Dispersion properties of a magnetoactive plasma-filled waveguide in the vicinity of the upper hybrid frequency. Part II

The dispersion properties of a magnetoactive plasma-filled waveguide in the vicinity of the upper hybrid frequency ω₁ = (ω _p ² + ω _B ² )^1/2 (ω₁ ? δ < ω < ω₁) are studied. It is shown that, in this frequency range, the eigenmodes of the plasma-filled waveguide are represented by the families of EH and cyclotron HE modes, the interaction between which is weak everywhere except for the vicinities of certain points in the (ω, k _z ) plane. The equations describing the behavior of the dispersion curves in these vicinities are derived. It is shown that, as a result of the interaction, the high-frequency branches of EH modes acquire the cutoff frequencies corresponding to the high-order propagating HE modes. It is established that the anisotropic HE_+l mode can also interact with cyclotron HE modes. In this case, its dispersion curve enters the lower half-vicinity of the upper hybrid frequency, where it is modified due to the interaction, and then leaves it.     

Raman spectroscopic study on low-frequency collective modes in self-associates of guanosine monophosphates

Low-frequency Raman spectra of the self-associates of guanosine monophosphates (GMPs) Na₂ · 5′GMP, K₂ · 5′GMP, Na₂ · 3′GMP, and K₂ · 3′GMP, and polyribonucleic acid K · poly(rG), were obtained. In acidic gels and dried fibers, GMP molecules are known to form helical stacks of hydrogen-bonded tetramers. Some low-frequency collective modes specific to the helically stacked structures were observed. We examined the dependence of these modes on counterions and water content. The lowest frequency mode at ca. 20 cm^?1 is sensitive to the water content of the sample and is clearly visible in solid-state samples, so it works as a marker band of the environmental condition of the helices. The intensity and the peak frequency of this mode in solid-state samples depend on the helical structure and counterions. The broad peaks in the vicinity of 100 cm^?1 are influenced by cations and are independent of water content.     

Vibrational Analysis of Phosphorothioate DNA: II. The POS Group in the Model Compound Dimethyl Phosphorothioate [(CH3O)2(POS)]-

Abstract

The results of Raman and Infrared (IR) spectroscopic investigations on the vibrational modes of dimethyl phosphorothioate (DMPS) anion, [(CH₃O)₂(POS)]^?, are reported. Ab initio calculations of the vibrational modes, the IR and Raman spectra and the interatomic force constants of DMPS were performed. A normal mode calculation was performed and the results were used to calculate the potential energy distribution for the vibrational modes. This analysis shows that in DMPS the P-S stretching mode has a frequency of about 630 cm^?1 and an angle bending mode involving the sulfur atom has a frequency of about 440 cm^?1. The proposed vibrational mode assignments will serve as marker bands in the conformational studies of phosphorothioate oligonucleotides which play a central role in the novel antisense therapeutic paradigm.     

Different Mode of Afferents Determines the Frequency Range of High Frequency Activities in the Human Brain: Direct Electrocorticographic Comparison between Peripheral Nerve and Direct Cortical Stimulation

Physiological high frequency activities (HFA) are related to various brain functions. Factors, however, regulating its frequency have not been well elucidated in humans. To validate the hypothesis that different propagation modes (thalamo-cortical vs. cortico-coritcal projections), or different terminal layers (layer IV vs. layer II/III) affect its frequency, we, in the primary somatosensory cortex (SI), compared HFAs induced by median nerve stimulation with those induced by electrical stimulation of the cortex connecting to SI. We employed 6 patients who underwent chronic subdural electrode implantation for presurgical evaluation. We evaluated the HFA power values in reference to the baseline overriding N20 (earliest cortical response) and N80 (late response) of somatosensory evoked potentials (HFA_SEP(N20) and HFA_SEP(N80)) and compared those overriding N1 and N2 (first and second responses) of cortico-cortical evoked potentials (HFA_CCEP(N1) and HFA_CCEP(N2)). HFA_SEP(N20) showed the power peak in the frequency above 200 Hz, while HFA_CCEP(N1) had its power peak in the frequency below 200 Hz. Different propagation modes and/or different terminal layers seemed to determine HFA frequency. Since HFA_CCEP(N1) and HFA induced during various brain functions share a similar broadband profile of the power spectrum, cortico-coritcal horizontal propagation seems to represent common mode of neural transmission for processing these functions.     

Density functional calculations modelling tyrosine oxidation in oxygenic photosynthetic electron transfer

Hybrid density functional calculations are used to model tyrosine oxidation during electron transfer reactions of photosystem II. The predicted frequency values for the 7a and δCOH modes of the reduced form and the 7a mode of the oxidised radical form are in excellent agreement with experimental data obtained for Mn and Ca depleted systems by Hienerwadel et al. [Biochemistry 36 (1997) 15447] and Berthomieu et al. [Biochemistry 37 (1998) 10547]. The calculations confirm that the two tyrosines Y_D and Y_Z are protonated in the reduced form. On oxidation the larger 7a frequency value observed experimentally for Y_Z can be best explained by a greater localisation of the protonic charge released on formation of this tyrosyl free radical.     

Characteristic vibration patterns of odor compounds from bread-baking volatiles upon protein binding: density functional and ONIOM study and principal component analysis

As the mechanism underlying the sense of smell is unclear, different models have been used to rationalize structure–odor relationships. To gain insight into odorant molecules from bread baking, binding energies and vibration spectra in the gas phase and in the protein environment [7-transmembrane helices (7TMHs) of rhodopsin] were calculated using density functional theory [B3LYP/6-311++G(d,p)] and ONIOM [B3LYP/6-311++G(d,p):PM3] methods. It was found that acetaldehyde (“acid” category) binds strongly in the large cavity inside the receptor, whereas 2-ethyl-3-methylpyrazine (“roasted”) binds weakly. Lys296, Tyr268, Thr118 and Ala117 were identified as key residues in the binding site. More emphasis was placed on how vibrational frequencies are shifted and intensities modified in the receptor protein environment. Principal component analysis (PCA) suggested that the frequency shifts of C–C stretching, CH₃ umbrella, C = O stretching and CH₃ stretching modes have a significant effect on odor quality. In fact, the frequency shifts of the C–C stretching and C = O stretching modes, as well as CH₃ umbrella and CH₃ symmetric stretching modes, exhibit different behaviors in the PCA loadings plot. A large frequency shift in the CH₃ symmetric stretching mode is associated with the sweet-roasted odor category and separates this from the acid odor category. A large frequency shift of the C–C stretching mode describes the roasted and oily-popcorn odor categories, and separates these from the buttery and acid odor categories.     

Dispersion properties of a magnetoactive plasma-filled waveguide in the vicinity of the upper hybrid frequency. Part I

The dispersion properties of a magnetoactive plasma-filled waveguide in the vicinity of the upper hybrid frequency ω₁ = (ω _p ² + ω _B ² )^1/2 (ω₁ ≤ ω < ω₁ + δ) are studied. In this frequency range, the eigenfrequency spectrum and the structure of the waveguide eigenfields are difficult to analyze, because one of the transverse wavenumbers tends to infinity as the upper hybrid frequency is approached. It is shown that this problem can be solved by transforming the dispersion relation into a form independent of this transverse wavenumber. It is also found that the upper hybrid frequency itself can also be a solution to the dispersion relation. The influence of the properties of the magnetoactive plasma-filled waveguide on such solutions is studied. The structure of the fields for modes with frequencies equal to the upper hybrid frequency and an infinitely large absolute value of one of the transverse wavenumbers is analyzed.     

Protein dynamics: conformational disorder,vibrational coupling and anharmonicity in deoxy-hemoglobin and myoglobin

In this work we study the temperature dependence of the Soret band lineshape of deoxymyoglobin and deoxyhemoglobin, in the range 300–20 K. To fit the measured spectra we use an approach originally proposed by Champion and coworkers (Srajer et al. 1986; Srajer and Champion 1991). The band profile is modelled as a Voigt function that accounts for the coupling with low frequency vibrational modes, whereas the coupling with high frequency modes is responsible for the vibronic structure of the spectra. Moreover, owing to the position of the iron atom out of the mean heme plane, inhomogeneous broadening brings about a non-Gaussian distribution of 0–0 electronic transition frequencies. The reported analysis enables us to isolate the various contributions to the overall bandwidth, and their temperature dependence points out the relevance of low frequency vibrations and of large scale anharmonic motions starting at temperatures higher than 170 K. Information on the mean iron-heme plane distance and on its temperature dependence, as well as on the heme pocket conformational disorder, is also obtained.Abbreviations Cc Carbon monoxide - Hb Human deoxyhemoglobin A - HbCO human carbonmonoxyhemoglobin A - SWMb spermwhale deoxymyoglobin - SWMbCO spermwhale carbonmonoxymyoglobin - HbO₂ human oxyhemoglobin A - SWMb³⁺-H₂O spermwhale aquometmyoglobin     

Drift stabilization of internal resistive-wall modes in tokamaks

The problem of drift stabilization of the internal resistive-wall modes (RWMs) in tokamaks is theoretically investigated. The basic assumption of the model is that, when the drift effects are neglected, these modes are unstable in the absence of a conducting wall and stable in the presence of a close-fitting perfectly conducting wall. In the former case, the instability condition is expressed as Δ′_∞>0, where Δ′_∞ is the matching parameter calculated under the assumption that the wall is removed to infinity. In the latter case, one has Δ _W ^′ <0, where Δ _W ^′ is the external matching parameter of tearing modes calculated assuming a perfectly conducting wall at the plasma boundary. In the case with a resistive wall, the relevant parameter can be either Δ′_∞ or Δ _W ^′ , depending on whether the value of the dimensionless parameter ωτ_s/2m is small or large, respectively (here ω is the mode frequency, τ_s is the resistive time constant of the wall, and m is the poloidal mode number). In the presence of drift effects, the mode frequency ω is approximately equal to the electron drift frequency, ω≈ω_*e. The value of the parameter ω_*eτ_s/2m, which therefore determines the behavior of internal RWMs, is estimated for several existing tokamaks, namely, AUG (ASDEX-Upgrade), DIII-D, JET, TFTR, and JT-60U, as well as for the projected ITER-FEAT. It is shown that, although drift effects do not stabilize internal RWMs in current devices, they should be efficient in suppressing these modes in reactor-grade tokamaks.     

The mechanism of the mixed inheritance of chloroplast genes in Pelargonium

Summary The distributions are given of gene frequencies among embryos after G X W and W X G plastid crosses within and between eight Pelargonium cultivars and some of their inbred or hybrid derivatives.Two distinct segregation patterns are recognized. Homozygous type I female parents (Pr₁Pr₁) have a high frequency of progeny with only maternal alleles, are intermediate for biparental and low for paternal offspring. Heterozygous type II female plants (Pr₁Pr₂) have an equally high frequency of maternal and paternal offspring and a generally low biparental frequency. These correspond to L-shaped and U-shaped gene frequency distributions respectively in which the only modes are at 0 per cent (maternal embryos) and 100 per cent (paternal embryos), with no mode corresponding to the population mean and no sign of a Gaussian distribution.The extremely variable plastid gene frequencies are strongly influenced by the maternal nuclear genotype and by the plastid genotype in which the wild-type allele is always more successful than the mutant in strict comparisons.The relative frequencies of maternal and paternal zygotes, and the mean gene frequency among all the zygotes in a cross, are explicable in terms of the input frequencies of genes from the two parents, their degree of mixing, and by some form of selective replication of plastids. This selection is controlled by nuclear and plastid genotypes which may act in the same direction, to increase the frequency of either the maternal or the paternal alleles, or in opposition. But selection alone is inadequate to explain the shapes of the gene frequency distributions. Instead, a model is proposed in which the segregation or replication of plastids appears to have a strong random element, which results in random drift of gene frequencies within a heteroplasmic zygote or embryo.     

Azimuthally asymmetric eigenmodes of a magnetized plasma cylinder around a dielectric rod in a circular waveguide

The electrodynamics of a circular waveguide with a dielectric rod surrounded by a magnetized plasma layer is considered. A general dispersion relation for azimuthally asymmetric perturbations is derived, and its solutions describing slow waves—specifically, electromagnetic and plasma modes, as well as (and primarily) hybrid waves that combine the properties of both mode types—are investigated numerically. For the fundamental waveguide mode of the system—the HE₁₁ mode—the parameters of the plasma layer are determined at which the mode cannot be subject to Cherenkov interaction with a relativistic electron beam at a given frequency. For both waveguide and plasma modes, the radial profiles of the longitudinal components of the electric field and Poynting vector, the fractions of RF power carried within the dielectric and plasma regions and vacuum gap, and the coupling impedance are calculated as functions of the parameters of the plasma layer. The evolution of the field structure during the formation of asymmetric hybrid waves is traced. The results of calculating the dispersion and coupling impedance are analyzed as applied to an antenna-amplifier—a relativistic traveling-wave tube operating on the HE₁₁ mode of the dielectric rod: specifically, the implementability of the concept in the presence of a plasma at the rod surface is estimated, and the possible role of azimuthally asymmetric and symmetric plasma modes is examined.     

Primary Conformation Change in Bacteriorhodopsin on Photoexcitation

Ultrafast dynamics of bacteriorhodopsin (bR) has been extensively studied experimentally and theoretically. However, there are several contradictory results reported, indicating that its detailed dynamics and initial process have not yet been fully clarified. In this work, changes in the amplitude and phase of molecular vibration in the isomerization process of bR were real-time probed simultaneously at 128 different wavelengths through intensity modulation of the electronic transition. Systematic information on the transient change in continuous spectrum extending from 505 nm (2.45 eV) to 675 nm (1.84 eV) showed different dynamics in each spectral region reflecting the difference in the excited states and intermediates dominating the dynamics during the photoisomerization. Careful analysis of the transient spectral changes and spectrograms calculated from the vibrational real-time traces elucidated that the primary event just after photoexcitation is the deformation of the retinal configuration, which decays within 30 fs near the C=N bond in the protonated Schiff base. The intensity of C=N stretching mode starts to decrease before the initiation of the frequency modulation of the C=C stretching mode. The C=C stretching mode frequency was modulated by a coupled torsion around the C₁₃=C₁₄ bond, leading to the photoisomerization around the bond. This study clarified the dynamics of the C=N and C=C stretching modes working as key vibration modes in the photoisomerization of bR. Furthermore, we have elucidated the modulation and decay dynamics of the C=C stretching mode in the photoreaction starting from H (Franck-Condon excited state) followed by I (twisted excited), and J (first intermediate) states.     

Zwitterion l-cysteine adsorbed on the Au20 cluster: enhancement of infrared active normal modes

The study reported herein addressed the structure, adsorption energy and normal modes of zwitterion l-cysteine (Z-cys) adsorbed on the Au₂₀ cluster by using density functional theory (DFT). It was found that four Z-cys are bound to the Au₂₀ apexes preferentially through S atoms. Regarding normal modes, after adsorption of four Z-cys molecules, a more intense infrared (IR) peak is maintained around 1,631.4 cm^?1 corresponding with a C=O stretching mode, but its intensity is enhanced approximately six times. The enhancement in the intensity of modes between 0 to 300 cm^?1 is around 4.5 to 5.0 times for normal modes that involve O–C=O and C-S bending modes. Other two normal modes in the range from 300 to 3,500 cm^?1 show enhancements of 6.0 and 7.4 times. In general, four peaks show major intensities and they are related with normal modes of carboxyl and NH₃ groups of Z-cys.     

Neutron scattering method for studying bound water in live tissue application to plant leaves

Illustrative neutron scattering studies are presented of rotational modes of bound H₂O in live leaves of Ficus elastica decora, Philodendron cordatum and Peperomia obtusifolia. Interpretation of data is based on the hypothesis that hindrance of rotational motion should result in shifts to higher frequency. Such shifts are verified by comparing scattering from water with that from ice and cytosine monohydrate. Statistical analysis of the scattering from plant leaves is based on the assumption that least-squares fitting can be carried out using variable percentages of ice and water spectra to describe hydrate and free water fractions. It is found that the amount of water present as a 4-fold bonded hydrate is very small, being of the order of a few percent or less.     

Muscarinic K+ Channel in the Heart : Modal Regulation by G Protein βγ Subunits

The membrane-delimited activation of muscarinic K⁺ channels by G protein βγ subunits plays a prominent role in the inhibitory synaptic transmission in the heart. These channels are thought to be heterotetramers comprised of two homologous subunits, GIRK1 and CIR, both members of the family of inwardly rectifying K⁺ channels. Here, we demonstrate that muscarinic K⁺ channels in neonatal rat atrial myocytes exhibit four distinct gating modes. In intact myocytes, after muscarinic receptor activation, the different gating modes were distinguished by differences in both the frequency of channel opening and the mean open time of the channel, which accounted for a 76-fold increase in channel open probability from mode 1 to mode 4. Because of the tetrameric architecture of the channel, the hypothesis that each of the four gating modes reflects binding of a different number of Gβγ subunits to the channel was tested, using recombinant Gβ₁γ₅. Gβ₁γ₅ was able to control the equilibrium between the four gating modes of the channel in a manner consistent with binding of Gβγ to four equivalent and independent sites in the protein complex. Surprisingly, however, Gβ₁γ₅ lacked the ability to stabilize the long open state of the channel that is responsible for the augmentation of the mean open time in modes 3 and 4 after muscarinic receptor stimulation. The modal regulation of muscarinic K⁺ channel gating by Gβγ provides the atrial cells with at least two major advantages: the ability to filter out small inputs from multiple membrane receptors and yet the ability to create the gradients of information necessary to control the heart rate with great precision.     

Planar Quadrature RF Transceiver Design Using Common-Mode Differential-Mode (CMDM) Transmission Line Method for 7T MR Imaging

The use of quadrature RF magnetic fields has been demonstrated to be an efficient method to reduce transmit power and to increase the signal-to-noise (SNR) in magnetic resonance (MR) imaging. The goal of this project was to develop a new method using the common-mode and differential-mode (CMDM) technique for compact, planar, distributed-element quadrature transmit/receive resonators for MR signal excitation and detection and to investigate its performance for MR imaging, particularly, at ultrahigh magnetic fields. A prototype resonator based on CMDM method implemented by using microstrip transmission line was designed and fabricated for 7T imaging. Both the common mode (CM) and the differential mode (DM) of the resonator were tuned and matched at 298MHz independently. Numerical electromagnetic simulation was performed to verify the orthogonal B₁ field direction of the two modes of the CMDM resonator. Both workbench tests and MR imaging experiments were carried out to evaluate the performance. The intrinsic decoupling between the two modes of the CMDM resonator was demonstrated by the bench test, showing a better than -36 dB transmission coefficient between the two modes at resonance frequency. The MR images acquired by using each mode and the images combined in quadrature showed that the CM and DM of the proposed resonator provided similar B₁ coverage and achieved SNR improvement in the entire region of interest. The simulation and experimental results demonstrate that the proposed CMDM method with distributed-element transmission line technique is a feasible and efficient technique for planar quadrature RF coil design at ultrahigh fields, providing intrinsic decoupling between two quadrature channels and high frequency capability. Due to its simple and compact geometry and easy implementation of decoupling methods, the CMDM quadrature resonator can possibly be a good candidate for design blocks in multichannel RF coil arrays.     

Estimation of formamide harmonic and anharmonic modes in the Kohn-Sham limit using the polarization consistent basis sets

Formamide harmonic and anharmonic frequencies of fundamental vibrations in the gas phase and in several solvents were successfully estimated in the B3LYP Kohn-Sham complete basis set limit (KS CBS). CBS results were obtained by extrapolating a power function (two-parameter formula) to the results calculated with polarization-consistent basis sets. Anharmonic corrections using the second order perturbation treatment (PT2) and hybrid B3LYP functional combined with polarization consistent pc-n (n = 0, 1, 2, 3, 4) and several Pople’s basis sets were analyzed for all fundamental formamide vibrational modes in the gas phase and solution. Solvent effects were modeled within a PCM method. The anharmonic frequency of diagnostic amide vibration C = O in the gas phase and the CCl₄ solution calculated with the VPT2 method was significantly closer to experimental data than the corresponding harmonic frequency. Both harmonic and anharmonic frequencies of C = O stretching mode decreased linearly with solvent polarity, expressed by relative environment permittivity (ε) ratio (ε − 1)/(2ε + 1). However, an unphysical behavior of solvent dependence of some low frequency anharmonic amide modes of formamide (e.g., CN stretch, NH₂ scissoring, and NH₂ in plane bend) was observed, probably due to the presence of severe anharmonicity and Fermi resonance.     

Influence of Low-Intensity Electromagnetic Field on Some Biological Parameters of Freshwater Crustaceans <Emphasis Type="Italic">Daphnia magna</Emphasis> Straus

We have studied the effects of a low-intensity electromagnetic field (EMF) with a frequency of 30 MHz in continuous-wave and amplitude-modulation modes on Daphnia magna in a laboratory culture. The exposure range is from 10 to 10000 s. We examine the parental generation (irradiated) and three subsequent (F₁–F₃) generations (nonirradiated). It is found that irradiation does not affect the total fertility of any specimen in four generations (P–F₃), except for continuous EMF exposure for 10000 s, which increases the total fertility in generations F₂ and F₃ by 23 and 43%, respectively. Electromagnetic radiation has a significant impact on offspring quality and causes fetal abnormalities in the offspring of all generations.     

Stability of hybrid modes of a single-component electron plasma containing an admixture of background gas ions

The spectrum of eigenmodes of a waveguide completely filled with a cold electron plasma containing a small admixture of ions produced due to electron-impact ionization of background gas atoms is calculated numerically. The calculations were performed within the entire range of allowable values of the radial electric and longitudinal magnetic fields for both magnetized and unmagnetized ions by using the earlier derived nonlocal dispersion relation [Plasma Phys. Rep. 36, 563 (2010)]. The spectrum consists of three families of electron modes with frequencies equal to the Doppler-shifted upper and lower hybrid frequencies and modified ion cyclotron (MIC) modes. When the Doppler shift caused by electron rotation in the crossed electric and magnetic fields compensates for the hybrid frequency, the electron modes become low-frequency modes and interact with the ion modes. For m = 1, only the lower hybrid modes can be low-frequency ones, whereas at m ≥ 2, both lower and upper hybrid modes can be low-frequency ones. The spectrum of modes having the azimuthal number m = 2 is thoroughly analyzed. It is shown that, in this case, the lower hybrid modes behave similar to the m = 1 modes. The dispersion curves of the upper hybrid modes intersect with all harmonics of the MIC frequency (positive, negative, and zero) and are unstable in the vicinities of the intersections. The maximum value of the instability growth rate is several times higher than the ion plasma frequency. The MIC modes are unstable within a wide range of the field strengths, and their growth rates are two orders of magnitude slower. Instabilities are caused by the relative motion of electrons and ions (the transverse current) and the anisotropy of the ion distribution function.     

Modification of cardiac RYR2 gating by a peptide from the central domain of the RYR2

The effect of a domain peptide DP_CPVTc from the central region of the RYR2 on ryanodine receptors from rat heart has been examined in planar lipid bilayers. At a zero holding potential and at 8 mmol L^?1 luminal Ca²⁺ concentration, DP_CPVTc induced concentrationdependent activation of the ryanodine receptor that led up to 20-fold increase of P_O at saturating DP_CPVTc concentrations. DP_CPVTc prolonged RyR2 openings and increased RyR2 opening frequency. At all peptide concentrations the channels displayed large variability in open probability, open time and frequency of openings. With increasing peptide concentration, the fraction of high open probability records increased together with their open time. The closed times of neither low- nor high-open probability records depended on peptide concentration. The concentration dependence of all gating parameters had EC₅₀ of 20 μmol L^?1 and a Hill slope of 2. Comparison of the effects of DP_CPVTc with the effects of ATP and cytosolic Ca²⁺ suggests that activation does not involve luminal feed-through and is not caused by modulation of the cytosolic activation A-site. The data suggest that although “domain unzipping” by DP_CPVTc occurs in both modes of RyR activity, it affects RyR gating only when the channel resides in the H-mode of activity.