Reduced Electron Density Research Articles

Measurements of high energy loss rates of fast highly charged U ions channeled in thin silicon crystals

The results of two channeling experiments show that highly charged heavy ions at moderate velocities ($v\ensuremath{\ll}{\mathit{Zv}}_{0}$) may lose more energy in the traversal of a thin crystal when they are injected along a major crystallographic direction than when they traverse the crystal in random conditions. This is due to the fact that the large reduction of electron capture probabilities allows them to keep their high electronic charge throughout the crystal, which is not the case for projectiles traveling in random conditions. Although channeled projectiles experience reduced electron densities, their energy loss rate, that is, at first order, proportional to the square of the ions charge, is then strongly enhanced. This feature could be used as a step for decelerating highly charged ions from the high energies that are needed to produce them, and also to improve our understanding of the slowing down of very highly charged projectiles at low velocities, for which the current perturbative models are not well suited.

Ionospheric disturbances produced by chemical releases and the resultant effects on short-wave ionospheric propagation

[1] As an effective means to actively modify the ionosphere, chemical releases can produce artificial ionospheric holes as a consequence of ionization reduction, which can have a great impact on radio wave propagation. To investigate the morphology control of ionospheric holes by various chemical releases and the resultant effects on radio wave propagation, a quantitative numerical model is developed on the basis of the approximate solutions of the diffusion equation of single-point release in uniform atmosphere. While single-point release produces ellipsoidal ionospheric holes, multipoint release can produce other types of ionospheric holes (such as parabola-like tubular ones), which is strongly dependent on changes in the release species, release altitude, and mass of released neutral gas. Releases of both H2O and SF6 can produce ionospheric holes with a similar spatial extent, but the latter tends to result in clearer boundaries and more pronounced electron density reductions. In addition, either an increase in released amount or releases at higher altitudes can lead to a broader hole. To evaluate the effects of an ionospheric hole on radio wave propagation, three-dimensional ray tracing simulations are performed. The ellipsoidal ionospheric holes can act as a lens focusing and bending radio waves, leading to multiple wave reflections inside the holes. In contrast, in the paraboloid tubular ionospheric holes, the rays can penetrate the disturbed region or reflect back, showing a strong dependence on radio frequency. It is well demonstrated that chemical releases can efficiently give rise to artificial ionospheric disturbances and thus modify ionospheric propagation of radio waves.

Mismatch of dielectric constants at the interface of nanometer metal-oxide-semiconductor devices with high-K gate dielectric impacts on the inversion charge density

The comparison of the inversion electron density between a nanometer metal-oxide-semiconductor (MOS) device with high-K gate dielectric and a SiO2 MOS device with the same equivalent oxide thickness has been discussed. A fully self-consistent solution of the coupled Schrodinger–Poisson equations demonstrates that a larger dielectric-constant mismatch between the gate dielectric and silicon substrate can reduce electron density in the channel of a MOS device under inversion bias. Such a reduction in inversion electron density of the channel will increase with increase in gate voltage. A reduction in the charge density implies a reduction in the inversion electron density in the channel of a MOS device. It also implies that a larger dielectric constant of the gate dielectric might result in a reduction in the source–drain current and the gate leakage current.

Comment on the paper “Total solar eclipse of July 22, 2009: Its impact on the total electron content and ionospheric electron density in the Indian zone” by Sharma et al.

By analyzing COSMIC data, Sharma et al. (2010) found more than 50% reduction in electron density during a solar eclipse at the F2-layer and above, with the peak of ∼70% at 370 km. So great eclipse effect on topside ionosphere was very abnormal and much different from previous studies. However, by comparing the cosmic data with IRI results, we find that the abnormal reduction comes mainly from the significant local time variation at sunrise, not from the eclipse effect. Furthermore, we simulated the eclipse effect by using a theoretical model to confirm our analysis.

Comparison of modeled electron densities and electron and ion temperatures with Arecibo observations during undisturbed and geomagnetic storm periods of 7-11 September 2005

[1] The electron density and the electron and ion temperatures measured by the Arecibo radar at 496 km altitude and NmF2 observed by the Puerto Rico ionosonde are compared with those produced by the model of the ionosphere and plasmasphere to study the time-dependent response of the ionosphere to geomagnetic forcing during the undisturbed and geomagnetic storm periods of 7–11 September 2005. The reasonable agreement between the model results and data requires the modified HWM90 wind and the modified NRLMSISE-00 neutral temperature. The pronounced positive daytime storm changes in NmF2 are created by increases in the upward wind-induced plasma drift due to the neutral wind, while the geomagnetic storm decreases in [N2] and [O2] and the enhanced disturbed upward wind-induced plasma drift cause the pronounced positive nighttime disturbances in NmF2. The storm neutral wind-induced plasma drift and neutral composition changes are responsible for the pronounced negative daytime NmF2 disturbances. The F2 layer transport from lower to higher altitudes by the upward wind-induced plasma drift decreases the distance between the hmF2 and our chosen altitude for study of the topside ionosphere. This results in the increase of the electron density at this chosen altitude due to a more weakly reduction in the electron density with altitude. The pronounced postmidnight peaks observed in the topside electron density over Arecibo are provided by these increases in the electron density.

A statistical study of the response of the dayside equatorialF2layer to the main phase of intense geomagnetic storms as an indicator of penetration electric field

[1] The response of the dayside equatorial F2 layer to the main phases of the 22 intense geomagnetic storms (Dst < −150 nT) in 1998–2008 is investigated using the digital ionosonde data from the equatorial stations in Brazilian, Indian, and Australian longitudes together with equatorial electrojet strength and IMF Bz; the storms include 15 superstorms (Dst < −200 nT). The observations show that there is a period during all MPs when the F2 layer peak rises (and falls) rapidly with large peak electron density (Nmax) reduction, the rise velocity strongly correlates with the intensity (Dst) of the storms, and the duration of the Nmax reduction corresponds to that of strong eastward electrojet when IMF Bz remains highly negative. The observations indicate the occurrence of strong eastward prompt penetration electric fields (PPEF) during the rapid F2 layer response. The PPEF drives the F2 layer peak rapidly upward, which reduces Nmax due to vertical expansion and diffusion. The results therefore suggest that the rapid F2 layer response (rapid rise (and fall) of peak height (hmax) with large Nmax reduction) observed by ionosondes can be used to detect the occurrence of the daytime eastward PPEF during intense geomagnetic storms irrespective of season and level of solar activity. The data also show two rare events of strong daytime westward electric fields due to disturbance dynamo and/or prompt penetration. The results are important when radars are not available to monitor the occurrence of the PPEF.

Coincident measurements of PMSE and NLC above ALOMAR (69° N, 16° E) by radar and lidar from 1999–2008

Abstract. Polar Mesosphere Summer Echoes (PMSE) and Noctilucent Clouds (NLC) have been routinely measured at the ALOMAR research facility in Northern Norway (69° N, 16° E) by lidar and radar, respectively. 2900 h of lidar measurements by the ALOMAR Rayleigh/Mie/Raman lidar were combined with almost 18 000 h of radar measurements by the ALWIN VHF radar, all taken during the years 1999 to 2008, to study simultaneous and common-volume observations of both phenomena. PMSE and NLC are known from both theory and observations to be positively linked. We quantify the occurrences of PMSE and/or NLC and relations in altitude, especially with respect to the lower layer boundaries. The PMSE occurrence rate is with 75.3% considerably higher than the NLC occurrence rate of 19.5%. For overlapping PMSE and NLC observations, we confirm the coincidence of the lower boundaries and find a standard deviation of 1.26 km, hinting at very fast sublimation rates. However, 10.1% of all NLC measurements occur without accompanying PMSE. Comparison of occurrence rates with solar zenith angle reveals that NLC without PMSE mostly occur around midnight indicating that the ice particles were not detected by the radar due to the reduced electron density.

Surface chemistry: a non-negligible parameter in determining optical properties of small colloidal metal nanoparticles

Surface chemistry can become pronounced in determining the optical properties of colloidal metal nanoparticles as the nanoparticles become so small (diameters <20 nm) that the surface atoms, which can undergo chemical interactions with the environment, represent a significant fraction of the total number of atoms although this effect is often ignored. For instance, formation of chemical bonds between surface atoms of small metal nanoparticles and capping molecules that help stabilize the nanoparticles can reduce the density of conduction band electrons in the surface layer of metal atoms. This reduced electron density consequently influences the frequency-dependent dielectric constant of the metal atoms in the surface layer and, for sufficiently high surface to volume ratios, the overall surface plasmon resonance (SPR) absorption spectrum. The important role of surface chemistry is highlighted here by carefully analyzing the classical Mie theory and a multi-layer model is presented to produce more accurate predictions by considering the chemically reduced density of conduction band electrons in the outer shell of metal atoms in nanoparticles. Calculated absorption spectra of small Ag nanoparticles quantitatively agree with the experimental results for our monodispersed Ag nanoparticles synthesized via a well-defined chemical reduction process, revealing an exceptional size-dependence of absorption peak positions: the peaks first blue-shift followed by a turnover and a dramatic red-shift as the particle size decreases. A comprehensive understanding of the relationship between surface chemistry and optical properties is beneficial to exploit new applications of small colloidal metal nanoparticles, such as colorimetric sensing, electrochromic devices, and surface enhanced spectroscopies.

Observation and modeling of inner divertor re-attachment in discharges with lithium coatings in NSTX

In the National Spherical Torus Experiment (NSTX), modifications to the inner divertor plasma regimes are observed in high triangularity, H-mode, NBI heated discharges due to lithium coatings evaporated on the plasma facing components. In particular, the drop in the recombination rate, the reduced neutral pressure and the reduced electron density (inferred from Stark broadening measurements of high-n deuterium Balmer lines) suggested that the inner divertor, which is usually detached in discharges without lithium, re-attached. Experimental results are compared to simulations obtained with a 1D partially ionized plasma transport model integrated in the non-local thermodynamic equilibrium radiation transport code CRETIN to understand how the reduced recycling affects the divertor parameters in NSTX discharges with lithium coatings.

Infant data from pre- and post-natal development studies in cynomolgus monkeys of different origins

In order to identify compounds with potential toxicity problems, particular attention is paid to structural alerts, which are high chemical reactivity molecular fragments or fragments that can be transformed via bioactivation by human enzymes into fragments with high chemical reactivity. The concept has been introduced in order to reduce the likelihood that future candidate substances as pharmaceuticals will have undesirable toxic effects. A significant proportion (∼78–86%) of drugs characterized by residual toxicity contain structural alerts; there is also evidence indicating the formation of active metabolites as a causal factor for the toxicity of 62–69% of these molecules. On the other hand, the pharmacological action of certain drugs depends on the formation of reactive metabolites. Detailed assessment of the potential for the formation of active metabolites is recommended to characterize a biologically active compound. Although many prescribed drugs frequently contain structural alerts and form reactive metabolites, the vast majority of these drugs are administered in low daily doses. Avoiding structural alerts has become almost a norm in new drug design. An in-depth review of the biochemical reactivity of these structural alerts for new drug candidates is critical from a safety point of view and is currently being monitored in the discovery of drugs. The chemical strategies applied to structural alerts in molecules to limit the toxicity are:•partial replacement or full replacement of the structural alert;•reduction of electronic density;•introduction of a structural element of metabolic interest (metabolic switching);•multiple approaches.Therefore, chemical intervention strategies to eliminate bioactivation are often interactive processes; their success depends largely on a close working relationship between drug chemists, pharmacologists and researchers in metabolic science.

Ionospheric Response to the Geomagnetic Storm on August 21, 2003 Over China Using GNSS-Based Tomographic Technique

The impacts of the August 21, 2003 geomagnetic storm on the ionosphere over China have been first investigated by using the so-called computerized ionospheric tomography (CIT) technique and the observations of the Crustal Movement Observation Network of China. Tomographic results show that the main ionospheric effects of this geomagnetic storm over China are as follows: (1) the negative storm phase effect appears in the F region and (2) the positive storm phase effect occurs above the F region. Meanwhile, some key features in the ionospheric structure have been revealed in the ionospheric images during the storm; this includes the disturbances and an elongated region of the reduced electron density at the latitude around 32°N. Statistical comparisons are carried out to confirm the reliability of the global-navigation-satellite-system-based CIT reconstruction results using the profile obtained from ionosonde observations.

Artificial plasma cave in the low‐latitude ionosphere results from the radio occultation inversion of the FORMOSAT‐3/COSMIC

Previous studies report unexpected electron density reductions, termed “plasma caves,” located underneath the equatorial ionization anomaly (EIA) crests. A radio occultation (RO) observation simulation experiment has been built to evaluate possible biases introduced by the spherical symmetry assumption in the standard (Abel) RO inversion processes. The experiment simulates the electron density profiles and reconstructs the plasma structure of the EIA at low latitudes, where the horizontal gradient is most significant. The reconstruction shows that artificial plasma caves are created underneath the EIA crests along with three density enhancements in adjacent latitudes. The artifact appears mainly below 250 km altitudes and becomes pronounced when the EIAs are well developed. Above that altitude, the two EIA features in the original (truth) model, the International Reference Ionosphere (IRI‐2007), and in the inversion are similar, but the inversion reconstructs less distinct EIA crests with underestimation of the electron density. A simple correction has been introduced by multiplying the ratio between the truth and inversion with actual FORMOSAT‐3/COSMIC observations. This initial correction shows that the artificial plasma caves are mitigated. Results also reveal that the RO technique is not suitable to detect or rule out possible existence of the plasma caves.

Diversity of Metal−Ligand Interactions in Halide (X = I, Br, Cl, F) and Halide-Free Ambiphilic Ligand Rhodium Complexes

Reaction of the neutral ambiphilic ligand 2,7-di-tert-butyl-5-diphenylboryl-4-diphenylphosphino-9,9-dimethylthioxanthene (TXPB) with [{Rh(mu-Cl)(CO)(2)}(2)] yields [RhCl(CO)(TXPB)] (1) (Emslie et al. Organometallics 2006, 25, 5835). Complex 1 is square planar with the TXPB ligand bound to rhodium via the phosphine and thioether donors (these are features common to complexes 2-5, vide infra). Treatment of 1 with Me(3)SiBr and Me(3)SiI allowed for halide substitution to afford [RhBr(CO)(TXPB)] (2) and [RhI(CO)(TXPB)] (3), respectively. The halide co-ligands in complexes 1 and 2 form a strong bridging interaction between rhodium and the borane group in TXPB. The presence of stronger borane-halide coordination in 1 is clearly illustrated by an (11)B NMR chemical shift of 12 ppm versus 27 ppm in 2. In contrast, the iodide ligand in 3 forms only a weak bridging interaction to boron, leading to a B...I distance of 3.125(7) A, and an (11)B NMR chemical shift of 56 ppm (versus 69 ppm for free TXPB). A lower carbonyl stretching frequency in 3 (2002 cm(-1)) versus 1 or 2 (2008 and 2013 cm(-1), respectively) could be attributed to weakening of the Rh-X bond in 1 and 2 as a consequence of halide-borane coordination and/or a shorter Rh-S bond in complex 3. [Rh(CO)(TXPB-F)] (4) and the halide-free cation [Rh(CO)(TXPB)][PF(6)] (5) were accessed by reaction of 1 with [NMe(4)]F and Tl[PF(6)], respectively. Complex 4 is zwitterionic with fluoride bound to boron [(11)B NMR delta 4 ppm; B-F = 1.445(6) A; Rh...F = 3.261(3) A] and an eta(2)-interaction between the cationic rhodium center and the ipso- and ortho-carbon atoms of a B-phenyl ring in TXPB-F. By contrast, rhodium in 5 engages in an eta(2)-interaction with boron and the ipso-carbon of one B-phenyl ring; Rh-B and Rh-C(ipso) bond lengths in 5 are 2.557(3) and 2.362(2) A, respectively. The long Rh-B distance and an (11)B NMR chemical shift of 57 ppm are consistent with only a weak Rh-B interaction in 5, and a CO stretching frequency of 2028 cm(-1) (Nujol), versus 2004-2013 cm(-1) for complexes 1-4, is indicative of greatly reduced electron density in 5, relative to 1-4.

Research of Ionospheric Instability Excited in Mid and Low Latitudes HF Heating

AbstractThe results of 2D simulation of ionospheric HF pump heating indicate that although the simulation results are affected by the background ionospheric conditions, the electron density and temperature tend towards stationary after heating simulation begins under most undisturbed circumstance. This result is proved by many experiments. Nevertheless on occasion the temporal and spatial distribution of the electron density and temperature near the reflection region of HF pump waves appear to be instable after turning on/off the HF heating equipment. This phenomenon is simulated and interpreted in this paper. The excitation of this instability is explained by a positive feedback mechanism as follows, when the electron temperature is heating up by the pump waves, the reduction of electron density in this region is generated by the plasma expansion. The electron energy decreases in the electron energy equation due to the collision between electron and ion which is influenced by the electron temperature and density. In consequence the positive feedback mechanism is set up as a result of electron temperature increase. It can be concluded that a more obvious change of electron density and temperature in HF pump heating is generated by an instability mechanism if three conditions are satisfied, (1) an evident two‐peak structure of ionospheric electron temperature; (2) a high electron temperature in the heated region; (3) electron and ion collision is the main proportion of the energy loss factor. These conditions are more easily to be satisfied in the afternoon. Key words Hight Frequency (HF) heating, Mid and low latitude ionosphere, Instability, Simulation

The effect of spin polarization on zero field splitting parameters in paramagnetic π-electron molecules

Spin polarization effects play an important role in the theory of isotropic hyperfine interactions for aromatic protons. The spin polarization gives rise to significant isotropic proton hyperfine interactions--spin-dependent one-electron properties--smaller than 0 MHz and the effect has been theoretically described [H. M. McConnell and D. B. J. Chesnut, Chem. Phys. 28, 107 (1958)]. The influence of spin polarization on the zero field splitting parameters, which are spin-dependent two-electron properties, has not been clearly identified yet. A phenomenological equation is proposed here for the contribution of spin polarization to the zero field splitting parameter D in analogy to McConnell's equation for hyperfine interactions. The presence of the effect is demonstrated in a series of calculations on polyacenes in the triplet state and turns out to be responsible for up to 50% of the D parameter in the case of naphthalene! It is found that spin-unrestricted single-determinant methods, including the widely used density functional theory methods, do not accurately reproduce the two-electron reduced electron density required for the evaluation of two-electron spin-dependent properties. For the accurate calculation of zero field splitting parameters by quantum chemical methods, it thus seems necessary to resort to correlated ab initio methods which do not give rise to spin contamination and which do provide an accurate description of the two-electron reduced electron density.

InAs Nanowire Transistors as Gas Sensor and the Response Mechanism

We report a study of the response of InAs nanowire field-effect transistor sensor devices to various gases and alcoholic vapors. It is concluded that the change in conductance of the device in response to chemical vapors is a combined result of both the charge transfer and modified electron mobility effects. In particular, we found that surface adsorption of most chemical molecules can reduce electron density in nanowires from approximately 10(4) to approximately 10(3)/microm and enhance the electron mobility greatly (from tens to a few hundred of cm(2)/(V s)) at the same time. These effects are attributed to the interactions between adsorbed molecules and the electron accumulation layer and rich surface states on the InAs nanowire surface.

Magnetism, magnetocaloric effect and positive magnetoresistance in Fe-doped antipervoskite compounds SnCMn 3−xFe x ( x=0.05–0.20)

The effects of Fe substitution on the structure, magnetic properties, magnetocaloric effect and positive magnetoresistance (MR) effect in antipervoskite compounds SnCMn 3− x Fe x ( x=0.05–0.20) have been investigated systematically. Partial substitution of Fe for Mn leads to the monotonic reduction in both the Curie temperature T C and saturated magnetization ( M S ). It can be attributed to the reduction of electronic density of state at the Fermi energy by Fe-doping. The maximum values of magnetic entropy change (−Δ S M ) and positive MR gradually decrease as x increases, due to the broadening of magnetic phase transition. The refrigerant capacity increases initially with x≤0.05, then decreases gradually as x increases further, which is suggested to originate from the competition between the decreasing −Δ S M and broadening temperature span. Our result indicates that the chemical doping on Mn site is an effective method for manipulating the properties of antiperovskite compounds AXMn 3.

Dust-Induced Modulation of the Atomic Emission in a Dusty Argon Discharge

The spectral emission of argon atoms in a dusty rf discharge plasma has been determined. For that purpose, the spatially and temporally resolved emission of the argon atoms during the rf cycle was measured using a gated intensified charge-coupled device camera. While dust particles of 2-3 microm diameter trapped in the sheath lead to an increased plasma emission during the sheath expansion phase, larger particles of 10-12 microm diameter result in a decreased emission. This behavior is explained by the combined action of electron density reduction due to the charging dynamics in the sheath and the increase of electron temperature to compensate plasma losses at the dust.

Ultrastructural evidence of a vesicle‐mediated mode of cell degranulation in chicken chromaffin cells during the late phase of embryonic development

In the present investigation, we attempted to determine whether ultrastructural features indicative of a vesicle-mediated mode of cell secretion were detectable in chick chromaffin cells during embryo development. The adrenal anlagen of domestic fowls were examined at embryonic days (E) 12, 15, 19 and 21 by electron microscopy quantitative analysis. Morphometric evaluation revealed a series of granule and cytoplasmic changes highly specific for piecemeal degranulation (PMD), a secretory process based on vesicular transport of cargoes from within granules for extracellular release. At E19 and E21 we found a significant peak in the percentage of granules exhibiting changes indicative of progressive release of secretory materials, i.e. granules with lucent areas in their cores, reduced electron density, disassembled matrices, residual cores and membrane empty containers. A dramatic raise in the density of 30-80-nm-diameter, membrane-bound, electron-dense and electron-lucent vesicles--which were located either next to granules or close to the plasma membrane--was recognizable at E19, that is, during the prehatching phase. The cytoplasmic burst of dense and clear vesicles was paralleled by the appearance of chromaffin granules showing outpouches or protrusions of their profiles ('budding features'). These ultrastructural data are indicative of an augmented vesicle-mediated transport of chromaffin granule products for extracellular release in chick embryo chromaffin cells during the prehatching stage. In conclusion, this study provides new data on the fine structure of chromaffin cell organelles during organ development and suggests that PMD may be part of an adrenomedullary secretory response that occurs towards the end of chicken embryogenesis. From an evolutionary point of view, this study lends support to the concept that PMD is a secretory mechanism highly conserved throughout vertebrate classes.

Characteristics of emissive spectrum and the removal of nitric oxide in N 2/O 2/NO plasma with argon additive

Although the approach using non-thermal plasma (NTP) for deNO x has been studied for over 15 years, how to achieve higher removal efficiency with lower cost is still a barrier for its industrial application. In order to investigate the impact of the argon additive on electron density, energy and nitric oxide reduction process in plasma, the spectrum of the dielectric barrier discharge at atmospheric pressure in a coaxial reactor was measured using the monochromater with high resolution. The comparative experiments for NO reduction were carried out simultaneously in N 2/O 2/NO plasma stream with and without argon, respectively. The nitrogen molecular spectrum which is attributed to the energy level transition (C 3π u → B3π g) was compared in the wavelength range 300–480 nm and the electron density and temperature were determined based on the relative intensities and Stark broadening width of spectral lines. The spectrum results indicated that the argon additive could enhance the intensity of emissive spectrum of plasma, thus the electron concentration as well as the energy was increased, and finally prompted the ionization rate to produce active N, O and O 3. The results of NO reduction showed that NO conversion efficiency increased in the range of 10%–30% with 5% addition of argon in stream comparing with the condition without argon additive. This study will play a positive role in the industrial application of dielectric barrier discharge deNO x reactor.