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Advanced Materials (Deerfield Beach,... Aug 2017A plasmonic metasurface with an electrically tunable optical response that operates at strikingly low modulation voltages is experimentally demonstrated. The fabricated...
A plasmonic metasurface with an electrically tunable optical response that operates at strikingly low modulation voltages is experimentally demonstrated. The fabricated metasurface shows up to 30% relative change in reflectance in the visible spectral range upon application of 5 mV and 78% absolute change in reflectance upon application of 100 mV of bias. The designed metasurface consists of nanostructured silver and indium tin oxide (ITO) electrodes which are separated by 5 nm thick alumina. The millivolt-scale optical modulation is attributed to a new modulation mechanism, in which transport of silver ions through alumina dielectric leads to bias-induced nucleation and growth of silver nanoparticles in the ITO counter-electrode, altering the optical extinction response. This transport mechanism, which occurs at applied electric fields of 1 mV nm , provides a new approach to use of ionic transport for electrical control over light-matter interactions.
PubMed: 28612946
DOI: 10.1002/adma.201701044 -
Journal of Neurophysiology Apr 2003Slow shifts in the human scalp-recorded EEG, including those related to changes in brain CO(2) levels, have been generally assumed to result from changes in the level of...
Slow shifts in the human scalp-recorded EEG, including those related to changes in brain CO(2) levels, have been generally assumed to result from changes in the level of tonic excitation of apical dendrites of cortical pyramidal neurons. We readdressed this issue using DC-EEG shifts elicited in healthy adult subjects by hypo- or hypercapnia. A 3-min period of hyperventilation resulted in a prompt negative shift with a rate of up to 10 microV/s at the vertex (Cz) and an extremely steep dependence (up to 100 microV/mmHg) on the end-tidal Pco(2). This shift had a maximum of up to -2 mV at Cz versus the temporal derivations (T3/T4). Hyperventilation-like breathing of 5% CO(2)-95% O(2), which does not lead to a significant hypocapnia, resulted in a near-complete block of the negative DC shift at Cz. Hypoventilation, or breathing 5% CO(2) in air at normal respiratory rate, induced a positive shift. The high amplitude of the voltage gradients on the scalp induced by hyperventilation is not consistent with a neuronal origin. Instead, the present data suggest that they are generated by extracortical volume currents driven by a Pco(2)-dependent potential difference across epithelia separating the cerebrospinal fluid and blood. Since changes in respiratory patterns and, hence, in the level of brain Pco(2), are likely to occur under a number of experimental conditions in which slow EEG responses have been reported (e.g., attention shifts, preparatory states, epileptic seizures, and hypoxic episodes), the present results call for a thorough reexamination of the mechanisms underlying scalp-recorded DC-EEG responses.
Topics: Adult; Blood-Brain Barrier; Carbon Dioxide; Cerebrovascular Circulation; Electroencephalography; Female; Humans; Hyperventilation; Hypoventilation; Male; Scalp
PubMed: 12612037
DOI: 10.1152/jn.00915.2002 -
Heart Rhythm Jan 2008We recently reported an ECG algorithm for differential diagnosis of regular wide QRS complex tachycardias that was superior to the Brugada algorithm. (Comparative Study)
Comparative Study
BACKGROUND
We recently reported an ECG algorithm for differential diagnosis of regular wide QRS complex tachycardias that was superior to the Brugada algorithm.
OBJECTIVE
The purpose of this study was to further simplify the algorithm by omitting the complicated morphologic criteria and restricting the analysis to lead aVR.
METHODS
In this study, 483 wide QRS complex tachycardias [351 ventricular tachycardias (VTs), 112 supraventricular tachycardias (SVTs), 20 preexcited tachycardias] from 313 patients with proven diagnoses were prospectively analyzed by two of the authors blinded to the diagnosis. Lead aVR was analyzed for (1) presence of an initial R wave, (2) width of an initial r or q wave >40 ms, (3) notching on the initial downstroke of a predominantly negative QRS complex, and (4) ventricular activation-velocity ratio (v(i)/v(t)), the vertical excursion (in millivolts) recorded during the initial (v(i)) and terminal (v(t)) 40 ms of the QRS complex. When any of criteria 1 to 3 was present, VT was diagnosed; when absent, the next criterion was analyzed. In step 4, v(i)/v(t) >1 suggested SVT, and v(i)/v(t) < or =1 suggested VT.
RESULTS
The accuracy of the new aVR algorithm and our previous algorithm was superior to that of the Brugada algorithm (P = .002 and P = .007, respectively). The aVR algorithm and our previous algorithm had greater sensitivity (P <.001 and P = .001, respectively) and negative predictive value for diagnosing VT and greater specificity (P <.001 and P = .001, respectively) and positive predictive value for diagnosing SVT compared with the Brugada criteria.
CONCLUSION
The simplified aVR algorithm classified wide QRS complex tachycardias with the same accuracy as standard criteria and our previous algorithm and was superior to the Brugada algorithm.
Topics: Adult; Algorithms; Brugada Syndrome; Diagnosis, Differential; Electrocardiography; Electrodes; Female; Humans; Male; Tachycardia, Supraventricular; Tachycardia, Ventricular
PubMed: 18180024
DOI: 10.1016/j.hrthm.2007.09.020 -
Microscopy and Microanalysis : the... Jun 2014The millivolt energy resolution now obtainable in electron energy-loss spectra (EELS) on the latest monochromated scanning transmission electron microscope corresponds,...
The millivolt energy resolution now obtainable in electron energy-loss spectra (EELS) on the latest monochromated scanning transmission electron microscope corresponds, via the uncertainty principle, to a time range of 414 fs (for 10 meV resolution), and a time resolution of 0.138 fs (for energy range of 30 eV). (Thus, the width of an EELS peak is inversely related to the lifetime of an excitation.) This compares favorably with the latest X-ray free electron lasers. The time evolution of a Drude-Lorentz oscillator may be obtained from an EELS using logarithmic deconvolution followed by Kramers-Kronig analysis to extract the frequency-dependent dielectric function, and a final Fourier transform from frequency to time domain. This time-dependent dielectric function was interpreted as the impulse response of electrons, phonons, or ions based on the Drude-Lorentz theory. The time evolution of electronic oscillators from ice and protein, extracted from low resolution experimental data, were compared. Using higher energy resolution data we have also extracted the time-resolved spectra from excitons in an alkali halide, BaF2. Despite the small scanning transmission electron microscope probe size, delocalization limits the spatial resolution to about 50 nm, which is, nevertheless, better than the millimeter resolution of infrared absorption spectroscopy or Raman spectroscopy.
PubMed: 24878029
DOI: 10.1017/S1431927614000890 -
Nature Communications Jun 2014Photon and neutron inelastic scattering spectrometers are microscopes for imaging condensed matter dynamics on very small length and time scales. Inelastic X-ray...
Photon and neutron inelastic scattering spectrometers are microscopes for imaging condensed matter dynamics on very small length and time scales. Inelastic X-ray scattering permitted the first quantitative studies of picosecond nanoscale dynamics in disordered systems almost 20 years ago. However, the nature of the liquid-glass transition still remains one of the great unsolved problems in condensed matter physics. It calls for studies at hitherto inaccessible time and length scales, and therefore for substantial improvements in the spectral and momentum resolution of the inelastic X-ray scattering spectrometers along with a major enhancement in spectral contrast. Here we report a conceptually new spectrometer featuring a spectral resolution function with steep, almost Gaussian tails, sub-meV (≃620 μeV) bandwidth and improved momentum resolution. The spectrometer opens up uncharted space on the dynamics landscape. New results are presented on the dynamics of liquid glycerol, in the regime that has become accessible with the novel spectrometer.
PubMed: 24953338
DOI: 10.1038/ncomms5219 -
Optics Express Jun 2007We describe a class of modulator design involving slot waveguides and electro-optic polymer claddings. Such geometries enable massive enhancement of index tuning when...
We describe a class of modulator design involving slot waveguides and electro-optic polymer claddings. Such geometries enable massive enhancement of index tuning when compared to more conventional geometries. We present a semi-analytic method of predicting the index tuning achievable for a given geometry and electro-optic material. Based on these studies, as well as previous experimental results, we show designs for slot waveguide modulators that, when realized in a Mach-Zehnder configuration, will allow for modulation voltages that are orders of magnitude lower than the state of the art. We also discuss experimental results for nano-slot waveguides.
PubMed: 19547171
DOI: 10.1364/oe.15.008401 -
Journal of Visualized Experiments : JoVE Jul 2022Ex vivo preparations enable the study of many neurophysiological processes in isolation from the rest of the body while preserving local tissue structure. This work...
Ex vivo preparations enable the study of many neurophysiological processes in isolation from the rest of the body while preserving local tissue structure. This work describes the preparation of rat sciatic nerves for ex vivo neurophysiology, including buffer preparation, animal procedures, equipment setup and neurophysiological recording. This work provides an overview of the different types of experiments possible with this method. The outlined method aims to provide 6 h of stimulation and recording on extracted peripheral nerve tissue in tightly controlled conditions for optimal consistency in results. Results obtained using this method are A-fibre compound action potentials (CAP) with peak-to-peak amplitudes in the millivolt range over the entire duration of the experiment. CAP amplitudes and shapes are consistent and reliable, making them useful to test and compare new electrodes to existing models, or the effects of interventions on the tissue, such as the use of chemicals, surgical alterations, or neuromodulatory stimulation techniques. Both conventional commercially available cuff electrodes with platinum-iridium contacts and custom-made conductive elastomer electrodes were tested and gave similar results in terms of nerve stimulus strength-duration response.
Topics: Action Potentials; Animals; Electric Conductivity; Electric Stimulation; Electrodes; Neurophysiology; Rats; Sciatic Nerve
PubMed: 35913135
DOI: 10.3791/63838 -
Current Opinion in Chemical Biology Aug 2015Neurons tightly regulate the electrical potential difference across the plasma membrane with millivolt accuracy and millisecond resolution. Membrane voltage dynamics... (Review)
Review
Neurons tightly regulate the electrical potential difference across the plasma membrane with millivolt accuracy and millisecond resolution. Membrane voltage dynamics underlie the generation of an impulse, the transduction of impulses from one end of the neuron to the other, and the release of neurotransmitters. Imaging these voltage dynamics in multiple neurons simultaneously is therefore crucial for understanding how neurons function together within circuits in intact brains. Genetically encoded fluorescent voltage sensors have long been desired to report voltage in defined subsets of neurons with optical readout. In this review, we discuss the diverse strategies used to design and optimize protein-based voltage sensors, and highlight the chemical mechanisms by which different classes of reporters sense voltage. To guide neuroscientists in choosing an appropriate sensor for their applications, we also describe operating trade-offs of each class of voltage indicators.
Topics: Action Potentials; Animals; Biosensing Techniques; Cell Membrane; Fluorescent Dyes; Humans; Luminescent Proteins; Neurons; Protein Binding; Voltage-Sensitive Dye Imaging
PubMed: 26079047
DOI: 10.1016/j.cbpa.2015.05.003 -
Scientific Reports Oct 2019A salinity gradient propels a DNA molecule through a solid-state nanopore and generates an ionic current whose change allows for the detection of the translocation....
A salinity gradient propels a DNA molecule through a solid-state nanopore and generates an ionic current whose change allows for the detection of the translocation. Measurements and theoretical analyses reveal the role of diffusio-osmosis in driving these phenomena: After accounting for known salinity-dependent electrode effects, the measured current change caused by the presence of a DNA molecule inside the nanopore and the DNA translocation speed through it both increase with the magnitude of the applied salinity gradients. The effects are consistent with the theory of diffuisio-osmosis and strong enough to enable DNA translocations to overcome an applied retarding potential of tens of millivolts. This work illustrates how salinity gradients can be used to power and operate a nanopore sensor.
Topics: DNA; Diffusion; Electricity; Nanopores; Osmosis; Salinity; Time Factors
PubMed: 31636288
DOI: 10.1038/s41598-019-51049-4 -
The Journal of Biological Chemistry Jun 2001The midpoint reduction potentials of the FAD cofactor in wild-type Methylophilus methylotrophus (sp. W3A1) electron-transferring flavoprotein (ETF) and the alphaR237A...
alpha Arg-237 in Methylophilus methylotrophus (sp. W3A1) electron-transferring flavoprotein affords approximately 200-millivolt stabilization of the FAD anionic semiquinone and a kinetic block on full reduction to the dihydroquinone.
The midpoint reduction potentials of the FAD cofactor in wild-type Methylophilus methylotrophus (sp. W3A1) electron-transferring flavoprotein (ETF) and the alphaR237A mutant were determined by anaerobic redox titration. The FAD reduction potential of the oxidized-semiquinone couple in wild-type ETF (E'(1)) is +153 +/- 2 mV, indicating exceptional stabilization of the flavin anionic semiquinone species. Conversion to the dihydroquinone is incomplete (E'(2) < -250 mV), because of the presence of both kinetic and thermodynamic blocks on full reduction of the FAD. A structural model of ETF (Chohan, K. K., Scrutton, N. S., and Sutcliffe, M. J. (1998) Protein Pept. Lett. 5, 231-236) suggests that the guanidinium group of Arg-237, which is located over the si face of the flavin isoalloxazine ring, plays a key role in the exceptional stabilization of the anionic semiquinone in wild-type ETF. The major effect of exchanging alphaArg-237 for Ala in M. methylotrophus ETF is to engineer a remarkable approximately 200-mV destabilization of the flavin anionic semiquinone (E'(2) = -31 +/- 2 mV, and E'(1) = -43 +/- 2 mV). In addition, reduction to the FAD dihydroquinone in alphaR237A ETF is relatively facile, indicating that the kinetic block seen in wild-type ETF is substantially removed in the alphaR237A ETF. Thus, kinetic (as well as thermodynamic) considerations are important in populating the redox forms of the protein-bound flavin. Additionally, we show that electron transfer from trimethylamine dehydrogenase to alphaR237A ETF is severely compromised, because of impaired assembly of the electron transfer complex.
Topics: Arginine; Base Sequence; Benzoquinones; DNA Primers; Electron-Transferring Flavoproteins; Flavoproteins; Kinetics; Methylophilus methylotrophus; Mutagenesis, Site-Directed; Oxidation-Reduction; Potentiometry; Quinones
PubMed: 11285259
DOI: 10.1074/jbc.M010853200