bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of incorporated CdS nanoparticles on the crystallinity and morphology of poly(styrene‐b‐ethylene oxide) diblock copolymers
Authors: Yeh Siao‐Wei , Wu Tzung‐Luen , Wei Kung‐Hwa , Sun Ya‐Sen , Liang Keng S.
Published: April 2005

Surface‐modified CdS nanoparticles selectively dispersed in hexagonally packed poly(ethylene oxide) (PEO) cylinders of poly(styrene‐b‐ethylene oxide) (PSEO) block copolymers were prepared. The photoluminescence and ultraviolet–visible characteristics of the presynthesized CdS nanoparticles inN,N‐dimethylformamide and in PEO domains of the PSEO block copolymers were determined. Because of strong interactions between the CdS nanoparticles and PEO chains, as shown by Fourier transform infrared spectroscopy, the incorporation of the CdS nanoparticles prevented the PEO cylinders from properly crystallizing; this was confirmed by differential scanning calorimetry and wide‐angle X‐ray diffraction measurements. The intercylinder distance between the swollen and reduced‐crystallinity CdS/PEO cylinders in turn increased, as confirmed by small‐angle X‐ray scattering and transmission electron microscopy. At a high CdS concentration (43 wt % or 8.3 vol % with respect to PEO), however, the hexagonally packed cylindrical nanostructure of the PSEO diblock copolymers was destroyed. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1220–1229, 2005
Impedance spectroscopy studies on Ga‐ion‐modified PLZT ceramics
Authors: Dutta Soma , Choudhary R. N. P. , Sinha P. K.
Published: April 2005

Polycrystalline samples of [Pb0.92(La1–zGaz)0.08][Zr0.65Ti0.35]0.98O3 (PLGZT) for z = 0.0, 0.3, 0.6, 0.9, and 1.0 were prepared by a solid‐state reaction technique. The single‐phase formation of the new compounds with tetragonal crystal structures was established by the room‐temperature X‐ray analysis. The occupancy of Ga ion in the La site has been confirmed by FTIR analysis. Complex impedance spectroscopy (CIS) has provided a convincing evidence for the existence of both grain (bulk) and grain boundary effects in the materials, which is also evident from the microstructures, comprise grains separated by well‐defined boundaries. The electrical processes in the sample have been modeled in the form of an electrical equivalent circuit made up of a series combination of two parallel RC circuits attributed to grains and grain boundaries. The real and imaginary parts of dielectric constants have been separated from impedance spectrum results and expressed in terms of loss tangent (tan δ). The ferroelectric transition temperature (Tc) of the materials is evaluated from the plot of real permittivity versus temperature and found to be shifted to higher temperature side with increasing Ga‐ion concentration. A sharp rise in conductivity is observed in the nature of temperature variation of the bulk electrical conductivity (σdc) at higher temperature for all the Ga‐modified PLZT samples. This type of behavior is typical to dielectric ceramics having conductive grain boundary arising out of a relaxation process of the Maxwell–Wagner type. At higher temperature a substantial increase in conductivity ∼10–3 S cm–1 is achieved for complete replacement of the La ion by Ga (z = 1.0). (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Relevance of phosphorus incorporation and hydrogen removal for Si:P δ‐doped layers fabricated using phosphine
Authors: Goh K. E. J. , Oberbeck L. , Simmons M. Y.
Published: April 2005

We present a study to determine the importance of phosphorus incorporation and hydrogen removal for the electrical activation of phosphorus dopants in Si:P δ‐doped samples fabricated using phosphine dosing and molecular beam epitaxy (MBE). The carrier densities in these samples were determined from Hall effect measurements at 4 K sample temperature. An anneal to incorporate phosphorus atoms into substitutional lattice sites is critical to achieving full dopant activation after Si encapsulation by MBE. Whilst the presence of hydrogen can degrade the quality of the Si encapsulation layer, we show that it does not adversely impact the electrical activation of the phosphorus dopants. We discuss the relevance of our results to the fabrication of nano‐scale Si:P devices. (© 2005 WILEY‐VCH Verlag GmbH & C o. KGaA, Weinheim)
High spatial resolution micro‐Raman temperature measurements of nitride devices (FETs and light emitters)
Authors: Kuball M. , Pomeroy J. W. , Rajasingam S. , Sarua A. , Uren M. J. , Martin T. , Lell A. , Härle V.
Published: April 2005

The cover picture of the present issue of physica status solidi (a) is a temperature map of a AlGaN/GaN heterostructure field effect transistor (HFET) obtained using micro‐Raman spectroscopy. The inset shows a photograph of the device with source (S), gate (G) and drain (D) positions marked. The paper by M. Kuball et al. [1] is an invited presentation from the International Workshop on Nitride Semiconductors (IWN 2004).

In the Rapid Research Letter by B. Lamprecht et al. [2] the authors report on the successful fabrication and characterization of working organic photodiodes deposited on ordinary newspaper sheets as an example for a flexible and very rough substrate with unfortunate mechanical properties.
Tamm and Shockley states in two superlattices coupled by a perturbed interface
Authors: Kłos Jarosław
Published: April 2005

Interface‐localized electronic states are investigated in a system composed of two identical superlattices coupled by a perturbed interface (with symmetric potential wells). A perturbation, in the form of a Dirac delta peak, is introduced on the interface. The effect of the symmetry point in which the superlattices communicate, as well as that of the perturbation strength, on conditions of Tamm and Shockley state existence are examined. The analysis is completed with numerical calculation of localized states in a system composed of two AlxGa1–xAs ‘square‐potential’ superlattices. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Electro‐optic investigation of the Coherent Hall Effect in semiconductor superlattices
Authors: Hummel Anne Beate , Blöser Claudia , Bauer Tobias , Roskos Hartmut G. , Kosevich Yuriy A. , Köhler Klaus
Published: April 2005

After the first observation of the Coherent Hall Effect in a GaAs/Al0.3Ga0.7As superlattice by means of THz‐emission spectroscopy, the dynamics of impulsively excited electron wavepackets in crossed electric and magnetic fields has now been investigated in more detail by reflective electro‐optic sampling (REOS). In agreement with the predictions of a semiclassical model, the experiments show the existence of two strictly separated regimes of charge‐carrier motion depending on the ratio E/B of applied electric and magnetic field. Both, the magneto‐Bloch regime for dominating electric field and the cyclotron‐like regime of motion for dominating magnetic field, exhibit a characteristic frequency dependence of the wavepacket oscillations on the external fields. The REOS measurements supplement our results achieved by THz‐emission spectroscopy by covering a much larger range of experimental parameters because REOS is not affected by absorption by the cryostat windows of our set‐up as is the THz radiation at frequencies above 2 THz, and the detection of high oscillation frequencies is possible. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Dephasing by electron–phonon interaction in an AB ring with an embedded quantum dot
Authors: Ueda Akiko , Eto Mikio
Published: April 2005

We study the dephasing effect on the transport properties in an Aharonov–Bohm ring with an embedded quantum dot, due to the electron–phonon interaction. The differential conductance is calculated under finite bias using Keldysh Green function. The electron–phonon interaction is treated (i) by the canonical transformation, or (ii) by the second‐order perturbation. By the latter method, we find that the Fano resonance is suppressed by the electron–phonon interaction and that the suppression increases with increasing bias voltage. The calculations by the former method do not yield the bias‐voltage dependence of the dephasing effect. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optical probing of the spin state of a single magnetic ion in an individual quantum dot
Authors: Besombes L. , Leger Y. , Maingault L. , Ferrand D. , Cibert J. , Mariette H.
Published: April 2005

The magnetic state of a single magnetic ion (Mn2+) embedded in an individual quantum dot is optically probed using micro‐spectroscopy. The fine structure of a confined exciton in the exchange field of the single Mn2+ ion is analyzed in detail. At zero magnetic field, the exciton–Mn exchange coupling lifts the degeneracy of the six Mn spin projections. Under magnetic field, the electron–Mn interaction induces a mixing of the bright and dark exciton states. Magneto‐optic measurements reveals that the polarisation of the Mn2+ spin distribution is controlled by the magnetic field and an effective manganese temperature depending on both the lattice temperature and the density of photo‐created carriers. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Validation of a high‐throughput absorption, distribution, metabolism, and excretion (ADME) system and results for 60 literature compounds
Authors: Yan Zhixia , Lu Chuang , Wu Jing‐Tao , Elvebak Larry , Brockman Adam
Published: April 2005

A high‐throughput analytical system for the support of absorption, distribution, metabolism, and excretion (ADME) was constructed in collaboration with Gubbs Inc. to commercialize corresponding software. We sought to quickly build and validate this system for microsomal clearance assessment using 60 commercially available non‐proprietary compounds that are non‐DEA‐restricted in addition to 36 proprietary Millennium compounds that had already been assessed using a low‐throughput infrastructure. The system was constructed such that a ∼45 second total cycle time was achieved injection‐to‐injection. Software was successfully coded to enable the analyst to submit multiple batches, and modify multiple methods very quickly for use with Applied Biosystems Analyst™ 1.3. After acquisition the software was used to simultaneously integrate multiple injection chromatograms, regress the data, and calculate clearance such that all of the data could be easily and immediately reviewed by both bioanalytical and enzymology personnel. Unfortunately, despite an exhaustive search of the literature, we were unable to find a large number of non‐proprietary compound data for validation, so we provide such a source of data here. Results are presented for the 60 literature compounds that were assessed. A good correlation was observed between literature results for 16 compounds that we were able to find and the results obtained using the system. The Millennium proprietary compounds that we assessed using both low‐ and high‐throughput approaches also correlated well. We present here a system for the support of high‐throughput in vitro ADME analysis and also present the results of 60 non‐proprietary, non‐DEA‐scheduled compounds to facilitate the validation efforts of others. Finally, we present commercially available software to facilitate high‐throughput ADME systems in the community. Copyright © 2005 John Wiley & Sons, Ltd.
Fick's law of diffusion depth profiles applied to the degradation of oxidized polystyrene during ARXPS analysis
Authors: Ménard M. , Paynter R. W.
Published: April 2005

Angle‐resolved x‐ray photoelectron spectroscopy (ARXPS) measurements were made, using Al Kα and Mg Kα radiation alternately, on a polystyrene sample that had been exposed to a helium plasma. It was observed that oxygen was introduced into the sample surface by the plasma treatment, and that some of it was lost over a period of 5 h under x‐ray irradiation in the vacuum of the spectrometer. Laplace transforms of Fick's law of diffusion profiles were derived and applied to the data. The ARXPS results obtained in this study are consistent with a sample history in which the oxidation of the polymer surface resulting from exposure to plasma is controlled by a diffusion process, whereas the loss of oxygen during exposure to x‐rays is principally controlled by a first‐order reaction such as the liberation of oxygen (presumably as CO2) from carbon–oxygen groups by the action of radicals created by the ionizing radiation. Copyright © 2005 John Wiley & Sons, Ltd.
Correlation between ultrasound and anatomical findings in fetuses with lower urinary tract obstruction in the first half of pregnancy
Authors: Robyr R. , Benachi A. , Daikha‐Dahmane F. , Martinovich J. , Dumez Y. , Ville Y.
Published: April 2005

Objective

The prognosis of fetal lower urinary tract obstruction (LUTO) depends upon renal function and also upon the underlying etiology. Precise identification of the latter remains a challenge antenatally. Our objective was to examine the underlying pathology in male fetuses with sonographic evidence of severe and isolated LUTO.

Methods

Detailed postmortem examination was carried out after termination of pregnancy in 24 male fetuses presenting before 25 weeks of gestation with ultrasound evidence of isolated severe LUTO.

Results

All fetuses had megacystis and hyperechogenic kidneys. There was anhydramnios/oligohydramnios and pelvicalyceal dilatation in 20 and 15 cases, respectively. Posterior urethral valves (PUV) were suspected antenatally in 20 cases and urethral atresia was not suspected antenatally. However, postmortem examination of the urethra demonstrated atresia in six cases, severe stenosis in eight cases, PUV in nine cases and an apparently normal urethra in one case. Renal dysplasia was found in all cases but one. Urethral atresia was the most common urethral anomaly at 12–17 weeks. Hydronephrosis was more frequent in cases with PUV (8/9) and urethral stenosis (6/8) than with urethral atresia (0/6). In LUTO presenting in the first and second trimester, hyperechogenic kidneys were predictive of renal dysplasia in 95% of cases. The association of a sagittal diameter of the bladder of at least 40 mm with hydronephrosis before 28 weeks was predictive of PUV with a positive (PPV) and negative (NPV) predictive value of 44.4% and 66.6%, respectively. Absence of hydronephrosis and a sagittal diameter of the bladder of less than 40 mm were predictive of urethral atresia or stenosis with a PPV and NPV of 100% and 47.6%, respectively. The absence of hydronephrosis was predictive of urethral atresia with a PPV and NPV of 66.6% and 100%, respectively.

Conclusion

LUTO in a male fetus presenting with megacystis in the first or second trimester of pregnancy is as likely to reflect urethral atresia or stenosis as it is PUV. The size of the bladder and the presence of hydronephrosis should be considered in order to improve prenatal diagnosis and counseling. Copyright © 2005 ISUOG. Published by John Wiley & Sons, Ltd.
Implicit difference methods for parabolic functional differential equations
Authors: Czernous W. , Kamont Z.
Published: April 2005

We present a new class of numerical methods for the solution of quasilinear parabolic functional differential equations. The numerical methods are difference schemes which are implicit with respect to time variable. We give a complete convergence analysis for the methods and we show by an example that the new methods are considerable better that the explicit schemes. The proof of the stability is based on a comparison technique with nonlinear estimates of the Perron type for given operators. Results obtained in the paper can be applied to differential integral problems and equations with retarded variables.
Possible configurations of the magnetic field in the outer magnetosphere during geomagnetic polarity reversals
Authors: Willis D. M. , Holder A. C. , Davis C. J.
Published: April 2005

Abstract. Possible configurations of the magnetic field in the outer magnetosphere during geomagnetic polarity reversals are investigated by considering the idealized problem of a magnetic multipole of order m and degree n located at the centre of a spherical cavity surrounded by a boundless perfect diamagnetic medium. In this illustrative idealization, the fixed spherical (magnetopause) boundary layer behaves as a perfectly conducting surface that shields the external diamagnetic medium from the compressed multipole magnetic field, which is therefore confined within the spherical cavity. For a general magnetic multipole of degree n, the non-radial components of magnetic induction just inside the magnetopause are increased by the factor {1 + [(n + 1)/n]} relative to their corresponding values in the absence of the perfectly conducting spherical magnetopause. An exact equation is derived for the magnetic field lines of an individual zonal (m = 0), or axisymmetric, magnetic multipole of arbitrary degree n located at the centre of the magnetospheric cavity. For such a zonal magnetic multipole, there are always two neutral points and n-1 neutral rings on the spherical magnetopause surface. The two neutral points are located at the poles of the spherical magnetopause. If n is even, one of the neutral rings is coincident with the equator; otherwise, the neutral rings are located symmetrically with respect to the equator. The actual existence of idealized higher-degree (n>1) axisymmetric magnetospheres would necessarily imply multiple (n + 1) magnetospheric cusps and multiple (n) ring currents. Exact equations are also derived for the magnetic field lines of an individual non-axisymmetric magnetic multipole, confined by a perfectly conducting spherical magnetopause, in two special cases; namely, a symmetric sectorial multipole (m = n) and an antisymmetric sectorial multipole (m = n-1). For both these non-axisymmetric magnetic multipoles, there exists on the spherical magnetopause surface a set of neutral points linked by a network of magnetic field lines. Novel magnetospheric processes are likely to arise from the existence of magnetic neutral lines that extend from the magnetopause to the surface of the Earth. Finally, magnetic field lines that are confined to, or perpendicular to, either special meridional planes or the equatorial plane, when the multipole is in free space, continue to be confined to, or perpendicular to, these same planes when the perfectly conducting magnetopause is present.Key words. Geomagnetism and paleomagnetism (reversals-process, time scale, magnetostratigraphy) · Magnetospheric physics (magnetopause, cusp, and boundary layers; magnetospheric configuration and dynamics)
Energy time dispersion of a new class of magnetospheric ion events observed near the Earth's bow shock
Authors: Anagnostopoulos G. C. , Paschalidis N. , Littas A. N.
Published: April 2005

Abstract. We have analyzed high time resolution (\\geq6 s) data during the onset and the decay phase of several energetic (\\geq35 keV) ion events observed near the Earth's bow shock by the CCE/AMPTE and IMP-7/8 spacecraft, during times of intense substorm/geomagnetic activity. We found that forward energy dispersion at the onset of events (earlier increase of middle energy ions) and/or a delayed fall of the middle energy ion fluxes at the end of events are often evident in high time resolution data. The energy spectra at the onset and the decay of this kind of events show a characteristic hump at middle (50-120 keV) energies and the angular distributions display either anisotropic or broad forms. The time scale of energy dispersion in the ion events examined was found to range from several seconds to \\sim1 h depending on the ion energies compared and on the rate of variation of the Interplanetary Magnetic Field (IMF) direction. Several canditate processes are discussed to explain the observations and it is suggested that a rigidity dependent transport process of magnetospheric particles within the magnetosheath is most probably responsible for the detection of this new type of near bow shock magnetospheric ion events. The new class of ion events was observed within both the magnetosheath and the upstream region.Key words. Interplanetary physics (energetic particles; planetary bow shocks)
Ionospheric signatures of magnetospheric boundaries in the post-noon sector
Authors: Berry S. T. , Kersley L. , Moen J. , Denig W. F.
Published: April 2005

Abstract. Spatial structures in ionospheric electron density revealed in a tomographic image have been identified with auroral forms and related to their sources in precipitating particles observed by DMSP satellites. The observations of plasma enhancements relate to discrete auroral arcs seen in the post-noon sector, identified by both red- and green-line emissions measured by a meridional scanning photometer. The features lie within a very narrow latitudinal band on L-shells where the satellite detectors observed electron precipitation classified as from the boundary plasma sheet (BPS). The harder particles are identified with an E-region structure, while further north the precipitation is softer, resulting in a localised F-layer blob and 630.0 nm emissions. A steep gradient in plasma density represent a signature in the ionosphere of the central plasma sheet (CPS)/BPS boundary. A transition to a less-structured F-layer is found on crossing the convection reversal boundary..Key words. Ionosphere (auroral ionosphere; ionosphere-magnetosphere interactions; polar ionosphere)
Multi-instrument probing of the polar ionosphere under steady northward IMF
Authors: Pryse S. E. , Smith A. M. , Kersley L. , Walker I. K. , Mitchell C. N. , Moen J. , Smith R. W.
Published: April 2005

Abstract. Observations are presented of the polar ionosphere under steady, northward IMF. The measurements, made by six complementary experimental techniques, including radio tomography, all-sky and meridian scanning photometer optical imaging, incoherent and coherent scatter radars and satellite particle detection, reveal plasma parameters consistent with ionospheric signatures of lobe reconnection. The optical green-line footprint of the reconnection site is seen to lie in the sunward plasma convection of the lobe cells. Downstream in the region of softer precipitation the reverse energy dispersion of the incoming ions can be identified. A steep latitudinal density gradient at the equatorward edge of the precipitation identifies the general location of an adiaroic boundary, separating the open field lines of polar lobe cells from the closed field of viscous-driven cells. Enhancements in plasma density to the south of the gradient are interpreted as ionisation being reconfigured as it is thrust against the boundary by the antisunward flow of the viscous cells near noon. Each of the instruments individually provides valuable information on certain aspects of the ionosphere, but the paper demonstrates that taken together the different experiments complement each other to give a consistent and comprehensive picture of the dayside polar ionosphere..Key words. Ionosphere (polar ionosphere) · Magnetospheric physics (magnetosphere-ionosphere interactions; polar cap phenomena)
Multi-instrument observations of the electric and magnetic field structure of omega bands
Authors: Wild J. A. , Yeoman T. K. , Eglitis P. , Opgenoorth H. J.
Published: April 2005

Abstract. High time resolution data from the CUTLASS Finland radar during the interval 01:30-03:30 UT on 11 May, 1998, are employed to characterise the ionospheric electric field due to a series of omega bands extending ~5° in latitude at a resolution of 45 km in the meridional direction and 50 km in the azimuthal direction. E-region observations from the STARE Norway VHF radar operating at a resolution of 15 km over a comparable region are also incorporated. These data are combined with ground magnetometer observations from several stations. This allows the study of the ionospheric equivalent current signatures and height integrated ionospheric conductances associated with omega bands as they propagate through the field-of-view of the CUTLASS and STARE radars. The high-time resolution and multi-point nature of the observations leads to a refinement of the previous models of omega band structure. The omega bands observed during this interval have scale sizes ~500 km and an eastward propagation velocity ~0.75 km s-1. They occur in the morning sector (~05 MLT), simultaneously with the onset/intensification of a substorm to the west during the recovery phase of a previous substorm in the Scandinavian sector. A possible mechanism for omega band formation and their relationship to the substorm phase is discussed..Key words. Ionosphere (auroral ionosphere; electric fields and currents) · Magnetospheric physics (magnetosphere-ionosphere interactions)
Comment on "Concerning the generation of geomagnetic giant pulsations by drift-bounce resonance ring current instabilities" by K.-H. Glassmeier et al., Ann. Geophysicae, 17, 338-350, (1999)
Authors: Mann I. R. , Chisham G.
Published: April 2005

Abstract. Not available.Key words: Magnetospheric physics (energetic particles, trapped; MHD waves and instabilities) - Space plasma physics (wave-particle interactions)
Geomagnetic control of polar mesosphere summer echoes
Authors: Bremer J. , Hoffmann P. , Hansen T. L.
Published: April 2005

Abstract. Using observations with the ALOMAR SOUSY radar near Andenes (69.3°N, 16.0°E) from 1994 until 1997 polar mesosphere summer echoes (PMSE) have been investigated in dependence on geomagnetic K indices derived at the Auroral Observatory Tromsø (69.66°N, 18.94°E). During night-time and morning hours a significant correlation between the signal-to-noise ratio (SNR) of the radar results and the geomagnetic K indices could be detected with a maximum correlation near midnight. The correlation becomes markedly smaller in the afternoon and early evening hours with a minimum near 17 UT. This diurnal variation is in reasonable agreement with riometer absorption at Ivalo (68.55°N, 27.28°E) and can be explained by the diurnal variation of ionization due to precipitating high energetic particles. Therefore, a part of the diurnal PMSE variation is caused by this particle precipitation. The variability of the solar EUV variation, however, has no significant influence on the PMSE during the observation period.Keywords: Ionosphere (auroral ionosphere) - Magnetospheric physics (energetic particles, precipitating) - Radio science (remote sensing)
Can origin of the 2400-year cycle of solar activity be caused by solar inertial motion?
Authors: Charvátová I.
Published: April 2005

Abstract. A solar activity cycle of about 2400 years has until now been of uncertain origin. Recent results indicate it is caused by solar inertial motion. First we describe the 178.7-year basic cycle of solar motion. The longer cycle, over an 8000 year interval, is found to average 2402.2 years. This corresponds to the Jupiter/Heliocentre/Barycentre alignments (9.8855 × 243). Within each cycle an exceptional segment of 370 years has been found characterized by a looping pattern by a trefoil or quasitrefoil geometry. Solar activity, evidenced by 14C tree-ring proxies, shows the same pattern. Solar motion is computable in advance, so this provides a basis for future predictive assessments. The next 370-year segment will occur between AD 2240 and 2610.Key words: Solar physics (celestial mechanics)
A case study of a radially polarized Pc4 event observed by the Equator-S satellite
Authors: Cramm R. , Glassmeier K. H. , Othmer C. , Fornacon K. H. , Auster H. U. , Baumjohann W. , Georgescu E.
Published: April 2005

Abstract. A 16 mHz Pc4 pulsation was recorded on March 17, 1998, in the prenoon sector of the Earth's magnetosphere by the Equator-S satellite. The event is strongly localized in radial direction at approximately L = 5 and exhibits properties of a field line resonance such as an ellipticity change as seen by applying the method of the analytical signal to the magnetic field data. The azimuthal wave number was estimated as m \\approx 150. We discuss whether this event can be explained by the FLR mechanism and find out that the change in ellipticity is more a general feature of a localized Alfvén wave than indicative of a resonant process.Key words: Magnetospheric physics (MHD waves and instabilities)
A new technique for evaluating mesospheric momentum balance utilizing radars and satellite data
Authors: Frame D. J. , Lawrence B. N. , Fraser G. J. , Vincent R. A. , Dudhia A.
Published: April 2005

Abstract. A new method for evaluating momentum balance in the mesosphere using radar and satellite data is presented. This method is applied to radar wind data from two medium frequency installations (near Adelaide, Australia and Christchurch, New Zealand) and satellite temperature data from the Improved Stratospheric and Mesospheric Sounder (ISAMS). Because of limitations in data availability and vertical extent, the technique can only be applied to evaluate the momentum balance at 80 km above the radar sites for May 1992. The technique allows the calculation of the residual terms in the momentum balance which are usually attributed to the effects of breaking gravity waves. Although the results are inconclusive above Adelaide, this method produces values of zonal and meridional residual accelerations above Christchurch which are consistent with expectation. In both locations it is apparent that geostrophic balance is a poor approximation of reality. (This result is not dependent on a mismatch between the radar and satellite derived winds, but rather is inherent in the satellite data alone.) Despite significant caveats about data quality the technique appears robust and could be of use with data from future instruments.Key words: Meteorology and atmospheric dynamics (middle atmosphere dynamics; waves and tides; instruments and techniques)
The ionospheric footprint of antiparallel merging regions on the dayside magnetopause
Authors: Coleman I. J. , Pinnock M. , Rodger A. S.
Published: April 2005

Abstract. The antiparallel merging hypothesis states that reconnection takes place on the dayside magnetopause where the solar and geomagnetic fields are oppositely directed. With this criterion, we have mapped the predicted merging regions to the ionosphere using the Tsyganenko 96 magnetic field model, distinguishing between regions of sub-Alfvénic and super-Alfvénic magnetosheath flow, and identifying the day-night terminator. We present the resulting shape, width and latitude of the ionospheric dayside merging regions in both hemispheres, showing their dependence on the Earth's dipole tilt. The resulting seasonal variation of the longitudinal width is consistent with the conjugate electric fields in the northern and southern cusps, as measured by the SuperDARN HF radars, for example. We also find a seasonal shift in latitude similar to that observed in satellite cusp data.Key words: Ionosphere (ionosphere-magnetosphere interactions) · Magnetospheric physics (magnetopause · cusp and boundary layers; magnetosphere-ionosphere interactions)
First in situ measurement of electric field fluctuations during strong spread F in the Indian zone
Authors: Sinha H. S. S. , Raizada S.
Published: April 2005

Abstract. An RH-560 rocket flight was conducted from Sriharikota rocket range (SHAR) (14°N, 80°E, dip 14°N) along with other experiments, as a part of equatorial spread F (ESF) campaign, to study the nature of irregularities in electric field and electron density. The rocket was launched at 2130 local time (LT) and it attained an apogee of 348 km. Results of vertical and horizontal electric field fluctuations are presented here. Scale sizes of electric field fluctuations were measured in the vertical direction only. Strong ESF irregularities were observed in three regions, viz., 160-190 km, 210-257 km and 290-330 km. Some of the valley region vertical electric field irregularities (at 165 km and 168 km), in the intermediate-scale size range, observed during this flight, show spectral peak at kilometer scales and can be interpreted in terms of the image striation theory suggested by Vickrey et al. The irregularities at 176 km do not exhibit any peak at kilometer scales and appear to be of a new type. Scale sizes of vertical electric field fluctuations showed a decrease with increasing altitude. The most prominent scales were of the order of a few kilometers around 170 km and a few hundred meters around 310 km. Spectra of intermediate-scale vertical electric field fluctuations below the base of the F region (210-257 km) showed a tendency to become slightly flatter (spectral index n = -2.1 ± 0.7) as compared to the valley region (n = -3.6 ± 0.8) and the region below the F peak (n = -2.8 ± 0.5). Correlation analysis of the electron density and vertical electric field fluctuations suggests the presence of a sheared flow of current in 160-330 km region.Keywords: Ionosphere (Electric fields and currents; ionospheric irregularities); Radio science (ionospheric physics)
The role played by thermal feedback in heated Farley-Buneman waves at high latitudes
Authors: St.-Maurice J.-P. , Kissack R. S.
Published: April 2005

Abstract. It is becoming increasingly clear that electron thermal effects have to be taken into account when dealing with the theory of ionospheric instabilities in the high-latitude ionosphere. Unfortunately, the mathematical complexity often hides the physical processes at work. We follow the limiting cases of a complex but systematic generalized fluid approach to get to the heart of the thermal processes that affect the stability of E region waves during electron heating events. We try to show as simply as possible under what conditions thermal effects contribute to the destabilization of strongly field-aligned (zero aspect angle) Farley-Buneman modes. We show that destabilization can arise from a combination of (1) a reduction in pressure gradients associated with temperature fluctuations that are out of phase with density fluctuations, and (2) thermal diffusion, which takes the electrons from regions of enhanced temperatures to regions of negative temperature fluctuations, and therefore enhanced densities. However, we also show that, contrary to what has been suggested in the past, for modes excited along the E0×B direction thermal feedback decreases the growth rate and raises the threshold speed of the Farley-Buneman instability. The increase in threshold speed appears to be important enough to explain the generation of `Type IV' waves in the high-latitude ionosphere.Key words: Ionosphere (auroral ionosphere; iono- spheric irregularities; plasma waves and instabilities)
Geomagnetic control of the foF2 long-term trends
Authors: Mikhailov A. V. , Marin D.
Published: April 2005

Abstract. Further development of the method proposed by Danilov and Mikhailov is presented. The method is applied to reveal the foF2 long-term trends on 30 Northern Hemisphere ionosonde stations. Most of them show significant foF2 trends. A pronounced dependence of trend magnitude on geomagnetic (invariant) latitude is confirmed. Periods of negative/positive foF2 trends corresponding to the periods of long-term increasing/decreasing geomagnetic activity are revealed for the first time. Pronounced diurnal variations of the foF2 trend magnitude are found. Strong positive foF2 trends in the post-midnight-early-morning LT sector and strong negative trends during daytime hours are found on the sub-auroral stations for the period with increasing geomagnetic activity. On the contrary middle and lower latitude stations demonstrate negative trends in the early-morning LT sector and small negative or positive trends during daytime hours for the same period. All the morphological features revealed of the foF2 trends may be explained in the framework of contemporary F2-region storm mechanisms. This newly proposed F2-layer geomagnetic storm concept casts serious doubts on the hypothesis relating the F2-layer parameter long-term trends to the thermosphere cooling due to the greenhouse effect.Key words: Ionosphere (ionosphere-atmosphere interactions; ionospheric disturbances)
Effect of remote clouds on surface UV irradiance
Authors: Degünther M. , Meerkötter R.
Published: April 2005

Abstract. Clouds affect local surface UV irradiance, even if the horizontal distance from the radiation observation site amounts to several kilometers. In order to investigate this effect, which we call remote clouds effect, a 3-dimensional radiative transfer model is applied. Assuming the atmosphere is subdivided into a quadratic based sector and its surrounding, we quantify the influence of changing cloud coverage within this surrounding from 0% to 100% on surface UV irradiance at the sector center. To work out this remote clouds influence as a function of sector base size, we made some calculations for different sizes between 10 km × 10 km and 100 km × 100 km. It appears that in the case of small sectors (base size < 20 km × 20 km) the remote clouds effect is highly variable: Depending on cloud structure, solar zenith angle and wavelength, the surface UV irradiance may be enhanced up to 15% as well as reduced by more than 50%. In contrast, for larger sectors it is always the case that enhancements become smaller by 5% if sector base size exceeds 60 km × 60 km. However, these values are upper estimates of the remote cloud effects and they are found only for special cloud structures. Since these structures might occur but cannot be regarded as typical, different satellite observed cloud formations (horizontal resolution about 1 km × 1 km) have also been investigated. For these more common cloud distributions we find remote cloud effects to be distinctly smaller than the corresponding upper estimates, e.g., for a sector with base size of 25 km × 25 km the surface UV irradiance error due to ignoring the actual remote clouds and replacing their influence with periodic horizontal boundary conditions is less than 3%, whereas the upper estimate of remote clouds effect would suggest an error close to 10%.Key words: Atmospheric composition and structure (transmission and scattering of radiation) - Meteorology and atmospheric dynamics (radiative process)
The equatorial F-layer: progress and puzzles
Authors: Rishbeth H.
Published: April 2005

Abstract. This work reviews some aspects of the ionospheric F-layer in the vicinity of the geomagnetic equator. Starting with a historical introduction, brief summaries are given of the physics that makes the equatorial ionosphere so interesting, concentrating on the large-scale structure rather than the smaller-scale instability phenomena. Several individual topics are then discussed, including eclipse effects, the asymmetries of the `equatorial trough', variations with longitude, the semiannual variation, the effects of the global thermospheric circulation, and finally the equatorial neutral thermosphere, including `superrotation' and possible topographic influences.Keyword: Ionosphere (equatorial ionosphere)
Annual and semiannual variations in the ionospheric F2-layer. I. Modelling
Authors: Zou L. , Rishbeth H. , Müller-Wodarg I. C. F. , Aylward A. D. , Millward G. H. , Fuller-Rowell T. J. , Idenden D. W. , Moffett R. J.
Published: April 2005

Abstract. Annual, seasonal and semiannual variations of F2-layer electron density (NmF2) and height (hmF2) have been compared with the coupled thermosphere-ionosphere-plasmasphere computational model (CTIP), for geomagnetically quiet conditions. Compared with results from ionosonde data from midlatitudes, CTIP reproduces quite well many observed features of NmF2, such as the dominant winter maxima at high midlatitudes in longitude sectors near the magnetic poles, the equinox maxima in sectors remote from the magnetic poles and at lower latitudes generally, and the form of the month-to-month variations at latitudes between about 60°N and 50°S. CTIP also reproduces the seasonal behaviour of NmF2 at midnight and the summer-winter changes of hmF2. Some features of the F2-layer, not reproduced by the present version of CTIP, are attributed to processes not included in the modelling. Examples are the increased prevalence of the winter maxima of noon NmF2 at higher solar activity, which may be a consequence of the increase of F2-layer loss rate in summer by vibrationally excited molecular nitrogen, and the semiannual variation in hmF2, which may be due to tidal effects. An unexpected feature of the computed distributions of NmF2 is an east-west hemisphere difference, which seems to be linked to the geomagnetic field configuration. Physical discussion is reserved to the companion paper by Rishbeth et al.Key words: Atmospheric composition and structure (thermosphere-composition and chemistry) - Ionosphere (mid-latitude ionosphere; modelling and forecasting)
Annual and semiannual variations in the ionospheric F2-layer: II. Physical discussion
Authors: Rishbeth H. , Müller-Wodarg I. C. F. , Zou L. , Fuller-Rowell T. J. , Millward G. H. , Moffett R. J. , Idenden D. W. , Aylward A. D.
Published: April 2005

Abstract. The companion paper by Zou et al. shows that the annual and semiannual variations in the peak F2-layer electron density (NmF2) at midlatitudes can be reproduced by a coupled thermosphere-ionosphere computational model (CTIP), without recourse to external influences such as the solar wind, or waves and tides originating in the lower atmosphere. The present work discusses the physics in greater detail. It shows that noon NmF2 is closely related to the ambient atomic/molecular concentration ratio, and suggests that the variations of NmF2 with geographic and magnetic longitude are largely due to the geometry of the auroral ovals. It also concludes that electric fields play no important part in the dynamics of the midlatitude thermosphere. Our modelling leads to the following picture of the global three-dimensional thermospheric circulation which, as envisaged by Duncan, is the key to explaining the F2-layer variations. At solstice, the almost continuous solar input at high summer latitudes drives a prevailing summer-to-winter wind, with upwelling at low latitudes and throughout most of the summer hemisphere, and a zone of downwelling in the winter hemisphere, just equatorward of the auroral oval. These motions affect thermospheric composition more than do the alternating day/night (up-and-down) motions at equinox. As a result, the thermosphere as a whole is more molecular at solstice than at equinox. Taken in conjunction with the well-known relation of F2-layer electron density to the atomic/molecular ratio in the neutral air, this explains the F2-layer semiannual effect in NmF2 that prevails at low and middle latitudes. At higher midlatitudes, the seasonal behaviour depends on the geographic latitude of the winter downwelling zone, though the effect of the composition changes is modified by the large solar zenith angle at midwinter. The zenith angle effect is especially important in longitudes far from the magnetic poles. Here, the downwelling occurs at high geographic latitudes, where the zenith angle effect becomes overwhelming and causes a midwinter depression of electron density, despite the enhanced atomic/molecular ratio. This leads to a semiannual variation of NmF2. A different situation exists in winter at longitudes near the magnetic poles, where the downwelling occurs at relatively low geographic latitudes so that solar radiation is strong enough to produce large values of NmF2. This circulation-driven mechanism provides a reasonably complete explanation of the observed pattern of F2 layer annual and semiannual quiet-day variations. Key words: Atmospheric composition and structure (thermosphere-composition and chemistry) - Ionosphere (mid-latitude ionosphere; modelling and forecasting)
On the possibility of ion-drag to induce dynamic instability in the lower thermosphere neutral gas
Authors: Hall C. M.
Published: April 2005

Abstract. Strong wind shears may result in dynamic instability, often characterised by the Richardson number lying between zero and 0.25. The extent to which electric-field driven ion flow may induce such neutral wind shears is examined. Further, it is proposed that, in the ionosphere, it is possible for electric fields to drive ion winds such that the collisionally induced neutral air response may be comparable to viscous damping of neutral motion. We shall present an analogy to the Reynolds Number Re to quantify this effect. In the same way that Re may be used to evaluate the likelihood of a flow being turbulent, the analagous metric may also indicate where in the atmosphere plasma dynamics may be strong enough to destabilise the neutral dynamics.Key words: Ionosphere (auroral ionosphere; ionosphere-atmosphere interactions) - Meteorology and atmospheric dynamics (turbulence)
Polar patches observed by ESR and their possible origin in the cusp region
Authors: Smith A. M. , Pryse S. E. , Kersley L.
Published: April 2005

Abstract. Observations by the EISCAT Svalbard radar in summer have revealed electron density enhancements in the magnetic noon sector under conditions of IMF Bz southward. The features were identified as possible candidates for polar-cap patches drifting anti-Sunward with the plasma flow. Supporting measurements by the EISCAT mainland radar, the CUTLASS radar and DMSP satellites, in a multi-instrument study, suggested that the origin of the structures lay upstream at lower latitudes, with the modulation in density being attributed to variability in soft-particle precipitation in the cusp region. It is proposed that the variations in precipitation may be linked to changes in the location of the reconnection site at the magnetopause, which in turn results in changes in the energy distribution of the precipitating particles.Key words: Ionosphere (ionosphere-magnetosphere interactions; plasma temperature and density; polar ionosphere)
Multi-instrument study of footprints of magnetopause reconnection in the summer ionosphere
Authors: Pryse S. E. , Smith A. M. , Walker I. K. , Kersley L.
Published: April 2005

Abstract. Results are presented from a multi-instrument investigation of the signatures of equatorial reconnection in the summer, sunlit ionosphere. Well-established ion dispersion signatures measured during three DMSP satellite passes were used to identify footprints in ionospheric observations made by radio tomography, and both the EISCAT ESR and mainland radars. Under the prevalent conditions of southward IMF with the Bz component increasing in magnitude, the reconnection footprint was seen to move equatorward through the ESR field-of-view. The most striking signature was in the electron temperatures of the F2 region measured by the EISCAT mainland radar that revealed significantly enhanced temperatures with a steep equatorward edge, in general agreement with the leading edge of the ion dispersion. It is suggested that this sharp transition in the electron temperature may be an indicator of the boundary, mapping from the reconnection site, between closed geomagnetic field lines and those opened along which magnetosheath ions precipitate.Key words: Ionosphere (ionosphere-magnetosphere interactions; particle precipitation; plasma temperature and density)