu, J. Chen, and D. H. Zhang, Chin. J. Chem. Phys. 27, 373 (2014)]. Reaction rate constants for both the H+CH{sub 4} reaction and the H{sub 2}+CH{sub 3} reaction are calculated. Simulations of the H+CH{sub 4} reaction based on the XCZ-NN PES show that the ZFWCZ PES predicts rate constants with reasonable highmore » accuracy for low temperatures while leads to slightly lower results for high temperatures, in line with the distribution of interpolation error associated with the ZFWCZ PES. The 8D H+CH{sub 4} rate constants derived on the ZFWCZ PES compare well with full-dimensional 12D results based on the equivalent m-ZFWCZ PES, with a maximum relative difference of no more than 20%. Additionally, very good agreement is shown by comparing the 8D XCZ-NN rate constants with the 12D results obtained on the ZFWCZ-WM PES, after considering the difference in static barrier height between these two PESs. The reaction rate constants calculated for the H{sub 2}+CH{sub 3} reaction are found to be in good consistency with experimental observations.« less

Calculations of rate constants for the three-body recombination of H2 in the presence of H2

NASA Technical Reports Server (NTRS)

Schwenke, David W.

1988-01-01

A new global potential energy hypersurface for H2 + H2 is constructed and quasiclassical trajectory calculations performed using the resonance complex theory and energy transfer mechanism to estimate the rate of three body recombination over the temperature range 100 to 5000 K. The new potential is a faithful representation of ab initio electron structure calculations, is unchanged under the operation of exchanging H atoms, and reproduces the accurate H3 potential as one H atom is pulled away. Included in the fitting procedure are geometries expected to be important when one H2 is near or above the dissociation limit. The dynamics calculations explicitly include the motion of all four atoms and are performed efficiently using a vectorized variable-stepsize integrator. The predicted rate constants are approximately a factor of two smaller than experimental estimates over a broad temperature range.

Large-Scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) Simulations of the Molecular Crystal alphaRDX

DTIC Science & Technology

2013-08-01

potential for HMX / RDX (3, 9). ...................................................................................8 1 1. Purpose This work...6 dispersion and electrostatic interactions. Constants for the SB potential are given in table 1. 8 Table 1. SB potential for HMX / RDX (3, 9...modeling dislocations in the energetic molecular crystal RDX using the Large-Scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) molecular

Confusing Aspects in the Calculation of the Electrostatic Potential of an Infinite Line of Charge

ERIC Educational Resources Information Center

Jimenez, J. L.; Campos, I.; Roa-Neri, J. A. E.

2012-01-01

In this work we discuss the trick of eliminating infinite potential of reference arguing that it corresponds to a constant of integration, in the problem of determining the electrostatic potential of an infinite line of charge with uniform density, and show how the problem must be tackled properly. The usual procedure is confusing for most…

Common Misconceptions about the Dynamical Theory of Crystal Lattices: Cauchy Relations, Lattice Potentials and Infinite Crystals

ERIC Educational Resources Information Center

Elcoro, Luis; Etxebarria, Jesus

2011-01-01

The requirement of rotational invariance for lattice potential energies is investigated. Starting from this condition, it is shown that the Cauchy relations for the elastic constants are fulfilled if the lattice potential is built from pair interactions or when the first-neighbour approximation is adopted. This is seldom recognized in widely used…

Rate Constants for Fine-Structure Excitations in O - H Collisions with Error Bars Obtained by Machine Learning

NASA Astrophysics Data System (ADS)

Vieira, Daniel; Krems, Roman

2017-04-01

Fine-structure transitions in collisions of O(3Pj) with atomic hydrogen are an important cooling mechanism in the interstellar medium; knowledge of the rate coefficients for these transitions has a wide range of astrophysical applications. The accuracy of the theoretical calculation is limited by inaccuracy in the ab initio interaction potentials used in the coupled-channel quantum scattering calculations from which the rate coefficients can be obtained. In this work we use the latest ab initio results for the O(3Pj) + H interaction potentials to improve on previous calculations of the rate coefficients. We further present a machine-learning technique based on Gaussian Process regression to determine the sensitivity of the rate coefficients to variations of the underlying adiabatic interaction potentials. To account for the inaccuracy inherent in the ab initio calculations we compute error bars for the rate coefficients corresponding to 20% variation in each of the interaction potentials. We obtain these error bars by fitting a Gaussian Process model to a data set of potential curves and rate constants. We use the fitted model to do sensitivity analysis, determining the relative importance of individual adiabatic potential curves to a given fine-structure transition. NSERC.

Phases of a fermionic model with chiral condensates and Cooper pairs in 1+1 dimensions

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

Mihaila, Bogdan; Blagoev, Krastan B.; MIND Institute, Albuquerque, New Mexico 87131

2006-01-01

We study the phase structure of a 4-fermi model with three bare coupling constants, which potentially has three types of bound states. This model is a generalization of the model discussed previously by [A. Chodos, F. Cooper, W. Mao, H. Minakata, and A. Singh, Phys. Rev. D 61, 045011 (2000).], which contained both chiral condensates and Cooper pairs. For this generalization we find that there are two independent renormalized coupling constants which determine the phase structure at finite density and temperature. We find that the vacuum can be in one of three distinct phases depending on the value of thesemore » two renormalized coupling constants.« less

Measurements of the time constant for steady ionization in shaped-charge barium releases

NASA Technical Reports Server (NTRS)

Hoch, Edward L.; Hallinan, Thomas J.

1993-01-01

Quantitative measurements of three solar illuminated shaped-charge barium releases injected at small angles to the magnetic field were made using a calibrated color television camera. Two of the releases were from 1989. The third release, a reanalysis of an event included in Hallinan's 1988 study of three 1986 releases, was included to provide continuity between the two studies. Time constants for ionization, measured during the first 25 s of each release, were found to vary considerably. The two 1989 time constants differed substantially, and both were significantly less than any of the 1986 time constants. On the basis of this variability, we conclude that the two 1989 releases showed evidence of continuous nonsolar ionization. One release showed nonsolar ionization which could not he attributed to Alfven's critical ionization velocity process, which requires a component of velocity perpendicular to the magnetic field providing a perpendicular energy greater than the ionization potential.

Facile synthesis of Ni/NiO@GO nanocomposites and its enhanced dielectric constant

NASA Astrophysics Data System (ADS)

Sarkar, S.; Giri, N.; Mondal, A.; Ray, R.

2018-05-01

Ni/NiO embedded Graphene Oxide (GO): Ni/NiO@GO is synthesized by citric acid assisted Pechini-type method. Structural and morphological characterizations are performed by X-ray powdered diffraction (XRD), field emission scanning electron microscopy (FESEM) and tunneling electron microscopy (TEM). Defects in GO sheets are probed by RAMAN spectroscopy. The temperature variation of dielectric constant (ɛR) and dielectric loss (tan δ) are investigated in the temperature range 300 - 400 K. Decoration of GO with Ni/NiO nanoparticles enhances its ɛR by˜55 times. Moreover, its dielectric constant measured at 5 MHz is found to be˜430 times to that of Ni/NiO along with the reduction of dielectric loss by a factor˜0.5. The enhanced dielectric constant makes the composite Ni/NiO@GO a potential candidate for using in ecologically friendly energy storage devices.

THE STUDY OF HIGH DIELECTRIC CONSTANT MECHANISM OF La-DOPED Ba0.67Sr0.33TiO3 CERAMICS

NASA Astrophysics Data System (ADS)

Xu, Jing; He, Bo; Liu, Han Xing

It is a common and effective method to enhance the dielectric properties of BST ceramics by adding rare-earth elements. In this paper, it is important to analyze the cause of the high dielectric constant behavior of La-doped BST ceramics. The results show that proper rare earth La dopant (0.2≤x≤0.7) may greatly increase the dielectric constant of BST ceramics, and also improve the temperature stability, evidently. According to the current-voltage (J-V) characteristics, the proper La-doped BST ceramics may reach the better semiconductivity, with the decrease and increase in La doping, the ceramics are insulators. By using the Schottky barrier model and electric microstructure model to find the surface or grain boundary potential barrier height, the width of the depletion layer and grain size do play an important role in impacting the dielectric constant.

Constraints on axion inflation from the weak gravity conjecture

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

Rudelius, Tom, E-mail: rudelius@physics.harvard.edu

2015-09-01

We derive constraints facing models of axion inflation based on decay constant alignment from a string-theoretic and quantum gravitational perspective. In particular, we investigate the prospects for alignment and 'anti-alignment' of C{sub 4} axion decay constants in type IIB string theory, deriving a strict no-go result in the latter case. We discuss the relationship of axion decay constants to the weak gravity conjecture and demonstrate agreement between our string-theoretic constraints and those coming from the 'generalized' weak gravity conjecture. Finally, we consider a particular model of decay constant alignment in which the potential of C{sub 4} axions in type IIBmore » compactifications on a Calabi-Yau three-fold is dominated by contributions from D7-branes, pointing out that this model evades some of the challenges derived earlier in our paper but is highly constrained by other geometric considerations.« less

Constraints on axion inflation from the weak gravity conjecture

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

Rudelius, Tom

2015-09-08

We derive constraints facing models of axion inflation based on decay constant alignment from a string-theoretic and quantum gravitational perspective. In particular, we investigate the prospects for alignment and ‘anti-alignment’ of C{sub 4} axion decay constants in type IIB string theory, deriving a strict no-go result in the latter case. We discuss the relationship of axion decay constants to the weak gravity conjecture and demonstrate agreement between our string-theoretic constraints and those coming from the ‘generalized’ weak gravity conjecture. Finally, we consider a particular model of decay constant alignment in which the potential of C{sub 4} axions in type IIBmore » compactifications on a Calabi-Yau three-fold is dominated by contributions from D7-branes, pointing out that this model evades some of the challenges derived earlier in our paper but is highly constrained by other geometric considerations.« less

Advanced concepts for transformers pressboard dielectric constant and mechanical strength

NASA Astrophysics Data System (ADS)

1982-03-01

Of the numerous electrical considerations in a material, the value of the dielectric constant serves as an important criterion in designing proper insulation systems. Ways to reduce the dielectric constant of solid (fibrous) insulating materials were investigated. A literature search was made on cellulosic and synthetic fibers and also additives which offered the potential for dielectric constant reduction of the solid insulation. Sample board structures were produced in the laboratory and tested for electrical, mechanical and chemical characteristics. Electrical tests determined the suitability of the material at transformer test and operating conditions. The mechanical tests established the physical characteristics of the modified board structures. Chemical tests checked the conductivity of the aqueous extract, acidity, and ash content. Further, compatibility with transformer oil and some aging tests were performed. An actual computer transformer design was made based on one of the modified board structures and the reduction in core steel and transformer losses were shown.

Gravitational lensing effects in a time-variable cosmological 'constant' cosmology

NASA Technical Reports Server (NTRS)

Ratra, Bharat; Quillen, Alice

1992-01-01

A scalar field phi with a potential V(phi) varies as phi exp -alpha(alpha is greater than 0) has an energy density, behaving like that of a time-variable cosmological 'constant', that redshifts less rapidly than the energy densities of radiation and matter, and so might contribute significantly to the present energy density. We compute, in this spatially flat cosmology, the gravitational lensing optical depth, and the expected lens redshift distribution for fixed source redshift. We find, for the values of alpha of about 4 and baryonic density parameter Omega of about 0.2 consistent with the classical cosmological tests, that the optical depth is significantly smaller than that in a constant-Lambda model with the same Omega. We also find that the redshift of the maximum of the lens distribution falls between that in the constant-Lambda model and that in the Einstein-de Sitter model.

Evaluation of molecular dynamics simulation methods for ionic liquid electric double layers.

PubMed

Haskins, Justin B; Lawson, John W

2016-05-14

We investigate how systematically increasing the accuracy of various molecular dynamics modeling techniques influences the structure and capacitance of ionic liquid electric double layers (EDLs). The techniques probed concern long-range electrostatic interactions, electrode charging (constant charge versus constant potential conditions), and electrolyte polarizability. Our simulations are performed on a quasi-two-dimensional, or slab-like, model capacitor, which is composed of a polarizable ionic liquid electrolyte, [EMIM][BF4], interfaced between two graphite electrodes. To ensure an accurate representation of EDL differential capacitance, we derive new fluctuation formulas that resolve the differential capacitance as a function of electrode charge or electrode potential. The magnitude of differential capacitance shows sensitivity to different long-range electrostatic summation techniques, while the shape of differential capacitance is affected by charging technique and the polarizability of the electrolyte. For long-range summation techniques, errors in magnitude can be mitigated by employing two-dimensional or corrected three dimensional electrostatic summations, which led to electric fields that conform to those of a classical electrostatic parallel plate capacitor. With respect to charging, the changes in shape are a result of ions in the Stern layer (i.e., ions at the electrode surface) having a higher electrostatic affinity to constant potential electrodes than to constant charge electrodes. For electrolyte polarizability, shape changes originate from induced dipoles that soften the interaction of Stern layer ions with the electrode. The softening is traced to ion correlations vertical to the electrode surface that induce dipoles that oppose double layer formation. In general, our analysis indicates an accuracy dependent differential capacitance profile that transitions from the characteristic camel shape with coarser representations to a more diffuse profile with finer representations.

Fluoro-polymer functionalized graphene for flexible ferroelectric polymer-based high-k nanocomposites with suppressed dielectric loss and low percolation threshold.

PubMed

Yang, Ke; Huang, Xingyi; Fang, Lijun; He, Jinliang; Jiang, Pingkai

2014-12-21

Flexible nanodielectric materials with high dielectric constant and low dielectric loss have huge potential applications in the modern electronic and electric industry. Graphene sheets (GS) and reduced-graphene oxide (RGO) are promising fillers for preparing flexible polymer-based nanodielectric materials because of their unique two-dimensional structure and excellent electrical and mechanical properties. However, the easy aggregation of GS/RGO significantly limits the potential of graphene in enhancing the dielectric constant of polymer composites. In addition, the poor filler/matrix nanoscale interfacial adhesion also causes difficulties in suppressing the dielectric loss of the composites. In this work, using a facile and environmentally friendly approach, polydopamine coated RGO (PDA-RGO) and fluoro-polymer functionalized RGO (PF-PDA-RGO) were prepared. Compared with the RGO prepared by the conventional methods [i.e. hydrazine reduced-graphene oxide (H-RGO)] and PDA-RGO, the resulting PF-PDA-RGO nanosheets exhibit excellent dispersion in the ferroelectric polymer matrix [i.e. poly(vinylidene fluoride-co-hexafluoro propylene), P(VDF-HFP)] and strong interfacial adhesion with the matrix, leading to a low percolation threshold (fc = 1.06 vol%) and excellent flexibility for the corresponding nanocomposites. Among the three nanocomposites, the P(VDF-HFP)/PF-PDA-RGO nanocomposites exhibited the optimum performance (i.e. simultaneously having high dielectric constant and low dielectric loss). For instance, at 1000 Hz, the P(VDF-HFP) nanocomposite sample with 1.0 vol% PF-PDA-RGO has a dielectric constant of 107.9 and a dielectric loss of 0.070, showing good potential for dielectric applications. Our strategy provides a new pathway to prepare high performance flexible nanodielectric materials.

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

Liu, Xiaobing; Zheng, O'Neill; Niu, Fuxin

Most commercial ground source heat pump systems (GSHP) in the United States are in a distributed configuration. These systems circulate water or an anti-freeze solution through multiple heat pump units via a central pumping system, which usually uses variable speed pump(s). Variable speed pumps have potential to significantly reduce pumping energy use; however, the energy savings in reality could be far away from its potential due to improper pumping system design and controls. In this paper, a simplified hydronic pumping system was simulated with the dynamic Modelica models to evaluate three different pumping control strategies. This includes two conventional controlmore » strategies, which are to maintain a constant differential pressure across either the supply and return mains, or at the most hydraulically remote heat pump; and an innovative control strategy, which adjusts system flow rate based on the demand of each heat pump. The simulation results indicate that a significant overflow occurs at part load conditions when the variable speed pump is controlled to main a constant differential pressure across the supply and return mains of the piping system. On the other hand, an underflow occurs at part load conditions when the variable speed pump is controlled to maintain a constant differential pressure across the furthest heat pump. The flow-demand-based control can provide needed flow rate to each heat pump at any given time, and with less pumping energy use than the two conventional controls. Finally, a typical distributed GSHP system was studied to evaluate the energy saving potential of applying the flow-demand-based pumping control strategy. This case study shows that the annual pumping energy consumption can be reduced by 62% using the flow-demand-based control compared with that using the conventional pressure-based control to maintain a constant differential pressure a cross the supply and return mains.« less

Properties of water along the liquid-vapor coexistence curve via molecular dynamics simulations using the polarizable TIP4P-QDP-LJ water model

PubMed Central

Bauer, Brad A.; Patel, Sandeep

2009-01-01

We present an extension of the TIP4P-QDP model, TIP4P-QDP-LJ, that is designed to couple changes in repulsive and dispersive nonbond interactions to changes in polarizability. Polarizability is intimately related to the dispersion component of classical force field models of interactions, and we explore the effect of incorporating this connection explicitly on properties along the liquid-vapor coexistence curve of pure water. Parametrized to reproduce condensed-phase liquid water properties at 298 K, the TIP4P-QDP-LJ model predicts density, enthalpy of vaporization, self-diffusion constant, and the dielectric constant at ambient conditions to about the same accuracy as TIP4P-QDP but shows remarkable improvement in reproducing the liquid-vapor coexistence curve. TIP4P-QDP-LJ predicts critical constants of Tc=623 K, ρc=0.351 g∕cm3, and Pc=250.9 atm, which are in good agreement with experimental values of Tc=647.1 K, ρc=0.322 g∕cm3, and Pc=218 atm, respectively. Applying a scaling factor correction (obtained by fitting the experimental vapor-liquid equilibrium data to the law of rectilinear diameters using a three-term Wegner expansion) the model predicts critical constants (Tc=631 K and ρc=0.308 g∕cm3). Dependence of enthalpy of vaporization, self-diffusion constant, surface tension, and dielectric constant on temperature are shown to reproduce experimental trends. We also explore the interfacial potential drop across the liquid-vapor interface for the temperatures studied. The interfacial potential demonstrates little temperature dependence at lower temperatures (300–450 K) and significantly enhanced (exponential) dependence at elevated temperatures. Terms arising from the decomposition of the interfacial potential into dipole and quadrupole contributions are shown to monotonically approach zero as the temperature approaches the critical temperature. Results of this study suggest that self-consistently treating the coupling of phase-dependent polarizability with dispersion interactions in classical water force fields may be an important effect for the extension of polarizable water force fields to reproduce properties along the liquid-vapor coexistence envelope as well as near critical conditions. More importantly, the present study demonstrates the rather remarkable transferability of a water model parametrized to a single state point to other thermodynamic states. Further studies are recommended. PMID:19725623

Properties of water along the liquid-vapor coexistence curve via molecular dynamics simulations using the polarizable TIP4P-QDP-LJ water model.

PubMed

Bauer, Brad A; Patel, Sandeep

2009-08-28

We present an extension of the TIP4P-QDP model, TIP4P-QDP-LJ, that is designed to couple changes in repulsive and dispersive nonbond interactions to changes in polarizability. Polarizability is intimately related to the dispersion component of classical force field models of interactions, and we explore the effect of incorporating this connection explicitly on properties along the liquid-vapor coexistence curve of pure water. Parametrized to reproduce condensed-phase liquid water properties at 298 K, the TIP4P-QDP-LJ model predicts density, enthalpy of vaporization, self-diffusion constant, and the dielectric constant at ambient conditions to about the same accuracy as TIP4P-QDP but shows remarkable improvement in reproducing the liquid-vapor coexistence curve. TIP4P-QDP-LJ predicts critical constants of T(c)=623 K, rho(c)=0.351 g/cm(3), and P(c)=250.9 atm, which are in good agreement with experimental values of T(c)=647.1 K, rho(c)=0.322 g/cm(3), and P(c)=218 atm, respectively. Applying a scaling factor correction (obtained by fitting the experimental vapor-liquid equilibrium data to the law of rectilinear diameters using a three-term Wegner expansion) the model predicts critical constants (T(c)=631 K and rho(c)=0.308 g/cm(3)). Dependence of enthalpy of vaporization, self-diffusion constant, surface tension, and dielectric constant on temperature are shown to reproduce experimental trends. We also explore the interfacial potential drop across the liquid-vapor interface for the temperatures studied. The interfacial potential demonstrates little temperature dependence at lower temperatures (300-450 K) and significantly enhanced (exponential) dependence at elevated temperatures. Terms arising from the decomposition of the interfacial potential into dipole and quadrupole contributions are shown to monotonically approach zero as the temperature approaches the critical temperature. Results of this study suggest that self-consistently treating the coupling of phase-dependent polarizability with dispersion interactions in classical water force fields may be an important effect for the extension of polarizable water force fields to reproduce properties along the liquid-vapor coexistence envelope as well as near critical conditions. More importantly, the present study demonstrates the rather remarkable transferability of a water model parametrized to a single state point to other thermodynamic states. Further studies are recommended.

Adapting to Changing Memory Retrieval Demands: Evidence from Event-Related Potentials

ERIC Educational Resources Information Center

Benoit, Roland G.; Werkle-Bergner, Markus; Mecklinger, Axel; Kray, Jutta

2009-01-01

This study investigated preparatory processes involved in adapting to changing episodic memory retrieval demands. Event-related potentials (ERPs) were recorded while participants performed a general old/new recognition task and a specific task that also required retrieval of perceptual details. The relevant task remained either constant or changed…

Potential-pH Diagrams.

ERIC Educational Resources Information Center

Barnum, Dennis W.

1982-01-01

Potential-pH diagrams show the domains of redoxpotential and pH in which major species are most stable. Constructing such diagrams provides students with opportunities to decide what species must be considered, search literature for equilibrium constants and free energies of formation, and practice in using the Nernst equation. (Author/JN)

Internet's Potential to Affect Social Studies and Democracy

ERIC Educational Resources Information Center

Friedman, Adam M.

2006-01-01

Technology, and the Internet in particular, is bringing constant change to American society, including the potential to enhance democracy by fostering participation in the electoral process. Because of the wealth of information available on candidates, issues, and policies, the Internet may foster citizens' ability to cast a more informed vote. As…

THE EFFECTS OF FUNCTIONALIZED AND NON-FUNCTIONALIZED CARBON NANOTUBES ON ROOT ELONGATION OF SELECTED CROP SPECIES

EPA Science Inventory

Single-walled carbon nanotubes (SWNT) have many potential beneficial uses with additional applications constantly being investigated. However, these unique properties create a potential cause for concern of toxicity, not only in humans and animals, but also in plants. Root elong...

Extending the Diffuse Layer Model of Surface Acidity Constant Behavior: IV. Diffuse Layer Charge/Potential Relationships

EPA Science Inventory

Most current electrostatic surface complexation models describing ionic binding at the particle/water interface rely on the use of Poisson - Boltzmann (PB) theory for relating diffuse layer charge densities to diffuse layer electrostatic potentials. PB theory is known to contain ...

Pancreatic acinar cells: ionic dependence of acetylcholine-induced membrane potential and resistance change.

PubMed Central

Nishiyama, A; Petersen, O H

1975-01-01

1. Intracellular recordings of membrane potential, input resistance and time constant have been made in vitro from the exocrine acinar cells of the mouse pancreas using glass micro-electrodes. The acinar cells were stimulated by acetylcholine (ACh). In some cases ACh was simply directly added to the tissue superfusion bath, in other experiments ACh was applied locally to pancreatic acini by micro-iontophoresis. 2. Current-voltage relations were investigated by injecting rectangular de- or hyperpolarizing current pulses through the recording micro-electrode. Within a relatively wide range (-20 to -70 mV) there was a linear relation between injected current and change in membrane potential. The slope of such linear curves corresponded to an input resistance of about 3-8 M omega. The membrane time constant was about 5-10 msec. 3. ACh depolarized the cell membrane and caused a marked reduction of input resistance and time constant. The minimum latency of the ACh-induced depolarization (microiontophoretic application) was 100-300 msec. Maximal depolarization was about 20 mV. The effect of this local ACh application was abolished by atropine (1-4 x 10-6 M). The blocking effect of atropine was fully reversible. 4. Stimulating with ACh during the passage of large depolarizing current pulses made it possible simultaneously to observe the effect of ACh at two different levels of resting potential (RP). At the spontaneous RP of about minus 40 mV ACh evoked a depolarization of usual magnitude (15-20 mV) while at the artificially displaced level of about -10 mV a small hyperpolarization (about 5 mV) was observed. It therefore appears that the reversal potential of the transmitter equilibrium potential is about -20 mV. 5. Replacement of the superfusion fluid C1 by sulphate or methylsulphate caused an initial short-lasting depolarization, thereafter the normal resting potential was reassumed... PMID:1142124

Alternative Derivations of the Statistical Mechanical Distribution Laws

PubMed Central

Wall, Frederick T.

1971-01-01

A new approach is presented for the derivation of statistical mechanical distribution laws. The derivations are accomplished by minimizing the Helmholtz free energy under constant temperature and volume, instead of maximizing the entropy under constant energy and volume. An alternative method involves stipulating equality of chemical potential, or equality of activity, for particles in different energy levels. This approach leads to a general statement of distribution laws applicable to all systems for which thermodynamic probabilities can be written. The methods also avoid use of the calculus of variations, Lagrangian multipliers, and Stirling's approximation for the factorial. The results are applied specifically to Boltzmann, Fermi-Dirac, and Bose-Einstein statistics. The special significance of chemical potential and activity is discussed for microscopic systems. PMID:16578712

Alternative derivations of the statistical mechanical distribution laws.

PubMed

Wall, F T

1971-08-01

A new approach is presented for the derivation of statistical mechanical distribution laws. The derivations are accomplished by minimizing the Helmholtz free energy under constant temperature and volume, instead of maximizing the entropy under constant energy and volume. An alternative method involves stipulating equality of chemical potential, or equality of activity, for particles in different energy levels. This approach leads to a general statement of distribution laws applicable to all systems for which thermodynamic probabilities can be written. The methods also avoid use of the calculus of variations, Lagrangian multipliers, and Stirling's approximation for the factorial. The results are applied specifically to Boltzmann, Fermi-Dirac, and Bose-Einstein statistics. The special significance of chemical potential and activity is discussed for microscopic systems.

Simulated Screens of DNA Encoded Libraries: The Potential Influence of Chemical Synthesis Fidelity on Interpretation of Structure-Activity Relationships.

PubMed

Satz, Alexander L

2016-07-11

Simulated screening of DNA encoded libraries indicates that the presence of truncated byproducts complicates the relationship between library member enrichment and equilibrium association constant (these truncates result from incomplete chemical reactions during library synthesis). Further, simulations indicate that some patterns observed in reported experimental data may result from the presence of truncated byproducts in the library mixture and not structure-activity relationships. Potential experimental methods of minimizing the presence of truncates are assessed via simulation; the relationship between enrichment and equilibrium association constant for libraries of differing purities is investigated. Data aggregation techniques are demonstrated that allow for more accurate analysis of screening results, in particular when the screened library contains significant quantities of truncates.

Semiclassical Models for Virtual Antiparticle Pairs, the Unit of Charge e, and the QCD Coupling alpha(sub s)

NASA Technical Reports Server (NTRS)

Batchelor, David; Zukor, Dorothy (Technical Monitor)

2001-01-01

New semiclassical models of virtual antiparticle pairs are used to compute the pair lifetimes, and good agreement with the Heisenberg lifetimes from quantum field theory (QFT) is found. The modeling method applies to both the electromagnetic and color forces. Evaluation of the action integral of potential field fluctuation for each interaction potential yields approximately Planck's constant/2 for both electromagnetic and color fluctuations, in agreement with QFT. Thus each model is a quantized semiclassical representation for such virtual antiparticle pairs, to good approximation. When the results of the new models and QFT are combined, formulae for e and alpha(sub s)(q) are derived in terms of only Planck's constant and c.

Auger electron spectroscopy and Rutherford backscattering studies of copper in 2024-T3 aluminum following electrochemical anodization in phosphoric acid

NASA Astrophysics Data System (ADS)

Solomon, J. S.

1981-05-01

The effects of the electrochemical anodization of dioxidized 2024-T3 aluminum on copper were characterized by Auger electron spectroscopy and Rutherford backscattering. Anodization was performed in phosphoric acid at constant potential. Data is presented which shows that constant potential anodization of 2024-T3 is more efficient than aluminum in terms of oxide growth rates for short anodization times. However the maximum anodic oxide thickness achievable on the alloy is less than the pure metal. Copper is shown to be enriched at the oxide metal interface because of its diffusion from the bulk during anodization. The presence of copper at the oxide-metal interface is shown to affect oxide morphology.

Tuning the effective fine structure constant in graphene: opposing effects of dielectric screening on short- and long-range potential scattering.

PubMed

Jang, C; Adam, S; Chen, J-H; Williams, E D; Das Sarma, S; Fuhrer, M S

2008-10-03

We reduce the dimensionless interaction strength alpha in graphene by adding a water overlayer in ultrahigh vacuum, thereby increasing dielectric screening. The mobility limited by long-range impurity scattering is increased over 30%, due to the background dielectric constant enhancement leading to a reduced interaction of electrons with charged impurities. However, the carrier-density-independent conductivity due to short-range impurities is decreased by almost 40%, due to reduced screening of the impurity potential by conduction electrons. The minimum conductivity is nearly unchanged, due to canceling contributions from the electron-hole puddle density and long-range impurity mobility. Experimental data are compared with theoretical predictions with excellent agreement.

Self-gravitating static non-critical black holes in 4 D Einstein-Klein-Gordon system with nonminimal derivative coupling

NASA Astrophysics Data System (ADS)

Gunara, Bobby Eka; Yaqin, Ainol

2018-06-01

We study static non-critical hairy black holes of four dimensional gravitational model with nonminimal derivative coupling and a scalar potential turned on. By taking an ansatz, namely, the first derivative of the scalar field is proportional to square root of a metric function, we reduce the Einstein field equation and the scalar field equation of motions into a single highly nonlinear differential equation. This setup implies that the hair is secondary-like since the scalar charge-like depends on the non-constant mass-like quantity in the asymptotic limit. Then, we show that near boundaries the solution is not the critical point of the scalar potential and the effective geometries become spaces of constant scalar curvature.

Double gauge invariance and covariantly-constant vector fields in Weyl geometry

NASA Astrophysics Data System (ADS)

Kassandrov, Vladimir V.; Rizcallah, Joseph A.

2014-08-01

The wave equation and equations of covariantly-constant vector fields (CCVF) in spaces with Weyl nonmetricity turn out to possess, in addition to the canonical conformal-gauge, a gauge invariance of another type. On a Minkowski metric background, the CCVF system alone allows us to pin down the Weyl 4-metricity vector, identified herein with the electromagnetic potential. The fundamental solution is given by the ordinary Lienard-Wiechert field, in particular, by the Coulomb distribution for a charge at rest. Unlike the latter, however, the magnitude of charge is necessarily unity, "elementary", and charges of opposite signs correspond to retarded and advanced potentials respectively, thus establishing a direct connection between the particle/antiparticle asymmetry and the "arrow of time".

Non-steady state mass action dynamics without rate constants: dynamics of coupled reactions using chemical potentials

NASA Astrophysics Data System (ADS)

Cannon, William R.; Baker, Scott E.

2017-10-01

Comprehensive and predictive simulation of coupled reaction networks has long been a goal of biology and other fields. Currently, metabolic network models that utilize enzyme mass action kinetics have predictive power but are limited in scope and application by the fact that the determination of enzyme rate constants is laborious and low throughput. We present a statistical thermodynamic formulation of the law of mass action for coupled reactions at both steady states and non-stationary states. The formulation uses chemical potentials instead of rate constants. When used to model deterministic systems, the method corresponds to a rescaling of the time dependent reactions in such a way that steady states can be reached on the same time scale but with significantly fewer computational steps. The relationships between reaction affinities, free energy changes and generalized detailed balance are central to the discussion. The significance for applications in systems biology are discussed as is the concept and assumption of maximum entropy production rate as a biological principle that links thermodynamics to natural selection.

(abstract) Characterization of Tree Water Status and Dielectric Constant Changes of North American Boreal Forests in Combination with Synthetic Aperture Radar Remote Sensing

NASA Technical Reports Server (NTRS)

McDonald, K. C.; Zimmerman, R.; Way, J. B.

1994-01-01

The occurrence and magnitude of temporal and spatial tree water status changes in the boreal environment were studied in a floodplain forest in Alaska and in four forest types of Central Canada. Under limited water supply conditions from the rooted soil zone in early spring (freeze/thaw transition) and during summer, trees show declining water potentials. Coincidental change in tree water potential, tree transpiration and tree dielectric constant had been observed in previous studies performed in Mediterranean ecotones. If radar is sensitive to chances in tree water status as reflected through changes in dielectric constant, then radar remote sensing could be used to monitor the water status of forests. The SAR imagery is examined to determine the response of the radar backscatter to the ground based observations of the water status of forest canopies. Comparisons are made between stands and also along the large North-South gradient between sites. Data from SAR are used to examine the radar response to canopy physiological state as related to vegetation freeze/thaw and growing season length.

Friedberg-Lee model at finite temperature and density

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

Mao Hong; CCAST; Yao Minjie

2008-06-15

The Friedberg-Lee model is studied at finite temperature and density. By using the finite temperature field theory, the effective potential of the Friedberg-Lee model and the bag constant B(T) and B(T,{mu}) have been calculated at different temperatures and densities. It is shown that there is a critical temperature T{sub C}{approx_equal}106.6 MeV when {mu}=0 MeV and a critical chemical potential {mu}{approx_equal}223.1 MeV for fixing the temperature at T=50 MeV. We also calculate the soliton solutions of the Friedberg-Lee model at finite temperature and density. It turns out that when T{<=}T{sub C} (or {mu}{<=}{mu}{sub C}), there is a bag constant B(T) [ormore » B(T,{mu})] and the soliton solutions are stable. However, when T>T{sub C} (or {mu}>{mu}{sub C}) the bag constant B(T)=0 MeV [or B(T,{mu})=0 MeV] and there is no soliton solution anymore, therefore, the confinement of quarks disappears quickly.« less

Calculated rate constants for the reaction ClO + O yields Cl + O2 between 220 and 1000 deg K. [molecular trajectories and stratospheric ozone

NASA Technical Reports Server (NTRS)

Jaffee, R. L.

1978-01-01

Classical trajectory calculations are presented for the reaction ClO + O yields Cl + O2, a reaction which is an important step in the chlorine-catalyzed destruction of ozone which is thought to occur in the 220 and 1000 K. The calculated rate constant is 4.36 x 10 to the minus 11th power exp (-191/T)cu cm molecule (-1)s(-1) and its value at 300 K is 2.3 plus or minus 10 to the 11th power cu cm molecule (-1)s(-1), about a factor of 2 lower than recent experimental data. The empirical potential energy surface used in the calculations was constructed to fit experimental data for ClO, O2 and ClOO molecules. Other important features of this potential surface, such as the barrier to reaction, were varied systematically and calculations were performed for a range of conditions to determine the best theoretical rate constants. Results demonstrate the utility of classical trajectory methods for determining activation energies and other kinetic data for important atmospheric reactions.

Ab initio structural and spectroscopic study of HPS{sup x} and HSP{sup x} (x = 0,+1,−1) in the gas phase

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

Yaghlane, Saida Ben; Cotton, C. Eric; Francisco, Joseph S., E-mail: francisc@purdue.edu, E-mail: hochlaf@univ-mlv.fr

2013-11-07

Accurate ab initio computations of structural and spectroscopic parameters for the HPS/HSP molecules and corresponding cations and anions have been performed. For the electronic structure computations, standard and explicitly correlated coupled cluster techniques in conjunction with large basis sets have been adopted. In particular, we present equilibrium geometries, rotational constants, harmonic vibrational frequencies, adiabatic ionization energies, electron affinities, and, for the neutral species, singlet-triplet relative energies. Besides, the full-dimensional potential energy surfaces (PESs) for HPS{sup x} and HSP{sup x} (x = −1,0,1) systems have been generated at the standard coupled cluster level with a basis set of augmented quintuple-zeta quality.more » By applying perturbation theory to the calculated PESs, an extended set of spectroscopic constants, including τ, first-order centrifugal distortion and anharmonic vibrational constants has been obtained. In addition, the potentials have been used in a variational approach to deduce the whole pattern of vibrational levels up to 4000 cm{sup −1} above the minima of the corresponding PESs.« less

An Analysis of Descriptors of Volatile Organic Compounds and Their Impact on Rate Constant for Reaction with Hydroxyl Radicals

DTIC Science & Technology

2018-05-01

the descriptors were correlated to experimental rate constants. The five descriptors fell into one of two categories: whole molecule descriptors or...model based on these correlations . Although that goal was not achieved in full, considerable progress has been made, and there is potential for a...readme.txt) and compiled. We then searched for correlations between the calculated properties from theory and the experimental measurements of reaction rate

String cosmology and the landscape

NASA Astrophysics Data System (ADS)

Bena, Iosif; Graña, Mariana

2017-03-01

String Theory is believed to have a landscape of 10500 vacua with properties that resemble those of our Universe. The existence of these vacua can be combined with anthropic reasoning to explain some of the hardest problems in cosmology and high-energy physics: the cosmological constant problem, the hierarchy problem, and the un-natural almost-flatness of the inflationary potential. We will explain the construction of these vacua, focusing on the challenges of obtaining vacua with a positive cosmological constant.

Crack Closure and Fatigue Crack Growth in 2219-T851 Aluminum Alloy

DTIC Science & Technology

1976-08-01

assumes the length of the crack perimeter to remain es - ’I sentially constant. At the maximum load, the crack is ap- proximately parabolic (or ellipical...for center cracked j specimens) in shape. With unloading, the parabola (or el- lipse) is collapsed. The resulting change in shape produces an apparent...reloading process, the electrical potential remained es - j sentially constant initially and was less than that at the corresponding load during unloading

Optical Properties of Lithium Terbium Fluoride and Implications for Performance in High Power Lasers (Postprint)

DTIC Science & Technology

2016-02-01

Maximum 200 words) LiTbF4 has the potential to replace traditional magneto-optic (MO) garnet materials as a Faraday rotator in high power laser systems...TERMS LiTbF4; magneto-optic (MO) garnet materials; Faraday rotator; high power laser; Verdet constant; Sellmeier; optical isolator 16. SECURITY... Faraday rotator in high power laser systems due to its high Verdet constant. New measurements are reported of the ordinary and extraor- dinary

Decision time, slow inhibition, and theta rhythm.

PubMed

Smerieri, Anteo; Rolls, Edmund T; Feng, Jianfeng

2010-10-20

In this paper, we examine decision making in a spiking neuronal network and show that longer time constants for the inhibitory neurons can decrease the reaction times and produce theta rhythm. We analyze the mechanism and find that the spontaneous firing rate before the decision cues are applied can drift, and thereby influence the speed of the reaction time when the decision cues are applied. The drift of the firing rate in the population that will win the competition is larger if the time constant of the inhibitory interneurons is increased from 10 to 33 ms, and even larger if there are two populations of inhibitory neurons with time constants of 10 and 100 ms. Of considerable interest is that the decision that will be made can be influenced by the noise-influenced drift of the spontaneous firing rate over many seconds before the decision cues are applied. The theta rhythm associated with the longer time constant networks mirrors the greater integration in the firing rate drift produced by the recurrent connections over long time periods in the networks with slow inhibition. The mechanism for the effect of slow waves in the theta and delta range on decision times is suggested to be increased neuronal spiking produced by depolarization of the membrane potential on the positive part of the slow waves when the neuron's membrane potential is close to the firing threshold.

A novel interdigitated capacitor based biosensor for detection of cardiovascular risk marker.

PubMed

Quershi, Anjum; Gurbuz, Yasar; Kang, Weng P; Davidson, Jimmy L

2009-12-15

C-reactive protein (CRP) is a potential biomarker whose elevated levels in humans determine cardiovascular disease risk and inflammation. In this study, we have developed a novel capacitive biosensor for detection of CRP-antigen using capacitor with interdigitated gold (GID) electrodes on nanocrystalline diamond (NCD) surface. The NCD surface served as a dielectric layer between the gold electrodes. GID-surface was functionalized by antibodies and the immobilization was confirmed by Fourier transform spectroscopy (FT-IR) and contact angle measurements. The CRP-antigen detection was performed by capacitive/dielectric-constant measurements. The relaxation time and polarizability constants were estimated using Cole-Cole model. Our results showed that the relaxation time constant (tau) of only CRP-antibody was within 10(-16)-10(-13)s, which was increased to 10(-11)s after the incubation with CRP-antigen, suggesting that the CRP-antigen was captured by the antibodies on GID-surface. In addition, polarizability constant (m) of CRP was also increased upon incubation with increasing concentration of CRP-antigen. Our results showed that the response of GID-NCD-based capacitive biosensor for CRP-antigen was dependent on both concentration (25-800ng/ml) as well as frequency (50-350MHz). Furthermore, using optimized conditions, the GID-NCD based capacitive biosensor developed in this study can potentially be used for detection of elevated levels of protein risk markers in suspected subjects for early diagnosis of disease.

Structural, electronic, elastic, and thermal properties of CaNiH3 perovskite obtained from first-principles calculations

NASA Astrophysics Data System (ADS)

Benlamari, S.; Bendjeddou, H.; Boulechfar, R.; Amara Korba, S.; Meradji, H.; Ahmed, R.; Ghemid, S.; Khenata, R.; Omran, S. Bin

2018-03-01

A theoretical study of the structural, elastic, electronic, mechanical, and thermal properties of the perovskite-type hydride CaNiH3 is presented. This study is carried out via first-principles full potential (FP) linearized augmented plane wave plus local orbital (LAPW+lo) method designed within the density functional theory (DFT). To treat the exchange–correlation energy/potential for the total energy calculations, the local density approximation (LDA) of Perdew–Wang (PW) and the generalized gradient approximation (GGA) of Perdew–Burke–Ernzerhof (PBE) are used. The three independent elastic constants (C 11, C 12, and C 44) are calculated from the direct computation of the stresses generated by small strains. Besides, we report the variation of the elastic constants as a function of pressure as well. From the calculated elastic constants, the mechanical character of CaNiH3 is predicted. Pertaining to the thermal properties, the Debye temperature is estimated from the average sound velocity. To further comprehend this compound, the quasi-harmonic Debye model is used to analyze the thermal properties. From the calculations, we find that the obtained results of the lattice constant (a 0), bulk modulus (B 0), and its pressure derivative ({B}0^{\\prime }) are in good agreement with the available theoretical as well as experimental results. Similarly, the obtained electronic band structure demonstrates the metallic character of this perovskite-type hydride.

Effects of Auroral Potential Drops on Field-Aligned Currents and Nightside Reconnection Dynamos

NASA Astrophysics Data System (ADS)

Lotko, W.; Xi, S.; Zhang, B.; Wiltberger, M. J.; Lyon, J.

2016-12-01

The reaction of the magnetosphere-ionosphere system to dynamic auroral potential drops is investigated using the Lyon-Fedder-Mobarry global model and, for the first time in a global simulation, including the dissipative load of field-aligned potential drops in the low-altitude boundary condition. This extra load reduces the demand for field-aligned current (j||) from nightside reconnection dynamos. The system adapts by forcing the nightside x-line closer to Earth to reduce current lensing (j||/B = constant) at the ionosphere, with the plasma sheet undergoing additional contraction during substorm recovery and steady magnetospheric convection. For steady and moderate solar wind driving and with constant ionospheric conductance, the cross-polar cap potential and hemispheric field-aligned current are lower by approximately the ratio of the peak field-aligned potential drop to the cross polar cap potential (10-15%) when potential drops are included. Hemispheric ionospheric Joule dissipation is less by 8%, while the area-integrated, average work done on the fluid by the reconnecting magnetotail field increases by 50% within |y| < 8 RE. Effects on the nightside plasma sheet include: (1) an average x-line 4 RE closer to Earth; (2) a 12% higher mean reconnection rate; and (3) dawn-dusk asymmetry in reconnection with a 17% higher rate in the premidnight sector.

Effects of auroral potential drops on plasma sheet dynamics

NASA Astrophysics Data System (ADS)

Xi, Sheng; Lotko, William; Zhang, Binzheng; Wiltberger, Michael; Lyon, John

2016-11-01

The reaction of the magnetosphere-ionosphere system to dynamic auroral potential drops is investigated using the Lyon-Fedder-Mobarry global model including, for the first time in a global simulation, the dissipative load of field-aligned potential drops in the low-altitude boundary condition. This extra load reduces the field-aligned current (j||) supplied by nightside reconnection dynamos. The system adapts by forcing the nightside X line closer to Earth, with a corresponding reduction in current lensing (j||/B = constant) at the ionosphere and additional contraction of the plasma sheet during substorm recovery and steady magnetospheric convection. For steady and moderate solar wind driving and with constant ionospheric conductance, the cross polar cap potential and hemispheric field-aligned current are lower by approximately the ratio of the peak field-aligned potential drop to the cross polar cap potential (10-15%) when potential drops are included. Hemispheric ionospheric Joule dissipation is less by 8%, while the area-integrated, average work done on the fluid by the reconnecting magnetotail field increases by 50% within |y| < 8 RE. Effects on the nightside plasma sheet include (1) an average X line 4 RE closer to Earth; (2) a 12% higher mean reconnection rate; and (3) dawn-dusk asymmetry in reconnection with a 17% higher rate in the premidnight sector.

The effect of PECVD plasma decomposition on the wettability and dielectric constant changes in silicon modified DLC films for potential MEMS and low stiction applications

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

Ogwu, A. A.; Okpalugo, T. I. T.; Nanotechnology Institute, School of Electrical and Mechanical Engineering, University of Ulster, Northern Ireland

We have carried out investigations aimed at understanding the mechanism responsible for a water contact angle increase of up to ten degrees and a decrease in dielectric constant in silicon modified hydrogenated amorphous carbon films compared to unmodified hydrogenated amorphous carbon films. Our investigations based on surface chemical constituent analysis using Raman spectroscopy, x-ray photoelectron spectroscopy (XPS), SIMS, FTIR, contact angle / surface energy measurements and spectroscopic ellipsometry suggests the presence of hydrophobic chemical entities on the surface of the films. This observation is consistent with earlier theoretical plasma chemistry predictions and observed Raman peak shifts in the films. Thesemore » surface hydrophobic entities also have a lower polarizability than the bonds in the un-modified films thereby reducing the dielectric constant of the silicon modified films measured by spectroscopic ellipsometry. Ellipsometric dielectric constant measurement is directly related to the surface energy through Hamaker's constant. Our current finding is expected to be of benefit to understanding stiction, friction and lubrication in areas that range from nano-tribology to microfluidics.« less

The effect of PECVD plasma decomposition on the wettability and dielectric constant changes in silicon modified DLC films for potential MEMS and low stiction applications

NASA Astrophysics Data System (ADS)

Ogwu, A. A.; Okpalugo, T. I. T.; McLaughlin, J. A. D.

2012-09-01

We have carried out investigations aimed at understanding the mechanism responsible for a water contact angle increase of up to ten degrees and a decrease in dielectric constant in silicon modified hydrogenated amorphous carbon films compared to unmodified hydrogenated amorphous carbon films. Our investigations based on surface chemical constituent analysis using Raman spectroscopy, x-ray photoelectron spectroscopy (XPS), SIMS, FTIR, contact angle / surface energy measurements and spectroscopic ellipsometry suggests the presence of hydrophobic chemical entities on the surface of the films. This observation is consistent with earlier theoretical plasma chemistry predictions and observed Raman peak shifts in the films. These surface hydrophobic entities also have a lower polarizability than the bonds in the un-modified films thereby reducing the dielectric constant of the silicon modified films measured by spectroscopic ellipsometry. Ellipsometric dielectric constant measurement is directly related to the surface energy through Hamaker's constant. Our current finding is expected to be of benefit to understanding stiction, friction and lubrication in areas that range from nano-tribology to microfluidics.

Resonances in piecewise potentials and Supersymmetric Quantum Mechanics (SUSY-QM) for the construction of optical potentials

NASA Astrophysics Data System (ADS)

Orozco Cortés, Luis Fernando; Fernández García, Nicolás

2014-05-01

A method to obtain the general solution of any constant piecewise potential is presented, this is achieved by means of the analysis of the transfer matrices in each cutoff. The resonance phenomenon together with the supersymmetric quantum mechanics technique allow us to construct a wide family of complex potentials which can be used as theoretical models for optical systems. The method is applied to the particular case for which the potential function has six cutoff points.

Xylary pH and Reduction Potential Levels of Iron-stressed Silver Maple (Acer saccharinum L.) 1

PubMed Central

Morris, Robert L.; Swanson, Bert T.

1980-01-01

Xylary fluid pH and reduction potentials were measured on silver maple (Acer saccharinum L.) grown under Fe and pH stress. Although pH and reduction potential (millivolt/59.2) varied significantly in the nutrient solution, xylary pH and reduction potential remained constant. It was concluded that changes in the pH and reduction potential in the xylary fluid of silver maple are not responsible for iron chlorosis. PMID:16661196

Nuclear-spin optical rotation in xenon

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

Savukov, Igor Mykhaylovich

We report that the nuclear-spin optical rotation (NSOR) effect, which has potential applications in correlated nuclear-spin-resonance optical spectroscopy, has previously been explored experimentally and theoretically in liquid Xe. Calculations of the Xe NSOR constant are very challenging because the result is sensitive to correlations, relativistic effects, and the choice of basis, with strong cancellation between contributions from lowest and remaining states. The relativistic configuration-interaction many-body-theory approach, presented here, is promising because this approach has been successful in predicting various properties of noble-gas atoms, such as energies, oscillator strengths (OSs), Verdet constants, and photoionization cross sections. However, correlations become stronger alongmore » the sequence of noble-gas atoms and the theoretical accuracy in Xe is not as high as, for example, in neon and argon. To improve the accuracy of the Xe Verdet and NSOR constants, which are calculated as explicit sums over the excited states, theoretical values for the several lowest levels are replaced with empirical values of energies, OSs, and hyperfine structure constants. We found that the Xe Verdet constant is in excellent agreement with accurate measurements. To take into account liquid effects, empirical data for energy shifts were also used to correct the NSOR constant. In conclusion, the resulting Xe NSOR constant is in a good agreement with experiment, although the liquid-state effect is treated quite approximately.« less

Nuclear-spin optical rotation in xenon

DOE PAGES

Savukov, Igor Mykhaylovich

2015-10-29

We report that the nuclear-spin optical rotation (NSOR) effect, which has potential applications in correlated nuclear-spin-resonance optical spectroscopy, has previously been explored experimentally and theoretically in liquid Xe. Calculations of the Xe NSOR constant are very challenging because the result is sensitive to correlations, relativistic effects, and the choice of basis, with strong cancellation between contributions from lowest and remaining states. The relativistic configuration-interaction many-body-theory approach, presented here, is promising because this approach has been successful in predicting various properties of noble-gas atoms, such as energies, oscillator strengths (OSs), Verdet constants, and photoionization cross sections. However, correlations become stronger alongmore » the sequence of noble-gas atoms and the theoretical accuracy in Xe is not as high as, for example, in neon and argon. To improve the accuracy of the Xe Verdet and NSOR constants, which are calculated as explicit sums over the excited states, theoretical values for the several lowest levels are replaced with empirical values of energies, OSs, and hyperfine structure constants. We found that the Xe Verdet constant is in excellent agreement with accurate measurements. To take into account liquid effects, empirical data for energy shifts were also used to correct the NSOR constant. In conclusion, the resulting Xe NSOR constant is in a good agreement with experiment, although the liquid-state effect is treated quite approximately.« less

Maximum Mass of Hybrid Stars in the Quark Bag Model

NASA Astrophysics Data System (ADS)

Alaverdyan, G. B.; Vartanyan, Yu. L.

2017-12-01

The effect of model parameters in the equation of state for quark matter on the magnitude of the maximum mass of hybrid stars is examined. Quark matter is described in terms of the extended MIT bag model including corrections for one-gluon exchange. For nucleon matter in the range of densities corresponding to the phase transition, a relativistic equation of state is used that is calculated with two-particle correlations taken into account based on using the Bonn meson-exchange potential. The Maxwell construction is used to calculate the characteristics of the first order phase transition and it is shown that for a fixed value of the strong interaction constant αs, the baryon concentrations of the coexisting phases grow monotonically as the bag constant B increases. It is shown that for a fixed value of the strong interaction constant αs, the maximum mass of a hybrid star increases as the bag constant B decreases. For a given value of the bag parameter B, the maximum mass rises as the strong interaction constant αs increases. It is shown that the configurations of hybrid stars with maximum masses equal to or exceeding the mass of the currently known most massive pulsar are possible for values of the strong interaction constant αs > 0.6 and sufficiently low values of the bag constant.

Constant pressure mode extended simple gradient liquid chromatography system for micro and nanocolumns.

PubMed

Šesták, Jozef; Kahle, Vladislav

2014-07-11

Performing gradient liquid chromatography at constant pressure instead of constant flow rate has serious potential for shortening the analysis time and increasing the productivity of HPLC instruments that use gradient methods. However, in the constant pressure mode the decreasing column permeability during a long period of time negatively affects the repeatability of retention time. Thus a volume-based approach, in which the detector signal is plotted as a function of retention volume, must be taken into consideration. Traditional HPLC equipment, however, requires quite complex hardware and software modifications in order to work at constant pressure and in the volume-based mode. In this short communication, a low cost and easily feasible pressure-controlled extension of the previously described simple gradient liquid chromatography platform is proposed. A test mixture of four nitro esters was separated by 10-60% (v/v) acetone/water gradient and a high repeatability of retention volumes at 20MPa (RSD less than 0.45%) was realized. Separations were also performed at different values of pressure (20, 25, and 31MPa), and only small variations of the retention volumes (up to 0.8%) were observed. In this particular case, the gain in the analysis speed of 7% compared to the constant flow mode was realized at a constant pressure. Copyright © 2014 Elsevier B.V. All rights reserved.

Effects of changing the ionic environment on passive and active membrane properties of pregnant rat uterus

PubMed Central

Abe, Y.

1971-01-01

1. In pregnant rat myometrium electrotonic potentials, produced by externally applied current, were recorded intracellularly. 2. The space constant, λ, was 1·8 mm, the time constant, τm, 120 msec. The values obtained on the 7th day and on the 20th day of pregnancy were the same. 3. The magnitude of the electrotonic potential and the time constant of the membrane were increased in the absence of potassium from the external solution and decreased by excess potassium. 4. The magnitude of the electrotonic potential and the time constant of the membrane were increased by the replacement of chloride with C6H5SO3- or SO42-, and decreased with NO3- or I- replacement. 5. When the sodium chloride was replaced with sucrose (16·7 mM sodium remaining in the buffers) the spontaneous spikes deteriorated and activity stopped within 30 min. However, for periods up to 4 hr, a spike of larger amplitude and faster rate of rise than in normal solution could be evoked when a depolarizing current was applied. 6. When the external calcium concentration was raised (5 and 10 mM) the amplitude and the rate of rise of the evoked spike were increased. They were decreased by reducing calcium. In zero calcium spontaneous activity stopped within 15 min. 7. The effects of calcium deficiency were much less marked and slower in onset when, simultaneously, the sodium concentration was reduced to 16·7 mM. 8. When calcium was replaced with strontium (2·5 mM), the membrane was depolarized and the duration of the spontaneous and evoked action potential was prolonged, mainly due to a slowed rate of repolarization. When the concentration of strontium was raised to 7·5 or 12·5 mM the membrane was hyperpolarized, the duration of the action potential became short and the amplitude of the spike was increased. 9. Addition of barium or the replacement of calcium with barium caused depolarization and oscillatory membrane activity. However, a spike could be evoked by applying conditioning hyperpolarization. 10. Manganese abolished the spontaneous and evoked spike. Tetrodotoxin had no effect. 11. The results show that rat uterus has cable-like properties. The action potential may be due to calcium entry, while sodium, by influencing the membrane potential in competition with calcium, may be involved in the spontaneous spike generation and the spread of excitation. PMID:5103422

Potential Energy Surface for Large Barrierless Reaction Systems: Application to the Kinetic Calculations of the Dissociation of Alkanes and the Reverse Recombination Reactions.

PubMed

Yao, Qian; Cao, Xiao-Mei; Zong, Wen-Gang; Sun, Xiao-Hui; Li, Ze-Rong; Li, Xiang-Yuan

2018-05-31

The isodesmic reaction method is applied to calculate the potential energy surface (PES) along the reaction coordinates and the rate constants of the barrierless reactions for unimolecular dissociation reactions of alkanes to form two alkyl radicals and their reverse recombination reactions. The reaction class is divided into 10 subclasses depending upon the type of carbon atoms in the reaction centers. A correction scheme based on isodesmic reaction theory is proposed to correct the PESs at UB3LYP/6-31+G(d,p) level. To validate the accuracy of this scheme, a comparison of the PESs at B3LYP level and the corrected PESs with the PESs at CASPT2/aug-cc-pVTZ level is performed for 13 representative reactions, and it is found that the deviations of the PESs at B3LYP level are up to 35.18 kcal/mol and are reduced to within 2 kcal/mol after correction, indicating that the PESs for barrierless reactions in a subclass can be calculated meaningfully accurately at a low level of ab initio method using our correction scheme. High-pressure limit rate constants and pressure dependent rate constants of these reactions are calculated based on their corrected PESs and the results show the pressure dependence of the rate constants cannot be ignored, especially at high temperatures. Furthermore, the impact of molecular size on the pressure-dependent rate constants of decomposition reactions of alkanes and their reverse reactions has been studied. The present work provides an effective method to generate meaningfully accurate PESs for large molecular system.

Channel gating kinetics and synaptic efficacy: a hypothesis for expression of long-term potentiation.

PubMed Central

Ambros-Ingerson, J; Lynch, G

1993-01-01

A kinetic model of the glutamate DL-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor/channel complex was used to test whether changes in the rate constants describing channel behavior could account for various features of long-term potentiation (LTP). Starting values for the kinetic parameters were set to satisfy experimental data (e.g., affinity, mean open time, mean burst length, etc.) and physical constraints (i.e., microreversibility). The resultant model exhibited a variety of dynamic properties known to be associated with the receptor. Increasing the rate constants governing opening/closing of the channel produced an unexpected increase in the probability of the channel being open shortly after transmitter binding. This would account for the enhanced response size with LTP. Increases in rate constants produced two other aspects of LTP: (i) an alteration of the waveform of the synaptic response and (ii) an interaction with changes in desensitization kinetics. The results obtained with the model corresponded closely to those found in LTP experiments. Thus, an increase in opening/closing rates for the postsynaptic receptor channel provides a single explanation for diverse characteristics of LTP. Finally, the kinetic manipulation reduced the coefficient of variation of synaptic currents in a model involving 250 receptors. This calls into question the use of variance measures for distinguishing pre- vs. postsynaptic sites of potentiation. PMID:8395058

Carbon Dioxide and Fruit Odor Transduction in Drosophila Olfactory Neurons. What Controls their Dynamic Properties?

PubMed Central

French, Andrew S.; Meisner, Shannon; Su, Chih-Ying; Torkkeli, Päivi H.

2014-01-01

We measured frequency response functions between odorants and action potentials in two types of neurons in Drosophila antennal basiconic sensilla. CO2 was used to stimulate ab1C neurons, and the fruit odor ethyl butyrate was used to stimulate ab3A neurons. We also measured frequency response functions for light-induced action potential responses from transgenic flies expressing H134R-channelrhodopsin-2 (ChR2) in the ab1C and ab3A neurons. Frequency response functions for all stimulation methods were well-fitted by a band-pass filter function with two time constants that determined the lower and upper frequency limits of the response. Low frequency time constants were the same in each type of neuron, independent of stimulus method, but varied between neuron types. High frequency time constants were significantly slower with ethyl butyrate stimulation than light or CO2 stimulation. In spite of these quantitative differences, there were strong similarities in the form and frequency ranges of all responses. Since light-activated ChR2 depolarizes neurons directly, rather than through a chemoreceptor mechanism, these data suggest that low frequency dynamic properties of Drosophila olfactory sensilla are dominated by neuron-specific ionic processes during action potential production. In contrast, high frequency dynamics are limited by processes associated with earlier steps in odor transduction, and CO2 is detected more rapidly than fruit odor. PMID:24466044

A time-based potential step analysis of electrochemical impedance incorporating a constant phase element: a study of commercially pure titanium in phosphate buffered saline.

PubMed

Ehrensberger, Mark T; Gilbert, Jeremy L

2010-05-01

The measurement of electrochemical impedance is a valuable tool to assess the electrochemical environment that exists at the surface of metallic biomaterials. This article describes the development and validation of a new technique, potential step impedance analysis (PSIA), to assess the electrochemical impedance of materials whose interface with solution can be modeled as a simplified Randles circuit that is modified with a constant phase element. PSIA is based upon applying a step change in voltage to a working electrode and analyzing the subsequent current transient response in a combined time and frequency domain technique. The solution resistance, polarization resistance, and interfacial capacitance are found directly in the time domain. The experimental current transient is numerically transformed to the frequency domain to determine the constant phase exponent, alpha. This combined time and frequency approach was tested using current transients generated from computer simulations, from resistor-capacitor breadboard circuits, and from commercially pure titanium samples immersed in phosphate buffered saline and polarized at -800 mV or +1000 mV versus Ag/AgCl. It was shown that PSIA calculates equivalent admittance and impedance behavior over this range of potentials when compared to standard electrochemical impedance spectroscopy. This current transient approach characterizes the frequency response of the system without the need for expensive frequency response analyzers or software. Copyright 2009 Wiley Periodicals, Inc.

Cutting through the Hype: Evaluating the Innovative Potential of New Educational Technologies through Business Model Analysis

ERIC Educational Resources Information Center

Kalman, Yoram M.

2016-01-01

In an era when novel educational technologies are constantly introduced to the marketplace, often accompanied by hyperbolic claims that these ground-breaking innovations will transform the educational landscape, decision makers in educational institutions need a methodological approach for examining the innovative potential of new educational…

Utilizing Teacher Leadership as a Catalyst for Change in Schools

ERIC Educational Resources Information Center

Ankrum, Raymond J.

2016-01-01

School leaders are constantly trying to find alternative ways to leverage and explore teacher leadership potential in their school building(s). Teachers leaders that are willing to go above and beyond their general duties. Teacher leaders are the type of educators that fall under the motif of potentially taking on additive responsibilities that…

Acetylcholine-induced current in perfused rat myoballs

PubMed Central

1980-01-01

Spherical "myoballs" were grown under tissue culture conditions from striated muscle of neonatal rat thighs. The myoballs were examined electrophysiologically with a suction pipette which was used to pass current and perfuse internally. A microelectrode was used to record membrane potential. Experiments were performed with approximately symmetrical (intracellular and extracellular) sodium aspartate solutions. The resting potential, acetylcholine (ACh) reversal potential, and sodium channel reversal potential were all approximately 0 mV. ACh-induced currents were examined by use of both voltage jumps and voltage ramps in the presence of iontophoretically applied agonist. The voltage-jump relaxations had a single exponential time-course. The time constant, tau, was exponentially related to membrane potential, increasing e-fold for 81 mV hyperpolarization. The equilibrium current- voltage relationship was also approximately exponential, from -120 to +81 mV, increasing e-fold for 104 mV hyperpolarization. The data are consistent with a first-order gating process in which the channel opening rate constant is slightly voltage dependent. The instantaneous current-voltage relationship was sublinear in the hyperpolarizing direction. Several models are discussed which can account for the nonlinearity. Evidence is presented that the "selectivity filter" for the ACh channel is located near the intracellular membrane surface. PMID:7381423

Dielectric spectroscopy of Ag-starch nanocomposite films

NASA Astrophysics Data System (ADS)

Meena; Sharma, Annu

2018-04-01

In the present work Ag-starch nanocomposite films were fabricated via chemical reduction route. The formation of Ag nanoparticles was confirmed using transmission electron microscopy (TEM). Further the effect of varying concentration of Ag nanoparticles on the dielectric properties of starch has been studied. The frequency response of dielectric constant (ε‧), dielectric loss (ε″) and dissipation factor tan(δ) has been studied in the frequency range of 100 Hz to 1 MHz. Dielectric data was further analysed using Cole-Cole plots. The dielectric constant of starch was found to be 4.4 which decreased to 2.35 in Ag-starch nanocomposite film containing 0.50 wt% of Ag nanoparticles. Such nanocomposites with low dielectric constant have potential applications in microelectronic technologies.

Solution of the Fokker-Planck equation with a logarithmic potential and mixed eigenvalue spectrum

NASA Astrophysics Data System (ADS)

Guarnieri, F.; Moon, W.; Wettlaufer, J. S.

2017-09-01

Motivated by a problem in climate dynamics, we investigate the solution of a Bessel-like process with a negative constant drift, described by a Fokker-Planck equation with a potential V (x ) =-[b ln(x ) +a x ] , for b >0 and a <0 . The problem belongs to a family of Fokker-Planck equations with logarithmic potentials closely related to the Bessel process that has been extensively studied for its applications in physics, biology, and finance. The Bessel-like process we consider can be solved by seeking solutions through an expansion into a complete set of eigenfunctions. The associated imaginary-time Schrödinger equation exhibits a mix of discrete and continuous eigenvalue spectra, corresponding to the quantum Coulomb potential describing the bound states of the hydrogen atom. We present a technique to evaluate the normalization factor of the continuous spectrum of eigenfunctions that relies solely upon their asymptotic behavior. We demonstrate the technique by solving the Brownian motion problem and the Bessel process both with a constant negative drift. We conclude with a comparison to other analytical methods and with numerical solutions.

Absorption coefficient and relative refractive index change for a double δ-doped GaAs MIGFET-like structure: Electric and magnetic field effects

NASA Astrophysics Data System (ADS)

Martínez-Orozco, J. C.; Rodríguez-Magdaleno, K. A.; Suárez-López, J. R.; Duque, C. A.; Restrepo, R. L.

2016-04-01

In this work we present theoretical results for the electronic structure as well as for the absorption coefficient and relative refractive index change for an asymmetric double δ-doped like confining potential in the active region of a Multiple Independent Gate Field Effect Transistor (MIGFET) system. We model the potential profile as a double δ-doped like potential profile between two Schottky (parabolic) potential barriers that are just the main characteristics of the MIGFET configuration. We investigate the effect of external electromagnetic fields in this kind of quantum structures, in particular we applied a homogeneous constant electric field in the growth direction z as well as a homogeneous constant magnetic field in the x-direction. In general we conclude that by applying electromagnetic fields we can modulate the resonant peaks of the absorption coefficient as well as their energy position. Also with such probes it is possible to control the nodes and amplitude of the relative refractive index changes related to resonant intersubband optical transitions.

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

Pribram-Jones, A.; Burke, K.

We show that the adiabatic connection formula of ground-state density functional theory relates the correlation energy to a coupling-constant integral over a purely potential contribution, and is widely used to understand and improve approximations. The corresponding formula for thermal density functional theory is cast as an integral over temperatures instead, ranging upward from the system's physical temperature. We also show how to relate different correlation components to each other, either in terms of temperature or coupling-constant integrations. Lastly, we illustrate our results on the uniform electron gas.

A Study of Terrain Reductions, Density Anomalies and Geophysical Inversion Methods in Gravity Field Modelling

DTIC Science & Technology

1984-04-01

5.15) where a is a positive constant and 11 IIH the Hilbert space norm associated with the chosen covariance function K. The constant a is arbitrary...Density Anomalies 14 5. Unknown Densities - Geophysical Inversion 16 6. Density Modelling Using Rectangular Prisms 24 6.1 Space Domain 24 6.2 Frequency...theory: to calculate the gravity potential and its derivatives in space due to 6 • given density distributions. When the prime interest is in "external

Motoneuron membrane potentials follow a time inhomogeneous jump diffusion process.

PubMed

Jahn, Patrick; Berg, Rune W; Hounsgaard, Jørn; Ditlevsen, Susanne

2011-11-01

Stochastic leaky integrate-and-fire models are popular due to their simplicity and statistical tractability. They have been widely applied to gain understanding of the underlying mechanisms for spike timing in neurons, and have served as building blocks for more elaborate models. Especially the Ornstein-Uhlenbeck process is popular to describe the stochastic fluctuations in the membrane potential of a neuron, but also other models like the square-root model or models with a non-linear drift are sometimes applied. Data that can be described by such models have to be stationary and thus, the simple models can only be applied over short time windows. However, experimental data show varying time constants, state dependent noise, a graded firing threshold and time-inhomogeneous input. In the present study we build a jump diffusion model that incorporates these features, and introduce a firing mechanism with a state dependent intensity. In addition, we suggest statistical methods to estimate all unknown quantities and apply these to analyze turtle motoneuron membrane potentials. Finally, simulated and real data are compared and discussed. We find that a square-root diffusion describes the data much better than an Ornstein-Uhlenbeck process with constant diffusion coefficient. Further, the membrane time constant decreases with increasing depolarization, as expected from the increase in synaptic conductance. The network activity, which the neuron is exposed to, can be reasonably estimated to be a threshold version of the nerve output from the network. Moreover, the spiking characteristics are well described by a Poisson spike train with an intensity depending exponentially on the membrane potential.

Effects of constant and fluctuating temperature on the development of the oriental fruit moth, Grapholita molesta (Lepidoptera: Tortricidae).

PubMed

Chen, Z-Z; Xu, L-X; Li, L-L; Wu, H-B; Xu, Y-Y

2018-06-21

The oriental fruit moth, Grapholita molesta, is an important pest in many commercial orchards including apple, pear and peach orchards, and responsible for substantial economic losses every year. To help in attaining a comprehensive and thorough understanding of the ecological tolerances of G. molesta, we collected life history data of individuals reared on apples under different constant temperature regimes and compared the data with moths reared under a variable outdoor temperature environment. Because G. molesta individuals reared at a constant 25°C had the heaviest pupal weight, the highest survival rate from egg to adult, highest finite rate of increase, and greatest fecundity, 25°C was considered as the optimum developmental temperature. The G. molesta population reared at a constant 31°C had the shortest development time, lowest survival rate and fecundity, resulting in population parameters of r < 0, λ < 1, lead to negative population growth. The population parameters r and λ reared under fluctuating temperature were higher than that reared under constant temperatures, the mean generation time (T) was shorter than it was in all of the constant temperatures treatments. This would imply that the outdoor G. molesta population would have a higher population growth potential and faster growth rate than indoor populations raised at constant temperatures. G. molesta moths reared under fluctuating temperature also had a higher fertility than moths reared under constant temperatures (except at 25°C). Our findings indicated that the population raised under outdoor fluctuating temperature conditions had strong environment adaptiveness.

Analysis of the axisymmetric indentation of a semi-infinite piezoelectric material: The evaluation of the contact stiffness and the effective piezoelectric constant

NASA Astrophysics Data System (ADS)

Yang, Fuqian

2008-04-01

A general solution of the axisymmetric indentation is obtained in the closed form for a semi-infinite, transverse isotropic piezoelectric material by a rigid-conducting indenter of arbitrary-axisymmetric profile. Explicit relationships are derived for dependences of the indentation depth and the indentation-induced charge on indentation force and applied electrical potential. Simple formulas are obtained for contact stiffness and effective piezoelectric constant, which can be used in indentation test and piezoresponse force microscopy to analyze the elastic and piezoelectric responses of piezoelectric materials. Depending on the direction of electric field (the potential difference), the electric field can either increase or suppress indentation deformation. The corresponding results are given for cylindrical, conical, and paraboloidal indenters.

Shielding requirements for constant-potential diagnostic x-ray beams determined by a Monte Carlo calculation.

PubMed

Simpkin, D J

1989-02-01

A Monte Carlo calculation has been performed to determine the transmission of broad constant-potential x-ray beams through Pb, concrete, gypsum wallboard, steel and plate glass. The EGS4 code system was used with a simple broad-beam geometric model to generate exposure transmission curves for published 70, 100, 120 and 140-kVcp x-ray spectra. These curves are compared to measured three-phase generated x-ray transmission data in the literature and found to be reasonable. For calculation ease the data are fit to an equation previously shown to describe such curves quite well. These calculated transmission data are then used to create three-phase shielding tables for Pb and concrete, as well as other materials not available in Report No. 49 of the NCRP.

Experimental validation of the Helmoltz equation for the surface potential of Langmuir monolayers

NASA Astrophysics Data System (ADS)

El Abed, Abdel I.

2009-10-01

We show in this paper that monolayers of the nonhydrophilic F8H18 semifluorinated n -alkane constitute when spread on the hydrophobic top of an alamethicin Langmuir monolayer, a very good experimental system in order to check the validity of Helmoltz equation. This system allows for a good agreement between measured and calculated surface potentials of unionized Langmuir monolayers. We show also that the relative dielectric constant of the F8H18 monolayer does not vary upon compression of the monolayer, the measured 2.9 value is in a very good agreement with literature data. We attribute this behavior to the self-aggregation of F8H18 molecules in nanosized circular domains whose size remains constant upon compression as shown by atomic force microscopy.

Limits on the dependence of the fine-structure constant on gravitational potential from white-dwarf spectra.

PubMed

Berengut, J C; Flambaum, V V; Ong, A; Webb, J K; Barrow, John D; Barstow, M A; Preval, S P; Holberg, J B

2013-07-05

We propose a new probe of the dependence of the fine-structure constant α on a strong gravitational field using metal lines in the spectra of white-dwarf stars. Comparison of laboratory spectra with far-UV astronomical spectra from the white-dwarf star G191-B2B recorded by the Hubble Space Telescope Imaging Spectrograph gives limits of Δα/α=(4.2±1.6)×10(-5) and (-6.1±5.8)×10(-5) from FeV and NiV spectra, respectively, at a dimensionless gravitational potential relative to Earth of Δφ≈5×10(-5). With better determinations of the laboratory wavelengths of the lines employed these results could be improved by up to 2 orders of magnitude.

Limits on the Dependence of the Fine-Structure Constant on Gravitational Potential from White-Dwarf Spectra

NASA Astrophysics Data System (ADS)

Berengut, J. C.; Flambaum, V. V.; Ong, A.; Webb, J. K.; Barrow, John D.; Barstow, M. A.; Preval, S. P.; Holberg, J. B.

2013-07-01

We propose a new probe of the dependence of the fine-structure constant α on a strong gravitational field using metal lines in the spectra of white-dwarf stars. Comparison of laboratory spectra with far-UV astronomical spectra from the white-dwarf star G191-B2B recorded by the Hubble Space Telescope Imaging Spectrograph gives limits of Δα/α=(4.2±1.6)×10-5 and (-6.1±5.8)×10-5 from FeV and NiV spectra, respectively, at a dimensionless gravitational potential relative to Earth of Δϕ≈5×10-5. With better determinations of the laboratory wavelengths of the lines employed these results could be improved by up to 2 orders of magnitude.

METHOD AND APPARATUS FOR DETERMINING AMALGAM DECOMPOSITION RATE

DOEpatents

Johnson, R.W.; Wright, C.C.

1962-04-24

A method and apparatus for measuring the rate at which an amalgam decomposes in contact with aqueous solutions are described. The amalgam and an aqueous hydroxide solution are disposed in an electrolytic cell. The amalgam is used as the cathode of the cell, and an electrode and anode are disposed in the aqueous solution. A variable source of plating potential is connected across the cell. The difference in voltage between the amalgam cathode and a calibrated source of reference potential is used to control the variable source to null the difference in voltage and at the same time to maintain the concentration of the amalgam at some predetermined constant value. The value of the current required to maintain this concentration constant is indicative of the decomposition rate of the amalgam. (AEC)

Cinetica de oxidacion de polimeros conductores: poli-3,4- etilendioxitiofeno

NASA Astrophysics Data System (ADS)

Caballero Romero, Maria

Films of poly-3,4-ethylenedioxythiophene (PEDOT) perchlorate used as electrodes in liquid electrolytes incorporate anions and solvent during oxidation for charge and osmotic balance: the film swells. During reduction the film shrinks, closes its structure trapping counterions getting then rising conformational packed states by expulsion of counterions and solvent. Here by potential step from the same reduced initial state to the same oxidized final state the rate coefficient, the activation energy and reaction orders related to the counterion concentration in solution and to the concentration of active centers in the polymer film, were attained following the usual methodology used for chemical and electrochemical kinetics. Now the full methodology was repeated using different reduced-shrunk or reduced-conformational compacted initial states every time. Those initial states were attained by reduction of the oxidized film at rising cathodic potentials for the same reduction time each. Rising reduced and conformational compacted states give slower subsequent oxidation rates by potential step to the same anodic potential every time. The activation energy, the reaction coefficient and reaction orders change for rising conformational compacted initial states. Decreasing rate constants and increasing activation energies are obtained for the PEDOT oxidation from increasing conformational compacted initial states. The experimental activation energy presents two linear ranges as a function of the initial reduced-compacted state. Using as initial states for the oxidation open structures attained by reduction at low cathodic potentials, activation energies attained were constant: namely the chemical activation energy. Using as initial states for the oxidation deeper reduced, closed and packed conformational structures, the activation energy includes two components: the constant chemical energy plus the conformational energy required to relax the conformational structure generating free volume which allows the entrance of the balancing counterions required for the reaction. The conformational energy increases linearly as a function of the reduction-compaction potential. The kinetic magnitudes include conformational and structural information. The Chemical Kinetics becomes Structural (or conformational) Chemical Kinetics.

Directly patching high-level exchange-correlation potential based on fully determined optimized effective potentials

NASA Astrophysics Data System (ADS)

Huang, Chen; Chi, Yu-Chieh

2017-12-01

The key element in Kohn-Sham (KS) density functional theory is the exchange-correlation (XC) potential. We recently proposed the exchange-correlation potential patching (XCPP) method with the aim of directly constructing high-level XC potential in a large system by patching the locally computed, high-level XC potentials throughout the system. In this work, we investigate the patching of the exact exchange (EXX) and the random phase approximation (RPA) correlation potentials. A major challenge of XCPP is that a cluster's XC potential, obtained by solving the optimized effective potential equation, is only determined up to an unknown constant. Without fully determining the clusters' XC potentials, the patched system's XC potential is "uneven" in the real space and may cause non-physical results. Here, we developed a simple method to determine this unknown constant. The performance of XCPP-RPA is investigated on three one-dimensional systems: H20, H10Li8, and the stretching of the H19-H bond. We investigated two definitions of EXX: (i) the definition based on the adiabatic connection and fluctuation dissipation theorem (ACFDT) and (ii) the Hartree-Fock (HF) definition. With ACFDT-type EXX, effective error cancellations were observed between the patched EXX and the patched RPA correlation potentials. Such error cancellations were absent for the HF-type EXX, which was attributed to the fact that for systems with fractional occupation numbers, the integral of the HF-type EXX hole is not -1. The KS spectra and band gaps from XCPP agree reasonably well with the benchmarks as we make the clusters large.

Some remarks on the attractor behaviour in ELKO cosmology

NASA Astrophysics Data System (ADS)

Pereira, S. H.; A. Pinho S., S.; Hoff da Silva, J. M.

2014-08-01

Recent results on the dynamical stability of a system involving the interaction of the ELKO spinor field with standard matter in the universe have been reanalysed, and the conclusion is that such system does not exhibit isolated stable points that could alleviate the cosmic coincidence problem. When a constant parameter δ related to the potential of the ELKO field is introduced in the system however, stable fixed points are found for some specific types of interaction between the ELKO field and matter. Although the parameter δ is related to an unknown potential, in order to satisfy the stability conditions and also that the fixed points are real, the range of the constant parameter δ can be constrained for the present time and the coincidence problem can be alleviated for some specific interactions. Such restriction on the ELKO potential opens possibility to apply the ELKO field as a candidate to dark energy in the universe, and so explain the present phase of acceleration of the universe through the decay of the ELKO field into matter.

Simple optimized Brenner potential for thermodynamic properties of diamond

NASA Astrophysics Data System (ADS)

Liu, F.; Tang, Q. H.; Shang, B. S.; Wang, T. C.

2012-02-01

We have examined the commonly used Brenner potentials in the context of the thermodynamic properties of diamond. A simple optimized Brenner potential is proposed that provides very good predictions of the thermodynamic properties of diamond. It is shown that, compared to the experimental data, the lattice wave theory of molecular dynamics (LWT) with this optimized Brenner potential can accurately predict the temperature dependence of specific heat, lattice constant, Grüneisen parameters and coefficient of thermal expansion (CTE) of diamond.

Determination of cable parameters in skeletal muscle fibres during repetitive firing of action potentials.

PubMed

Riisager, Anders; Duehmke, Rudy; Nielsen, Ole Bækgaard; Huang, Christopher L; Pedersen, Thomas Holm

2014-10-15

Recent studies in rat muscle fibres show that repetitive firing of action potentials causes changes in fibre resting membrane conductance (Gm) that reflect regulation of ClC-1 Cl(-) and KATP K(+) ion channels. Methodologically, these findings were obtained by inserting two microelectrodes at close proximity in the same fibres enabling measurements of fibre input resistance (Rin) in between action potential trains. Since the fibre length constant (λ) could not be determined, however, the calculation of Gm relied on the assumptions that the specific cytosolic resistivity (Ri) and muscle fibre volume remained constant during the repeated action potential firing. Here we present a three-microelectrode technique that enables determinations of multiple cable parameters in action potential-firing fibres including Rin and λ as well as waveform and conduction velocities of fully propagating action potentials. It is shown that in both rat and mouse extensor digitorum longus (EDL) fibres, action potential firing leads to substantial changes in both muscle fibre volume and Ri. The analysis also showed, however, that regardless of these changes, rat and mouse EDL fibres both exhibited initial decreases in Gm that were eventually followed by a ∼3-fold, fully reversible increase in Gm after the firing of 1450-1800 action potentials. Using this three-electrode method we further show that the latter rise in Gm was closely associated with excitation failures and loss of action potential signal above -20 mV. © 2014 The Authors. The Journal of Physiology © 2014 The Physiological Society.

Determination of cable parameters in skeletal muscle fibres during repetitive firing of action potentials

PubMed Central

Riisager, Anders; Duehmke, Rudy; Nielsen, Ole Bækgaard; Huang, Christopher L; Pedersen, Thomas Holm

2014-01-01

Recent studies in rat muscle fibres show that repetitive firing of action potentials causes changes in fibre resting membrane conductance (Gm) that reflect regulation of ClC-1 Cl− and KATP K+ ion channels. Methodologically, these findings were obtained by inserting two microelectrodes at close proximity in the same fibres enabling measurements of fibre input resistance (Rin) in between action potential trains. Since the fibre length constant (λ) could not be determined, however, the calculation of Gm relied on the assumptions that the specific cytosolic resistivity (Ri) and muscle fibre volume remained constant during the repeated action potential firing. Here we present a three-microelectrode technique that enables determinations of multiple cable parameters in action potential-firing fibres including Rin and λ as well as waveform and conduction velocities of fully propagating action potentials. It is shown that in both rat and mouse extensor digitorum longus (EDL) fibres, action potential firing leads to substantial changes in both muscle fibre volume and Ri. The analysis also showed, however, that regardless of these changes, rat and mouse EDL fibres both exhibited initial decreases in Gm that were eventually followed by a ∼3-fold, fully reversible increase in Gm after the firing of 1450–1800 action potentials. Using this three-electrode method we further show that the latter rise in Gm was closely associated with excitation failures and loss of action potential signal above −20 mV. PMID:25128573

Coupling time constants of striated and copper-plated coated conductors and the potential of striation to reduce shielding-current-induced fields in pancake coils

NASA Astrophysics Data System (ADS)

Amemiya, Naoyuki; Tominaga, Naoki; Toyomoto, Ryuki; Nishimoto, Takuma; Sogabe, Yusuke; Yamano, Satoshi; Sakamoto, Hisaki

2018-07-01

The shielding-current-induced field is a serious concern for the applications of coated conductors to magnets. The striation of the coated conductor is one of the countermeasures, but it is effective only after the decay of the coupling current, which is characterised with the coupling time constant. In a non-twisted striated coated conductor, the coupling time constant is determined primarily by its length and the transverse resistance between superconductor filaments, because the coupling current could flow along its entire length. We measured and numerically calculated the frequency dependences of magnetisation losses in striated and copper-plated coated conductors with various lengths and their stacks at 77 K and determined their coupling time constants. Stacked conductors simulate the turns of a conductor wound into a pancake coil. Coupling time constants are proportional to the square of the conductor length. Stacking striated coated conductors increases the coupling time constants because the coupling currents in stacked conductors are coupled to one another magnetically to increase the mutual inductances for the coupling current paths. We carried out the numerical electromagnetic field analysis of conductors wound into pancake coils and determined their coupling time constants. They can be explained by the length dependence and mutual coupling effect observed in stacked straight conductors. Even in pancake coils with practical numbers of turns, i.e. conductor lengths, the striation is effective to reduce the shielding-current-induced fields for some dc applications.

Action potential propagation: ion current or intramembrane electric field?

PubMed

Martí, Albert; Pérez, Juan J; Madrenas, Jordi

2018-01-01

The established action potential propagation mechanisms do not satisfactorily explain propagation on myelinated axons given the current knowledge of biological channels and membranes. The flow across ion channels presents two possible effects: the electric potential variations across the lipid bilayers (action potential) and the propagation of an electric field through the membrane inner part. The proposed mechanism is based on intra-membrane electric field propagation, this propagation can explain the action potential saltatory propagation and its constant delay independent of distance between Ranvier nodes in myelinated axons.

Earth’s gravity and the cosmological constant: a worked example

NASA Astrophysics Data System (ADS)

Pereira, J. A. M.

2016-03-01

The cosmological constant regained the attention of the scientific community following the recent discovery of the accelerated expansion of the Universe. Consequently, interest in the subject increased amongst the public such that it now often appears in the classroom and popular science publications. The purpose of this article is to use basic concepts of Newtonian mechanics, like dynamics, kinetic energy and potential energy diagrams, in a scenario where the cosmological constant’s action, considered as being an inertial force driven by the accelerated expansion of the Universe, could counteract Earth’s gravity. The effect that the cosmological constant might have near the Earth’s surface is discussed showing how everyday life would change. This is done in such a way that makes it accessible to students in their first year of college. Finally, the modern interpretation of the cosmological constant, associated with the existence of dark energy, is briefly discussed along with upper limit estimations for its value based on the anthropic principle.

Characterization of Receptor Binding Profiles of Influenza A Viruses Using An Ellipsometry-Based Label-Free Glycan Microarray Assay Platform

PubMed Central

Fei, Yiyan; Sun, Yung-Shin; Li, Yanhong; Yu, Hai; Lau, Kam; Landry, James P.; Luo, Zeng; Baumgarth, Nicole; Chen, Xi; Zhu, Xiangdong

2015-01-01

A key step leading to influenza viral infection is the highly specific binding of a viral spike protein, hemagglutinin (HA), with an extracellular glycan receptor of a host cell. Detailed and timely characterization of virus-receptor binding profiles may be used to evaluate and track the pandemic potential of an influenza virus strain. We demonstrate a label-free glycan microarray assay platform for acquiring influenza virus binding profiles against a wide variety of glycan receptors. By immobilizing biotinylated receptors on a streptavidin-functionalized solid surface, we measured binding curves of five influenza A virus strains with 24 glycans of diverse structures and used the apparent equilibrium dissociation constants (avidity constants, 10–100 pM) as characterizing parameters of viral receptor profiles. Furthermore by measuring binding kinetic constants of solution-phase glycans to immobilized viruses, we confirmed that the glycan-HA affinity constant is in the range of 10 mM and the reaction is enthalpy-driven. PMID:26193329

Characterization of Receptor Binding Profiles of Influenza A Viruses Using An Ellipsometry-Based Label-Free Glycan Microarray Assay Platform.

PubMed

Fei, Yiyan; Sun, Yung-Shin; Li, Yanhong; Yu, Hai; Lau, Kam; Landry, James P; Luo, Zeng; Baumgarth, Nicole; Chen, Xi; Zhu, Xiangdong

2015-07-16

A key step leading to influenza viral infection is the highly specific binding of a viral spike protein, hemagglutinin (HA), with an extracellular glycan receptor of a host cell. Detailed and timely characterization of virus-receptor binding profiles may be used to evaluate and track the pandemic potential of an influenza virus strain. We demonstrate a label-free glycan microarray assay platform for acquiring influenza virus binding profiles against a wide variety of glycan receptors. By immobilizing biotinylated receptors on a streptavidin-functionalized solid surface, we measured binding curves of five influenza A virus strains with 24 glycans of diverse structures and used the apparent equilibrium dissociation constants (avidity constants, 10-100 pM) as characterizing parameters of viral receptor profiles. Furthermore by measuring binding kinetic constants of solution-phase glycans to immobilized viruses, we confirmed that the glycan-HA affinity constant is in the range of 10 mM and the reaction is enthalpy-driven.

Elastic constants from microscopic strain fluctuations

PubMed

Sengupta; Nielaba; Rao; Binder

2000-02-01

Fluctuations of the instantaneous local Lagrangian strain epsilon(ij)(r,t), measured with respect to a static "reference" lattice, are used to obtain accurate estimates of the elastic constants of model solids from atomistic computer simulations. The measured strains are systematically coarse-grained by averaging them within subsystems (of size L(b)) of a system (of total size L) in the canonical ensemble. Using a simple finite size scaling theory we predict the behavior of the fluctuations as a function of L(b)/L and extract elastic constants of the system in the thermodynamic limit at nonzero temperature. Our method is simple to implement, efficient, and general enough to be able to handle a wide class of model systems, including those with singular potentials without any essential modification. We illustrate the technique by computing isothermal elastic constants of "hard" and "soft" disk triangular solids in two dimensions from Monte Carlo and molecular dynamics simulations. We compare our results with those from earlier simulations and theory.

Making the Impossible Possible: Strategies for Fast POMDP Monitoring

NASA Technical Reports Server (NTRS)

Washington, Richard; Lau, Sonie (Technical Monitor)

1998-01-01

Systems modeled as partially observable Markov decision processes (POMDPs) can be tracked quickly with three restrictions: all actions are grouped together, the out-degree of each system state is bounded by a constant, and the number of non-zero elements in the belief state is bounded by a (different) constant. With these restrictions, the tracking algorithm operates in constant time and linear space. The first restriction assumes that the action itself is unobservable. The second restriction defines a subclass of POMDPs that covers however a wide range of problems. The third restriction is an approximation technique that can lead to a potentially vexing problem: an observation may be received that has probability according to the restricted belief state. This problem of impossibility will cause the belief state to collapse. In this paper we discuss the tradeoffs between the constant bound on the belief state and the quality of the solution. We concentrate on strategies for overcoming the impossibility problem and demonstrate initial experimental results that indicate promising directions.

Stiffness-constant variation in nickel-based alloys: Experiment and theory

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

Hennion, M.; Hennion, B.

1979-01-01

Recent measurements of the spin-wave stiffness constant in several nickel alloys at various concentrations are interpreted within a random-phase approximation, coherent-potential approximation (RPA-CPA) band model which uses the Hartree-Fock approximation to treat the intraatomic correlations. We give a theoretical description of the possible impurity states in the Hartree-Fock approximation. This allows the determination of the Hartree-Fock solutions which can account for the stiffness-constant behavior and the magnetic moment on the impurity for all the investigated alloys. For alloys such as NiCr, NiV, NiMo, and NiRu, the magnetizations of which deviate from the Slater-Pauling curve, our determination does not correspond tomore » previous works and is consequently discussed. The limits of the model appear mainly due to local-environment effects; in the case of NiMn, it is found that a ternary-alloy model with some Mn atoms in the antiferromagnetic state can account for both stiffness-constant and magnetization behaviors.« less

Charged rotating black holes in Einstein-Maxwell-Chern-Simons theory with a negative cosmological constant

NASA Astrophysics Data System (ADS)

Blázquez-Salcedo, Jose Luis; Kunz, Jutta; Navarro-Lérida, Francisco; Radu, Eugen

2017-03-01

We consider rotating black hole solutions in five-dimensional Einstein-Maxwell-Chern-Simons theory with a negative cosmological constant and a generic value of the Chern-Simons coupling constant λ . Using both analytical and numerical techniques, we focus on cohomogeneity-1 configurations, with two equal-magnitude angular momenta, which approach at infinity a globally anti-de Sitter background. We find that the generic solutions share a number of basic properties with the known Cvetič, Lü, and Pope black holes which have λ =1 . New features occur as well; for example, when the Chern-Simons coupling constant exceeds a critical value, the solutions are no longer uniquely determined by their global charges. Moreover, the black holes possess radial excitations which can be labelled by the node number of the magnetic gauge potential function. Solutions with small values of λ possess other distinct features. For instance, the extremal black holes there form two disconnected branches, while not all near-horizon solutions are associated with global solutions.

Determination of Hamaker constants of polymeric nanoparticles in organic solvents by asymmetrical flow field-flow fractionation.

PubMed

Noskov, Sergey; Scherer, Christian; Maskos, Michael

2013-01-25

Interaction forces between all objects are either of repulsive or attractive nature. Concerning attractive interactions, the determination of dispersion forces are of special interest since they appear in all colloidal systems and have a crucial influence on the properties and processes in these systems. One possibility to link theory and experiment is the description of the London-Van der Waals forces in terms of the Hamaker constant, which leads to the challenging problem of calculating the van der Waals interaction energies between colloidal particles. Hence, the determination of a Hamaker constant for a given material is needed when interfacial phenomena such as adhesion are discussed in terms of the total potential energy between particles and substrates. In this work, the asymmetrical flow field-flow fractionation (AF-FFF) in combination with a Newton algorithm based iteration process was used for the determination of Hamaker constants of different nanoparticles in toluene. Copyright © 2012 Elsevier B.V. All rights reserved.

Theoretical study of phonon dispersion, elastic, mechanical and thermodynamic properties of barium chalcogenides

NASA Astrophysics Data System (ADS)

Musari, A. A.; Orukombo, S. A.

2018-03-01

Barium chalcogenides are known for their high-technological importance and great scientific interest. Detailed studies of their elastic, mechanical, dynamical and thermodynamic properties were carried out using density functional theory and plane-wave pseudo potential method within the generalized gradient approximation. The optimized lattice constants were in good agreement when compared with experimental data. The independent elastic constants, calculated from a linear fit of the computed stress-strain function, were used to determine the Young’s modulus (E), bulk modulus (B), shear modulus (G), Poisson’s ratio (σ) and Zener’s anisotropy factor (A). Also, the Debye temperature and sound velocities for barium chalcogenides were estimated from the three independent elastic constants. The calculations of phonon dispersion showed that there are no negative frequencies throughout the Brillouin zone. Hence barium chalcogenides have dynamically stable NaCl-type crystal structure. Finally, their thermodynamic properties were calculated in the temperature range of 0-1000 K and their constant-volume specific heat capacities at room-temperature were reported.

Comparative Studies on the Toxicokinetics of Benzo[a]pyrene in Pinctada martensii and Perna viridis.

PubMed

Wang, Haihua; Cui, Lili; Cheng, Huamin; Zhang, Yu; Diao, Xiaoping; Wang, Jun

2017-05-01

Research on the kinetics of Benzo[a]pyrene (B[a]P) bioaccumulation in the clam Pinctada martensii and mussel Perna viridis showed that the initial rate of uptake was directly related to the PAH concentrations in the ambient environment. The uptake and depuration rate constants were different at the four B[a]P exposure levels, which indicated that the toxicokinetic rate constants mainly depended on the exposure levels of pollutants to the environment. In addition, the uptake rate constants of B[a]P were higher than the depuration rate constants in the entire experiment. The comparison demonstrated that mussels release B[a]P more rapidly than clams. The bioconcentration factors (BCFs) of B[a]P varied from 3335 to 12892 in the clam and 2373-6235 in the mussel. These findings on the bioaccumulation kinetics for petroleum hydrocarbons, in association with the critical body residue, will be valuable when choosing sensitive organisms to assess the potential ecotoxicological risk to the marine environment.

The Stark Effect in Linear Potentials

ERIC Educational Resources Information Center

Robinett, R. W.

2010-01-01

We examine the Stark effect (the second-order shifts in the energy spectrum due to an external constant force) for two one-dimensional model quantum mechanical systems described by linear potentials, the so-called quantum bouncer (defined by V(z) = Fz for z greater than 0 and V(z) = [infinity] for z less than 0) and the symmetric linear potential…

The Beat Goes on: Rhythmic Modulation of Cortical Potentials by Imagined Tapping

ERIC Educational Resources Information Center

Osman, Allen; Albert, Robert; Ridderinkhof, K. Richard; Band, Guido; van der Molen, Maurits

2006-01-01

A frequency analysis was used to tag cortical activity from imagined rhythmic movements. Participants synchronized overt and imagined taps with brief visual stimuli presented at a constant rate, alternating between left and right index fingers. Brain potentials were recorded from across the scalp and topographic maps made of their power at the…

The Influence of a Presence of a Heavy Atom on (13)C Shielding Constants in Organomercury Compounds and Halogen Derivatives.

PubMed

Wodyński, Artur; Gryff-Keller, Adam; Pecul, Magdalena

2013-04-09

(13)C nuclear magnetic resonance shielding constants have been calculated by means of density functional theory (DFT) for several organomercury compounds and halogen derivatives of aliphatic and aromatic compounds. Relativistic effects have been included through the four-component Dirac-Kohn-Sham (DKS) method, two-component Zeroth Order Regular Approximation (ZORA) DFT, and DFT with scalar effective core potentials (ECPs). The relative shieldings have been analyzed in terms of the position of carbon atoms with respect to the heavy atom and their hybridization. The results have been compared with the experimental values, some newly measured and some found in the literature. The main aim of the calculations has been to evaluate the magnitude of heavy atom effects on the (13)C shielding constants and to check what are the relative contributions of scalar relativistic effects and spin-orbit coupling. Another object has been to compare the DKS and ZORA results and to check how the approximate method of accounting for the heavy-atom-on-light-atom (HALA) relativistic effect by means of scalar effective core potentials on heavy atoms performs in comparison with the more rigorous two- and four-component treatment.

Uniform function constants of motion and their first-order perturbation

NASA Astrophysics Data System (ADS)

Prato, Domingo; Hamity, Victor H.

2005-05-01

The main purpose of this work is to present some uniform function constants of motion rather than the well-known quantities arising from spacetime symmetries. These constants are usually associated with the intrinsic characteristics of the trajectories of a particle in a central potential field. We treat two cases. The first is the Lenz vector which sometimes is found in the literature [1, 2]; the other is associated with the isotropic harmonic oscillator, of relative importance in some simple models of the classical molecular interaction. The first example is applied to describe the perturbation of the trajectories in the Rutherford scattering and the precession of the Keplerian orbit of a planet. In the other case the conserved quantity is a symmetric tensor. We find the eigenvectors and eigenvalues of that tensor while at the same time we obtain the solution to the problem of calculating the rotation rate of the orbits in first order of a perturbation parameter in the potential energy, by performing a simple coordinate transformation in the Cartesian plane. We think that the present work addresses many aspects of mechanics with a didactical interest in other physics or mathematics courses.

Nonassociative plasticity model for cohesionless materials and its implementation in soil-structure interaction

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

Hashmi, Q.S.E.

A constitutive model based on rate-independent elastoplasticity concepts is developed and used to simulate the behavior of geologic materials under arbitrary three-dimensional stress paths. The model accounts for various factors such as friction, stress path, and stress history that influence the behavior of geologic materials. A hierarchical approach is adopted whereby models of progressively increasing sophistication are developed from a basic isotropic-hardening associate model. Nonassociativeness is introduced as correction or perturbation to the basic model. Deviation of normality of the plastic-strain increments to the yield surface F is captured through nonassociativeness. The plastic potential Q is obtained by applying amore » correction to F. This simplified approach restricts the number of extra parameters required to define the plastic potential Q. The material constants associated with the model are identified, and they are evaluated for three different sands (Leighton Buzzard, Munich and McCormick Ranch). The model is then verified by comparing predictions with laboratory tests from which the constants were found, and typical tests not used for finding the constants. Based on the above findings, a soil-footing system is analyzed using finite-element techniques.« less

Unruh thermal hadronization and the cosmological constant

NASA Astrophysics Data System (ADS)

Frassino, Antonia M.; Bleicher, Marcus; Mann, Robert B.

2018-05-01

We use black holes with a negative cosmological constant to investigate aspects of the freeze-out temperature for hadron production in high energy heavy-ion collisions. The two black hole solutions present in the anti-de Sitter geometry have different mass and are compared to the data showing that the small black hole solution is in good agreement. This is a new feature in the literature since the small black hole in general relativity has different thermodynamic behavior from that of the large black hole solution. We find that the inclusion of the cosmological constant (which can be interpreted as the plasma pressure) leads to a lowering of the temperature of the freeze-out curve as a function of the baryochemical potential, improving the description previously suggested by Castorina, Kharzeev, and Satz.

Ultrasonic Determination of the Elastic Constants of Epoxy-natural Fiber Composites

NASA Astrophysics Data System (ADS)

Valencia, C. A. Meza; Pazos-Ospina, J. F.; Franco, E. E.; Ealo, Joao L.; Collazos-Burbano, D. A.; Garcia, G. F. Casanova

This paper shows the applications ultrasonic through-transmission technique to determine the elastic constants of two polymer-natural fiber composite materials with potential industrial application and economic and environmental advantages. The transversely isotropic coconut-epoxy and fique-epoxy samples were analyzed using an experimental setup which allows the sample to be rotated with respect to transducers faces and measures the time-of-flight at different angles of incidence. Then, the elastic properties of the material were obtained by fitting the experimental data to the Christoffel equation. Results show a good agreement between the measured elastic constants and the values predicted by an analytical model. The velocities as a function of the incidence angle are reported and the effect of the natural fiber on the stiffness of the composite is discussed.

Gap solitons in PT-symmetric optical lattices with higher-order diffraction.

PubMed

Ge, Lijuan; Shen, Ming; Ma, Chunlan; Zang, Taocheng; Dai, Lu

2014-12-01

The existence and stability of gap solitons are investigated in the semi-infinite gap of a parity-time (PT)-symmetric periodic potential (optical lattice) with a higher-order diffraction. The Bloch bands and band gaps of this PT-symmetric optical lattice depend crucially on the coupling constant of the fourth-order diffraction, whereas the phase transition point of this PT optical lattice remains unchangeable. The fourth-order diffraction plays a significant role in destabilizing the propagation of dipole solitons. Specifically, when the fourth-order diffraction coupling constant increases, the stable region of the dipole solitons shrinks as new regions of instability appear. However, fundamental solitons are found to be always linearly stable with arbitrary positive value of the coupling constant. We also investigate nonlinear evolution of the PT solitons under perturbation.

Use of photovoltaic detector for photocatalytic activity estimation

NASA Astrophysics Data System (ADS)

Das, Susanta Kumar; Satapathy, Pravakar; Rao, P. Sai Shruti; Sabar, Bilu; Panda, Rudrashish; Khatua, Lizina

2018-05-01

Photocatalysis is a very important process and have numerous applications. Generally, to estimate the photocatalytic activity of newly grown material, its reaction rate constant w.r.t to some standard commercial TiO2 nanoparticles like Degussa P25 is evaluated. Here a photovoltaic detector in conjunction with laser is used to determine this rate constant. This method is tested using Zinc Orthotitanate (Zn2TiO4) nanoparticles prepared by solid state reaction and it is found that its reaction rate constant is six times higher than that of P25. The value is found to be close to the value found by a conventional system. Our proposed system is much more cost-effective than the conventional one and has the potential to do real time monitoring of the photocatalytic activity.

Development and characterization of a diamond-insulated graphitic multi electrode array realized with ion beam lithography.

PubMed

Picollo, Federico; Battiato, Alfio; Carbone, Emilio; Croin, Luca; Enrico, Emanuele; Forneris, Jacopo; Gosso, Sara; Olivero, Paolo; Pasquarelli, Alberto; Carabelli, Valentina

2014-12-30

The detection of quantal exocytic events from neurons and neuroendocrine cells is a challenging task in neuroscience. One of the most promising platforms for the development of a new generation of biosensors is diamond, due to its biocompatibility, transparency and chemical inertness. Moreover, the electrical properties of diamond can be turned from a perfect insulator into a conductive material (resistivity ~mΩ·cm) by exploiting the metastable nature of this allotropic form of carbon. A 16‑channels MEA (Multi Electrode Array) suitable for cell culture growing has been fabricated by means of ion implantation. A focused 1.2 MeV He+ beam was scanned on a IIa single-crystal diamond sample (4.5 × 4.5 × 0.5 mm3) to cause highly damaged sub-superficial structures that were defined with micrometric spatial resolution. After implantation, the sample was annealed. This process provides the conversion of the sub-superficial highly damaged regions to a graphitic phase embedded in a highly insulating diamond matrix. Thanks to a three-dimensional masking technique, the endpoints of the sub-superficial channels emerge in contact with the sample surface, therefore being available as sensing electrodes. Cyclic voltammetry and amperometry measurements of solutions with increasing concentrations of adrenaline were performed to characterize the biosensor sensitivity. The reported results demonstrate that this new type of biosensor is suitable for in vitro detection of catecholamine release.

Comparative analysis of single-walled and multi-walled carbon nanotubes for electrochemical sensing of glucose on gold printed circuit boards.

PubMed

Alhans, Ruby; Singh, Anukriti; Singhal, Chaitali; Narang, Jagriti; Wadhwa, Shikha; Mathur, Ashish

2018-09-01

In the present work, a comparative study was performed between single-walled carbon nanotubes and multi-walled carbon nanotubes coated gold printed circuit board electrodes for glucose detection. Various characterization techniques were demonstrated in order to compare the modified electrodes viz. cyclic voltammetry, electrochemical impedance spectroscopy and chrono-amperometry. Results revealed that single-walled carbon nanotubes outperformed multi-walled carbon nanotubes and proved to be a better sensing interface for glucose detection. The single-walled carbon nanotubes coated gold printed circuit board electrodes showed a wide linear sensing range (1 mM to 100 mM) with detection limit of 0.1 mM with response time of 5 s while multi-walled carbon nanotubes coated printed circuit board gold electrodes showed linear sensing range (1 mM to 100 mM) with detection limit of 0.1 mM with response time of 5 s. This work provided low cost sensors with enhanced sensitivity, fast response time and reliable results for glucose detection which increased the affordability of such tests in remote areas. In addition, the comparative results confirmed that single-walled carbon nanotubes modified electrodes can be exploited for better amplification signal as compared to multi-walled carbon nanotubes. Copyright © 2018. Published by Elsevier B.V.

Electrochemically assisted fabrication of size-exclusion films of organically modified silica and application to the voltammetry of phospholipids.

PubMed

Mehdi, B Layla; Rutkowska, Iwona A; Kulesza, Pawel J; Cox, James A

2013-06-01

Modification of electrodes with nm-scale organically modified silica films with pores diameters controlled at 10- and 50-nm is described. An oxidation catalyst, mixed-valence ruthenium oxide with cyano crosslinks or gold nanoparticles protected by dirhodium-substituted phosophomolybdate (AuNP-Rh 2 PMo 11 ), was immobilized in the pores. These systems comprise size-exclusion films at which the biological compounds, phosphatidylcholine and cardiolipin, were electrocatalytically oxidized without interference from surface-active concomitants such as bovine serum albumin. 10-nm pores were obtained by adding generation-4 poly(amidoamine) dendrimer, G4-PAMAM, to a (CH 3 ) 3 SiOCH 3 sol. 50-nm pores were obtained by modifying a glassy carbon electrode (GC) with a sub-monolayer film of aminopropyltriethoxylsilane, attaching 50-nm diameter poly(styrene sulfonate), PSS, spheres to the protonated amine, transferring this electrode to a (CH 3 ) 3 SiOCH 3 sol, and electrochemically generating hydronium at uncoated GC sites, which catalyzed ormosil growth around the PSS. Voltammetry of Fe(CN) 6 3- and Ru(NH 3 ) 6 3+ demonstrated the absence of residual charge after removal of the templating agents. With the 50-nm system, the pore structure was sufficiently defined to use layer-by-layer electrostatic assembly of AuNP-Rh 2 PMo 11 therein. Flow injection amperometry of phosphatidylcholine and cardiolipin demonstrated analytical utility of these electrodes.

Electrochemical affinity biosensors for fast detection of gene-specific methylations with no need for bisulfite and amplification treatments.

PubMed

Povedano, Eloy; Vargas, Eva; Montiel, Víctor Ruiz-Valdepeñas; Torrente-Rodríguez, Rebeca M; Pedrero, María; Barderas, Rodrigo; Segundo-Acosta, Pablo San; Peláez-García, Alberto; Mendiola, Marta; Hardisson, David; Campuzano, Susana; Pingarrón, José M

2018-04-23

This paper describes two different electrochemical affinity biosensing approaches for the simple, fast and bisulfite and PCR-free quantification of 5-methylated cytosines (5-mC) in DNA using the anti-5-mC antibody as biorecognition element. One of the biosensing approaches used the anti-5-mC as capture bioreceptor and a sandwich type immunoassay, while the other one involved the use of a specific DNA probe and the anti-5-mC as a detector bioreceptor of the captured methylated DNA. Both strategies, named for simplicity in the text as immunosensor and DNA sensor, respectively, were implemented on the surface of magnetic microparticles and the transduction was accomplished by amperometry at screen-printed carbon electrodes by means of the hydrogen peroxide/hydroquinone system. The resulting amperometric biosensors demonstrated reproducibility throughout the entire protocol, sensitive determination with no need for using amplification strategies, and competitiveness with the conventional enzyme-linked immunosorbent assay methodology and the few electrochemical biosensors reported so far in terms of simplicity, sensitivity and assay time. The DNA sensor exhibited higher sensitivity and allowed the detection of the gene-specific methylations conversely to the immunosensor, which detected global DNA methylation. In addition, the DNA sensor demonstrated successful applicability for 1 h-analysis of specific methylation in two relevant tumor suppressor genes in spiked biological fluids and in genomic DNA extracted from human glioblastoma cells.

Escherichia coli Nissle 1917 enhances bioavailability of serotonin in gut tissues through modulation of synthesis and clearance

PubMed Central

Nzakizwanayo, Jonathan; Dedi, Cinzia; Standen, Guy; Macfarlane, Wendy M.; Patel, Bhavik A.; Jones, Brian V.

2015-01-01

Accumulating evidence shows indigenous gut microbes can interact with the human host through modulation of serotonin (5-HT) signaling. Here we investigate the impact of the probiotic Escherichia coli Nissle 1917 (EcN) on 5-HT signalling in gut tissues. Ex-vivo mouse ileal tissue sections were treated with either EcN or the human gut commensal MG1655, and effects on levels of 5-HT, precursors, and metabolites, were evaluated using amperometry and high performance liquid chromatography with electrochemical detection (HPLC-EC). Exposure of tissue to EcN cells, but not MG1655 cells, was found to increase levels of extra-cellular 5-HT. These effects were not observed when tissues were treated with cell-free supernatant from bacterial cultures. In contrast, when supernatant recovered from untreated ileal tissue was pre-incubated with EcN, the derivative cell-free supernatant was able to elevate 5-HT overflow when used to treat fresh ileal tissue. Measurement of 5-HT precursors and metabolites indicated EcN also increases intracellular 5-HTP and reduces 5-HIAA. The former pointed to modulation of tryptophan hydroxylase-1 to enhance 5-HT synthesis, while the latter indicates an impact on clearance into enterocytes through SERT. Taken together, these findings show EcN is able to enhance 5-HT bioavailability in ileal tissues through interaction with compounds secreted from host tissues. PMID:26616662

Emerging nanotechnology-based strategies for the identification of microbial pathogenesis.

PubMed

Kaittanis, Charalambos; Santra, Santimukul; Perez, J Manuel

2010-03-18

Infectious diseases are still a major healthcare problem. From food intoxication and contaminated water, to hospital-acquired diseases and pandemics, infectious agents cause disease throughout the world. Despite advancements in pathogens' identification, some of the gold-standard diagnostic methods have limitations, including laborious sample preparation, bulky instrumentation and slow data readout. In addition, new field-deployable diagnostic modalities are urgently needed in first responder and point-of-care applications. Apart from compact, these sensors must be sensitive, specific, robust and fast, in order to facilitate detection of the pathogen even in remote rural areas. Considering these characteristics, researchers have utilized innovative approaches by employing the unique properties of nanomaterials in order to achieve detection of infectious agents, even in complex media like blood. From gold nanoparticles and their plasmonic shifts to iron oxide nanoparticles and changes in magnetic properties, detection of pathogens, toxins, antigens and nucleic acids has been achieved with impressive detection thresholds. Additionally, as bacteria become resistant to antibiotics, nanotechnology has achieved the rapid determination of bacterial drug susceptibility and resistance using novel methods, such as amperometry and magnetic relaxation. Overall, these promising results hint to the adoption of nanotechnology-based diagnostics for the diagnosis of infectious diseases in diverse settings throughout the globe, preventing epidemics and safeguarding human and economic wellness. Copyright 2009 Elsevier B.V. All rights reserved.

3D nanostructured inkjet printed graphene via UV-pulsed laser irradiation enables paper-based electronics and electrochemical devices.

PubMed

Das, Suprem R; Nian, Qiong; Cargill, Allison A; Hondred, John A; Ding, Shaowei; Saei, Mojib; Cheng, Gary J; Claussen, Jonathan C

2016-09-21

Emerging research on printed and flexible graphene-based electronics is beginning to show tremendous promise for a wide variety of fields including wearable sensors and thin film transistors. However, post-print annealing/reduction processes that are necessary to increase the electrical conductivity of the printed graphene degrade sensitive substrates (e.g., paper) and are whole substrate processes that are unable to selectively anneal/reduce only the printed graphene-leaving sensitive device components exposed to damaging heat or chemicals. Herein a pulsed laser process is introduced that can selectively irradiate inkjet printed reduced graphene oxide (RGO) and subsequently improve the electrical conductivity (Rsheet∼0.7 kΩ□(-1)) of printed graphene above previously published reports. Furthermore, the laser process is capable of developing 3D petal-like graphene nanostructures from 2D planar printed graphene. These visible morphological changes display favorable electrochemical sensing characteristics-ferricyanide cyclic voltammetry with a redox peak separation (ΔEp) ≈ 0.7 V as well as hydrogen peroxide (H2O2) amperometry with a sensitivity of 3.32 μA mM(-1) and a response time of <5 s. Thus this work paves the way for not only paper-based electronics with graphene circuits, it enables the creation of low-cost and disposable graphene-based electrochemical electrodes for myriad applications including sensors, biosensors, fuel cells, and theranostic devices.

Gold nanocages decorated biocompatible amine functionalized graphene as an efficient dopamine sensor platform.

PubMed

Daemi, Sahar; Ashkarran, Ali Akbar; Bahari, Ali; Ghasemi, Shahram

2017-05-15

Nanocomposite of gold nanocages and chemically modified graphene oxide (GNCs/CMG) was synthesized in N,N-dimethylformamide (DMF) for sensitive detection of dopamine (DA). DA is widely spread in central nervous system which can regulates essential body functions like movement and emotional behaviour. In this regard sensitive and fast detection of DA level in human body is still challenging considering its interference with other biomolecules in biological samples. CMG was synthesized through amine modification of graphene oxide (GO) with DMF at relatively high temperature followed by attachment of GNCs, fabricated using a galvanic replacement between silver nanocubes and HAuCl 4 solution in the DMF. X-ray diffraction (XRD) pattern of GNCs/CMG nanocomposite revealed high crystallization of GNCs attached to the graphene nanosheets and microscopic images revealed relatively uniform decoration of GNCs on the surface of CMG. Nanocomposite modified glassy carbon electrode (GNCs/CMG/GCE) was used to investigate the electrochemical behaviour of DA with cyclic voltammetry and amperometry techniques. The linear range for dopamine was between 0.1 and 80μM with a low detection limit of 0.02μM. Furthermore, GNCs/CMG/GCE exhibited satisfying reproducibility, long-term stability and high selectivity for DA detection in large amount of ascorbic acid with good results for determination in human serum samples. Copyright © 2017 Elsevier Inc. All rights reserved.

Midbrain Gene Screening Identifies a New Mesoaccumbal Glutamatergic Pathway and a Marker for Dopamine Cells Neuroprotected in Parkinson’s Disease

PubMed Central

Viereckel, Thomas; Dumas, Sylvie; Smith-Anttila, Casey J. A.; Vlcek, Bianca; Bimpisidis, Zisis; Lagerström, Malin C.; Konradsson-Geuken, Åsa; Wallén-Mackenzie, Åsa

2016-01-01

The ventral tegmental area (VTA) and substantia nigra pars compacta (SNc) of the midbrain are associated with Parkinson’s disease (PD), schizophrenia, mood disorders and addiction. Based on the recently unraveled heterogeneity within the VTA and SNc, where glutamate, GABA and co-releasing neurons have been found to co-exist with the classical dopamine neurons, there is a compelling need for identification of gene expression patterns that represent this heterogeneity and that are of value for development of human therapies. Here, several unique gene expression patterns were identified in the mouse midbrain of which NeuroD6 and Grp were expressed within different dopaminergic subpopulations of the VTA, and TrpV1 within a small heterogeneous population. Optogenetics-coupled in vivo amperometry revealed a previously unknown glutamatergic mesoaccumbal pathway characterized by TrpV1-Cre-expression. Human GRP was strongly detected in non-melanized dopaminergic neurons within the SNc of both control and PD brains, suggesting GRP as a marker for neuroprotected neurons in PD. This study thus unravels markers for distinct subpopulations of neurons within the mouse and human midbrain, defines unique anatomical subregions within the VTA and exposes an entirely new glutamatergic pathway. Finally, both TRPV1 and GRP are implied in midbrain physiology of importance to neurological and neuropsychiatric disorders. PMID:27762319

3D-Printed Fluidic Devices for Nanoparticle Preparation and Flow-Injection Amperometry Using Integrated Prussian Blue Nanoparticle-Modified Electrodes

PubMed Central

Bishop, Gregory W.; Satterwhite, Jennifer E.; Bhakta, Snehasis; Kadimisetty, Karteek; Gillette, Kelsey M.; Chen, Eric; Rusling, James F.

2015-01-01

A consumer-grade fused filament fabrication (FFF) 3D printer was used to construct fluidic devices for nanoparticle preparation and electrochemical sensing. Devices were printed using poly(ethylene terephthalate) and featured threaded ports to connect polyetheretherketone (PEEK) tubing via printed fittings prepared from acrylonitrile butadiene styrene (ABS). These devices included channels designed to have 800 × 800 µm2 square cross sections and were semitransparent to allow visualization of the solution-filled channels. A 3D-printed device with a Y-shaped mixing channel was used to prepare Prussian blue nanoparticles (PBNPs) under flow rates of 100 to 2000 µL min−1. PBNPs were then attached to gold electrodes for hydrogen peroxide sensing. 3D-printed devices used for electrochemical measurements featured threaded access ports into which a fitting equipped with reference, counter, and PBNP-modified working electrodes could be inserted. PBNP-modified electrodes enabled amperometric detection of H2O2 in the 3D-printed channel by flow-injection analysis, exhibiting a detection limit of 100 nM and linear response up to 20 µM. These experiments show that a consumer-grade FFF printer can be used to fabricate low-cost fluidic devices for applications similar to those that have been reported with more expensive 3D-printing methods. PMID:25901660

Amperometric L-glutamate biosensor based on bacterial cell-surface displayed glutamate dehydrogenase.

PubMed

Liang, Bo; Zhang, Shu; Lang, Qiaolin; Song, Jianxia; Han, Lihui; Liu, Aihua

2015-07-16

A novel L-glutamate biosensor was fabricated using bacteria surface-displayed glutamate dehydrogenase (Gldh-bacteria). Here the cofactor NADP(+)-specific dependent Gldh was expressed on the surface of Escherichia coli using N-terminal region of ice nucleation protein (INP) as the anchoring motif. The cell fractionation assay and SDS-PAGE analysis indicated that the majority of INP-Gldh fusion proteins were located on the surface of cells. The biosensor was fabricated by successively casting polyethyleneimine (PEI)-dispersed multi-walled carbon nanotubes (MWNTs), Gldh-bacteria and Nafion onto the glassy carbon electrode (Nafion/Gldh-bacteria/PEI-MWNTs/GCE). The MWNTs could not only significantly lower the oxidation overpotential towards NAPDH, which was the product of NADP(+) involving in the oxidation of glutamate by Gldh, but also enhanced the current response. Under the optimized experimental conditions, the current-time curve of the Nafion/Gldh-bacteria/PEI-MWNTs/GCE was performed at +0.52 V (vs. SCE) by amperometry varying glutamate concentration. The current response was linear with glutamate concentration in two ranges (10 μM-1 mM and 2-10 mM). The low limit of detection was estimated to be 2 μM glutamate (S/N=3). Moreover, the proposed biosensor is stable, specific, reproducible and simple, which can be applied to real samples detection. Copyright © 2015 Elsevier B.V. All rights reserved.

Analysis of the Dielectric constant of saline-alkali soils and the effect on radar backscattering coefficient: a case study of soda alkaline saline soils in Western Jilin Province using RADARSAT-2 data.

PubMed

Li, Yang-yang; Zhao, Kai; Ren, Jian-hua; Ding, Yan-ling; Wu, Li-li

2014-01-01

Soil salinity is a global problem, especially in developing countries, which affects the environment and productivity of agriculture areas. Salt has a significant effect on the complex dielectric constant of wet soil. However, there is no suitable model to describe the variation in the backscattering coefficient due to changes in soil salinity content. The purpose of this paper is to use backscattering models to understand behaviors of the backscattering coefficient in saline soils based on the analysis of its dielectric constant. The effects of moisture and salinity on the dielectric constant by combined Dobson mixing model and seawater dielectric constant model are analyzed, and the backscattering coefficient is then simulated using the AIEM. Simultaneously, laboratory measurements were performed on ground samples. The frequency effect of the laboratory results was not the same as the simulated results. The frequency dependence of the ionic conductivity of an electrolyte solution is influenced by the ion's components. Finally, the simulated backscattering coefficients measured from the dielectric constant with the AIEM were analyzed using the extracted backscattering coefficient from the RADARSAT-2 image. The results show that RADARSAT-2 is potentially able to measure soil salinity; however, the mixed pixel problem needs to be more thoroughly considered.

An experimental and theoretical method for determination of standard electrode potential for the redox couple diphenyl sulfone/diphenyl sulfide

NASA Astrophysics Data System (ADS)

Song, Y. Z.; Wei, K. X.; Lv, J. S.

2013-12-01

DFT calculations were performed for diphenyl sulfide and diphenyl sulfone. The electrochemistry of diphenyl sulfide on the gold electrode was investigated by cyclic voltammety and the results show that standard electrode potential for redox couple diphenyl sulfone/diphenyl sulfide is 1.058 V, which is consistent with that of 1.057 calculated at B3LYP/6-31++G( d, p)-IEFPCM level. The front orbit theory and Mulliken charges of molecular explain well on the oxidation of diphenyl sulfide in oxidative desulfurization. According to equilibrium theory the experimental equilibrium constant in the oxidative desulfurization of H2O2, is 1.17 × 1048, which is consistent with the theoretical equilibrium constant is 2.18 × 1048 at B3LYP/6-31++G( d, p)-IEFPCM level.

Conductive polymer nanotube patch for fast and controlled ex vivo transdermal drug delivery.

PubMed

Nguyen, Thao M; Lee, Sebin; Lee, Sang Bok

2014-10-01

To uptake and release hydrophilic model drugs and insulin in a novel conductive polymer (CP) nanotube transdermal patch. The externally controlled transdermal delivery of model drugs and insulin were tested ex vivo and results were compared with CP films. The unique intrinsic properties of CPs provide electrostatic interaction between the model drugs and polymer backbone. When a pulsed potential was applied, the drug delivery release profile mimics that of injection delivery. With a constant potential applied, the release rate constants of the patch system were up to three-times faster than the control (0 V) and released approximately 80% more drug molecules over 24 h. The CP nanotube transdermal patch represents a new and promising drug method, specifically for hydrophilic molecules, which have been a large obstacle for conventional transdermal drug delivery systems.

Inflation from higher dimensions

NASA Astrophysics Data System (ADS)

Nakada, Hiroshi; Ketov, Sergei V.

2017-12-01

We derive the scalar potential in four spacetime dimensions from an eight-dimensional (R +γ R4-2 Λ -F42) gravity model in the presence of the 4-form F4, with the (modified gravity) coupling constant γ and the cosmological constant Λ , by using the flux compactification of four extra dimensions on a 4-sphere with the warp factor. The scalar potential depends upon two scalar fields: the scalaron and the 4-sphere volume modulus. We demonstrate that it gives rise to a viable description of cosmological inflation in the early universe, with the scalaron playing the role of inflaton and the volume modulus to be (almost) stabilized at its minimum. We also speculate about a possibility of embedding our model in eight dimensions into a modified eight-dimensional supergavity that, in its turn, arises from a modified eleven-dimensional supergravity.

Rate constants of chemical reactions from semiclassical transition state theory in full and one dimension.

PubMed

Greene, Samuel M; Shan, Xiao; Clary, David C

2016-06-28

Semiclassical Transition State Theory (SCTST), a method for calculating rate constants of chemical reactions, offers gains in computational efficiency relative to more accurate quantum scattering methods. In full-dimensional (FD) SCTST, reaction probabilities are calculated from third and fourth potential derivatives along all vibrational degrees of freedom. However, the computational cost of FD SCTST scales unfavorably with system size, which prohibits its application to larger systems. In this study, the accuracy and efficiency of 1-D SCTST, in which only third and fourth derivatives along the reaction mode are used, are investigated in comparison to those of FD SCTST. Potential derivatives are obtained from numerical ab initio Hessian matrix calculations at the MP2/cc-pVTZ level of theory, and Richardson extrapolation is applied to improve the accuracy of these derivatives. Reaction barriers are calculated at the CCSD(T)/cc-pVTZ level. Results from FD SCTST agree with results from previous theoretical and experimental studies when Richardson extrapolation is applied. Results from our implementation of 1-D SCTST, which uses only 4 single-point MP2/cc-pVTZ energy calculations in addition to those for conventional TST, agree with FD results to within a factor of 5 at 250 K. This degree of agreement and the efficiency of the 1-D method suggest its potential as a means of approximating rate constants for systems too large for existing quantum scattering methods.

The enduring legacy of the “constant-field equation” in membrane ion transport

PubMed Central

2017-01-01

In 1943, David Goldman published a seminal paper in The Journal of General Physiology that reported a concise expression for the membrane current as a function of ion concentrations and voltage. This body of work was, and still is, the theoretical pillar used to interpret the relationship between a cell’s membrane potential and its external and/or internal ionic composition. Here, we describe from an historical perspective the theory underlying the constant-field equation and its application to membrane ion transport. PMID:28931632

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

Saha, J.; Chaudhary, S.; Majumdar, P.

We report a study on potential multiferroic characteristics of Yttrium Iron Garnet (YIG). The emergence of ferroelectricity in YIG is in debate but we provide evidence for strong magneto-electric coupling above room temperature from dielectric constant measurement with and without magnetic field. We find that the apparent pseudo-ferroelectric crossover temperature in YIG varies with frequency. For higher frequency the transition shifts towards higher temperature. This is indicative of relaxor behavior. We have also measured the dielectric constant in the presence of external magnetic field at high temperature that confirms interdependence of magnetic and dielectric properties.

A Reactive-Heat-Pipe for Combined Heat Generation and Transport

DTIC Science & Technology

1977-12-01

The Lennard - Jones potential parameters a and F-1 can be found in Ar Ar Table 2.3 of Reference [26]. They are a Ar =3.542 A ~Ar -=93.3 K The above...Specific Heat Ratio Wire Spacing of Screen S Volume Fraction of Solid Phase in Wick or Lennard Jones Force Constant e’ Wick Void Fraction 1Viscusity p...Density a Surface Tension G Condensation Coefficient c e Evaporation Coefficient*e U Lennard - Jones Force Constant Subscripts A Position A in Figure 13 Ar

Quality Control of Meteorological Data for the Chemical Stockpile Emergency Preparedness Program

DTIC Science & Technology

2009-03-01

Time constant 10 s — Solar radiation Eppley 8–48 pyranometer Resolution 10 W m22 10 W m22 Accuracy 65% 65% Time constant 5 s 5 s Spectral response 285...sensor above 90% RH. c 22 W m22 allows for the potential negative offset produced by radiative cooling of the dome of the pyranometer on clear nights...and the winds are light, which suggests that frost may be forming on the pyranometer dome during the night. (The pyranometers are not equipped with

Enhanced laboratory sensitivity to variation of the fine-structure constant using highly charged ions.

PubMed

Berengut, J C; Dzuba, V A; Flambaum, V V

2010-09-17

We study atomic systems that are in the frequency range of optical atomic clocks and have enhanced sensitivity to potential time variation of the fine-structure constant α. The high sensitivity is due to coherent contributions from three factors: high nuclear charge Z, high ionization degree, and significant differences in the configuration composition of the states involved. Configuration crossing keeps the frequencies in the optical range despite the large ionization energies. We discuss a few promising examples that have the largest α sensitivities seen in atomic systems.

Connection formulas for thermal density functional theory

DOE PAGES

Pribram-Jones, A.; Burke, K.

2016-05-23

We show that the adiabatic connection formula of ground-state density functional theory relates the correlation energy to a coupling-constant integral over a purely potential contribution, and is widely used to understand and improve approximations. The corresponding formula for thermal density functional theory is cast as an integral over temperatures instead, ranging upward from the system's physical temperature. We also show how to relate different correlation components to each other, either in terms of temperature or coupling-constant integrations. Lastly, we illustrate our results on the uniform electron gas.

Study of charge transfer complexes of menadione (vitamin K 3) with a series of anilines

NASA Astrophysics Data System (ADS)

Pal, Purnendu; Saha, Avijit; Mukherjee, Asok K.; Mukherjee, Dulal C.

2004-01-01

Menadione (vitamin K 3) has been shown to form charge transfer complexes with N, N-dimethyl aniline, N, N-dimethyl p-toluidine and N, N-dimethyl m-toluidine in CCl 4 medium. The CT transition energies are well correlated with the ionisation potentials of the anilines. The formation constants of the complexes have been determined at a number of temperatures from which the enthalpies and entropies of formation have been obtained. The formation constants exhibit a very good linear free energy relationship (Hammett) at all the temperatures studied.

On inflation, cosmological constant, and SUSY breaking

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

Linde, Andrei

2016-11-02

We consider a broad class of inflationary models of two unconstrained chiral superfields, the stabilizer S and the inflaton Φ, which can describe inflationary models with nearly arbitrary potentials. These models include, in particular, the recently introduced theories of cosmological attractors, which provide an excellent fit to the latest Planck data. We show that by adding to the superpotential of the fields S and Φ a small term depending on a nilpotent chiral superfield P one can break SUSY and introduce a small cosmological constant without affecting main predictions of the original inflationary scenario.

A Simulation Analysis of Errors in the Measurement of Standard Electrochemical Rate Constants from Phase-Selective Impedance Data.

DTIC Science & Technology

1987-09-30

RESTRICTIVE MARKINGSC Unclassif ied 2a SECURIly CLASSIFICATION ALIIMOA4TY 3 DIS1RSBj~jiOAVAILAB.I1Y OF RkPORI _________________________________ Approved...of the AC current, including the time dependence at a growing DME, at a given fixed potential either in the presence or the absence of an...the relative error in k b(app) is ob relatively small for ks (true) : 0.5 cm s-, and increases rapidly for ob larger rate constants as kob reaches the

Acoustic Studies of Colloidal Suspensions and Marine Sediments. I. Theoretical Considerations and High Frequency Measurements.

DTIC Science & Technology

1980-01-15

coth(KH/2) - 1] (5) 16 Similarly, Hamaker has shown that the potential energy of in- teraction due to van der Waals-London attractive forces between...two flat plates of thickness t is given by AIVA 121r [=H0 (Ho0’+2t)-" (Ho0+t)/z (6 where A is the Hamaker constant for interaction of the particles. It...deflocculation by adsorption of montmorillonite particles. K I1 - 54 - Key to Symbols A Hamaker constant VA attractive energy A area in eq. (44) V

Studies on niobium triselenide cathode material for lithium rechargeable cells

NASA Technical Reports Server (NTRS)

Ratnakumar, B. V.; Ni, C. L.; Distefano, S.; Somoano, R. B.; Bankston, C. P.

1988-01-01

NbSe3 exhibits superior characteristics such as high capacity, high volumetric and gravimetric energy densities, and high discharge rate capability, as compared to other intercalating cathodes. This paper reports the preparation, characterization, and performance of NbSe3. Several electrochemical techniques, such as cyclic voltammetry, constant-current/constant-potential discharges, dc potentiodynamic scans, ac impedance, and ac voltammetry, have been used to give insight to the mechanisms of intercalation of three lithiums with NbSe3 and also into the rate determining process in the reduction of NbSe3.

Response of lead-acid batteries to chopper-controlled discharge: Preliminary results

NASA Technical Reports Server (NTRS)

Cataldo, R. L.

1978-01-01

The preliminary results of simulated electric vehicle, chopper, speed controller discharge of a battery show energy output losses up to 25 percent compared to constant current discharges at the same average discharge current of 100 amperes. These energy losses are manifested as temperature rises during discharge, amounting to a two-fold increase for a 400-ampere pulse compared to the constant current case. Because of the potentially large energy inefficiency, the results suggest that electric vehicle battery/speed controller interaction must be carefully considered in vehicle design.

Response of lead-acid batteries to chopper-controlled discharge

NASA Technical Reports Server (NTRS)

Cataldo, R. L.

1978-01-01

The preliminary results of simulated electric vehicle, chopper, speed controller discharge of a battery show energy output losses at up to 25 percent compared to constant current discharges at the same average discharge current of 100 A. These energy losses are manifested as temperature rises during discharge, amounting to a two-fold increase for a 400-A pulse compared to the constant current case. Because of the potentially large energy inefficiency, the results suggest that electric vehicle battery/speed controller interaction must be carefully considered in vehicle design.

A simulation-based study on different control strategies for variable speed pump in distributed ground source heat pump systems

DOE PAGES

Liu, Xiaobing; Zheng, O'Neill; Niu, Fuxin

2016-01-01

Most commercial ground source heat pump systems (GSHP) in the United States are in a distributed configuration. These systems circulate water or an anti-freeze solution through multiple heat pump units via a central pumping system, which usually uses variable speed pump(s). Variable speed pumps have potential to significantly reduce pumping energy use; however, the energy savings in reality could be far away from its potential due to improper pumping system design and controls. In this paper, a simplified hydronic pumping system was simulated with the dynamic Modelica models to evaluate three different pumping control strategies. This includes two conventional controlmore » strategies, which are to maintain a constant differential pressure across either the supply and return mains, or at the most hydraulically remote heat pump; and an innovative control strategy, which adjusts system flow rate based on the demand of each heat pump. The simulation results indicate that a significant overflow occurs at part load conditions when the variable speed pump is controlled to main a constant differential pressure across the supply and return mains of the piping system. On the other hand, an underflow occurs at part load conditions when the variable speed pump is controlled to maintain a constant differential pressure across the furthest heat pump. The flow-demand-based control can provide needed flow rate to each heat pump at any given time, and with less pumping energy use than the two conventional controls. Finally, a typical distributed GSHP system was studied to evaluate the energy saving potential of applying the flow-demand-based pumping control strategy. This case study shows that the annual pumping energy consumption can be reduced by 62% using the flow-demand-based control compared with that using the conventional pressure-based control to maintain a constant differential pressure a cross the supply and return mains.« less

Direct Correlations of Grain Boundary Potentials to Chemical States and Dielectric Properties of Doped CaCu3Ti4O12 Thin Films.

PubMed

Cho, Ahra; Han, Chan Su; Kang, Meenjoo; Choi, Wooseok; Lee, Jihwan; Jeon, Jaecheol; Yu, Sujae; Jung, Ye Seul; Cho, Yong Soo

2018-05-09

Colossal dielectric constant CaCu 3 Ti 4 O 12 has been recognized as one of the rare materials having intrinsic interfacial polarization and thus unusual dielectric characteristics, in which the electrical state of the grain boundary is critical. Here, the direct correlation between the grain boundary potential and relative permittivity is proposed for the CaCu 3 Ti 4 O 12 thin films doped with Zn, Ga, Mn, and Ag as characterized by Kelvin probe force microscopy. The dopants are intended to provide the examples of variable grain boundary potentials that are driven by chemical states including Cu + , Ti 3+ , and oxygen vacancy. Grain boundary potential is nearly linearly proportional to the dielectric constant. This effect is attributed to the increased charge accumulation near the grain boundary, depending on the choice of the dopant. As an example, 1 mol % Ag-doped CaCu 3 Ti 4 O 12 thin films demonstrate the best relative permittivity as associated with a higher grain boundary potential of 120.3 mV compared with 82.6 mV for the reference film. The chemical states across grain boundaries were further verified by using spherical aberration-corrected scanning transmission electron microscopy with the simultaneous electron energy loss spectroscopy.

Revisiting the relevance of using a constant voltage step to improve electrochemical performances of Li-rich lamellar oxides

NASA Astrophysics Data System (ADS)

Pradon, A.; Caldes, M. T.; Petit, P.-E.; La Fontaine, C.; Elkaim, E.; Tessier, C.; Ouvrard, G.; Dumont, E.

2018-03-01

A Li-rich lamellar oxide was cycled at high potential and the relevance of using a constant voltage step (CVS) at the end of the charge, needed for industrial application, was investigated by electrochemical performance, X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM). Electrochemical studies at 4.7 and 4.5 V with and without CVS showed that capacity and voltage fading occurred mostly when cells operated at high potential. After cycling, 3D-type defects involving transition metals trapped in lithium layer were observed by HRTEM into the electrode bulk. These defects are responsible for the voltage fading. XRD microstrain parameter was used to evaluate defects rate in aged materials subjected to a CVS, showing more 3D-type defects when cycled at 4.7 V than at 4.5 V. The time spent at high potential at the end of the charge as well as the value of the upper potential limit, are both relevant parameters to voltage decay. The use of a CVS at the end of the charge needs at the same time, a reduced upper potential window in order to minimize 3D-type defects occurrence. Unfortunately, this approach is still not sufficient to prevent voltage fading.

Detecting High Leadership Potential and Promoting Talent: An Example of an Evidence-Based Approach in a French Blue-Chip Company

ERIC Educational Resources Information Center

Hicheri, Ida Gennari-El; Caroff, Xavier; Paroche, Pauline; Chemolle, Elise; Lubart, Todd

2013-01-01

In a time of economic turmoil, finding executive managers with high potential is increasingly important in the business world. Structural constraints (such as flexibility and reactivity linked to constant environmental change), and demographic trends (such as replacement of leaders who retire) are two challenges, among others, that companies have…

Potential Impacts of two SO2 oxidation pathways on regional sulfate concentrations: acqueous-hase oxidation by NO2 and gas-phase oxidation by Stabilized Criegee Intermediates

EPA Science Inventory

We examine the potential impacts of two additional sulfate production pathways using the Community Multiscale Air Quality modeling system. First we evaluate the impact of the aqueous-phase oxidation of S(IV) by nitrogen dioxide using two published rate constants, differing by 1-2...

The gravitational potential of a homogeneous polyhedron or don't cut corners

NASA Technical Reports Server (NTRS)

Werner, Robert A.

1994-01-01

A polyhedron can model irregularly shaped objects such as asteroids, comet nuclei, and small planetary satellites. With minor effort, such a model can incorporate important surface features such as large craters. Here we develop closed-form expressions for the exterior gravitational potential and acceleration components due to a constant-density polyhedron. An equipotential surface of Phobos is illustrated.

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

Lu, Y.; Xie, D.; Yan, G.

Accurate knowledge of the potential energy surface (PES) and the spectroscopic properties of carbon dioxide plays an important role in understanding the greenhouse effect. The potential energy surface for the electronic ground state of CO{sub 2} is refined by means of a two-step variational procedure using the exact rovibrational Hamiltonian in the bond length-bond angle coordinates. In the refinement, the observed rovibrational energy levels for J = 0-4 below 16,000 cm {sup -1}, obtained from the effective spectroscopic constants of CO{sub 2} given by Rothman et al. (J Quant Spectrosc Radiat Transfer 1992, 48, 537) in HITRAN data base, aremore » used as the input data points. The accurate ab initio force constants of Martin et al. (Chem Phys Lett 1993, 205, 535) are taken as the initial guess for the potential. The root-mean-square error of this fit to the 431 observed rovibrational energy levels is 0.05 cm{sup {minus}1}. With the optimized potential energy surface, the authors also calculate the rovibrational energy levels of {sup 13}C{sup 16}O{sub 2} and {sup 12}C{sup 18}O{sub 2}. The results are in good agreement with experimental data.« less

Anisotropic k-essence cosmologies

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

Chimento, Luis P.; Forte, Monica

We investigate a Bianchi type-I cosmology with k-essence and find the set of models which dissipate the initial anisotropy. There are cosmological models with extended tachyon fields and k-essence having a constant barotropic index. We obtain the conditions leading to a regular bounce of the average geometry and the residual anisotropy on the bounce. For constant potential, we develop purely kinetic k-essence models which are dust dominated in their early stages, dissipate the initial anisotropy, and end in a stable de Sitter accelerated expansion scenario. We show that linear k-field and polynomial kinetic function models evolve asymptotically to Friedmann-Robertson-Walker cosmologies.more » The linear case is compatible with an asymptotic potential interpolating between V{sub l}{proportional_to}{phi}{sup -{gamma}{sub l}}, in the shear dominated regime, and V{sub l}{proportional_to}{phi}{sup -2} at late time. In the polynomial case, the general solution contains cosmological models with an oscillatory average geometry. For linear k-essence, we find the general solution in the Bianchi type-I cosmology when the k field is driven by an inverse square potential. This model shares the same geometry as a quintessence field driven by an exponential potential.« less

Local-spin-density calculations for iron: Effect of spin interpolation on ground-state properties

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

MacLaren, J.M.; Clougherty, D.P.; Albers, R.C.

1990-08-15

Scalar-relativistic self-consistent linear muffin-tin orbital (LMTO) calculations for bcc and fcc Fe have been performed with several different local approximations to the exchange and correlation energy density and potential. Overall, in contrast to the conclusions of previous studies, we find that the local-spin-density approximation to exchange and correlation can provide an adequate description of bulk Fe {ital provided} that a proper parametrization of the correlation energy density and potential of the homogeneous electron gas over both spin and density is used. Lattice constants, found from the position of the minimum of the total energy as a function of Wigner-Seitz radius,more » agree to within 1% (for {ital s},{ital p},{ital d} LMTO's only) and within 1--2% (for {ital s},{ital p},{ital d},{ital f} LMTO's) of the experimental lattice constants for all forms used for the local correlation. The best agreement, however, was obtained using a local correlation potential derived from the Vosko-Wilk-Nusair form for the spin dependence of the correlation energy density. The calculation performed with this correlation potential was also the only calculation to correctly predict a bcc ferromagnetic ground state.« less

[Study of the electrical properties of retinal horizontal cell syncytia by the technic of uniform polarization].

PubMed

Shura-Bura, T M; Trifonov, Iu A

1980-01-01

For uniform polarization of syncytial or cable structures at a large area with current passed via extracellular electrodes the extracellular longitudinal gradient of potential must be proportional to distance from the edge of preparation. In this paper the profile of conducting plate was found analytically which allows to obtain such a distribution of potentials. The profile is formed by hyperbola and its orthogonal asymptotes. Two polarizing electrodes are applied to places where the hyperbola is near to asymptotes. On the surfaces formed by asymptotes the gradient of potential is proportional to distance from intersection of these surfaces. Such a conducting plate was made as cavity in plexiglas filled by Ringer solution in agar. The plate was used for obtaining the voltage-current curves of horizontal cell membrane in gold fish retina. The area of uniform polarization was 4-5 mm long. Measurements inside this area allowed to determine the space constant of horizontal cell layer. The space constant measured in bright light (when resistance of subsynaptic membrane is high) depends on the membrane potential, being high (approximately 1,5 mm) during depolarization and low (0,2-0,4 mm) during hyperpolarization.

RHYTHMICITY IN THE PROTOPLASMIC STREAMING OF A SLIME MOLD, PHYSARUM POLYCEPHALUM

PubMed Central

Kishimoto, Uichiro

1958-01-01

The electric potential difference (1 to 15 mv.) between two loci of the slime mold connected with a strand of protoplasm changes rhythmically with the same period (60 to 180 seconds) as that of the back and forth protoplasmic streaming along the strand. Generally some phase difference is observed between them. Periods of the electric potential rhythm show a Gaussian distribution. Amplitudes give a somewhat different distribution curve. Wave forms are not always simple harmonic ones, but are distorted more or less. However, auto-correlation analysis proves that there is a dominant rhythm of a nearly constant period which coincides with the mean period of the Gaussian distribution curve. Calculations made on an assumption that the electric potential rhythm is the result of many elementary rhythms (i.e., same periodicity, arbitrary phase angles) distributed throughout the plasmodium, give a satisfactory coincidence with the observed distribution for the amplitude. The predominance of a rhythm of a nearly constant periodicity suggests the existence of well organized interactions among components of a contractile protein network, the rhythmic deformation of which is supposed to be responsible for the protoplasmic streaming and for the electric potential rhythm. PMID:13563808

On the v-representability of ensemble densities of electron systems

NASA Astrophysics Data System (ADS)

Gonis, A.; Däne, M.

2018-05-01

Analogously to the case at zero temperature, where the density of the ground state of an interacting many-particle system determines uniquely (within an arbitrary additive constant) the external potential acting on the system, the thermal average of the density over an ensemble defined by the Boltzmann distribution at the minimum of the thermodynamic potential, or the free energy, determines the external potential uniquely (and not just modulo a constant) acting on a system described by this thermodynamic potential or free energy. The paper describes a formal procedure that generates the domain of a constrained search over general ensembles (at zero or elevated temperatures) that lead to a given density, including as a special case a density thermally averaged at a given temperature, and in the case of a v-representable density determines the external potential leading to the ensemble density. As an immediate consequence of the general formalism, the concept of v-representability is extended beyond the hitherto discussed case of ground state densities to encompass excited states as well. Specific application to thermally averaged densities solves the v-representability problem in connection with the Mermin functional in a manner analogous to that in which this problem was recently settled with respect to the Hohenberg and Kohn functional. The main formalism is illustrated with numerical results for ensembles of one-dimensional, non-interacting systems of particles under a harmonic potential.

Efficient chemical potential evaluation with kinetic Monte Carlo method and non-uniform external potential: Lennard-Jones fluid, liquid, and solid

NASA Astrophysics Data System (ADS)

Ustinov, E. A.

2017-07-01

The aim of this paper is to present a method of a direct evaluation of the chemical potential of fluid, liquid, and solid with kinetic Monte Carlo simulation. The method is illustrated with the 12-6 Lennard-Jones (LJ) system over a wide range of density and temperature. A distinctive feature of the methodology used in the present study is imposing an external potential on the elongated simulation box to split the system into two equilibrium phases, one of which is substantially diluted. This technique provides a reliable direct evaluation of the chemical potential of the whole non-uniform system (including that of the uniformly distributed dense phase in the central zone of the box), which, for example, is impossible in simulation of the uniform crystalline phase. The parameters of the vapor-liquid, liquid-solid, and fluid-solid transitions have been reliably determined. The chemical potential and the pressure are defined as thermodynamically consistent functions of density and temperature separately for the liquid and the solid (FCC) phases. It has been shown that in two-phase systems separated by a flat interface, the crystal melting always occurs at equilibrium conditions. It is also proved that in the limit of zero temperature, the specific heat capacity of an LJ crystal at constant volume is exactly 3Rg (where Rg is the gas constant) without resorting to harmonic oscillators.

Charge optimized many body (COMB) potentials for Pt and Au.

PubMed

Antony, A C; Akhade, S A; Lu, Z; Liang, T; Janik, M J; Phillpot, S R; Sinnott, S B

2017-06-07

Interatomic potentials for Pt and Au are developed within the third generation charge optimized many-body (COMB3) formalism. The potentials are capable of reproducing phase order, lattice constants, and elastic constants of Pt and Au systems as experimentally measured or calculated by density functional theory. We also fit defect formation energies, surface energies and stacking fault energies for Pt and Au metals. The resulting potentials are used to map a 2D contour of the gamma surface and simulate the tensile test of 16-grain polycrystalline Pt and Au structures at 300 K. The stress-strain behaviour is investigated and the primary slip systems {1 1 1}〈1 [Formula: see text] 0〉 are identified. In addition, we perform high temperature (1800 K for Au and 2300 K for Pt) molecular dynamics simulations of 30 nm Pt and Au truncated octahedron nanoparticles and examine morphological changes of each particle. We further calculate the activation energy barrier for surface diffusion during simulations of several nanoseconds and report energies of [Formula: see text] eV for Pt and [Formula: see text] eV for Au. This initial parameterization and application of the Pt and Au potentials demonstrates a starting point for the extension of these potentials to multicomponent systems within the COMB3 framework.

On post-inflation validity of perturbation theory in Horndeski scalar-tensor models

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

Germani, Cristiano; Kudryashova, Nina; Watanabe, Yuki, E-mail: germani@icc.ub.edu, E-mail: nina.kudryashova@campus.lmu.de, E-mail: yuki.watanabe@nat.gunma-ct.ac.jp

By using the newtonian gauge, we re-confirm that, as in the minimal case, the re-scaled Mukhanov-Sasaki variable is conserved leading to a constraint equation for the Newtonian potential. However, conversely to the minimal case, in Horndeski theories, the super-horizon Newtonian potential can potentially grow to very large values after inflation exit. If that happens, inflationary predictability is lost during the oscillating period. When this does not happen, the perturbations generated during inflation can be standardly related to the CMB, if the theory chosen is minimal at low energies. As a concrete example, we analytically and numerically discuss the new Higgsmore » inflationary case. There, the Inflaton is the Higgs boson that is non-minimally kinetically coupled to gravity. During the high-energy part of the post-inflationary oscillations, the system is anisotropic and the Newtonian potential is largely amplified. Thanks to the smallness of today's amplitude of curvature perturbations, however, the system stays in the linear regime, so that inflationary predictions are not lost. At low energies, when the system relaxes to the minimal case, the anisotropies disappear and the Newtonian potential converges to a constant value. We show that the constant value to which the Newtonian potential converges is related to the frozen part of curvature perturbations during inflation, precisely like in the minimal case.« less

On the v-representability of ensemble densities of electron systems

DOE PAGES

Gonis, A.; Dane, M.

2017-12-30

Analogously to the case at zero temperature, where the density of the ground state of an interacting many-particle system determines uniquely (within an arbitrary additive constant) the external potential acting on the system, the thermal average of the density over an ensemble defined by the Boltzmann distribution at the minimum of the thermodynamic potential, or the free energy, determines the external potential uniquely (and not just modulo a constant) acting on a system described by this thermodynamic potential or free energy. The study describes a formal procedure that generates the domain of a constrained search over general ensembles (at zeromore » or elevated temperatures) that lead to a given density, including as a special case a density thermally averaged at a given temperature, and in the case of a v-representable density determines the external potential leading to the ensemble density. As an immediate consequence of the general formalism, the concept of v-representability is extended beyond the hitherto discussed case of ground state densities to encompass excited states as well. Specific application to thermally averaged densities solves the v-representability problem in connection with the Mermin functional in a manner analogous to that in which this problem was recently settled with respect to the Hohenberg and Kohn functional. Finally, the main formalism is illustrated with numerical results for ensembles of one-dimensional, non-interacting systems of particles under a harmonic potential.« less

Path Following in the Exact Penalty Method of Convex Programming.

PubMed

Zhou, Hua; Lange, Kenneth

2015-07-01

Classical penalty methods solve a sequence of unconstrained problems that put greater and greater stress on meeting the constraints. In the limit as the penalty constant tends to ∞, one recovers the constrained solution. In the exact penalty method, squared penalties are replaced by absolute value penalties, and the solution is recovered for a finite value of the penalty constant. In practice, the kinks in the penalty and the unknown magnitude of the penalty constant prevent wide application of the exact penalty method in nonlinear programming. In this article, we examine a strategy of path following consistent with the exact penalty method. Instead of performing optimization at a single penalty constant, we trace the solution as a continuous function of the penalty constant. Thus, path following starts at the unconstrained solution and follows the solution path as the penalty constant increases. In the process, the solution path hits, slides along, and exits from the various constraints. For quadratic programming, the solution path is piecewise linear and takes large jumps from constraint to constraint. For a general convex program, the solution path is piecewise smooth, and path following operates by numerically solving an ordinary differential equation segment by segment. Our diverse applications to a) projection onto a convex set, b) nonnegative least squares, c) quadratically constrained quadratic programming, d) geometric programming, and e) semidefinite programming illustrate the mechanics and potential of path following. The final detour to image denoising demonstrates the relevance of path following to regularized estimation in inverse problems. In regularized estimation, one follows the solution path as the penalty constant decreases from a large value.

Path Following in the Exact Penalty Method of Convex Programming

PubMed Central

Zhou, Hua; Lange, Kenneth

2015-01-01

Classical penalty methods solve a sequence of unconstrained problems that put greater and greater stress on meeting the constraints. In the limit as the penalty constant tends to ∞, one recovers the constrained solution. In the exact penalty method, squared penalties are replaced by absolute value penalties, and the solution is recovered for a finite value of the penalty constant. In practice, the kinks in the penalty and the unknown magnitude of the penalty constant prevent wide application of the exact penalty method in nonlinear programming. In this article, we examine a strategy of path following consistent with the exact penalty method. Instead of performing optimization at a single penalty constant, we trace the solution as a continuous function of the penalty constant. Thus, path following starts at the unconstrained solution and follows the solution path as the penalty constant increases. In the process, the solution path hits, slides along, and exits from the various constraints. For quadratic programming, the solution path is piecewise linear and takes large jumps from constraint to constraint. For a general convex program, the solution path is piecewise smooth, and path following operates by numerically solving an ordinary differential equation segment by segment. Our diverse applications to a) projection onto a convex set, b) nonnegative least squares, c) quadratically constrained quadratic programming, d) geometric programming, and e) semidefinite programming illustrate the mechanics and potential of path following. The final detour to image denoising demonstrates the relevance of path following to regularized estimation in inverse problems. In regularized estimation, one follows the solution path as the penalty constant decreases from a large value. PMID:26366044

On the Henry constant and isosteric heat at zero loading in gas phase adsorption.

PubMed

Do, D D; Nicholson, D; Do, H D

2008-08-01

The Henry constant and the isosteric heat of adsorption at zero loading are commonly used as indicators of the strength of the affinity of an adsorbate for a solid adsorbent. It is assumed that (i) they are observable in practice, (ii) the Van Hoff's plot of the logarithm of the Henry constant versus the inverse of temperature is always linear and the slope is equal to the heat of adsorption, and (iii) the isosteric heat of adsorption at zero loading is either constant or weakly dependent on temperature. We show in this paper that none of these three points is necessarily correct, first because these variables might not be observable since they are outside the range of measurability; second that the linearity of the Van Hoff plot breaks down at very high temperature, and third that the isosteric heat versus loading is a strong function of temperature. We demonstrate these points using Monte Carlo integration and Monte Carlo simulation of adsorption of various gases on a graphite surface. Another issue concerning the Henry constant is related to the way the adsorption excess is defined. The most commonly used equation is the one that assumes that the void volume is the volume extended all the way to a boundary passing through the centres of the outermost solid atoms. With this definition the Henry constant can become negative at high temperatures. Although adsorption at these temperatures may not be practical because of the very low value of the Henry constant, it is more useful to define the Henry constant in such a way that it is always positive at all temperatures. Here we propose the use of the accessible volume; the volume probed by the adsorbate when it is in nonpositive regions of the potential, to calculate the Henry constant.

Thermal decay of a metastable state: Influence of rescattering on the quasistationary dynamical rate

NASA Astrophysics Data System (ADS)

Chushnyakova, M. V.; Gontchar, I. I.

2018-03-01

We study the effect of backscattering of the Brownian particles as they escape out of a metastable state overcoming the potential barrier. For this aim, we model this process numerically using the Langevin equations. This modeling is performed for the wide range of the friction constant covering both the energy and spatial diffusion regimes. It is shown how the influence of the descent stage on the quasistationary decay rate gradually disappears as the friction constant decreases. It is found that, in the energy diffusion regime, the rescattering absents and the descent stage does not influence the decay rate. As the value of friction increases, the descent alters the value of the rate by more than 50% for different values of thermal energy and different shapes of the potential. To study the influence of the backscattering on the decay rate, four potentials have been considered which coincide near the potential well and the barrier but differ beyond the barrier. It is shown that the potential for which the well and the barrier are described by two smoothly joined parabolas ("the parabolic potential") plays a role of a dividing range for the mutual layout of the quasistationary dynamical rate and the widely used in the literature Kramers rate. Namely, for the potentials with steeper tails, the Kramers rate RKM underestimates the true quasistationary dynamical rate RD, whereas for the less steep tails the opposite holds (inversion of RD/RKM ). It is demonstrated that the mutual layout of the values of RD for different potentials is explained by the rescattering of the particles from the potential tail.

PRECISION INTEGRATOR FOR MINUTE ELECTRIC CURRENTS

DOEpatents

Hemmendinger, A.; Helmer, R.J.

1961-10-24

An integrator is described for measuring the value of integrated minute electrical currents. The device consists of a source capacitor connected in series with the source of such electrical currents, a second capacitor of accurately known capacitance and a source of accurately known and constant potential, means responsive to the potentials developed across the source capacitor for reversibly connecting the second capacitor in series with the source of known potential and with the source capacitor and at a rate proportional to the potential across the source capacitor to maintain the magnitude of the potential across the source capacitor at approximately zero. (AEC)

The electrical response of turtle cones to flashes and steps of light.

PubMed

Baylor, D A; Hodgkin, A L; Lamb, T D

1974-11-01

1. The linear response of turtle cones to weak flashes or steps of light was usually well fitted by equations based on a chain of six or seven reactions with time constants varying over about a 6-fold range.2. The temperature coefficient (Q(10)) of the reciprocal of the time to peak of the response to a flash was 1.8 (15-25 degrees C), corresponding to an activation energy of 10 kcal/mole.3. Electrical measurements with one internal electrode and a balancing circuit gave the following results on red-sensitive cones of high resistance: resistance across cell surface in dark 50-170 MOmega; time constant in dark 4-6.5 msec. The effect of a bright light was to increase the resistance and time constant by 10-30%.4. If the cell time constant, resting potential and maximum hyperpolarization are known, the fraction of ionic channels blocked by light at any instant can be calculated from the hyperpolarization and its rate of change. At times less than 50 msec the shape of this relation is consistent with the idea that the concentration of a blocking molecule which varies linearly with light intensity is in equilibrium with the fraction of ionic channels blocked.5. The rising phase of the response to flashes and steps of light covering a 10(5)-fold range of intensities is well fitted by a theory in which the essential assumptions are that (i) light starts a linear chain of reactions leading to the production of a substance which blocks ionic channels in the outer segment, (ii) an equilibrium between the blocking molecules and unblocked channels is established rapidly, and (iii) the electrical properties of the cell can be represented by a simple circuit with a time constant in the dark of about 6 msec.6. Deviations from the simple theory which occur after 50 msec are attributed partly to a time-dependent desensitization mechanism and partly to a change in saturation potential resulting from a voltage-dependent change in conductance.7. The existence of several components in the relaxation of the potential to its resting level can be explained by supposing that the ;substance' which blocks light sensitive ionic channels is inactivated in a series of steps.

Ab initio based potential energy surface and kinetics study of the OH + NH3 hydrogen abstraction reaction.

PubMed

Monge-Palacios, M; Rangel, C; Espinosa-Garcia, J

2013-02-28

A full-dimensional analytical potential energy surface (PES) for the OH + NH3 → H2O + NH2 gas-phase reaction was developed based exclusively on high-level ab initio calculations. This reaction presents a very complicated shape with wells along the reaction path. Using a wide spectrum of properties of the reactive system (equilibrium geometries, vibrational frequencies, and relative energies of the stationary points, topology of the reaction path, and points on the reaction swath) as reference, the resulting analytical PES reproduces reasonably well the input ab initio information obtained at the coupled-cluster single double triple (CCSD(T)) = FULL/aug-cc-pVTZ//CCSD(T) = FC/cc-pVTZ single point level, which represents a severe test of the new surface. As a first application, on this analytical PES we perform an extensive kinetics study using variational transition-state theory with semiclassical transmission coefficients over a wide temperature range, 200-2000 K. The forward rate constants reproduce the experimental measurements, while the reverse ones are slightly underestimated. However, the detailed analysis of the experimental equilibrium constants (from which the reverse rate constants are obtained) permits us to conclude that the experimental reverse rate constants must be re-evaluated. Another severe test of the new surface is the analysis of the kinetic isotope effects (KIEs), which were not included in the fitting procedure. The KIEs reproduce the values obtained from ab initio calculations in the common temperature range, although unfortunately no experimental information is available for comparison.

Linearized modified gravity theories with a cosmological term: advance of perihelion and deflection of light

NASA Astrophysics Data System (ADS)

Özer, Hatice; Delice, Özgür

2018-03-01

Two different ways of generalizing Einstein’s general theory of relativity with a cosmological constant to Brans–Dicke type scalar–tensor theories are investigated in the linearized field approximation. In the first case a cosmological constant term is coupled to a scalar field linearly whereas in the second case an arbitrary potential plays the role of a variable cosmological term. We see that the former configuration leads to a massless scalar field whereas the latter leads to a massive scalar field. General solutions of these linearized field equations for both cases are obtained corresponding to a static point mass. Geodesics of these solutions are also presented and solar system effects such as the advance of the perihelion, deflection of light rays and gravitational redshift were discussed. In general relativity a cosmological constant has no role in these phenomena. We see that for the Brans–Dicke theory, the cosmological constant also has no effect on these phenomena. This is because solar system observations require very large values of the Brans–Dicke parameter and the correction terms to these phenomena becomes identical to GR for these large values of this parameter. This result is also observed for the theory with arbitrary potential if the mass of the scalar field is very light. For a very heavy scalar field, however, there is no such limit on the value of this parameter and there are ranges of this parameter where these contributions may become relevant in these scales. Galactic and intergalactic dynamics is also discussed for these theories at the latter part of the paper with similar conclusions.

The effect of concentration- and temperature-dependent dielectric constant on the activity coefficient of NaCl electrolyte solutions

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

Valiskó, Mónika; Boda, Dezső, E-mail: boda@almos.vein.hu

2014-06-21

Our implicit-solvent model for the estimation of the excess chemical potential (or, equivalently, the activity coefficient) of electrolytes is based on using a dielectric constant that depends on the thermodynamic state, namely, the temperature and concentration of the electrolyte, ε(c, T). As a consequence, the excess chemical potential is split into two terms corresponding to ion-ion (II) and ion-water (IW) interactions. The II term is obtained from computer simulation using the Primitive Model of electrolytes, while the IW term is estimated from the Born treatment. In our previous work [J. Vincze, M. Valiskó, and D. Boda, “The nonmonotonic concentration dependencemore » of the mean activity coefficient of electrolytes is a result of a balance between solvation and ion-ion correlations,” J. Chem. Phys. 133, 154507 (2010)], we showed that the nonmonotonic concentration dependence of the activity coefficient can be reproduced qualitatively with this II+IW model without using any adjustable parameter. The Pauling radii were used in the calculation of the II term, while experimental solvation free energies were used in the calculation of the IW term. In this work, we analyze the effect of the parameters (dielectric constant, ionic radii, solvation free energy) on the concentration and temperature dependence of the mean activity coefficient of NaCl. We conclude that the II+IW model can explain the experimental behavior using a concentration-dependent dielectric constant and that we do not need the artificial concept of “solvated ionic radius” assumed by earlier studies.« less

Small dark energy and stable vacuum from Dilaton-Gauss-Bonnet coupling in TMT

NASA Astrophysics Data System (ADS)

Guendelman, Eduardo I.; Nishino, Hitoshi; Rajpoot, Subhash

2017-04-01

In two measures theories (TMT), in addition to the Riemannian measure of integration, being the square root of the determinant of the metric, we introduce a metric-independent density Φ in four dimensions defined in terms of scalars \\varphi _a by Φ =\\varepsilon ^{μ ν ρ σ } \\varepsilon _{abcd} (partial _{μ }\\varphi _a)(partial _{ν }\\varphi _b) (partial _{ρ }\\varphi _c) (partial _{σ }\\varphi _d). With the help of a dilaton field φ we construct theories that are globally scale invariant. In particular, by introducing couplings of the dilaton φ to the Gauss-Bonnet (GB) topological density {√{-g}} φ ( R_{μ ν ρ σ }^2 - 4 R_{μ ν }^2 + R^2 ) we obtain a theory that is scale invariant up to a total divergence. Integration of the \\varphi _a field equation leads to an integration constant that breaks the global scale symmetry. We discuss the stabilizing effects of the coupling of the dilaton to the GB-topological density on the vacua with a very small cosmological constant and the resolution of the `TMT Vacuum-Manifold Problem' which exists in the zero cosmological-constant vacuum limit. This problem generically arises from an effective potential that is a perfect square, and it gives rise to a vacuum manifold instead of a unique vacuum solution in the presence of many different scalars, like the dilaton, the Higgs, etc. In the non-zero cosmological-constant case this problem disappears. Furthermore, the GB coupling to the dilaton eliminates flat directions in the effective potential, and it totally lifts the vacuum-manifold degeneracy.

A methodology for constraining power in finite element modeling of radiofrequency ablation.

PubMed

Jiang, Yansheng; Possebon, Ricardo; Mulier, Stefaan; Wang, Chong; Chen, Feng; Feng, Yuanbo; Xia, Qian; Liu, Yewei; Yin, Ting; Oyen, Raymond; Ni, Yicheng

2017-07-01

Radiofrequency ablation (RFA) is a minimally invasive thermal therapy for the treatment of cancer, hyperopia, and cardiac tachyarrhythmia. In RFA, the power delivered to the tissue is a key parameter. The objective of this study was to establish a methodology for the finite element modeling of RFA with constant power. Because of changes in the electric conductivity of tissue with temperature, a nonconventional boundary value problem arises in the mathematic modeling of RFA: neither the voltage (Dirichlet condition) nor the current (Neumann condition), but the power, that is, the product of voltage and current was prescribed on part of boundary. We solved the problem using Lagrange multiplier: the product of the voltage and current on the electrode surface is constrained to be equal to the Joule heating. We theoretically proved the equality between the product of the voltage and current on the surface of the electrode and the Joule heating in the domain. We also proved the well-posedness of the problem of solving the Laplace equation for the electric potential under a constant power constraint prescribed on the electrode surface. The Pennes bioheat transfer equation and the Laplace equation for electric potential augmented with the constraint of constant power were solved simultaneously using the Newton-Raphson algorithm. Three problems for validation were solved. Numerical results were compared either with an analytical solution deduced in this study or with results obtained by ANSYS or experiments. This work provides the finite element modeling of constant power RFA with a firm mathematical basis and opens pathway for achieving the optimal RFA power. Copyright © 2016 John Wiley & Sons, Ltd.

Variable energy constant current accelerator structure

DOEpatents

Anderson, O.A.

1988-07-13

A variable energy, constant current ion beam accelerator structure is disclosed comprising an ion source capable of providing the desired ions, a pre-accelerator for establishing an initial energy level, a matching/pumping module having means for focusing means for maintaining the beam current, and at least one main accelerator module for continuing beam focus, with means capable of variably imparting acceleration to the beam so that a constant beam output current is maintained independent of the variable output energy. In a preferred embodiment, quadrupole electrodes are provided in both the matching/pumping module and the one or more accelerator modules, and are formed using four opposing cylinder electrodes which extend parallel to the beam axis and are spaced around the beam at 90/degree/ intervals with opposing electrodes maintained at the same potential. 12 figs., 3 tabs.

Interstate vibronic coupling constants between electronic excited states for complex molecules

NASA Astrophysics Data System (ADS)

Fumanal, Maria; Plasser, Felix; Mai, Sebastian; Daniel, Chantal; Gindensperger, Etienne

2018-03-01

In the construction of diabatic vibronic Hamiltonians for quantum dynamics in the excited-state manifold of molecules, the coupling constants are often extracted solely from information on the excited-state energies. Here, a new protocol is applied to get access to the interstate vibronic coupling constants at the time-dependent density functional theory level through the overlap integrals between excited-state adiabatic auxiliary wavefunctions. We discuss the advantages of such method and its potential for future applications to address complex systems, in particular, those where multiple electronic states are energetically closely lying and interact. We apply the protocol to the study of prototype rhenium carbonyl complexes [Re(CO)3(N,N)(L)]n+ for which non-adiabatic quantum dynamics within the linear vibronic coupling model and including spin-orbit coupling have been reported recently.

Multiphoton amplitude in a constant background field

NASA Astrophysics Data System (ADS)

Ahmad, Aftab; Ahmadiniaz, Naser; Corradini, Olindo; Kim, Sang Pyo; Schubert, Christian

2018-01-01

In this contribution, we present our recent compact master formulas for the multiphoton amplitudes of a scalar propagator in a constant background field using the worldline fomulation of quantum field theory. The constant field has been included nonperturbatively, which is crucial for strong external fields. A possible application is the scattering of photons by electrons in a strong magnetic field, a process that has been a subject of great interest since the discovery of astrophysical objects like radio pulsars, which provide evidence that magnetic fields of the order of 1012G are present in nature. The presence of a strong external field leads to a strong deviation from the classical scattering amplitudes. We explicitly work out the Compton scattering amplitude in a magnetic field, which is a process of potential relevance for astrophysics. Our final result is compact and suitable for numerical integration.

The effect of long-range order on the elastic properties of Cu3Au

NASA Astrophysics Data System (ADS)

Wang, Gui-Sheng; Krisztina Delczeg-Czirjak, Erna; Hu, Qing-Miao; Kokko, Kalevi; Johansson, Börje; Vitos, Levente

2013-02-01

Ab initio calculations, based on the exact muffin-tin orbitals method are used to determine the elastic properties of Cu-Au alloys with Au/Cu ratio 1/3. The compositional disorder is treated within the coherent potential approximation. The lattice parameters and single-crystal elastic constants are calculated for different partially ordered structures ranging from the fully ordered L12 to the random face centered cubic lattice. It is shown that the theoretical elastic constants follow a clear trend with the degree of chemical order: namely, C11 and C12 decrease, whereas C44 remains nearly constant with increasing disorder. The present results are in line with the experimental findings that the impact of the chemical ordering on the fundamental elastic parameters is close to the resolution of the available experimental and theoretical tools.

Evaluating variability with atomistic simulations: the effect of potential and calculation methodology on the modeling of lattice and elastic constants

NASA Astrophysics Data System (ADS)

Hale, Lucas M.; Trautt, Zachary T.; Becker, Chandler A.

2018-07-01

Atomistic simulations using classical interatomic potentials are powerful investigative tools linking atomic structures to dynamic properties and behaviors. It is well known that different interatomic potentials produce different results, thus making it necessary to characterize potentials based on how they predict basic properties. Doing so makes it possible to compare existing interatomic models in order to select those best suited for specific use cases, and to identify any limitations of the models that may lead to unrealistic responses. While the methods for obtaining many of these properties are often thought of as simple calculations, there are many underlying aspects that can lead to variability in the reported property values. For instance, multiple methods may exist for computing the same property and values may be sensitive to certain simulation parameters. Here, we introduce a new high-throughput computational framework that encodes various simulation methodologies as Python calculation scripts. Three distinct methods for evaluating the lattice and elastic constants of bulk crystal structures are implemented and used to evaluate the properties across 120 interatomic potentials, 18 crystal prototypes, and all possible combinations of unique lattice site and elemental model pairings. Analysis of the results reveals which potentials and crystal prototypes are sensitive to the calculation methods and parameters, and it assists with the verification of potentials, methods, and molecular dynamics software. The results, calculation scripts, and computational infrastructure are self-contained and openly available to support researchers in performing meaningful simulations.

Cd and proton adsorption onto bacterial consortia grown from industrial wastes and contaminated geologic settings.

PubMed

Borrok, David M; Fein, Jeremy B; Kulpa, Charles F

2004-11-01

To model the effects of bacterial metal adsorption in contaminated environments, results from metal adsorption experiments involving individual pure stains of bacteria must be extrapolated to systems in which potentially dozens of bacterial species are present. This extrapolation may be made easier because bacterial consortia from natural environments appear to exhibit similar metal binding properties. However, bacteria that thrive in highly perturbed contaminated environments may exhibit significantly different adsorptive behavior. Here we measure proton and Cd adsorption onto a range of bacterial consortia grown from heavily contaminated industrial wastes, groundwater, and soils. We model the results using a discrete site surface complexation approach to determine binding constants and site densities for each consortium. The results demonstrate that bacterial consortia from different contaminated environments exhibit a range of total site densities (approximately a 3-fold difference) and Cd-binding constants (approximately a 10-fold difference). These ranges for Cd binding constants may be small enough to suggest that bacteria-metal adsorption in contaminated environments can be described using relatively few "averaged" bacteria-metal binding constants (in conjunction with the necessary binding constants for competing surfaces and ligands). However, if additional precision is necessary, modeling parameters must be developed separately for each contaminated environment of interest.

Propagation rate constants for the peroxidation of sterols on the biosynthetic pathway to cholesterol.

PubMed

Lamberson, Connor R; Muchalski, Hubert; McDuffee, Kari B; Tallman, Keri A; Xu, Libin; Porter, Ned A

2017-10-01

The free radical chain autoxidation of cholesterol and the oxidation products formed, i.e. oxysterols, have been the focus of intensive study for decades. The peroxidation of sterol precursors to cholesterol such as 7-dehydrocholesterol (7-DHC) and desmosterol as well as their oxysterols has received less attention. The peroxidation of these sterol precursors can become important under circumstances in which genetic conditions or exposures to small molecules leads to an increase of these biosynthetic intermediates in tissues and fluids. 7-DHC, for example, has a propagation rate constant for peroxidation some 200 times that of cholesterol and this sterol is found at elevated levels in a devastating human genetic condition, Smith-Lemli-Opitz syndrome (SLOS). The propagation rate constants for peroxidation of sterol intermediates on the biosynthetic pathway to cholesterol were determined by a competition kinetic method, i.e. a peroxyl radical clock. In this work, propagation rate constants for lathosterol, zymostenol, desmosterol, 7-dehydrodesmosterol and other sterols in the Bloch and Kandutsch-Russell pathways are assigned and these rate constants are related to sterol structural features. Furthermore, potential oxysterols products are proposed for sterols whose oxysterol products have not been determined. Copyright © 2017 Elsevier B.V. All rights reserved.

Optical constants, single-oscillator modal and refractive index dispersion analysis of lithium zinc bismuth borate glasses doped with Eu{sup 3+} ions

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

Boda, Ramesh; Srinivas, G.; Komaraiah, D.

2016-05-06

The glasses of composition xLi{sub 2}O-15ZnO- 20Bi{sub 2}O{sub 3}- (64 - x) B{sub 2}O{sub 3}- 1EuO (ZLB) (where x=0, 5, 10, 15, 20 mole %) prepared by melt-quenching technique. The amorphous nature of the prepared glasses was confirmed by XRD spectra. The UV-Vis optical absorption spectrum was recorded in the wave length range of 200-1000 nm. It is observed that the optical band gap is inversely changing with Urbach energy. The optical constants such as G (a constant proportional to the second-order deformation potential) and E{sub f} (a constant that depends on local coordination and is called as free energy ofmore » the glass system). The most significant result of the present work is the refractive index dispersion curves of the ZLB glasses obey the single-oscillator model and oscillator parameters (E{sub o}, E{sub d}) changed with the Li{sub 2}O content. the absorption edge, band gap and Urbach energy is changing nonlinearly with increasing content of Li{sub 2}O, which can be used to calculate the optical, physical, and other constants.« less

Rate constant for the reaction SO + BrO yields SO2 + Br

NASA Technical Reports Server (NTRS)

Brunning, J.; Stief, L.

1986-01-01

The rate of the radical-radical reaction SO + BrO yields SO2 + Br has been determined at 298 K in a discharge flow system near 1 torr pressure with detection of SO and BrO via collision-free sampling mass spectrometry. The rate constant was determined using two different methods: measuring the decay of SO radicals in the presence of an excess of BrO and measuring the decay of BrO radicals in excess SO. The results from the two methods are in reasonable agreement and the simple mean of the two values gives the recommended rate constant at 298 K, k = (5.7 + or - 2.0) x 10 to the -11th cu cm/s. This represents the first determination of this rate constant and it is consistent with a previously derived lower limit based on SO2 formation. Comparison is made with other radical-radical reactions involving SO or BrO. The reaction SO + BrO yields SO2 + Br is of interest for models of the upper atmosphere of the earth and provides a potential coupling between atmospheric sulfur and bromine chemistry.

Mechanism of Kinetically Controlled Capillary Condensation in Nanopores: A Combined Experimental and Monte Carlo Approach.

PubMed

Hiratsuka, Tatsumasa; Tanaka, Hideki; Miyahara, Minoru T

2017-01-24

We find the rule of capillary condensation from the metastable state in nanoscale pores based on the transition state theory. The conventional thermodynamic theories cannot achieve it because the metastable capillary condensation inherently includes an activated process. We thus compute argon adsorption isotherms on cylindrical pore models and atomistic silica pore models mimicking the MCM-41 materials by the grand canonical Monte Carlo and the gauge cell Monte Carlo methods and evaluate the rate constant for the capillary condensation by the transition state theory. The results reveal that the rate drastically increases with a small increase in the chemical potential of the system, and the metastable capillary condensation occurs for any mesopores when the rate constant reaches a universal critical value. Furthermore, a careful comparison between experimental adsorption isotherms and the simulated ones on the atomistic silica pore models reveals that the rate constant of the real system also has a universal value. With this finding, we can successfully estimate the experimental capillary condensation pressure over a wide range of temperatures and pore sizes by simply applying the critical rate constant.

Investigation of common fluorophores for the detection of nitrated explosives by fluorescence quenching.

PubMed

Meaney, Melissa S; McGuffin, Victoria L

2008-03-03

Previous studies have indicated that nitrated explosives may be detected by fluorescence quenching of pyrene and related compounds. The use of pyrene, however, invokes numerous health and waste disposal hazards. In the present study, ten safer fluorophores are identified for quenching detection of target nitrated compounds. Initially, Stern-Volmer constants are measured for each fluorophore with nitrobenzene and 4-nitrotoluene to determine the sensitivity of the quenching interaction. For quenching constants greater than 50 M(-1), sensitivity and selectivity are investigated further using an extended set of target quenchers. Nitromethane, nitrobenzene, 4-nitrotoluene, and 2,6-dinitrotoluene are chosen to represent nitrated explosives and their degradation products; aniline, benzoic acid, and phenol are chosen to represent potential interfering compounds. Among the fluorophores investigated, purpurin, malachite green, and phenol red demonstrate the greatest sensitivity and selectivity for nitrated compounds. Correlation of the quenching rate constants for these fluorophores to Rehm-Weller theory suggests an electron-transfer quenching mechanism. As a result of the large quenching constants, purpurin, malachite green, and phenol red are the most promising for future detection of nitrated explosives via fluorescence quenching.

Efficient Computation of Anharmonic Force Constants via q-space, with Application to Graphene

NASA Astrophysics Data System (ADS)

Kornbluth, Mordechai; Marianetti, Chris

We present a new approach for extracting anharmonic force constants from a sparse sampling of the anharmonic dynamical tensor. We calculate the derivative of the energy with respect to q-space displacements (phonons) and strain, which guarantees the absence of supercell image errors. Central finite differences provide a well-converged quadratic error tail for each derivative, separating the contribution of each anharmonic order. These derivatives populate the anharmonic dynamical tensor in a sparse mesh that bounds the Brillouin Zone, which ensures comprehensive sampling of q-space while exploiting small-cell calculations for efficient, high-throughput computation. This produces a well-converged and precisely-defined dataset, suitable for big-data approaches. We transform this sparsely-sampled anharmonic dynamical tensor to real-space anharmonic force constants that obey full space-group symmetries by construction. Machine-learning techniques identify the range of real-space interactions. We show the entire process executed for graphene, up to and including the fifth-order anharmonic force constants. This method successfully calculates strain-based phonon renormalization in graphene, even under large strains, which solves a major shortcoming of previous potentials.

Precision atomic spectroscopy for improved limits on variation of the fine structure constant and local position invariance.

PubMed

Fortier, T M; Ashby, N; Bergquist, J C; Delaney, M J; Diddams, S A; Heavner, T P; Hollberg, L; Itano, W M; Jefferts, S R; Kim, K; Levi, F; Lorini, L; Oskay, W H; Parker, T E; Shirley, J; Stalnaker, J E

2007-02-16

We report tests of local position invariance and the variation of fundamental constants from measurements of the frequency ratio of the 282-nm 199Hg+ optical clock transition to the ground state hyperfine splitting in 133Cs. Analysis of the frequency ratio of the two clocks, extending over 6 yr at NIST, is used to place a limit on its fractional variation of <5.8x10(-6) per change in normalized solar gravitational potential. The same frequency ratio is also used to obtain 20-fold improvement over previous limits on the fractional variation of the fine structure constant of |alpha/alpha|<1.3x10(-16) yr-1, assuming invariance of other fundamental constants. Comparisons of our results with those previously reported for the absolute optical frequency measurements in H and 171Yb+ vs other 133Cs standards yield a coupled constraint of -1.5x10(-15)