Potential Difference Measurements Research Articles

Effect of Chloride Ion Concentration on the Galvanic Corrosion of α Phase Brass by Eccrine Sweat

Inductively coupled plasma mass spectrometry measurement of the relative concentration of sodium, chloride, calcium, and potassium ions in eccrine sweat deposits from 40 donors revealed positive correlations between chloride and sodium (ρ = 0.684, p < 0.01) and chloride and calcium ions (ρ = 0.91, p < 0.01). Correlations between ion concentration and the corrosion of α phase brass by the donated sweat were investigated by visual grading of the degree of corrosion, by measuring the copper/zinc ratio using energy-dispersive X-ray spectroscopy, and from a measurement of the potential difference between corroded and uncorroded brass when a large potential was applied to the uncorroded brass. An increasing copper/zinc ratio (indicative of dezincification) was found to correlate positively to both chloride ion concentration and visual grading of corrosion, while visual grading gave correlations with potential difference measurements that were indicative of the preferential surface oxidation of zinc rather than copper.

Interaction of ytterbium nanofilms grown on tungsten substrates with oxygen

The interaction of ytterbium nanofilms evaporated on tungsten substrates with oxygen has been studied by Auger electron spectroscopy, thermal desorption spectroscopy, and contact potential difference measurements. It has been shown that at room temperature, no oxide is formed in the above interaction. In place of the oxide, a chemisorbed layer of nondissociated O2 molecules is formed on the surface of the ytterbium nanofilms. This layer modifies the ytterbium. This modification transforms ytterbium from the divalent state into the trivalent state.

Comparative Variability of Nasal Potential Difference Measurements in Human and Mice

Background: Nasal potential difference (NPD) test has long been used to assist in the diagnosis of Cystic Fibrosis (CF) and more recently as an outcome measure in clinical trials of new CF therapies. This test has also been adapted to the mouse nose. Objectives: We aimed at evaluating variability of the NPD measurements in CF patients displaying two severe CFTR mutations and in sex-matched healthy controls. NPD recorded from F508del-CF and normal wild-type mice were also compared. Methods and results: In each setting, tests were performed by a single qualified operator. In the clinical setting, the latest standardized operation protocol of the CF foundation was followed. A total of 80 tracings were obtained from 10 patients (23.2 y; range 14 to 32) and 10 healthy subjects (34 y; range 24 to 53), each tested twice, in both nostrils. Two CF and two controls were excluded from the statistical data analysis due to the presence of a single non interpretable NPD tracing (4/80, 5%). To achieve equal sample size, tests were obtained from 8 CF mice and normal wild-type. Comprehensive multivariate analysis of paired data showed a good reproducibility of NPD parameters in the clinical and the preclinical setting; lower variability was observed in mice. However, 95% repeatability limits of NPD parameters were large indicating a large measurement error, poor precision and low within-subject repeatability. In both settings, chloride secretion was shown to be the most reproducible and repeatable parameter. Conclusion: In human as in mice, NPD showed good reproducibility but limited within-subject repeatability.

T4 Safety and expression of a single dose of lipid-mediated CFTR gene therapy to the upper and lower airways of patients with Cystic Fibrosis

Introduction and ObjectivesWe undertook a clinical trial of non-viral CFTR gene therapy assessing safety, dose and transgene expression in preparation for a Multi-dose trial (MDT) designed to assess clinical efficacy.MethodsA...

Activity Coefficients of Electrolytes in the NaCl + Na2SO4 + H2O Ternary System from Potential Difference Measurements at (298.15, 303.15, and 308.15) K

Potential difference measurements have been used to obtain the mean ionic activity and osmotic coefficients of NaCl and Na2SO4 in their aqueous solutions. Also, the mean ionic activity coefficients of NaCl in NaCl–Na2SO4–H2O ternary system with sodium as a common ion have been determined from cell potential measurements using: Na-ISE/NaCl (mNaCl); Na2SO4 (mNa2SO4)/Ag/AgCl combined with the reference cell: Na-ISE/NaCl (I = mNaCl + 3mNa2SO4), AgCl(s)/Ag. The measurements were made at ionic strength ratios for Na2SO4, yNa2SO4, of (0.0, 0.2, 0.4, 0.6, 0.8, and 1.0), at constant total ionic strengths, I, of (0.1, 0.5, 1.0, 2.0, 3.0, and 4.0) mol·kg–1 and at temperatures of (298.15, 303.15, and 308.15) K. The experimental mean ionic activity coefficients of NaCl were correlated and analyzed with the Harned rule and Scatchard and Pitzer models. The excess free Gibbs energies of mixing were calculated from the trace activity coefficient data of NaCl and analyzed versus system composition at different temperatures...

Spatially resolved electronic inhomogeneities of graphene due to subsurface charges

We probe the local inhomogeneities in the electronic properties of exfoliated graphene due to the presence of charged impurities in the SiO 2 substrate using a combined scanning tunneling and electrostatic force microscope. Contact potential difference measurements using electrostatic force microscopy permit us to obtain the average charge density but it does not provide enough resolution to identify individual charges. We find that the tunneling current decay constant, which is related to the local tunneling barrier height, enables one to probe the electronic properties of graphene distorted at the nanometer scale by individual charged impurities. We observe that such inhomogeneities do not show long-range ordering and their surface density obtained by direct counting is consistent with the value obtained by macroscopic charge density measurements. These microscopic perturbations of the carrier density significantly alter the electronic properties of graphene, and their characterization is essential for improving the performance of graphene based devices.

Activity Coefficients of NaBr in Aqueous Mixtures with High Relative Permittivity Cosolvent: Formamide + Water at 298.15 K

The mean ionic activity coefficients of NaBr were experimentally determined in formamide + water mixtures at 298.15 K from potential difference measurements of the following electrochemical cell containing two ion selective electrodes (ISEs): Na-ISE|NaBr (m), formamide (w), H2O (1–w)|Br-ISE. The molality (m) varied between 0.02 mol·kg–1 and almost saturation, whereas the mass fraction of formamide in the mixture (w) was varied between 0 and 1 in 0.1-unit steps. The determination of E0* (molal scale) was carried out following a method similar to that proposed by Hitchcock and using the classical extended Debye–Hückel and Scatchard equations. We also use for this purpose a modification of the Pitzer equation proposed by Rard and Archer and the most recent modified three-characteristic-parameter-correlation model. The results obtained produced good internal consistency, within the normal limits of experimental error in these types of measurement. Once E0* was determined, the mean ionic activity coefficients of NaBr (γ), the Gibbs energy of transfer of the NaBr from the water to the formamide + water mixture (ΔGt0), standard solubility product of NaBr in formamide + water (Ksp0), and NaBr primary hydration number (nhyd) were estimated. The results were comparatively analyzed with those of NaF and NaCl previously obtained in similar mixtures.

Surface Termination Control in Chemically Deposited PbS Films: Nucleation and Growth on GaAs(111)A and GaAs(111)B

This study addresses the question of whether chemically deposited PbS thin films grown on GaAs(111) are affected by the oppositely terminated substrate surfaces, gallium terminated GaAs(111)A and arsenic terminated GaAs(111)B. The differences in PbS film deposition pathway in both cases of substrate surface termination were investigated using X-ray photoelectron spectroscopy (XPS), Raman scattering, and contact potential difference (CPD) measurements. The morphology, microstructure, and crystallographic orientation of the films were studied using scanning electron microscopy, X-ray diffraction, and transmission electron microscopy. XPS and CPD measurements indicated that PbS films deposited on oppositely terminated GaAs(111) surfaces possessed corresponding surface terminations, with PbS(111)B obtained on GaAs(111)B and PbS(111)A on GaAs(111)A. Subsequently, different surface oxides were detected by XPS on A and B terminated PbS(111), with lead oxide obtained on PbS(111)A and PbSO3 obtained on PbS(111)B. ...

Electronic structure of the poly(3-hexylthiophene):indene-C60 bisadduct bulk heterojunction

The electronic structure of the poly(3-hexylthiophene):indene-C60 bisadduct (P3HT:ICBA) blend is investigated with direct and inverse photoemission spectroscopy. The energy gap between the lowest unoccupied molecular orbital (LUMO) of ICBA and the highest occupied molecular orbital (HOMO) of P3HT, which is central to the performance of photovoltaic cells made with this blend, is found equal to 1.68 eV. This value is larger than the difference between the ionization energy of the donor and the electron affinity of the acceptor, implying the existence of an interface dipole barrier between these two materials. Complementary contact potential difference measurements are done with a Kelvin probe in the dark on similar donor/acceptor pairs, e.g., P3HT:C60 and copper phthalocyanine (CuPc):C60, and confirm the existence of a dipole at these interfaces. It is estimated that a 0.3–0.4 eV ground state dipole exists at the P3HT:ICBA interface.

Update in Cystic Fibrosis 2010

Update in Cystic Fibrosis 2010

31 Modified nasal catheter for measurement of nasal potential difference improves reproducibility

31 Modified nasal catheter for measurement of nasal potential difference improves reproducibility

32 Adverse events (AE) in nasal potential difference (NPD) measurements under the inferior turbinate in healthy adults

32 Adverse events (AE) in nasal potential difference (NPD) measurements under the inferior turbinate in healthy adults

New clinical diagnostic procedures for cystic fibrosis in Europe

In the majority of cases, there is no difficulty in diagnosing Cystic Fibrosis (CF). However, there may be wide variation in signs and symptoms between individuals which encourage the scientific community to constantly improve the diagnostic tests available and develop better methods to come to a final diagnosis in patients with milder phenotypes. This paper is the result of discussions held at meetings of the European Cystic Fibrosis Society Diagnostic Network supported by EuroCareCF. CFTR bioassays in the nasal epithelium (nasal potential difference measurements) and the rectal mucosa (intestinal current measurements) are discussed in detail including efforts to standardize the techniques across Europe. New approaches to evaluate the sweat gland, future of genetic testing and methods on the horizon like CFTR expression in human leucocytes and erythrocytes are discussed briefly.

Electrical passivation and chemical functionalization of SiC surfaces by chlorine termination

We have developed a straightforward plasma-based method which yields chlorine-terminated n-type 6H-SiC surfaces. Atomic force microscopy shows that the surface roughness is not affected by the plasma processing. Additionally, x-ray photoelectron spectroscopy reveals a significant reduction in oxygen, and a corresponding rise of chlorine core level intensities, following halogen termination. Contact potential difference and surface photovoltage measurements show formation of negative surface dipoles and approximately flat band surface potentials after chlorine termination of (0001) n-type 6H-SiC (built-in voltage Vbi&amp;lt;20 meV). Starting from halogenated surfaces, we demonstrate both ultraviolet light-induced and thermally-induced functionalization with alkene-derived self-assembled organic monolayers.

Neurodynamic measures of functional connectivity and cognition

Exploring the structure and function of the human brainrelies on a range of non-invasive measures and computa-tional approaches. Neurodynamic functional brain imagingmethods offer unique insight into the human brain pro-cesses by capturing neuronal activity in real time. Mea-surements of scalp potential differences of spontaneous andevoked activity were the first electrophysiological measurethat revealed differences in the measured waveforms whichwere state, stimulus, task, context etc. dependant. Fourdecades ago the application of ultrasensitive supercon-ducting quantum interference device (SQUID) for themeasurements of extremely week magnetic fields of thehuman brain led to a dynamic development of magnetoe-cephalography (MEG) research [2]. Development of thisnew functional brain imaging method resulted in openingnew questions and furthering the analysis of the EEG/ERPas well since the interest of MEG researchers moved fromthe analysis based on the evaluations of the measuredwaveforms to explore the approaches to identify and trackcortical activations in space and time. Spatio-temporalsource localization models and inverse bio-electro-mag-netic problem estimation approaches were developed toestimate the underlying neuronal substrates of the evokedactivity related to sensory perception, movement, andcognition. Exploration of the underlying dynamic corticalnetworks of the working human brain was made possiblenot only in the measurement space but also at the func-tional source level.During the 1990s, The Decade of the Brain, non-inva-sive structural and functional brain imaging methods wereregarded as revolutionary in exploring the structure andfunction of the human brain in healthy and diseased states.The wealth of data regarding sensory, motor, and cognitiveprocesses provided initially by positron emission tomog-raphy (PET) is dominated during the last two decades by anexplosion of research using functional magnetic resonanceimaging (fMRI). fMRI is often reported to offer superbmillimeter spatial resolution, almost uniform throughoutthe brain. EEG and MEG were, however, regarded asmodel dependent and consequently prone to erroneoussource location estimation. Multi-modal integrationappeared in mid 1990’ as a solution to overcome ill-posednature of the bio-electro-magnetic problem and a low, 2 sand even 40 s, temporal resolutions of fMRI and PET,respectively. The initial confidence that PET or fMRIidentified functional foci could be used to constrain EEG orMEG solution was soon reconsidered.Unlike in EEG and MEG, there is a great degree ofstandardization regarding preprocessing and statisticalapproaches in fMRI. During a rather intensive data gath-ering period since its discovery important questions such asthe reliability of the fMRI results remain almost uncon-sidered and unanswered [3]. Another open question is therelationship of the hemodynamic and/or metabolicresponse and the neuronal activity of interest. Despite awidely used terminology referring to PET and fMRI data asneuroimaging their data represent only correlates of theneuronal activity. Consequently, there is an increasingawareness that all noninvasive functional brain imagingmethods are in fact subject to solving inverse problems tomove from the measurement space to the source space in

Gender Differences in Motility of the Large and Small Intestine in Patients With IBS

Background: Visceral hypersensitivity, and altered gastrointestinal motility and secretion, are considered to be key pathophysiological factors in irritable bowel syndrome (IBS), and of great importance for symptom generation. The symptom pattern differs between female and male IBS patients , with more severe abdominal pain, bloating and constipation in females (Khatai et al. DDW 2010). Whether this can be explained by gender differences in pathophysiological alterations is incompletely understood. Aim: To evaluate potential gender differences in small intestinal motility and secretion, colonic motility and rectal sensorimotor function in patients with IBS. Methods: We included 36 male and 36 female IBS patients, matched for age (mean age 39 (20-64) years), who fulfilled the ROME II criteria. All patients underwent investigations to assess colonic motility (colonic transit time using radiopaque markers), small intestinal motility and secretion (antroduodenojejunal manometry with jejunal transmural potential difference (PD) measurement in the fasting state (3h) and after meal intake (1h)) and rectal sensorimotor function (rectal balloon distensions before and after meal intake; 800kcal; 60% fat). Results: Colonic transit time differed between female and male IBS patients, with slower transit in females (2.1±1.3 (mean±SD) vs. 1.2±0.8 days; p<0.0001). Differences were also found in the small intestinal motility with slower propagation velocity of phase III in females (8.7±4.5 vs. 15±9.4 cm/min; p<0.01), and a tendency towards shorter duration of phase III in females (p<0.1). The motility indices in the jejunum also tended to be lower in female versus male IBS patients, but this only reached statistical significance in the fasting state (last 30 min of phase II) (3310±1040 vs. 4510±2730 mmHg x sec; p<0.05). No gender differences were seen in PD measurements in the small intestine, reflecting chloride secretion, or in rectal compliance, tone or sensitivity. Conclusion: We have demonstrated gender differences in small and large intestinal motility in IBS patients, but not in small intestinal secretion or rectal sensorimotor function. These findings are of potential importance for observed differences in the symptom pattern between male and female IBS patients.

Assessment of CFTR function in homozygous R117H-7T subjects

Background R117H is a frequent missense mutation included in most CFTR mutation panels. However knowledge about the residual function of R117H-CFTR channels in cystic fibrosis-affected organs, e.g. airways, intestines and sweat glands is presently lacking. Methods We evaluated clinical CF symptoms and assessed CFTR function by sweat tests, nasal potential difference and intestinal current measurements in 2 homozygous R117H individuals (7T variant). Results The CFTR activity in airways and intestine was within the normal range. However both individuals presented with a borderline sweat test and the male patient was infertile. Conclusions The lack of impact of the R117H mutation on chloride secretion in intestine and nose contrasts with the ~ 80% loss of CFTR activity reported in patch clamp studies. Apparently CFTR activity is not rate-limiting for chloride secretion in both tissues at levels > 20% of normal, or compensatory factors may operate that are absent in heterologous host cells in vitro.

Electronic nature of potassium promotion effect in Co–Mn–Al mixed oxide on the catalytic decomposition of N2O

Abstract A series of Co–Mn–Al mixed oxides was prepared by a thermal treatment of coprecipitated layered double hydroxide precursors modified with different amount of potassium (0–3 wt.%) and tested in N2O catalytic decomposition. Chemical analysis, XRD, XPS, surface area measurements, SEM, and contact potential difference measurements were used for bulk and surface characterization of the catalysts. The Co–Mn–Al mixed oxide with 1.1–1.8 wt.% K exhibited the highest conversion of N2O and minimum value of the catalyst surface work function. Direct correlation between the work function values and the activity of the catalysts demonstrates that N2O decomposition over K-promoted Co–Mn–Al mixed oxides proceeds via the cationic redox mechanism and controlled modification of surface electronic properties provides the essential factor for catalyst optimization.

Synthesis of Some 2‐Amino‐5‐substituted‐1,3,4‐oxadiazole Derivatives in the Acetic Acid

An environmentally benign method for the preparation of 2‐amino‐5‐substituted‐1,3,4‐oxadiazoles (1a-n) at platinum electrode through the electrooxidation of semicarbazone at room temperature is reported. The electrolysis were carried out at controlled potential in acetic acid solvent using lithium perchlorate as supporting electrolyte in an undivided cell assembly. Square shaped plates of platinum were used for working as well as counter electrode and a third electrode saturated calomel electrode was used as a reference electrode for the measurement of potential difference between two electrodes during the electrolysis.

Nasal potential difference to detect Na+channel dysfunction in acute lung injury

Pulmonary fluid clearance is regulated by the active transport of Na(+) and Cl(-) through respiratory epithelial ion channels. Ion channel dysfunction contributes to the pathogenesis of various pulmonary fluid disorders including high-altitude pulmonary edema (HAPE) and neonatal respiratory distress syndrome (RDS). Nasal potential difference (NPD) measurement allows an in vivo investigation of the functionality of these channels. This technique has been used for the diagnosis of cystic fibrosis, the archetypal respiratory ion channel disorder, for over a quarter of a century. NPD measurements in HAPE and RDS suggest constitutive and acquired dysfunction of respiratory epithelial Na(+) channels. Acute lung injury (ALI) is characterized by pulmonary edema due to alveolar epithelial-interstitial-endothelial injury. NPD measurement may enable identification of critically ill ALI patients with a susceptible phenotype of dysfunctional respiratory Na(+) channels and allow targeted therapy toward Na(+) channel function.