bluuebunny/crossref_metadata_2025 huggingface dataset:
Mastery learning of thoracentesis skills by internal medicine residents using simulation technology and deliberate practice
Authors: Wayne Diane B. , Barsuk Jeffrey H. , O'Leary Kevin J. , Fudala Monica J. , McGaghie William C.
Published: February 2008

BACKGROUND

Thoracentesis has been identified as a core competency for hospitalists. Residency training may not provide adequate preparation to perform this procedure.

OBJECTIVE

Our aim was to use a thoracentesis simulation to assess graduating residents' proficiency in thoracentesis procedural skills and to evaluate the impact of an educational intervention on skill development to mastery standards.

DESIGN

This was a pretest–posttest mastery learning design without a control group.

SETTING

Participants were 40 third‐year internal medicine residents in a university‐affiliated program.

INTERVENTION

Using an observational checklist, each resident underwent baseline assessment of thoracentesis skill using a standardized clinical history, radiograph, and thoracentesis simulation. After baseline testing, residents received two 2‐hour education sessions featuring a videotaped presentation and deliberate practice with the thoracentesis simulator.

MEASUREMENTS

Residents were retested after the intervention. Skill mastery was defined as meeting or exceeding the minimum passing score (MPS) set by an expert panel at thoracentesis posttest. Those who did not achieve the MPS had additional deliberate practice and were retested until the MPS was reached.

RESULTS

Performance improved 71% from pretest to posttest on the clinical skills examination. All residents met or exceeded the mastery standard. The amount of practice time needed to reach the MPS was the only predictor (negative) of posttest performance. The education program was rated highly.

CONCLUSIONS

A curriculum featuring deliberate practice dramatically increased the skills of residents in thoracentesis. Residents enjoy training and receiving evaluation and feedback in a simulated clinical environment. This mastery program illustrates a feasible and reliable mechanism to achieve procedural competency. Journal of Hospital Medicine 2008;3:48–54. © 2008 Society of Hospital Medicine.
Six Sigma engages physicians in achieving strategic performance improvement at OSF Saint Francis Medical Center
Authors: Thompson Jody , Miller Tim , Krantz Amy , Thomas Tom
Published: February 2008

Driven largely by a desire to improve the safety and quality of its healthcare services, a large medical center has achieved dramatic and sustained improvement in core clinical processes, in part by getting residents and attending physicians involved in Six Sigma process improvement teams and change leadership. SFMC aligned the Six Sigma management system with its strategy and other performance improvement methods; implemented a 100‐day plan to launch the initiative; and built credibility through significant sustained improvements in nonclinical processes that mattered to physicians, before successfully extending the effort into the clinical and academic arenas to support evidence‐based care. © 2008 Wiley Periodicals, Inc.
From vendor to partner: Why and how leading companies collaborate with suppliers for competitive advantage
Authors: Hughes Jonathan
Published: February 2008

Despite the emergence of supplier relationship management, many
types of barriers prevent companies from transforming traditional purchasing relationships with key suppliers into powerful collaborations that can produce substantial value for both parties. The secret of collaborative customer‐supplier relationships is not only what the parties do together but also what they believe about each other and how they interact. Using recent survey data, the author discusses the behaviors, perceptions, and practices that inhibit vendor‐customer collaboration; examines several successful partnerships involving leading companies; examines what constitutes a “good” business‐to‐business relationship; and recommends steps companies can take to begin to transform their key supplier relationships into real partnerships. © 2008 Wiley Periodicals, Inc.
Executive derailment: Three cases in point and how to prevent it
Authors: Capretta Cara , Clark Lawrence P. , Dai Guangrong
Published: February 2008

The high rate of executive derailment is cause for concern, especially as large numbers of less experienced individuals begin to move into executive roles vacated by retiring Baby Boomers. Research has identified the most prevalent causes of derailment, and company intervention—along with the individual's resolve to improve—can successfully put an otherwise talented executive or high potential back on track. The authors discuss the most common factors in the failure of CEOs, executives, and high potentials; examine three cases where companies implemented well‐designed plans to save a career in trouble; and provide recommendations to individuals and organizations alike for preventing promising careers from stalling out. © 2008 Wiley Periodicals, Inc.
Auxetic properties and anisotropy of elastic material constants of 2D crystalline media
Authors: Jasiukiewicz Cz. , Paszkiewicz T. , Wolski S.
Published: February 2008

Anisotropies of Young's modulus E, the shear modulus G, and Poisson's ratio ν of all 2D symmetry systems are studied. The shear modulus and the ratio ν /ε of 2D crystals have fourfold symmetry. Simple necessary and sufficient conditions on their elastic compliances are derived to identify if any of these crystals is completely auxetic, non‐auxetic or auxetic. Examples of all types of auxetic properties of crystals of oblique and rectangular symmetry are presented. Particular attention is paid to 2D crystals of quadratic symmetry. All mechanically stable quadratic crystals are characterized by three parameters belonging to a prism with the stability triangle in the base. Regions in the stability triangle in which quadratic materials are completely auxetic, non‐auxetic, and auxetic are established. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
An experimental study of thermal post‐production processing of auxetic polypropylene fibres
Authors: Simkins V. R. , Ravirala N. , Davies P. J. , Alderson A. , Alderson K. L.
Published: February 2008

Following the successful batch production of auxetic ultra high molecular weight polyethylene, polypropylene and nylon, in the form of 10 mm diameter cylinders, a continuous melt extrusion route was adapted from conventional melt extrusion routes to produce fibres. Previous studies have shown that, once drawing has occurred, the auxetic effect is lost and, consequently, the mechanical properties of these fibres have been restricting their otherwise great potential in a wide range of applications. Research has therefore been undertaken into improving this matter by subjecting the auxetic fibres to a range of different thermal post‐production processing conditions. The fibres then underwent mechanical testing, Differential Scanning Calorimetry and Video Extensometry. Results suggest that annealing enhances the mechanical properties of these fibres and may provide a further route to enhancing auxeticity in improving homogeneity by over 40%. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Ab initio study of the photochemistry of aminopyrimidine
Authors: Zechmann Gunther , Barbatti Mario
Published: February 2008

Complete active space self‐consistent field (CASSCF), multi‐reference configuration interaction calculations (MR‐CISD), and equation of motion coupled‐cluster with singles and doubles (EOM‐CCSD) calculations are presented in order to elucidate the photodeactivation pathways of 6‐aminopyrimidine after vertical excitation to the S1 1nπ* state. Vertical excitation energies are reported up to the S7 state. Two S1 excited state minima, both of 1nπ* character, and three strongly puckered 1ππ* minima on the crossing seam (MXS) between the S0 and the S1 potential energy surface were found. Nonadiabatic reaction paths are discussed by linearly interpolating between the two minima and all MXS, which explain and extend observations made in recent surface‐hopping dynamics CASSCF investigations [Barbatti and Lischka, J Phys Chem A 2007, 111, 2852]. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008
50 Jahre Aluminiumbrücke über den Datteln‐Hamm‐Kanal
Authors: Mader Werner , Pieper August
Published: February 2008

1956 wurde die erste Straßenbrücke aus Aluminium in Deutschland über den Datteln‐Hamm‐Kanal bei Lünen dem Verkehr übergeben. Es handelt sich dabei um eine Fachwerkkonstruktion aus Strangpressprofilen und Blechen aus der Legierung AlMgSi 1 (heute: EN AW‐6082). Die Schwansbellbrücke hat eine Stützweite von 44,20 m und ist bei einem Eigengewicht von 25 t für ein Fahrzeuggewicht von bis zu 12 t zugelassen. Der Entwurf einer vergleichbaren Stahlbrücke ergab ein Eigengewicht von 60 t. Damit lag die Gewichtseinsparung durch Aluminium bei 58%. Als Verbindungsmittel wurden fast ausschließlich Aluminiumniete ebenfalls aus dem Werkstoff AlMgSi 1 eingesetzt. Die Nietform wurde zuvor in Versuchen ermittelt und optimiert. Man hatte seinerzeit vor dem Einbau entschieden, die Schwansbellbrücke zunächst ohne eine Beschichtung zu belassen, um das Korrosionsverhalten des Aluminiums zu prüfen. Bis heute ist weder ein zusätzlicher Korrosionsschutz durch eine Beschichtung noch ist eine Instandsetzung aufgrund von Korrosion erforderlich gewesen. Das Ergebnis der regelmäßigen Brückenprüfungen unterstreicht den ausgezeichneten Zustand, was umso bemerkenswerter ist, da sich das Bauwerk im Ruhrgebiet befindet und über 50 Jahre der Industrieatmosphäre ausgesetzt ist. Sowohl die Kosten für einen Korrosionsschutz als auch für eine Instandsetzung aufgrund von Korrosion konnten während der gesamten Standzeit eingespart werden.
Kinetics and Mechanism of the Synthesis of a Novel Protein‐Based Plastic Using Subcritical Water
Authors: Abdelmoez Wael , Yoshida Hiroyuki
Published: February 2008

We investigated the intermolecular mechanism and kinetics of the synthesis of a novel biodegradable protein‐based plastic from bovine serum albumin under subcritical water conditions using batch reactors. The reaction mechanism could be viewed as a chain reaction stabilized by the formation of intermolecular disulfide bonds. The kinetic analysis was based on non‐steady‐state kinetics using a theoretical model developed in one of our previous works. The activation energy and pre‐exponential factor were found to be 7.2 kJ/mol and 0.9 s−1, respectively. These low values signify that the reaction is relatively temperature‐insensitive with some diffusion limitation.
Forest canopy uptake of atmospheric nitrogen deposition at eastern U.S. conifer sites: Carbon storage implications?
Authors: Sievering Herman , Fernandez Ivan , Lee John , Hom John , Rustad Lindsey
Published: February 2008

Dry deposition determinations, along with wet deposition and throughfall (TF) measurements, at a spruce fir forest in central Maine were used to estimate the effect of atmospherically deposited nitrogen (N) uptake on forest carbon storage. Using nitric acid and particulate N as well as TF ammonium and nitrate data, the growing season (May‐October) net canopy uptake of atmospheric, predominantly anthropogenic, N deposition was found to be 1‐5 kg N ha−1. The ratio of growing season net canopy N uptake to that of recycled root N uptake (10‐30 kg N ha−1 during the growing season) suggests a substantial modification of the N cycle at this Maine spruce fir forest over the past decade. The growing season 1–5 kg ha−1canopy N uptake may induce an enhanced annual carbon (C) storage of 250‐1350 kg C ha−1 yr−1. This magnitude of N‐stimulated C storage may be compared with measured annual C sequestration of ∼2000 kg C ha−1 for each of the years 1996–1998 at this Maine site. Consideration of four other eastern U.S. forest sites for which net canopy N uptake data are available suggests that from 285 to 2950 kg C ha−1, annual C sequestration may be occurring at these conifer sites, consistent with the Maine site results.
Phanerozoic evolution of atmospheric methane
Authors: Bartdorff Oliver , Wallmann Klaus , Latif Mojib , Semenov Vladimir
Published: February 2008

A simple geochemical box model for the global cycle of methane (CH4) has been developed and applied to reconstruct the evolution of atmospheric CH4 over the entire Phanerozoic. According to the model, the partial pressure of atmospheric CH4 (pCH4) increased up to approximately 10 ppmv during the Carboniferous coal swamp era. This implies a maximum radiative forcing of about 3.5 W m−2 via CH4. Through its radiative forcing, CH4 heated the average global surface temperature by up to 1°C. The elevated pCH4 values during the Permian‐Carboniferous cold period may have moderated the temperature decline caused by the coeval drawdown of atmospheric CO2. Additional runs with a global carbon model indicate that the heating induced by elevated pCH4 favored the drawdown of atmospheric pCO2 via enhanced rates of silicate weathering. Simulations with a state‐of‐the‐art climate model reveal that the effects of atmospheric CH4 on average global surface temperature also depend on the partial pressures of CO2. The CH4 climate effect is amplified by high background levels of atmospheric CO2 such that a coeval increase in the partial pressure of both greenhouse gases has a much stronger climate effect than previously anticipated.
Threshold radar reflectivity for drizzling clouds
Authors: Liu Yangang , Geerts Bart , Miller Mark , Daum Peter , McGraw Robert
Published: February 2008

Empirical studies have suggested the existence of a threshold radar reflectivity between nonprecipitating and precipitating clouds; however, there has been neither a rigorous theoretical basis for the threshold reflectivity nor a sound explanation as to why empirically determined threshold reflectivities differ among studies. Here we present a theory for the threshold reflectivity by relating it to the autoconversion process. This theory not only demonstrates the sharp transition from cloud to rain when the radar reflectivity exceeds some value (threshold reflectivity) but also reveals that the threshold reflectivity is an increasing function of the cloud droplet concentration. The dependence of threshold reflectivity on droplet concentration suggests that the differences in empirically determined threshold reflectivity arise from the differences in droplet concentration. The favorable agreement with measurements collected over a wide range of conditions further provides observational support for the theoretical formulation. The results have many potential applications, especially to remote sensing of cloud properties and studies of the second aerosol indirect effect.
Probable mixing state of aerosols in the Indo‐Gangetic Basin, northern India
Authors: Dey Sagnik , Tripathi S. N. , Mishra S. K.
Published: February 2008

To investigate the probable mixing state of aerosols in the Indo‐Gangetic Basin, six different mixing cases, viz. external mixing, internal mixing, and four combinations of core‐shell type mixing (black carbon, BC over dust, water‐soluble over dust, BC over water‐soluble and water‐soluble over BC) have been considered. Composite single scattering albedo (SSA) have been computed for six cases for post‐monsoon, winter and pre‐monsoon seasons and are compared with the Aerosol Robotic Network (AERONET) retrieved SSA values. The most probable mixing state in the post‐monsoon season seems either to be external mixing or water‐soluble coating over dust and in the winter season, the external mixing seems to be the probable mixing state. However, in the pre‐monsoon season, BC coating over dust seems to be the most probable mixing state. This type of mixing leads to enhanced absorption and needs future attention to better understand the aerosol radiative effect in this region.
Southern hemisphere tropospheric aerosol backscatter measurements—Implications for a laser wind system
Authors: Gras J. L. , Platt C. M. R. , Jones W. D. , Huffaker R. M. , Young S. A. , Banks S. M. , Booth D. J.
Published: February 2008

Values of backscatter coefficient at 0.532 μm, 0.694 μm, and 10.6 μm were determined both by direct measurement and by Mie computation from measured aerosol microphysical properties in the eastern Australian region from 4°S to 41°S. Volume backscatter coefficients at 10.6 μm were typically in the range 1×10−11 to 3×10−11 m−1 sr−1 for both approaches, although the experimental uncertainty in both cases was quite large. Agreement between the shorter wavelength lidars and the aerosol data was typically within the combined experimental uncertainties, although direct measurements were systematically larger than values derived from the aerosol data; individual regions were observed where the disagreement was larger than the combined error. Backscatter at 10.6 μm and at visible wavelengths was found to be sensitive to essentially different regions of the aerosol size spectrum, questioning to some degree the validity of using short‐wavelength extinction and backscatter data to infer the global distribution of backscatter at wavelengths around 10.6 μm. Considerable day‐to‐day variability in backscatter was observed at all wavelengths. The implications of the very low backscatter values found, compared to northern hemisphere values, should be considered in the design of the Laser Atmospheric Wind Sounder (LAWS).
Radiation and cloud radiative properties in the European Centre for Medium Range Weather Forecasts forecasting system
Authors: Morcrette Jean‐Jacques
Published: February 2008

The successive versions (EC1, EC2, and EC3) of the radiation scheme used in the European Centre for Medium Range Weather Forecasts (ECMWF) operational model, including the version which became operational on May 2, 1989, are reviewed and their results are compared to results of more detailed radiation models made available thanks to the Intercomparison of Radiation Codes Used in Climate Models (ICRCCM) program. For clear‐sky conditions, the shortwave H2O absorptivity is overestimated in EC1‐EC2, which leads to too large shortwave atmospheric absorption (by up to 20%) and too small downward shortwave radiation at the surface (by 5–10%). EC1 and EC2 both significantly underestimate the longwave radiative cooling, with main errors in the lower troposphere with EC1, and between 700 and 300 hPa with EC2. Therefore EC1 and, to a smaller extent, EC2 underestimate the outgoing longwave radiation at the top of the atmosphere. In cloudy conditions, EC1 shows an exaggerated sensitivity to small amounts of scatterer, a problem corrected in EC2. Due an unrealistic model cloud embedded in EC1‐EC2, these schemes cannot properly represent both the shortwave planetary albedo and outgoing longwave radiation for realistic cloud liquid water contents. EC3 corrects most of these deficiencies and gives results in better agreement with those of more detailed models.
Numerical simulation of the formation of thin ionization layers at high latitudes
Authors: Bristow W. A. , Watkins B. J.
Published: February 2008

A one‐dimensional simulation of high latitude sporadic‐E layers has been developed to investigate the role of electric field in layer formation. The simulation model computes the ion densities (O+, O2+, N+, N2+, NO+, Fe+) and temperatures as a function of altitude. The stationary state momentum equation and continuity equation is solved for each ion species. Then the energy equation is solved for electrons, neutrals, and a generic ion having the mean ion mass and velocity. The model does not include any photoionization or particle precipitation. Chemical production and loss are included for the five standard ion species, but not for the Fe+ ions. An initial altitude profile is assumed for the ions, and the model computes the altitude distribution as a function of time. The horizontal direction of the electric field is important for determining the layer structure and its altitude. An electric field directed between magnetic west and north results in convergent plasma flow and thus layer formation at about 120–130 km altitude. For fields directed to the west and south layers form at lower altitudes(100–115km). With an assumed dip angle of 75° the layers formed by the N‐W quadrant fields form quickly (<10min), are quite thin, and remain stationary in altitude. Layers formed by S‐W quadrant fields are initially thick but compress in time (15–20 min). Additionally they move down in altitude as they compress. The large perpendicular electric field (50 mV/m) used in the simulation leads to significant heating of the ions and to a smaller extent the electrons and neutrals. The layer formed by the field directed in the N‐W quadrant occurs in the region of significant heating, and the temperature profile shows some enhancement at the layer altitude.
KOSI?
Authors: Keller H. Uwe , Markiewicz Wojciech J.
Published: February 2008

KOSI experiments are discussed from the point of view of their possible applications to cometary sciences. Scales and geometries of KOSI and comets are compared, making it obvious that laboratory simulation of any global cometary features is impossible. To indicate the difficulties in process simulation, we discuss in some detail the properties of the gas flow generated by the sublimating ice/dust samples, the interaction of the gas with the emitted grains and heat transport within the sample. Some emphasis is laid on the gas‐grain interaction showing that large grains have to be very fluffy (fractal) if gas drag is responsible for their emission.
Spatial and temporal variability of the extent of chemically processed stratospheric air
Authors: Kaye Jack A. , Douglass Anne R. , Rood Richard B. , Stolarski Richard S. , Newman Paul A. , Allen Dale J. , Larson Edmund M.
Published: February 2008

Simulations of the spatial and temporal variability of the extent of chemically processed air in the Arctic stratosphere have been carried out using a three‐dimensional chemistry‐transport model for the winters of 1979 and 1989, Chemically processed air is identified in the model as that in which the amounts of hydrogen chloride (HCl) calculated with parameterized loss for conditions appropriate to polar stratospheric cloud (PSC) formation are substantially smaller than those calculated in a model with gas phase chemistry only. It is seen that chemically processed air may be identified over much of the Arctic lower stratosphere from early January to late February, with HCl depletions being larger in 1989 than in 1979. Near the latitude of the Arctic circle, there is important spatial and temporal variability in the extent of chemically processed air. There is some evidence for transport to mid‐latitudes of processed air during these winters, but the HCl reductions are much smaller and more sporadic than those near the pole. At 62 and 42N, processed air is calculated to occur preferentially over the longitude regions from 60‐120E and 270‐330E.
Sensitivity of stratospheric ozone to heterogeneous chemistry on sulfate aerosols
Authors: Pitari Giovanni , Visconti Guido , Rizi Vincenzo
Published: February 2008

The effects of sulfate aerosols on stratospheric ozone have been studied with a 2D model. The model includes a comprehensive chemical code for homogeneous and heterogeneous reactions; both background and volcanic aerosols have been taken into account according to different scenarios. The basic temperature field is prescribed, while the perturbation introduced by the presence of volcanic aerosols is predicted. Increase of total chlorine in the stratosphere causes a well known ozone depletion by itself, but. the effects could be highly enhanced in presence of a large amount of volcanic aerosols that affect the balance of nitrogen and chlorine reservoirs through heterogeneous chemical reactions. For a volcanic eruption similar to El Chichon we show that the maximumO3depletion (7% for a 2.5ppbv amount of stratospheric chlorine and 12% by doubling Cl) is to be expected at high latitudes in spring, because of a large chemical destruction acting in situ.
Enhancement of wave growth for warm plasmas with a high‐energy tail distribution
Authors: Thorne Richard M. , Summers Danny
Published: February 2008

We consider the classical linear theory of electromagnetic wave growth in a warm plasma for waves propagating parallel to a uniform ambient magnetic field. Wave growth rates γ are calculated for ion‐driven right‐hand mode waves for Kappa (bi‐Lorentzian) and Maxwellian particle distribution functions. Systematic calculations of γ are carried out for various values of the spectral index κ, the temperature anisotropy A+ = 1 ‐ (T⊥+ / T∥+), and the ratio β+ of plasma pressure to magnetic pressure, appropriate to the solar wind. When the anisotropy is low (A+ ≪ 1), the wave growth is limited to frequencies below the proton gyrofrequency, and the growth rate increases dramatically as the spectral index κ is reduced (i.e., as the high‐energy tail becomes more pronounced). The growth rate for any Kappa distribution greatly exceeds (often by several orders of magnitude) that for a Maxwellian with the same bulk properties. For large thermal anisotropy (T∥+, ≫ T⊥+) the growth rate from either distribution is greatly enhanced. In comparison to a Maxwellian distribution the growth rates from a Kappa distribution are generally larger, and significant wave growth occurs over a broader range of frequencies. Evidently, the theory is important in the study of microinstabilities in space plasmas in which a high‐energy tail distribution is generally present.
Tidal Winds from the Mesosphere, Lower Thermosphere Global Radar Network during the second LTCS Campaign: December 1988
Authors: Manson A. H. , Meek C. E. , Avery S. K. , Fraser G. J. , Vincent R. A. , Phillips A. , Clark R. R. , Schminder R. , Kurschner D. , Kazimirovsky E. S.
Published: February 2008

Winds and tides were measured by nine MLT (mesosphere, lower thermosphere) radars with locations between 70°N and 78°S, including an equatorial station at Christmas Island, 2°N (Avery et al., 1990). The mean winds were eastward (westward) in the northern (southern) hemisphere mesosphere, consistent with midwinter circulations. For the 12‐hour (semidiurnal) tide, observations and the model of Forbes and Vial (1989) were in generally good agreement: in both cases northward components were closer to being in phase in the two hemispheres, and winter wavelengths were shorter than those of the mid‐latitude summer. Major differences were large (small) amplitudes at 70°N for model (observations); and poor agreement of equatorial tidal profiles. For the 24‐hour (diurnal tide), the radar observations and model of Forbes and Hagan (1988) were in useful agreement in the summer hemisphere. However, the short (long) wavelengths at mid (high) latitudes of the model's winter hemisphere were not observed during LTCS (Lower Thermosphere Coupling Study) 2, nor in climatologies for December. Suggestions as to the reasons for this disparity are presented.
The electrodynamic, thermal, and energetic character of intense Sun‐aligned arcs in the polar cap
Authors: Valladares C. E. , Carlson H. C.
Published: February 2008

The electrodynamic, thermal, and energetic character of stable Sun‐aligned arcs in the polar cap can be meaningfully diagnosed by an incoherent scatter radar, provided a suitable observing scheme is selected. We report here such measurements of two intense Sun‐aligned arcs. The two arcs were diagnosed on two different nights (February 26 and March 1, 1987) using the Sondre Stromfjord radar as a stand‐alone diagnostic. Repeatable patterns are found in mesoscale area (order 10³ km by 10³ km) maps of altitude profiles for observed electron and ion gas number densities, temperatures, and line‐of‐sight velocities, and projected mesoscale area maps of derived electric fields, Pedersen and Hall conductivities (Ne, Te, Ti, V, E, ΣP, ΣH), horizontal and field‐aligned currents, joule heating rate, and Poynting flux. We confirm, for the first time with continuous mesoscale area maps, that the arcs have the anticipated simple arc electrodynamics. That is, the visual and enhanced ionization signatures of the arc are produced by incoming energetic electrons carrying the outgoing current from the electric field convergence in the arc. Strong electron temperature enhancements (>2000 K) are found as expected within the sheets of ionizing particle precipitation. Dawn to dusk decreases in the antisunward plasma flow of order 1 km s−1, across order 100 km, correspond to peak electron densities of order 105 cm−3 down to altitudes as low as 120 km, and upward currents of order 1 µA m−2. These data also lead to important implications for the physics of polar cap arcs. The high‐velocity (antisunward flow on the dawnside) edge of the arc marks the location of strong persistent Joule heating driven by downward Poynting flux. There is a channel of strongly enhanced ion temperature (well above the electron temperature) along the high‐velocity edge of the arc, quantitatively accounted for by ion frictional heating as the strong electric field drags the ions through the neutral gas. The deposition rate into the atmosphere of the net electromagnetic energy well exceeds the net particle energy deposited by the ionizing energetic electron flux. This heating is a substantial source of heat into the polar thermosphere. As estimated by heat into the ions, heat lost by the ions to the neutrals, or energy available from the Poynting and energetic particle flux, several ergs cm−2 s−1 are deposited in channels of order 100 km for good fractions of an hour in these arcs; this contributes to resolving the problem of the missing polar thermosphere heat source. Finally, a reasonably simple yet self‐consistent, accurate, and comprehensive representation of stable intense Sun‐aligned arcs is presented, including the electrodynamic, thermal, and energetic character.
Ionospheric traveling vortex generation by solar wind buffeting of the magnetosphere
Authors: Kivelson Margaret G. , Southwood David J.
Published: February 2008

Traveling ionospheric vortices observed near the polar cusp boundary have been interpreted as signatures of impulsive reconnection (or flux transfer events) on the magnetopause, but neither the sense of motion nor the phase speed of the disturbances is consistent with the assumed generation mechanism. An alternative interpretation as the ionospheric signature of the response to fluctuating solar wind pressure can account for the reported features of the ionospheric perturbations. The solar wind pressure perturbation establishes vortical flow on magnetopause flux tubes and drives a guided shear wave along polar cusp field lines into the ionosphere. The guided shear wave carries the field‐aligned currents needed to couple the magnetopause flow to ionospheric flow. The elementary form of the ionospheric disturbance in horizontal flow, electric field, and field‐aligned current is dipolar in structure, with the flow near the center predominantly meridional and of the order of 100 km s−1 for pressure perturbations reported as typical in the solar wind. The phase velocity is 3–10 km s−3 in the east‐west sense as inferred from mapping of a disturbance carried along the magnetopause at the magnetosheath flow velocity. A significant conclusion of this analysis is that the ionospheric signature of a traveling front across which pressure changes monotonically is a pair of vortices of opposite polarizations. A pressure pulse will produce two pairs of vortices, with the sense of polarization reversed in the trailing pair. Compressional perturbations of the boundary cannot produce isolated vortical flows in the ionosphere, although temporally very nonsymmetric perturbations could produce signatures that appear to have such symmetry.
Solar wind fluctuations at large scale: A comparison between low and high solar activity conditions
Authors: Bavassano B. , Bruno R.
Published: February 2008

The influence of the Sun's activity cycle on the solar wind fluctuations at time scales from 1 hour to 3 days in the inner heliosphere (0.3 to 1 AU) is investigated. Hourly averages of plasma and magnetic field data by Helios spacecraft are used. Since fluctuations behave quite differently with changing scale the analysis is performed separately for two different ranges in time scale. Between 1 and 6 hours Alfvénic fluctuations and pressure‐balanced structures are extensively observed. At low solar activity and close to 0.3 AU Alfvénic fluctuations are more frequent than pressure‐balanced structures. This predominance, however, weakens for rising solar activity and radial distance, to the point that a role exchange, in terms of occurrence rate, is found at the maximum of the cycle close to 1 AU. On the other hand, in all cases Alfvénic fluctuations have a larger amplitude than pressure‐balanced structures. On the whole, the Alfvénic contribution to the solar wind energy spectrum comes out to be dominant at all solar activity conditions. At scales from 0.5 to 3 days the most important feature is the growth, as the solar wind expansion develops, of strong positive correlations between magnetic and thermal pressures. These structures are progressively built up by the interaction between different wind flows. This effect is more pronounced at low than at high activity. Our findings support the conclusion that the solar cycle evolution of the large‐scale velocity pattern is the factor governing the observed variations.
Heating of O+ ions in the cusp/cleft: double‐cyclotron absorption versus cyclotron resonance
Authors: Ball Lewis , André Mats
Published: February 2008

The process of double‐cyclotron absorption, where an ion simultaneously absorbs two waves whose frequencies sum to the ion gyrofrequency, can heat ions perpendicular to the ambient magnetic field. It has been suggested that this process may play a role in the production of ion conics. The low‐energy oxygen (O+) distributions and the electric spectral densities observed by DE 1 in the cusp/cleft during an O+ conic event are used as inputs to a Monte Carlo simulation of the heating of the O+ ions due to double‐cyclotron absorption of waves near half the ion gyrofrequency. The results are compared with the observed O+ conics and with the results of simulations of ion heating via the process of cyclotron resonance involving left‐hand polarized waves near the ion gyrofrequency. The simulations show that for any particular event cyclotron resonance can probably heat ions over a much greater altitude range than double‐cyclotron absorption is capable of doing. They also demonstrate the much stronger dependence of the heating due to double‐cyclotron absorption on local intensifications of the spectral density, and they indicate that a relatively narrow region of intense wave activity may be sufficient for this heating process to produce O+ conics with energies comparable to those observed. Heating via double‐cyclotron absorption may therefore be important for relatively local heating of O+ ions. However, cyclotron resonance heating by waves around the gyrofrequency is probably more important in the majority of O+ conic events in the cusp/cleft.
Effects of size‐dependent emissivity on maximum temperatures during micrometeorite entry
Authors: Rizk B. , Hunten D. M. , Engel S.
Published: February 2008

We have numerically examined the effects of adopting the absorption efficiencies predicted by the Mie theory for spheres on the maximum temperature of pure olivine and pure iron micrometeorites entering the Earth's atmosphere and pure water ice micrometeorites entering the Uranian atmosphere. We found that particles of micron and submicron size with the optical properties that characterize these substances tend not to radiate away their frictional heat of entry as efficiently as classical micrometeorite theory predicts. Consequently, the degree to which these particles are heated and altered during entry is increased. We conclude that micron and submicron‐sized particles are more realistically treated as Mie spheres than as blackbodies, when accurate values exist for the imaginary index of refraction at wavelengths of a few microns.
Opening the cusp
Authors: Crooker N. U. , Toffoletto F. R. , Gussenhoven M. S.
Published: February 2008

Defining the equatorward boundary of the cusp region in the ionosphere as the projection of the merging line from the magnetopause, we use a quantitative, geometrically realistic model to show how the local time span of the cusp increases with increasing merging rate for southward interplanetary magnetic field. Since the merging rate is fixed by the magnitude of the magnetic field component normal to the model magnetopause and then normalized to the cross‐polar‐cap potential, the result gives the variation of cusp local time span as a function of potential. From 0 kV up to 60 kV, the cusp expands from a point at noon to 2 hours on either side. Nearly tripling the voltage to 170 kV adds one more hour to each side, yielding a span from 0900 to 1500 LT. As an example of broad local time span during magnetically active periods, we present spacecraft observations of cusp particles during the great storm of March 1989 that cover more than 8 hours of local time. An important aspect of the result is the demonstration that a merging line of fixed length on the magnetopause, as assumed in the model, maps to a projected length in the ionosphere that increases as the funnel‐shaped cusp opens. This behavior contrasts with earlier models that have cleft rather than cusp geometry, where the projected merging line length is proportional only to its length on the magnetopause. The model results are used to construct the footprint of a flux transfer event caused by time variations of the merging rate, uniform along the length of the merging line. The cusp geometry distorts the field lines mapped from the magnetopause to yield footprints with dawn and dusk protrusions into the region of closed magnetic flux.
Magnetospheric boundary dynamics: DE 1 and DE 2 observations near the magnetopause and cusp
Authors: Maynard N. C. , Aggson T. L. , Basinska E. M. , Burke W. J. , Craven P. , Peterson W. K. , Sugiura M. , Weimer D. R.
Published: February 2008

A broad spectrum of particle and field measurements was taken near local noon by the Dynamics Explorer satellites during the magnetic storm of September 6, 1982. While at apogee, DE 1 sampled the magnetospheric boundary layer at mid southern latitudes and, due to the passage of an intense solar wind burst, briefly penetrated into the magnetosheath. In the boundary layer and the adjacent magnetosheath the plasma flow was directed toward dawn. Variance and de Hoffmann‐Teller analyses of electric and magnetic field data during the magnetopause crossing showed the magnetopause structure to be that of a rotational discontinuity or an intermediate shock with a substantial normal magnetic field component. This is consistent with an open magnetosphere model in which significant magnetic merging occurs at the local time of the spacecraft. The orbit of DE 2 carried it through the morning sector of the low‐altitude, southern cusp. The measurements show a well‐defined, cusp current system occurring on open magnetic field lines. At both cusp and subcusp latitudes the electric field was equatorward indicating a strongly eastward plasma flow. The boundary between these two regions was marked by the onset of magnetosheath precipitation and an electric field structure containing both poleward and equatorward spikes. The poleward spike has associated field‐aligned currents which are closed by Pedersen currents and, from force balance considerations, is interpreted as the signature of a magnetic merging event at the magnetopause. The equatorward spike has the characteristics of a down‐coming and reflected Alfven wave packet of finite dimensions. The high‐altitude measurements suggest that the dayside boundary layer is made up of closed magnetic flux tubes, a large fraction of which drift to the magnetopause where merging with the IMF occurs. The merging line maps to the ionosphere as a “gap” across which the polar cap potential is applied to the magnetosphere. The potential is applied from a magnetosheath generator to the polar ionosphere by means of the cusp, field‐aligned current system. The electric fields provide an ionospheric indicator of the mapping of the merging line location.
Low‐frequency radio emissions in the outer heliosphere
Authors: Macek W. M. , Cairns I. H. , Kurth W. S. , Gurnett D. A.
Published: February 2008

Low‐frequency radio emissions at 2 and 3 kHz were observed by the plasma wave receivers on both Voyager 1 and Voyager 2 during the interval 1983–1987 at radial distances from the Sun greater than 17 AU and 13 AU, respectively. We present a report on progress toward a model in which the emitted radio waves are generated near multiples of the plasma frequency ƒp by nonlinear processes involving electrostatic Langmuir waves at a source in the outer heliosphere. Constraints on the emission processes and source characteristics are discussed. The observed spectral flux density of ∼10−17 W m−2 Hz−1 corresponds to an inferred minimum brightness temperature of ∼1015 K, comparable to the most intense type III solar radio bursts and more intense than the 2ƒp radiation generated at the Earth's bow shock. Minimum Langmuir wave electric fields in the source region, based on the kinematics of the radiation processes at 2ƒp, lie in the range ∼3–30 µV/m for nominal source and electron beam parameters. This field strength is plausible based on the intensity of Langmuir waves observed upstream of planetary bow shocks in the solar wind.
Transpolar auroras, their particle precipitation, and IMF By component
Authors: Makita K. , Meng C.‐I. , Akasofu S.‐I.
Published: February 2008

Transpolar auroras, their associated particle precipitation, and their occurrence with respect to the IMF By polarity are examined on the basis of DMSP F6 auroral images and the corresponding particle data. It is found that the transpolar arcs are located in the poleward edge of the soft particle precipitation region extending from either the dawn or dusk part of the auroral oval precipitation; they are not embedded in the polar rain region. This finding suggests that the transpolar arcs are located along the poleward boundary of the closed field line region (or the equatorward boundary of the open region) as suggested by Meng (1981). Further, the appearance of the extended precipitation region from the oval depends on the polarity of the IMF By, in the northern hemisphere morning sector for IMF By < 0 or in the evening sector for IMF By > 0. In general, the precipitating particle flux in the extended precipitation region is not high enough to produce appreciable luminosity. Thus only the transpolar arcs (associated with relatively intense precipitation) near the poleward boundary tend to become much more luminous, forming the so‐called “theta aurora.”
Idealized Voyager Jovian magnetosphere shape and field
Authors: Engle Irene M.
Published: February 2008

A magnetic field arising from the Jovian equatorial sheet current deduced from Voyager 1 and 2 observations has been added to a planetary dipole field to provide a model of magnetic field inside the magnetopause. This internal field was used to calculate the magnetopause surface in a cyclic process. During each cycle, the surface was calculated, and the resulting field due to currents on the magnetopause was calculated for inclusion in the total field used to calculate the next‐order surface. The resulting magnetopause is, as anticipated, flatter in shape than one resulting primarily from a dipole internal field source, but not dissimilar in overall height‐to‐width configuration to that of the magnetopause calculated for the larger inflated magnetopause observed by Pioneer 10. An array of magnetic field values for locations internal and external to the magnetopause due to currents on the surface has been computed by integrating over the entire magnetopause. A model for the total magnetospheric field of this semi‐inflated magnetosphere has been constructed by adding this latter contribution to the internal source fields to obtain a global model of a semi‐inflated Jovianlike magnetospheric field. The magnitude of the contribution of the surface currents to the total magnetic field in the region of the orbits of the Galilean satellites is calculated to be considerably larger for this Voyager model than for the Pioneer model.
Control of plasma waves associated with the space shuttle by the angle between the orbiter's Velocity vector and the magnetic field
Authors: Cairns Iver H. , Gurnett Donald A.
Published: February 2008

The interaction between water outgassed from the space shuttle and the ionospheric plasma leads to production of water ions by charge exchange and an active and complex plasma wave environment for the space shuttle. We show that the amplitude and spectral character of some of these waves are controlled by the angle between the magnetic field and the shuttle's velocity vector VT relative to the ionospheric plasma. When the flow is approximately perpendicular to the magnetic field (V∥/VT ∼ 0), large wave amplitudes and characteristic “mushroom” wave structures are observed, whereas more nearly parallel flows |V∥| ∼ V⊥ are characterized by low wave levels. We show that linear instability theory predicts the growth of Doppler‐shifted lower hybrid waves in the observed frequency range when driven by the ring and/or beam distributions of water ions produced by charge exchange in the vicinity of the space shuttle. Two mutually compatible interpretations for the V∥/VT effect exist. The first interpretation involves the path lengths available for growth of waves driven by pickup ions varying with the quantity V∥/VT and being limited by spatial variations in the water ion distribution. The second interpretation follows directly from the linear theory: decreasing the ring/beam speed V⊥ of the pickup ions driving the waves (increasing V∥/VT) results in smaller growth rates, with zero growth rate below some threshold value of V⊥. The linear theory shows that decreased growth lengths or growth rates should naturally produce the observed amplitude and bandwidth changes constituting the V∥/VT effect. These results have immediate implications for future shuttle missions and orbiting platforms subject to outgassing of water. If these facilities are used for ionospheric plasma studies or active experiments involving plasma waves, the plasma wave background due to pickup ions associated with the orbiter should be minimized. This requires orbits with large |V∥| ≥ V⊥; that is, orbital velocities within about 45° of the magnetic field over as much of the orbit as possible. These constraints favor more nearly polar orbits and argue strongly against equatorial orbits. Alternatively, free‐flying spacecraft situated upstream from the orbiter's water cloud should be used.