The lead hydroxide stain of Watson (1958) used for increasing contrast in thin sections for electron microscopy has found acceptance in many laboratories. However, this stain has an unfortunate tendency to form precipitates (probably of lead carbonate (5)) on exposure to the air, thus contaminating the sections and irritating the observer. This drawback has led to the development of several modifications (2, 3) of the original method of staining and the use of ingenious devices (4, 5) for preventing exposure to air and consequent precipitate formation. We offer the following alternative methods which, we believe, are simpler to perform than those hitherto described. They have the additional advantages mentioned below. The methods are based on the observation that highly alkaline solutions of lead salts (pH > 11.5) yield relatively stable solutions which stain rapidly and intensely, thus obviating the hazard of precipitation to a marked degree. The methods have these additional advantages: the staining solutions are easily and rapidly prepared, are simply stored, and are stable for long periods of time. Furthermore, they can be efficiently used, many grids being treated simultaneously, without excessive precautions being taken against lead carbonate precipitation. Finally, "difficult" material, embedded in media which characteristically yield rather low contrast, such as epoxide resins, can be rapidly and easily stained. "C lean" preparations, of high contrast, are routinely obtained. As will be discussed later, it is thought that in these highly alkaline staining solutions lead is present as an hydroxide complex anion (plumbite ion) and that this anion is responsible for the staining. The methods of preparation are based on this hypothesis. Two methods for preparing the staining solutions have been found useful:
The effect of alterations in extracellular pH on cellular and humoral immune function is reviewed. Because acidic pH predominates at inflammatory loci and other sites of immune activity, most studies to date focus on the effect of acidic rather than alkaline pH. Investigations on polymorphonuclear leukocytes demonstrate mainly inhibition of chemotaxis, respiratory activity, and bactericidal capacity at reduced pH. Evidence of impaired lymphocyte cytotoxicity and proliferation at acidic pH is also beginning to emerge. Many of the clinical acidoses are accompanied similarly by immunodeficiency. Studies on macrophages and eosinophils are few and inconclusive. A small number of studies demonstrate acid‐induced activation of complement proteins and the alternative complement pathway, plus increased antibody‐binding to leukocytes at lowered pH. A differential effect of acidic pH on humoral and cellular immunity may, therefore, exist. Increasing recognition of the significance of extracellular pH in relation to immune function warrants further studies in this presently incomplete but rewarding field.
The capacity of bacteria to survive and grow at alkaline pH values is of widespread importance in the epidemiology of pathogenic bacteria, in remediation and industrial settings, as well as in marine, plant-associated and extremely alkaline ecological niches. Alkali-tolerance and alkaliphily, in turn, strongly depend upon mechanisms for alkaline pH homeostasis, as shown in pH shift experiments and growth experiments in chemostats at different external pH values. Transcriptome and proteome analyses have recently complemented physiological and genetic studies, revealing numerous adaptations that contribute to alkaline pH homeostasis. These include elevated levels of transporters and enzymes that promote proton capture and retention (e.g., the ATP synthase and monovalent cation/proton antiporters), metabolic changes that lead to increased acid production, and changes in the cell surface layers that contribute to cytoplasmic proton retention. Targeted studies over the past decade have followed up the long-recognized importance of monovalent cations in active pH homeostasis. These studies show the centrality of monovalent cation/proton antiporters in this process while microbial genomics provides information about the constellation of such antiporters in individual strains. A comprehensive phylogenetic analysis of both eukaryotic and prokaryotic genome databases has identified orthologs from bacteria to humans that allow better understanding of the specific functions and physiological roles of the antiporters. Detailed information about the properties of multiple antiporters in individual strains is starting to explain how specific monovalent cation/proton antiporters play dominant roles in alkaline pH homeostasis in cells that have several additional antiporters catalyzing ostensibly similar reactions. New insights into the pH-dependent Na(+)/H(+) antiporter NhaA that plays an important role in Escherichia coli have recently emerged from the determination of the structure of NhaA. This review highlights the approaches, major findings and unresolved problems in alkaline pH homeostasis, focusing on the small number of well-characterized alkali-tolerant and extremely alkaliphilic bacteria.
Stimuli-responsive hydrogels are materials with great potential for development of active functionalities in fluidics and micro-fluidics. Based on the current state of research on pH sensors, hydrogel sensors are described qualitatively and quantitatively for the first time. The review introduces the physical background of the special properties of stimuli-responsive hydrogels. Following, transducers are described which are able to convert the non-electrical changes of the physical properties of stimuli-responsive hydrogels into an electrical signal. Finally, the specific sensor properties, design rules and general conditions for sensor applications are discussed.
Konstantinos Horaites, Juan V. Rodriguez, Ying Liu
Solar sail technology is ready to be deployed in a satellite mission carrying a science-grade magnetometer. In preparation for such a mission, it is essential to characterize the interactions between the sail and the ambient plasma that could affect the magnetometer readings. The solar wind magnetic field is a key parameter in space weather prediction, because it governs the energy-releasing magnetic reconnection process at Earth's magnetopause. This paper investigates the influence of solar sails on the ambient magnetic field, particularly focusing on two critical electromagnetic effects: eddy currents and magnetic pileup. We find the induced eddy currents in the metallic sail can significantly perturb the local magnetic field at high frequencies. We also suggest that magnetic pileup can influence the spacecraft's environment when the sail size is comparable to the electron kinetic scales of the surrounding plasma. This research provides an initial guide for determining when sail-plasma interactions could impact magnetometer performance.
Jinsong Zhao, Trevor A. Bowen, Stuart D. Bale
et al.
We report observations of solar wind turbulence derived from measurements by the Parker Solar Probe. Our findings reveal the emergence of finite magnetic helicity within the transition range of the turbulence, aligning with signatures of kinetic Alfvén waves (KAWs). Notably, as the wave scale transitions from super-ion to sub-ion scales, the ratio of KAWs with opposing signs of magnetic helicity initially increases from approximately 1 to 6.5 before returning to 1. This observation provides, for the first time, compelling evidence for the transition from imbalanced kinetic Alfvénic turbulence to balanced kinetic Alfvénic turbulence.
Jeremiah Lübke, Frederic Effenberger, Mike Wilbert
et al.
Synthetic turbulence is a relevant tool to study complex astrophysical and space plasma environments inaccessible by direct simulation. However, conventional models lack intermittent coherent structures, which are essential in realistic turbulence. We present a novel method, featuring coherent structures, conditional structure function scaling and fieldline curvature statistics comparable to magnetohydrodynamic turbulence. Enhanced transport of charged particles is investigated as well. This method presents significant progress towards physically faithful synthetic turbulence.
Peter Montag, Gregory Howes, Daniel McGinnis
et al.
Collisionless shocks play a key role in the heliosphere at planetary bow shocks by governing the conversion of the upstream bulk kinetic energy of the solar wind flow to other forms of energy in the downstream, including bulk plasma heat, acceleration of particles, and magnetic energy. Here we present the first observational identification of the velocity-space signature of shock-drift acceleration of ions at a perpendicular collisionless shock, previously predicted using kinetic numerical simulations, using a field-particle correlation analysis of Magnetospheric Multiscale (\emph{MMS}) observations of Earth's bow shock. Furthermore, by resolving the ion energization rates as a function of particle velocity, the field-particle correlation technique facilitates a clean quantitative separation of the energization rate of the reflected ions from that of the incoming ion beam, enabling a more complete characterization of the energy conversion at the shock.
Current sheets are an essential element of the planetary magnetotails, where strong plasma currents self-consistently support magnetic field gradients. The current sheet configuration is determined by plasma populations that contribute to the current density. The most commonly investigated configuration is supported by diamagnetic cross-field currents of hot ions, typical for the magnetospheres of magnetized planets. In this study, we examine a new type of the current sheet configuration supported by field-aligned currents from electron streams in the Jovian magnetodisk. Such bi-directional streams increase the electron thermal anisotropy close to the fire-hose instability threshold and lead to strong magnetic field shear. The current sheet configuration supported by electron streams is nearly force-free, with B=const across the sheet. Using Juno plasma and magnetic field measurements, we investigate the internal structure of such current sheets and discuss possible mechanisms for their formation.
Solar wind measurements carried out by NASA's Wind spacecraft before, during and after the passing of an interplanetary coronal mass ejection (ICME) detected on 12-14 September 2014 have been used in order to examine several properties of magnetohydrodynamic (MHD) turbulence. Spectral indices and flatness scaling exponents of magnetic field, velocity and proton density measurements were obtained, and provided a standard description of the characteristics of turbulence within different sub-regions of the ICME and its surroundings. This analysis was followed by the validation of the third-order moment scaling law for isotropic, incompressible MHD turbulence in the same sub-regions, which confirmed the fully developed nature of turbulence in the ICME plasma. The energy transfer rate was also estimated in each ICME sub-region and in the surrounding solar wind. An exceptionally high value was found within the ICME sheath, accompanied by enhanced intermittency, possibly related to the powerful energy injection associated with the arrival of the ICME.
We study the existence and property of Fast magnetosonic modes in 3D compressible MHD turbulence by carrying out a number of simulations with compressible and incompressible driving conditions. We use two approaches to determine the presence of Fast modes: mode decomposition based on spatial variations only and spatio-temporal 4D-FFT analysis of all fluctuations. The latter method enables us to quantify fluctuations that satisfy the dispersion relation of Fast modes with finite frequency. Overall, we find that the fraction of Fast modes identified via spatio-temporal 4D FFT approach in total fluctuation power is either tiny with nearly incompressible driving or ~2% with highly compressible driving. We discuss the implications of our results for understanding the compressible fluctuations in space and astrophysics plasmas.
Abstract Ultraviolet-visible spectroscopy provides color information on organic compounds during chemical reactions. Absorption spectra of a pH indicator during protonation show absorption bands from electronic transitions based on molecular structure. Information from the bands including the wavelength of maximum absorption and calculated molar extinction coefficient can provide specific parameters for the reactant (the indicator) and the product (the protonated indicator). However, these parameters never directly present what chemical reaction is occurring, which is typically only determined after identification of the compounds with other characterization methods. Here, we show that a geometric object, which was built out of the loci of chromaticity points for a polymer pH-indicator in CIELAB color space, indicates that the reaction is protonation. The object contains information about species, i.e., the pH-indicating portion and its protonated form. Each locus for different initial concentrations was a line segment, which corresponded to the protonation process. The segments for a polymer pH indicator with azobenzene as the pH-indicating dye portion at different initial concentrations created a planar triangle in CIELAB color space. For another polymer pH indicator of nitrophenol, the geometric space was a half line. The corresponding geometric equations may be specific to protonation including information about the chemical species.