scholarly journals THE DIRECT CURRENT RESISTANCE OF NITELLA

1930 ◽  
Vol 13 (4) ◽  
pp. 495-508 ◽  
Author(s):  
L. R. Blinks
Keyword(s):  
Direct Current ◽  
Tap Water ◽  
High Mobility ◽  
Wheatstone Bridge ◽  
Living Cells ◽  
Transient Effects ◽  
Intact Cells ◽  
Direct Current Resistance ◽  
Opening And Closing ◽  
String Galvanometer

The electrical resistance of Nitella cells to direct current is determined in a Wheatstone bridge, using a vacuum-tube detector, and string galvanometer. Very small currents are passed through the cells, to avoid stimulation. The galvanometer record shows typical transient effects in the living cells at opening and closing of the circuit, due to the development of back E.M.F. With 1 cm. contacts of tap water, and 1 cm. between contacts the resistances of living cells are usually between 1,000,000 and 2,000,000 ohms. They go as high as 3,500,000 ohms when the cells are in the best condition. The resistance falls to about 50,000 ohms immediately after killing. Leakage around the cell is small because the wall is imbibed with tap water. By measuring the resistance of the isolated wall (air-filled), and by varying the areas of contact with intact cells, the effective protoplasmic resistance is calculated. This varies from 100,000 to 700,000 ohms per square centimeter of surface, with a typical value of about 250,000 ohms per square centimeter. This high resistance represents a low permeability for most ions, since the values are nearly as high with contacts of 0.01 M NaCl, CaCl2, LiCl, NH4Cl, and MgSO4. The resistances are greatly reduced however by solutions of KCl, which is correlated with a high mobility of the K+ ion in the protoplasm. Electrical stimulation causes a marked reduction of resistance, which may be due to exomosis of KCl.

scholarly journals THE DIRECT CURRENT RESISTANCE OF VALONIA

1930 ◽  
Vol 13 (3) ◽  
pp. 361-378 ◽  
Author(s):  
L. R. Blinks
Keyword(s):  
Cell Wall ◽  
Direct Current ◽  
Living Cells ◽  
Effective Resistance ◽  
Vacuum Tube ◽  
Direct Current Resistance ◽  
Valonia Ventricosa ◽  
Current Resistance

A direct current bridge with vacuum tube detector is described for measuring the resistance of living cells. Methods for evaluating the surface of contact with the protoplasm, and the leakage around the cell wall, allow us to calculate the effective resistance of the protoplasm. In Valonia ventricosa this is usually at least 10,000 ohms per square centimeter and is often much higher. This is in agreement with the very slight ionic interchange observed in normal Valonia.

scholarly journals On the construction of a standard high-frequency inductive resistance and its measurement by a thermal method

1925 ◽  
Vol 109 (751) ◽  
pp. 508-522
Keyword(s):  
Radio Frequency ◽  
Direct Current ◽  
High Frequency ◽  
Wheatstone Bridge ◽  
Effective Resistance ◽  
Thermal Method ◽  
Thermal Methods ◽  
Direct Current Resistance ◽  
Complete Circuit ◽  
Parasitic Currents

The ordinary methods of measuring the radio-frequency resistance of inductance coils depend on the measurement of the resistance of a complete circuit, containing, usually, the coil, a thermo-ammeter, a condenser and leads. The lack of knowledge of the effective resistance of the circuit outside the coil, of the losses induced in the surrounding objects, and of the distribution of parasitic currents, leave some doubt on the reliability of the value of the resistance obtained by these methods. To obtain reliable measurements it is necessary to fall back on some thermal method by means of which the power lost in the coil itself can be measured quite independently of the circuit and neighbouring bodies. The method described in this paper was carried out essentially as a check to the usual methods of measurement. A number of investigators have used thermal methods to measure the effective resistance of coils. Amongst them may be mentioned T. P. Black, L. W. Austin, H. Abrahams, Gr. W. O. Howe, and L. Lehrs. T. P. Black (1) compared the effective resistance of long solenoids with the effective resistance of straight wires, employing a method resembling that of J. A. Fleming (2) for measuring the high-frequency resistance of straight wires by means of a differential air thermometer. L. W. Austin (3) compared the heat given out by a coil when current at radio frequencies and direct current were passed through two similar coils. The coils were immersed in oil, and the equality of temperature noted by thermo-junctions connected in opposition in the two vessels. H. Abrahams (4) compared the rise of temperature of coils after passing radio-frequency current and then direct current by quickly finding the change in the direct-current resistance measured by a Wheatstone bridge. G. W. O. Howe (5) found the rise of temperature of long solenoids by means of a thermojunction placed near the centre, and compared the effect of direct and highfrequency currents. He thus assumed that the loss is uniformly distributed along the coil, an assumption which will hold only if the coil is long. L. Lehrs (6) enclosed the coil in a vessel connected to a very sensitive manometer, and adjusted the alternating and direct currents so that no change could be observed on switching from one to the other.

scholarly journals Trends in SPR Cytometry: Advances in Label-Free Detection of Cell Parameters

Biosensors ◽  
2018 ◽  
Vol 8 (4) ◽  
pp. 102 ◽  
Author(s):  
Richard Schasfoort ◽  
Fikri Abali ◽  
Ivan Stojanovic ◽  
Gestur Vidarsson ◽  
Leon Terstappen
Keyword(s):  
Surface Plasmon Resonance ◽  
Surface Plasmon ◽  
Plasmon Resonance ◽  
Mammalian Cells ◽  
Living Cells ◽  
Label Free ◽  
Intact Cells ◽  
Cell Parameters ◽  
Spr Imaging ◽  
Label Free Detection

SPR cytometry entails the measurement of parameters from intact cells using the surface plasmon resonance (SPR) phenomenon. Specific real-time and label-free binding of living cells to sensor surfaces has been made possible through the availability of SPR imaging (SPRi) instruments and researchers have started to explore its potential in the last decade. Here we will discuss the mechanisms of detection and additionally describe the problems and issues of mammalian cells in SPR biosensing, both from our own experience and with information from the literature. Finally, we build on the knowledge and applications that has already materialized in this field to give a forecast of some exciting applications for SPRi cytometry.

Simulation of cavitation in outward-opening piezo-type pintle injector nozzles

2008 ◽  
Vol 222 (10) ◽  
pp. 1895-1910 ◽  
Author(s):  
E Giannadakis ◽  
D Papoulias ◽  
A Theodorakakos ◽  
M Gavaises
Keyword(s):  
Bubble Growth ◽  
Large Scale ◽  
Direct Injection ◽  
Bubble Formation ◽  
Needle Valve ◽  
Transient Effects ◽  
Cavitation Model ◽  
Gasoline Engines ◽  
Opening And Closing ◽  
Vapour Film

The onset and development of cavitation in the annular needle seat passage of piezo-driven outward-opening pintle injector nozzles used with spray-guided direct-injection gasoline engines are studied using a Eulerian-Lagrangian computational fluid dynamics cavitation model. Cavitation is formed because of the fluid acceleration taking place at the needle sealing area and it has been found to be affected by its geometric details. Various submodels for nucleation and bubble formation, further bubble growth and collapse, as well as bubble break-up and transport are incorporated into the model. Qualitative model validation is performed against experimental data reported elsewhere in large-scale nozzle replicas, showing similar cavitation patterns to be formed. These consist of vapour pockets rather than a continuous vapour film and develop transiently in a rather chaotic manner around the circumferential needle sealing area, even under stationary geometry and fixed-flowrate conditions. Further transient effects associated with the fast opening and closing of the piezo-controlled needle valve are also presented.

Study of the current waveform effect on the formation of cathode deposits during direct electrolysis Part 1. Electrolysis of fresh water

2021 ◽  
pp. 18-25
Author(s):  
И.В. Пчельников ◽  
Т.Т.З. Нгуен ◽  
Л.Н. Фесенко
Keyword(s):  
Fresh Water ◽  
Sodium Hypochlorite ◽  
Direct Current ◽  
Water Oxidation ◽  
Tap Water ◽  
Reverse Current ◽  
Raw Material ◽  
Half Cycle ◽  
Current Output ◽  
Direct Electrolysis

При электрохимической обработке хлоридсодержащих природных вод в бездиафрагменном электролизере образуются соли хлорноватистой кислоты, проявляющие окислительные свойства. Этот процесс широко используется для производства дезинфицирующих растворов на основе гипохлорита натрия. Сырьем для производства гипохлорита натрия могут быть не только искусственно приготовленные солевые растворы, но и природные минеральные воды, содержащие хлориды. Электролиз таких растворов приводит к образованию на катоде электролизера нерастворимых солей кальция и магния, что препятствует массообмену в межэлектродном пространстве, а также к возникновению аварийных ситуаций. В первой части статьи приведены результаты исследований прямого электролиза постоянным и реверсным током пресной воды г. Донгхой, Республика Вьетнам. В проведенных испытаниях определяли влияние реверсного тока в сравнении с постоянным током на снижение образования нерастворимых веществ на катодах электролизера. Эксперименты показали преимущество реверсного тока над постоянным. Так, при электролизе реверсным током продолжительностью периода до 6 часов масса отложений на электродах не увеличивалась, а на постоянном токе накапливалась с момента начала электролиза. Это связано с тем, что осадок, образующийся в катодный полупериод, растворяется в анодный полупериод кислотой – продуктом окисления воды. Выход хлора по току для водопроводной воды составил не более 23% с плотностью тока 100 А/м2. During the electrochemical processing of chloride-containing natural water in a membraneless electrolyzer, salts of hypochlorous acid are formed that are exhibiting oxidizing properties. This process is widely used for the production of sodium hypochlorite disinfectants. The raw material for the production of sodium hypochlorite can be not only artificially prepared saline solutions, but also natural mineral water containing chlorides. The electrolysis of such solutions results in the formation of insoluble calcium and magnesium salts at the cathode of the electrolyzer thus inhibiting mass transfer in the interelectrode space and the occurrence of emergency situations. The first part of the article presents the results of studies of direct electrolysis of fresh water with constant and reverse current in Dong Hoi city, Republic of Vietnam. In the conducted tests the effect of reverse current in comparison with direct current on the reduction of the formation of insoluble substances at the cathodes of the electrolyzer was determined. The experiments have shown the advantage of reverse current over direct current. So, during the electrolysis with reverse current for a period of up to 6 hours, the amount of deposits on the electrodes did not increase, however, with direct current the deposits accumulated from the very beginning of the electrolysis process. This is due to the fact that the precipitate formed during the cathodic half cycle is dissolved during the anodic half cycle by acid, a product of water oxidation. The current output of chlorine for tap water was no more than 23% with a current density of 100 A/m2.

Insights into chaperonin function from studies on archaeal thermosomes

2011 ◽  
Vol 39 (1) ◽  
pp. 94-98 ◽  
Author(s):  
Peter Lund
Keyword(s):  
Cell Death ◽  
Protein Folding ◽  
Recent Work ◽  
Mechanism Of Action ◽  
Molecular Chaperones ◽  
Short Review ◽  
Living Cells ◽  
Living Organisms ◽  
Opening And Closing ◽  
Hydrolysis Of

It is now well understood that, although proteins fold spontaneously (in a thermodynamic sense), many nevertheless require the assistance of helpers called molecular chaperones to reach their correct and active folded state in living cells. This is because the pathways of protein folding are full of traps for the unwary: the forces that drive proteins into their folded states can also drive them into insoluble aggregates, and, particularly when cells are stressed, this can lead, without prevention or correction, to cell death. The chaperonins are a family of molecular chaperones, practically ubiquitous in all living organisms, which possess a remarkable structure and mechanism of action. They act as nanoboxes in which proteins can fold, isolated from their environment and from other partners with which they might, with potentially deleterious consequences, interact. The opening and closing of these boxes is timed by the binding and hydrolysis of ATP. The chaperonins which are found in bacteria are extremely well characterized, and, although those found in archaea (also known as thermosomes) and eukaryotes have received less attention, our understanding of these proteins is constantly improving. This short review will summarize what we know about chaperonin function in the cell from studies on the archaeal chaperonins, and show how recent work is improving our understanding of this essential class of molecular chaperones.

scholarly journals Imaging kinase–AKAP79–phosphatase scaffold complexes at the plasma membrane in living cells using FRET microscopy

2002 ◽  
Vol 160 (1) ◽  
pp. 101-112 ◽  
Author(s):  
Seth F. Oliveria ◽  
Lisa L. Gomez ◽  
Mark L. Dell'Acqua
Keyword(s):  
Signal Transduction ◽  
Glutamate Receptors ◽  
Direct Evidence ◽  
Protein A ◽  
Resonance Energy Transfer ◽  
Resonance Energy ◽  
Adaptor Proteins ◽  
Living Cells ◽  
Intact Cells ◽  
Anchoring Protein

Scaffold, anchoring, and adaptor proteins coordinate the assembly and localization of signaling complexes providing efficiency and specificity in signal transduction. The PKA, PKC, and protein phosphatase-2B/calcineurin (CaN) scaffold protein A–kinase anchoring protein (AKAP) 79 is localized to excitatory neuronal synapses where it is recruited to glutamate receptors by interactions with membrane-associated guanylate kinase (MAGUK) scaffold proteins. Anchored PKA and CaN in these complexes could have important functions in regulating glutamate receptors in synaptic plasticity. However, direct evidence for the assembly of complexes containing PKA, CaN, AKAP79, and MAGUKs in intact cells has not been available. In this report, we use immunofluorescence and fluorescence resonance energy transfer (FRET) microscopy to demonstrate membrane cytoskeleton–localized assembly of this complex. Using FRET, we directly observed binding of CaN catalytic A subunit (CaNA) and PKA-RII subunits to membrane-targeted AKAP79. We also detected FRET between CaNA and PKA-RII bound simultaneously to AKAP79 within 50 Å of each other, thus providing the first direct evidence of a ternary kinase–scaffold–phosphatase complex in living cells. This finding of AKAP-mediated PKA and CaN colocalization on a nanometer scale gives new appreciation to the level of compartmentalized signal transduction possible within scaffolds. Finally, we demonstrated AKAP79-regulated membrane localization of the MAGUK synapse-associated protein 97 (SAP97), suggesting that AKAP79 functions to organize even larger signaling complexes.

scholarly journals Programmable RNA-binding protein composed of repeats of a single modular unit

2016 ◽  
Vol 113 (19) ◽  
pp. E2579-E2588 ◽  
Author(s):  
Katarzyna P. Adamala ◽  
Daniel A. Martin-Alarcon ◽  
Edward S. Boyden
Keyword(s):  
Rna Binding ◽  
Rna Binding Proteins ◽  
Binding Protein ◽  
Rna Binding Protein ◽  
Living Cells ◽  
Target Sequence ◽  
Rna Sequences ◽  
Intact Cells ◽  
Rna Translation ◽  
Protein Architecture

The ability to monitor and perturb RNAs in living cells would benefit greatly from a modular protein architecture that targets unmodified RNA sequences in a programmable way. We report that the RNA-binding protein PumHD (Pumilio homology domain), which has been widely used in native and modified form for targeting RNA, can be engineered to yield a set of four canonical protein modules, each of which targets one RNA base. These modules (which we call Pumby, for Pumilio-based assembly) can be concatenated in chains of varying composition and length, to bind desired target RNAs. The specificity of such Pumby–RNA interactions was high, with undetectable binding of a Pumby chain to RNA sequences that bear three or more mismatches from the target sequence. We validate that the Pumby architecture can perform RNA-directed protein assembly and enhancement of translation of RNAs. We further demonstrate a new use of such RNA-binding proteins, measurement of RNA translation in living cells. Pumby may prove useful for many applications in the measurement, manipulation, and biotechnological utilization of unmodified RNAs in intact cells and systems.

A reaction-based fluorescent probe for rapid detection of hypochlorite in tap water, serum, and living cells

2016 ◽  
Vol 232 ◽  
pp. 300-305 ◽  
Author(s):  
Xilang Jin ◽  
Yifan Jia ◽  
Weixing Chen ◽  
Ping Chui ◽  
Zhenhua Yang
Keyword(s):  
Fluorescent Probe ◽  
Rapid Detection ◽  
Tap Water ◽  
Living Cells
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