Search results for "Polarization"

Chapter 27: Peptidergic and cholinergic receptors on cultured astrocytes of different regions of the rat CNS

1992

Publisher Summary This chapter discusses whether astrocytes possess peptidergic and cholinergic receptors. There is strong evidence that in addition to neurons, astrocytes also express receptors for neurotransmitters and neuromodulators. The investigations were carried out in explant cultures of the spinal cord, brain-stem, cerebellum, and neocortex of fetal and newborn rats. By the means of autoradiography, it was demonstrated that astrocytes possess binding sites for the vasoactive peptides 3 H-Ang II, 125 I- VIP, 125 I-ET-l, ET-3, and 125 I-AVP. These findings are consistent with electrophysiological studies demonstrating that Ang II, ET, and AVP cause a depolarization of the glial membr…

Photochemically induced dynamic nuclear polarization of heteronuclear singlet order

2021

Photochemically induced dynamic nuclear polarization (photo-CIDNP) is a method to hyperpolarize nuclear spins using light. In most cases, CIDNP experiments are performed in high magnetic fields and the sample is irradiated by light inside a nuclear magnetic resonance (NMR) spectrometer. Here we demonstrate photo-CIDNP hyperpolarization generated in the Earth's magnetic field and under zero- to ultralow-field (ZULF) conditions. Irradiating a sample containing tetraphenylporphyrin and para-benzoquinone for several seconds with light-emitting diodes produces strong hyperpolarization of 1H and 13C nuclear spins, enhancing the NMR signals more than 200 times. The hyperpolarized spin states at th…

Synergies between Hyperpolarized NMR and Microfluidics: A Review

2021

Hyperpolarized nuclear magnetic resonance and lab-on-a-chip microfluidics are two dynamic, but until recently quite distinct, fields of research. Recent developments in both areas increased their synergistic overlap. By microfluidic integration, many complex experimental steps can be brought together onto a single platform. Microfluidic devices are therefore increasingly finding applications in medical diagnostics, forensic analysis, and biomedical research. In particular, they provide novel and powerful ways to culture cells, cell aggregates, and even functional models of entire organs. Nuclear magnetic resonance is a non-invasive, high-resolution spectroscopic technique which allows real-…

Chemical Reaction Monitoring Using Zero-Field Nuclear Magnetic Resonance Enables Study of Heterogeneous Samples in Metal Containers

2020

Abstract We demonstrate that heterogeneous/biphasic chemical reactions can be monitored with high spectroscopic resolution using zero‐field nuclear magnetic resonance spectroscopy. This is possible because magnetic susceptibility broadening is negligible at ultralow magnetic fields. We show the two‐step hydrogenation of dimethyl acetylenedicarboxylate with para‐enriched hydrogen gas in conventional glass NMR tubes, as well as in a titanium tube. The low frequency zero‐field NMR signals ensure that there is no significant signal attenuation arising from shielding by the electrically conductive sample container. This method paves the way for in situ monitoring of reactions in complex heteroge…

Femtosecond polarization spectroscopy in molecular gas mixtures: Macroscopic interference and concentration measurements

2000

0021-9606; Raman-induced polarization spectroscopy (RIPS) experiments combined with homodyne detection have been conducted with a femtosecond laser at room temperature and low pressure (p < 2 atm) in CO2-N2 mixtures as well as in air (O2-N2 mixtures). Each molecule of the mixture produces its own time-dependent signal, measured as a series of recurring transients. Macroscopic interference is observed when transients of both molecules overlap in the time domain. This interference leads to a large modification of the signal, which is well reproduced by calculations. The total signal recorded in CO2-N2 or O2-N2 mixtures of known concentration is analyzed in order to measure the polarizability …

Electrical impedance spectroscopy of ionic liquid 1-ethyl-3-methylimidazolium methanesulfonate (ECOENG™ 110)

2011

Abstract Ionic liquid “ECOENG™ 110”, a promising electrolyte for electrochemical devices, was investigated by impedance spectroscopy. Metallic electrodes (Pt, Cu, Ag, and Mo) as well as carbon were used for the electrochemical characterization. The dependences of the real and imaginary impedance, polarization resistance and electrochemical capacity of the double layer on the electrode potential were investigated using electrical equivalent circuits of R1(QR2) and R1[Q(R2W)] types.

Temperature measurement in gas mixtures by femtosecond Raman-induced polarization spectroscopy

2003

The potential of femtosecond Raman-induced polarization spectroscopy (RIPS) for the simultaneous determination of temperature and concentrations was investigated. These measurements were related to the rotational time response of the molecular gas mixture, which was measured as a function of the pump-probe time delay. The change of the polarizability anisotropy with respect to the vibrational levels was taken into account. The results of temperature measurements in pure CO2 showed good agreement with the values obtained by a thermocouple. The RIPS technique was also applied to a CO2-N2 gas mixture to determine simultaneously temperatures and concentrations at temperatures up to 600 K. The a…

Determination of concentrations in ternary and quaternary molecular gas mixtures using femtosecond Raman spectroscopy

2002

Measurements of concentrations in gas mixtures of three and four molecular components are presented. They rely on a femtosecond time-resolved pump–probe technique based on Raman-induced polarization spectroscopy. The rotational time response of the molecular gas mixture is measured as a function of the pump–probe time delay. No selective frequency tunability is needed as the molecular rotational spectra are excited within the laser bandwidth. The results obtained from experiments performed at room temperature in N2O–CO2–N2 and N2O–CO2–O2–N2 mixtures are presented and the accuracy of the method is discussed. Copyright © 2002 John Wiley & Sons, Ltd.

Interacting induced dipoles polarization model for molecular polarizabilities. Reference molecules, amino acids and model peptides

1999

Abstract We outline a method for the calculation of molecular dipole ( μ ) and quadrupole ( Θ = ) moments and dipole–dipole polarizabilities ( α = ) which we have successfully applied to a series of reference molecules, amino acids and model peptides. The results for μ are in line with CPHF reference calculations. In particular, the calculated positive value of CO is in agreement with both experimental and CI calculations. The computation of ( α = ) has been performed by the interacting induced dipoles polarization model that calculates tensor effective anisotropic point polarizabilities (method of Applequist et al.). The POLAR program cannot be used as a black box. Some tests should be per…

2016

This commentary describes important findings of the article published by Sheroziya and Timofeev in The Journal of Neuroscience in 2015. The authors use moderate cortical temperature change, local cooling or heating of somatosensory cortex, to modulate excitable states of the brain. These changes, under physiological conditions, result from neuromodulation, as well as other network effects. They report that cooling disrupts thalamocortical slow oscillations and induces an activated cortical state, while mild heating has the opposite effect and increases slow-wave rhythmicity. We evaluate these findings regarding their utility for inducing and investigating cortical state fluctuations, compar…