Boltzmann Relation Research Articles

P2Y1 receptor modulation of Ca2+-activated K+ currents in medium-sized neurons from neonatal rat striatal slices

ATP signaling to neurons and glia in the nervous system occurs via activation of both P2Y and P2X receptors. Here, we investigated the effects of P2Y1 receptor stimulation in developing striatal medium-sized neurons using patch-clamp recordings from acute brain slices of 7- and 28-day-old rats. Application of the selective P2Y1 receptor agonist 2-(Methylthio) ADP trisodium salt (2-MeSADP; 250 nM) increased outward K+ currents evoked by a ramp depolarization protocol in voltage-clamp recordings. This effect was observed in 59 out of 82 cells (72%) and was blocked completely by the P2Y1 antagonist, 2′-deoxy-N6-methyl adenosine 3′,5′-diphosphate. The averaged 2-MeSADP-sensitive conductance was fitted by the sum of a linear conductance and a Boltzmann relation, giving one-half activation voltage of −14.2 mV and an equivalent charge of 2.91. The 2MeSADP-mediated effect was sensitive to submillimolar concentrations of tetraethylammonium (TEA; 200 μM), to 200 nM iberiotoxin and to 100 nM apamin, suggesting the involvement of both big and small potassium (BK and SK, respectively) calcium-activated channels. In current-clamp experiments, 2-MeSADP decreased depolarization-evoked action potential (AP) firing in all 26 cells investigated, and this effect was reversed by TEA and by apamin but not by iberiotoxin. We conclude that the stimulation of P2Y1 receptors in developing striatal neurons leads to activation of calcium-activated potassium channels [IK(Ca)] of both BK and SK subtypes, the latter responsible for decreasing the frequency of AP firing in response to current injection. Therefore, P2Y1 signaling leading to activation of IK(Ca) may be important in regulating the activity of medium-sized neurons in the striatum.

Corrosion properties of thermally annealed and co-sputtered nickel silicide thin films

The corrosion properties of nickel silicide thin films are addressed by means of polarisation experiments in combination with X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) characterisation before and after the polarisation runs. The thin films studied included two pairs of nickel silicide of different compositions fabricated on Si wafer by means of ion-beam sputter deposition technique. For one pair, thin films were prepared by co-sputtering Si and Ni targets. To achieve higher crystallinity, the other pair was prepared by Ni sputter deposition followed by subsequent thermal annealing at 280 °C and 480 °C to develop single silicide phase of Ni 2Si and NiSi in individual film, respectively. The variation of the binding energy (BE) of Ni 2p 3/2 core-level peak in the XPS measurement in accordance with the Si content for this binary system follows a Boltzmann's relationship. The electrochemical polarisation tests conducted in 1.00 M HCl solution showed almost the same behaviour for the tested specimens irrespective of structure or film composition, still, the SEM and XPS studies together with optical microscopy showed that the Ni 2Si, leaner in Si, experienced thin film corrosion, whilst the NiSi appeared to be more resistant. Clearly, composition is found to be a more important design factor to tailor the corrosion properties than the structure for this binary silicide system.

The Boltzmann relation and its validity in magnetized plasmas

AbstractThis paper is concerned to give a definitive account of a physical situation of current practical interest by examining the plasma solution for a plasma in coaxial geometry with an applied axial magnetic field. It builds on earlier work concerned with plasma diamagnetism and concentrates on the parameters involved at low pressures and low collisionalities but can be extended to situations where the ions are magnetized.

Numerical Approximation of the Euler-Poisson-Boltzmann Model in the Quasineutral Limit

This paper analyzes various schemes for the Euler-Poisson-Boltzmann (EPB) model of plasma physics. This model consists of the pressureless gas dynamics equations coupled with the Poisson equation and where the Boltzmann relation relates the potential to the electron density. If the quasi-neutral assumption is made, the Poisson equation is replaced by the constraint of zero local charge and the model reduces to the Isothermal Compressible Euler (ICE) model. We compare a numerical strategy based on the EPB model to a strategy using a reformulation (called REPB formulation). The REPB scheme captures the quasi-neutral limit more accurately.

On the Boltzmann relation in a cold magnetized plasma

A systematic and exact comparison between the forces acting on magnetized electrons in a current-free plasma is considered within a fluid model. We show that the Boltzmann relation is fulfilled in the drift-diffusion approximation when (hi/he)(1+he2)/(1+hi2)⪡1 where he (or hi) is the ratio of the electron (or ion) cyclotron to the collision frequency. When the nonlinear inertia terms are taken into account, the previous criterion is too rough and must be modified. In particular it is proved that the Boltzmann relation is not uniformly valid in the plasma. The case of bounded plasmas where the electron temperature must be determined self-consistently is discussed in detail.

Protein dynamics: dancing on an ever-changing free energy stage

Protein dynamics: dancing on an ever-changing free energy stage

Effect of Prestrain on Fracture Toughness of Welded Joint

The tension, Charpy notch impact and fracture toughness tests on structural steels Q235B and Q345 were carried out under different prestrains. Ductile to brittle transition curves are investigated using Charpy impact tests. The results indicate that the prestrain decreases the impact toughness of both base metal (BM) and weld metal (WM); and increases the ductile-brittle transition temperature as well as the risk of fracture. The prestrain is also found to have a more significant effect in a less ductile material. River marking, the characteristic of cleavage fracture, is observed in the Q235B WM specimens 10% prestrain conditions at 0°C. The fracture surfaces of Q345 WM specimens are characterized by dimple-like structures. The depth of these dimples is decreased under prestrain applied before welding. The CTOD-prestrain curves are obtained using Boltzmann relation.

Fluorescence-Tracking of Activation Gating in Human ERG Channels Reveals Rapid S4 Movement and Slow Pore Opening

BackgroundhERG channels are physiologically important ion channels which mediate cardiac repolarization as a result of their unusual gating properties. These are very slow activation compared with other mammalian voltage-gated potassium channels, and extremely rapid inactivation. The mechanism of slow activation is not well understood and is investigated here using fluorescence as a direct measure of S4 movement and pore opening.Methods and FindingsTetramethylrhodamine-5-maleimide (TMRM) fluorescence at E519 has been used to track S4 voltage sensor movement, and channel opening and closing in hERG channels. Endogenous cysteines (C445 and C449) in the S1–S2 linker bound TMRM, which caused a 10 mV hyperpolarization of the V½ of activation to −27.5±2.0 mV, and showed voltage-dependent fluorescence signals. Substitution of S1–S2 linker cysteines with valines allowed unobstructed recording of S3–S4 linker E519C and L520C emission signals. Depolarization of E519C channels caused rapid initial fluorescence quenching, fit with a double Boltzmann relationship, F-VON, with V½ ,1 = −37.8±1.7 mV, and V½ ,2 = 43.5±7.9 mV. The first phase, V½ ,1, was ∼20 mV negative to the conductance-voltage relationship measured from ionic tail currents (G-V½ = −18.3±1.2 mV), and relatively unchanged in a non-inactivating E519C:S620T mutant (V½ = −34.4±1.5 mV), suggesting the fast initial fluorescence quenching tracked S4 voltage sensor movement. The second phase of rapid quenching was absent in the S620T mutant. The E519C fluorescence upon repolarization (V½ = −20.6±1.2, k = 11.4 mV) and L520C quenching during depolarization (V½ = −26.8±1.0, k = 13.3 mV) matched the respective voltage dependencies of hERG ionic tails, and deactivation time constants from −40 to −110 mV, suggesting they detected pore-S4 rearrangements related to ionic current flow during pore opening and closing.ConclusionThe data indicate: 1) that rapid environmental changes occur at the outer end of S4 in hERG channels that underlie channel activation gating, and 2) that secondary slower changes reflect channel pore opening during sustained depolarizations, and channel closing upon repolarization. 3) No direct evidence was obtained of conformational changes related to inactivation from fluorophores attached at the outer end of S4.

Coaxial discharge with axial magnetic field: Demonstration that the Boltzmann relation for electrons generally does not hold in magnetized plasmas

A one-dimensional two-fluid model is used to describe the quasineutral plasma of a discharge formed between coaxial cylinders under the influence of an axial magnetic field. The geometry treated in this paper is symmetric about the z-axis and is radially varying. The nested cylinders are necessarily different in size, leading to a potential difference between the sheath edges of the discharge plasma. This can be removed by applying a strong enough magnetic field, which also has the effect of flattening the potential profile, i.e., reducing the electric field in the plasma volume. In a previous publication [T. M. G. Zimmermann et al., Phys. Plasmas 16, 043501 (2009)], the authors examined the validity of the Boltzmann relation for electrons when applied to a similar geometry. When the magnetic field becomes strong enough to affect the electron flow in the radial direction, this expression breaks down. It was further discovered that certain situations require a self-consistent treatment of magnetic fields, since significant azimuthal currents can arise in such geometries. This work is applied and extended to offer a complete description of the electron density.

Two Structurally Distinct Pathways for the Voltage-Sensing S4 Helices

In voltage-dependent ion channels, the movement of the voltage-sensing S4 helices produces gating currents. The charge displaced as a function of the membrane potential (Q-V) is well described by a sequential two-state Boltzmann relation, indicating that there are at least two steps of gating charge movement from their Resting state to the Active state. In addition, it has been shown that at a maintained positive potential, the S4 helices of voltage-gated Na, Ca and K channels and the voltage sensitive phosphatase Ci-VSP, undergo a slower secondary conformational transition stabilizing the sensor in a Relaxed (inactivated) state. From the Relaxed state, the Q-V relation exhibits a strong shift towards negative potentials when compared to the Q-V relation measured from the resting state. We engineered gating perturbations in the Shaker potassium channel, by substituting specific aromatic residues in positions spatially close to the S4. One of these mutants, in position I241 of S1, part of the hydrophobic plug of the voltage sensor, when mutated to tryptophan (I241W), produces a strong split in the Q-V when measured from the resting state. By labeling M356C with TMRM we also find the same split in the fluorescence-voltage curve. We propose that the presence of the tryptophan in the 241 position favors an interaction with one of the positively-charged arginines along the S4, thus stabilizing a fleeting intermediate state in the gating pathway. However, in the I241W mutant, the split in the Q-V almost disappears when the gating currents are measured from the relaxed state and the same result is seen with the fluorescence-voltage curve. This result and the effect of other tryptophan perturbations near the S4 segment strongly support the existence of two structurally distinct gating pathways for the movement of the S4 helices. Supported: NIHGM030376.

Carbonization and Treatment the High Temperature Distortion of Thoriated Tungsten Cathode for High Power Electronic Tubes

A metal mandrel was designed for manufacturing the cathodes of high power electron tube ( Tetrode ) used in broadcasting transmitting tubes type TH558 and CQS200.The cathodes were manufactured in the present work from thoriated tungsten wires ( 2? ThO2- W) with different diameters .These cathodes were carbonized in sequences of processes to determine the carbonization parameters (temperature, pressure, time, current and voltage).Then the carbonized cathodes dimension were accurately measured to determine the deviation due to the high temperature distortion effect at about 1800°C .the distorted cathodes due to the carbonization process was treated when it was subjected inside the vacuum chamber and heat treated again .The carbonized cathode distortions as a function of temperature were measured in the range of (1500°C-1800°C).The temperature was determined using an optical pyrometer and also calculated using Stephan's-Boltzmann relation.

Carbonization and Treatment the High Temperature Distortion of Thoriated Tungsten Cathode for High Power Electronic Tubes

A metal mandrel was designed for manufacturing the cathodes of high power electron tube ( Tetrode ) used in broadcasting transmitting tubes type TH558 and CQS200.The cathodes were manufactured in the present work from thoriated tungsten wires ( 2? ThO2- W) with different diameters .These cathodes were carbonized in sequences of processes to determine the carbonization parameters (temperature, pressure, time, current and voltage).Then the carbonized cathodes dimension were accurately measured to determine the deviation due to the high temperature distortion effect at about 1800°C .the distorted cathodes due to the carbonization process was treated when it was subjected inside the vacuum chamber and heat treated again .The carbonized cathode distortions as a function of temperature were measured in the range of (1500°C-1800°C).The temperature was determined using an optical pyrometer and also calculated using Stephan's-Boltzmann relation.

Parametric analysis of a magnetized cylindrical plasma

The relevant macroscopic model, the spatial structure, and the parametric regimes of a low-pressure plasma confined by a cylinder and an axial magnetic field is discussed for the small-Debye length limit, making use of asymptotic techniques. The plasma response is fully characterized by three-dimensionless parameters, related to the electron gyroradius, and the electron and ion collision mean-free-paths. There are the unmagnetized regime, the main magnetized regime, and, for a low electron-collisionality plasma, an intermediate-magnetization regime. In the magnetized regimes, electron azimuthal inertia is shown to be a dominant phenomenon in part of the quasineutral plasma region and to set up before ion radial inertia. In the main magnetized regime, the plasma structure consists of a bulk diffusive region, a thin layer governed by electron inertia, a thinner sublayer controlled by ion inertia, and the non-neutral Debye sheath. The solution of the main inertial layer yields that the electron azimuthal energy near the wall is larger than the electron thermal energy, making electron resistivity effects non-negligible. The electron Boltzmann relation is satisfied only in the very vicinity of the Debye sheath edge. Ion collisionality effects are irrelevant in the magnetized regime. Simple scaling laws for plasma production and particle and energy fluxes to the wall are derived.

Experimental investigation of the Boltzmann relation for a bi-Maxwellian distribution in inductively coupled plasmas

In plasma, the Boltzmann relation is often used to connect the electron density to the plasma potential because it is not easy to calculate electric potentials on the basis of the Poisson equation due to the quasineutrality. From the Boltzmann relation, the electric potential can be simply obtained from the electron density or vice versa. However, the Boltzmann relation assumes that electrons are in thermal equilibrium and have a Maxwellian distribution, so it cannot be applied to non-Maxwellian distributions. In this paper, the Boltzmann relation for bi-Maxwellian distributions was newly derived from fluid equations and the comparison with the experimental results was given by measuring electron energy probability functions in an inductively coupled plasma. It was found that the spatial distribution of the electron density in bulk plasma is governed by the effective electron temperature, while that of the cold and hot electrons are governed by each electron temperature.

Numerical Study of Nonlinear Coupling of a Lower-hybrid Wave in KSTAR

The nonlinear coupling to the tokamak plasma of the slow wave launched by the 5.0 GHz LowerHybrid (LH) system, which will be used for the non-inductive current drive in the Korea Superconducting Tokamak Advanced Research (KSTAR), has been studied by using a numerical computation. The numerical analysis is based on a nonlinear equation for an electric field, with a linear plasma density profile and a linear electron temperature profile near the grill. The radiated highpower density of the LH-wave perturbs the edge plasma density and even heats the plasma in front of the grill because of ponderomotive forces resulting from the RF pressure. This paper describes the nonlinear eect of the ponderomotive force on the coupling of the slow wave at the grill edge by considering only the axial component of the ponderomotive force along the waveguide grill and the associated perturbed plasma density given by the Boltzmann relation.

Supersonic Ion Beam Driven by Permanent-Magnets-Induced Double Layer in an Expanding Plasma

Plasma potential structures and ion-energy distribution functions are measured in a magnetically expanding radio-frequency plasma using permanent magnets (PMs) and in a geometrically expanding one, where the radio-frequency power and the argon-gas pressure are maintained at 250 W and 1 mtorr, respectively. In the magnetically expanding plasma, a rapid potential drop like a double-layer structure and a subsequent supersonic ion beam are detected by retarding field energy analyzers. On the other hand, a plasma potential structure following Boltzmann relation accelerates the ions in the geometrically expanding plasma. The comparison between the results in both cases indicates that the existence of the PMs is effective for the generation of the high-speed ion beam, where the mach number of the ion beam is increased to about 3.5 by using the PMs compared with the mach number of 2.3 in the operation mode of the geometrically expanding plasma.

Evaluation of models for numerical simulation of the non-neutral region of sheath plasma

Four different electron models are used to simulate the nonequilibrium plasma flow around a representative cylindrical Faraday probe geometry. Each model is implemented in a two-dimensional axisymmetric hybrid electron fluid and particle in cell method. The geometric shadowing model is derived from kinetic theory on the basis that physical obstruction of part of the velocity distribution leads to many of the expected sheath features. The Boltzmann electron fluid model relates the electron density to the plasma potential through the Boltzmann relation. The non-neutral detailed electron fluid model is derived from the electron conservation equations under the assumption of neutrality, and then modified to include non-neutral effects through the electrostatic Poisson equation. The Poisson-consistent detailed electron fluid model is also derived from the conservation equations and the electrostatic Poisson equation, but uses an alternative method that is inherently non-neutral from the outset. Simulations using the geometric shadowing and non-neutral detailed models do not yield satisfactory sheath structures, indicating that these models are not appropriate for sheath simulations. Simulations using the Boltzmann and Poisson-consistent models produce sheath structures that are in excellent agreement with the planar Bohm sheath solution near the centerline of the probe. The computational time requirement for the Poisson-consistent model is much higher than for the Boltzmann model and becomes prohibitive for larger domains.

A librational entropy mechanism for elastomers with repeating peptide sequences in helical array

A librational entropy mechanism is proposed for the elastomeric polypentapeptide of elastin which derives from the particular properties of a previously described dynamic β-spiral structure comprised of the repeating pentamer sequence. Using a cutoff energy of 2 kcal/mol residue, it is shown that the number of conformational states accessible to a single pentamer segment without perturbing the rest of the β-spiral is large in the relaxed state but becomes greatly decreased on extension. With use of the Boltzmann relation, it is seen that the effect of identical repeating units in a dynamic β-spiral is to linearly increase the entropy as the chain length increases. This occurs in spite of the valyl and prolyl side chains that significantly limit the states of the polymer and the Pro-Gly sequence which inserts a flexible β-turn. The aggregated states of the dynamic β-spiral with their weak hydrophobic intermolecular interactions that occur at high concentrations of chains and at physiologic temperatures are presented as an effective means of avoiding the entanglements that can limit numbers of accessible states for a concentrated random tangle of chains. Thus, a new mechanism is presented for an entropic elastomer which does not require that the relaxed state be totally random.

The effect of a magnetic field on a cylindrical object in a plasma

A two fluid model is applied to the presheath of a cylindrical object immersed in plasma under the influence of an axial magnetic field. The impact of the magnetic field on presheath behavior is studied and quantified by calculating the sheath edge potential and floating potential of the object. The latter is of great interest since it determines the cylinder’s charge. It is found that the density distribution in the presheath deviates significantly from the Boltzmann relation for electrons due to the presence of the magnetic field. This occurs because B opposes the radial flow of charge. However, the field not only inhibits transport of charge to the cylinder, but also deflects both fluids, setting up currents in the system, which increase the externally applied field. This effect can alter the field topology around the object significantly and makes it necessary to solve for the magnetic field self-consistently in some situations. The relevant parameter range is identified and a sample calculation with nonuniform B is shown. Interestingly, the magnetic field contribution due to the cylinder adds to the applied field, such that the object behaves as if it were ferromagnetic.

The Plasma Boundary in a Magnetic Field

AbstractPlasmas in the presence of a magnetic field can be divided into two categories, (a) those in which very small electron currents flow and the Boltzmann relation may be employed and (b) those in which there are appreciable electron currents and the use of the Boltzmann relation needs to be re‐examined. The present paper deals with the latter case. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)