bluuebunny/crossref_metadata_2025 huggingface dataset:
Improving glycemic control in medical inpatients: A pilot study
Authors: Trujillo Jennifer M. , Barsky Emily E. , Greenwood Bonnie C. , Wahlstrom Stephanie A. , Shaykevich Shimon , Pendergrass Merri L. , Schnipper Jeffrey L.
Published: February 2008

BACKGROUND

Inpatient hyperglycemia is associated with poor patient outcomes. Current guidelines recommend that in an inpatient non‐ICU setting there be treatment to achieve a glucose level below 180 mg/dL.

METHODS

Objectives of this prospective quality‐improvement pilot study were to implement a subcutaneous insulin protocol on a general medicine service, to identify barriers to implementation, and to determine the effect of this protocol on glycemic control. Eighty‐nine patients with a preexisting diagnosis of type 2 diabetes or inpatient hyperglycemia were eligible. Study outcomes included resident acceptance of the protocol, insulin‐ordering practices, and mean rate of hyperglycemia (glucose > 180 mg/dL) per person. Results were compared with those of a previously conducted observational study.

RESULTS

Residents agreed to use the protocol in 56% of cases. Reasons for declining the protocol included severity of a patient's other disease states, desire to titrate oral medications, and fear of hypoglycemia. Basal and nutritional insulin were prescribed more often in the pilot group compared with at baseline (64% vs. 49% for basal, P = .05; 13% vs. 0% for nutritional, P < .001). Basal insulin was started after the first full hospital day in 42% of patients, and only one‐third of patients with any hypo‐ or hyperglycemia had any subsequent changes in their insulin orders. The mean rate of hyperglycemia was not significantly different between groups (31.6% of measurements per patient vs. 33.3%, P = .85).

CONCLUSIONS

Adherence to a new inpatient subcutaneous insulin protocol was fair. Barriers included fear of hypoglycemia, delays in starting basal insulin, and clinical inertia. Quality improvement efforts likely need to target these barriers to successfully improve inpatient glycemic control. Journal of Hospital Medicine 2008;3:55–63. © 2008 Society of Hospital Medicine.
Comparison of practice patterns of hospitalists and community physicians in the care of patients with congestive heart failure
Authors: Roytman Marina M. , Thomas Sean M. , Jiang Caroline S.
Published: February 2008

OBJECTIVE

The objective of the present study was to compare the practice patterns of hospitalists and community physicians in the care of patients with congestive heart failure.

DESIGN/PARTICIPANTS/SETTING

The study was a retrospective chart review of 342 patients treated for congestive heart failure at a community‐based teaching hospital.

MEASUREMENTS

Use of established therapeutic modalities for congestive heart failure and utilization of resources by hospitalists and nonhospitalists were compared. Outcome measures were adjusted length of stay (LOS), costs per case, in‐hospital mortality, acute renal failure rate, and readmission rate.

RESULTS

The patients of hospitalist were more likely to receive ACE‐I or ARB therapy within 24 hours of admission (86% vs. 72%; P = .003), intravenous diuretics (90% vs. 73%; P < .001), and social work consultation (48% vs. 29%; P < .001). They were less likely to have had serial chest radiographs (4% vs. 13%; P = .01) and multiple consultants (8% vs. 16%; P = .03). Hospitalists' patients with an illness whose severity was categorized as minor had a 40% reduction in LOS, those with a moderately severe illness had a 20% reduction, and those with an extremely severe illness had a 13% reduction (P = .002). Costs per case were reduced by $1000‐$3100 across all severity categories (P < .001). Rates of acute renal failure and readmission were similar between the groups.

CONCLUSIONS

Early use of ACE‐I/ARB, aggressive approach to diuresis, greater involvement of social work services and decreased use of chest radiographs and medical consultants were identified as distinct practices of hospitalists in this medical center. These practices may have led to a shorter LOS and lower costs while preserving quality of care and possibly improving clinical outcomes. Journal of Hospital Medicine 2008;3:35–41. © 2008 Society of Hospital Medicine.
Simulation of the Coulomb gap evolution in the Coulomb glass
Authors: Matulewski J. , Baranovskii S. D. , Thomas P.
Published: February 2008

Time dependent relaxation in the Coulomb glass from the random distribution of electrons via localized states towards the distribution prescribed by the long‐range Coulomb interactions is studied by computer simulations. The time evolution of the single particle density of states is followed in course of the relaxation. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The electron glass: conduction, glassy dynamics and relation to other glasses
Authors: Pollak M.
Published: February 2008

A theory for linear response conduction in an electron glass, based on scaling, is developed that includes all the important correlations due to many‐body effects. The theory yields the same functional dependence of the conductance on tempera‐ture as the Efros‐Shklovskii (ES) theory which neglects many body effects. On excitation out of equilibrium the conduction has been observed to display glassy dynamics. A model developed recently to explain such experiments showed some shortcomings in the light of newer experiments. Some possible causes for this failure are being discussed. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Helping elementary preservice teachers learn to use curriculum materials for effective science teaching
Authors: Schwarz Christina V. , Gunckel Kristin L. , Smith Ed L. , Covitt Beth A. , Bae Minjung , Enfield Mark , Tsurusaki Blakely K.
Published: February 2008

Curriculum analysis, modification, and enactment are core components of teacher practice. Beginning teachers rely heavily on curriculum materials that are often of poor quality to guide their practice. As a result, we argue that preservice teachers need to learn how to use curriculum materials for effective teaching. To address this concern, the authors conducted a study in which three teacher educators taught elementary science methods courses incorporating a major focus on curriculum analysis and modification based on Project 2061 Instructional Analysis Criteria. Analysis of pre–post assessments, classroom artifacts, classroom dialogue, and postcourse interviews indicated that preservice teachers accurately applied and appropriated a modest set of criteria whose intended meanings most closely matched their own understandings, were most closely aligned with their own goals and criteria, or were made accessible through systematic use and attention within the methods sections. However, many did not find the materials analysis criteria useful or comprehensible and based their curricular decisions on their own criteria. Furthermore, some preservice teachers resisted engaging in these practices that may have seemed too analytical, inauthentic, and destabilizing. These findings pointed us toward a revised theoretical framework and new approaches to better support preservice teachers' effective participation with curriculum materials. © 2008 Wiley Periodicals, Inc. Sci Ed 92:345–377, 2008
Impact of mis‐specification of the treatment model on estimates from a marginal structural model
Authors: Lefebvre Geneviève , Delaney Joseph A. C. , Platt Robert W.
Published: February 2008

Inverse probability of treatment weighted (IPTW) estimation for marginal structural models (MSMs) requires the specification of a nuisance model describing the conditional relationship between treatment allocation and confounders. However, there is still limited information on the best strategy for building these treatment models in practice. We developed a series of simulations to systematically determine the effect of including different types of candidate variables in such models. We explored the performance of IPTW estimators across several scenarios of increasing complexity, including one designed to mimic the complexity typically seen in large pharmacoepidemiologic studies.

Our results show that including pure predictors of treatment (i.e. not confounders) in treatment models can lead to estimators that are biased and highly variable, particularly in the context of small samples. The bias and mean‐squared error of the MSM‐based IPTW estimator increase as the complexity of the problem increases. The performance of the estimator is improved by either increasing the sample size or using only variables related to the outcome to develop the treatment model. Estimates of treatment effect based on the true model for the probability of treatment are asymptotically unbiased.

We recommend including only pure risk factors and confounders in the treatment model when developing an IPTW‐based MSM. Copyright © 2008 John Wiley & Sons, Ltd.
Seilverspanntes Portal am McCormick Place in Chicago
Authors: Michalowsky Wolfgang , Stephan Sören , Stief Udo
Published: February 2008

McCormick Place in Chicago, Illinois, ist das größte Tagungs‐ und Kongresszentrum in den USA und das drittgrößte weltweit. Am Südeingang zu diesem Kongresszentrum wurde das hier beschriebene Eingangsportal errichtet. Der eigenwillige Entwurf und die Spannweite von 55 m bei einer Höhe von 17 m stellten eine reizvolle Aufgabe für Berechnung, Konstruktion und Montage dar. Im Beitrag konzentrieren sich die Autoren auf eine Beschreibung des Projektes und gehen dabei auf die besonderen Problemlösungen ein, die sich aus der 3D‐Modellierung der seilverspannten Konstruktion, der Windeinwirkung und der Montage ergaben.
Theories about the formation of lineage system since the Song and Ming dynasties
Authors: Jianhua CHANG
Published: February 2008

The discussion of the formation of patriarchal lineage system since the Song and Ming dynasties can be divided by the turn of 1980s and 1990s. The earlier period research is rationalized by four theories under the perspective of feudal society: the theory of village commune, the theory of lineage authority, the theory of patriarchal thought, and the theory of the restriction of land relations. The theoretical breakthroughs of the latter focused on the lineage’s popularization, “three changes” of the kinship organization and the social vicissitude, the national identity, the lineage’s community-compactization, and the generalized analysis on the reason of patriarchal lineage’s formation.
Streptococcus suisinfection in Hong Kong: an emerging infectious disease?
Authors: MA E. , CHUNG P. H. , SO T. , WONG L. , CHOI K. M. , CHEUNG D. T. , KAM K. M. , CHUANG S. K. , TSANG T. ,   on behalf of the Collaborative Study Group on Streptococcus suis infection in Hong Kong
Published: February 2008

We conducted a 31-month retrospective review of all laboratory-confirmedStreptococcus suisinfections admitted to public hospitals in Hong Kong. Strain identification, serotyping and antibiotic susceptibility tests were conducted onS. suisisolates. Twenty-one sporadic cases were identified, comprising 18 (86%) males and 3 (14%) females. About half were patients aged ⩾65 years. More cases occurred during summer. Occupational exposure was documented in five (24%) cases. The estimated annual incidence was 0·09/100 000 in the general population and 32/100 000 in people with occupational exposure to pigs and raw pork. The primary clinical manifestations were meningitis (48%), septicaemia (38%) and endocarditis (14%). The case-fatality rate was 5%. All available isolates from 15 patients were serotype 2, sensitive to penicillin, ampicillin, ceftriaxone, but resistant to tetracycline. Injury prevention and proper handling of pigs or raw pork should be advocated to both at-risk occupational groups and the general population.
Tsunami detection by satellite altimetry
Authors: Okal Emile A. , Piatanesi Alessio , Heinrich Philippe
Published: February 2008

We present what is to our knowledge the first direct observation of the deformation of the surface of the ocean upon passage of a tsunami wave, on the high seas, far from the influence of shorelines and continental shelves. We use satellite altimetry data from the ERS‐1 and TOPEX/POSEIDON programs, complemented by spectrogram techniques and synthetic maregrams to examine the case of seven recent tsunamigenic earthquakes. We make a positive identification of the tsunami wave field in the case of the 1992 Nicaraguan tsunami, which we detect at 15°S, 106°W, five hours after origin time. We model the observed spectrogram by injecting a synthetic of variable amplitude into the signal of a repetitive cycle of the satellite along the same track, concluding that the Nicaraguan tsunami had a zero‐to‐peak amplitude of 8 cm in that region. In the case of the 1995 Chilean tsunami, a large scatter in the spectral properties of the reference tracks renders the detection tentative. We fail to detect the tsunamis of five other large events, including the 1996 Biak and 1996 Peru earthquakes, primarily on account of unfavorable source directivity in the geometry of existing satellite tracks, and of the strong and incoherent noise produced by large current systems, such as the Kuroshio in the Northwest Pacific.
Origin of ocean island basalts: A new model based on lead and helium isotope systematics
Authors: Kamber Balz S. , Collerson Kenneth D.
Published: February 2008

Current models of ocean island basalt (OIB) Pb isotope systematics based on longterm isolation of recycled oceanic crust (with or without sediment) are not supported by solutions to both terrestrial Pb paradoxes. It follows that the linear arrays of OIB data in Pb isotope diagrams are mixing lines and have no age significance. A new model is presented that takes into account current solutions to both terrestrial Pb paradoxes and that explains combined Pb and He isotope evidence in terms of binary mixing. The key feature of this model is a two‐stage evolution: first, long‐term separation of depleted mantle from undepleted lowermost lower mantle. Mixing between these two reservoirs results in the wide spread in 207Pb/204Pb ratios and generally high (but variable) 3He/4He ratios that typify enriched mantle 1 (EM1) OIBs. The second stage involves metasomatism of depleted upper mantle by EM1 type, lowermost mantle‐derived melts. Evolution in the metasomatized environment is characterized by variable but generally high (Th+U)/(Pb+He) ratio that leads to a rapid increase in 208Pb/204Pb and 206Pb/204Pb ratios and decrease in 3He/4He. Mixing between depleted mantle and melts from metasomatized mantle portions reproduces the characteristics of high μ (HIMU) OIBs. The Sr versus Nd isotope array is compatible with binary mixing between depleted mantle and near‐chondritic lowermost mantle because of the large variation in Sr/Nd ratios observed in EM1 and HIMU OIBs. OIBs contaminated by subcontinental lithospheric mantle (EM2) exhibit more complex isotope systematics that mask their primary geochemical evolution.
Modeling the evolution of meso‐scale ionospheric irregularites at high latitudes
Authors: Sojka J. J. , Zhu L. , David M. , Schunk R. W.
Published: February 2008

The modeling of ionospheric plasma density irregularities (ΔN/N) is a necessary first step towards forecasting ionospheric scintillation effects. This modeling challenge is difficult not only because the linear‐nonlinear saturation levels of instabilities are not completely understood but also because ΔN/N often evolves on time scales which are long compared to the characteristic time constants of the instability drivers. In this study, the linear 1‐D gradient drift instability (GDI) is used in a high latitude simulation of ΔN/N evolution. For the first time snapshots (maps) of ΔN/N are presented demonstrating that it is possible to use a physical model simulation of the ionosphere coupled with a time dependent convection electric field to simulate meso‐scale irregularities. It is found that to evaluate the density irregularity in any given location, it is not sufficient to know the instantaneous growth rate; it is necessary to follow the history of the plasma along the convection streamlines.
The role of rift zone storage in controlling the site and timing of eruptions and intrusions of Kilauea Volcano, Hawaii
Authors: Parfitt Elisabeth A.
Published: February 2008

Repeated eruptive and intrusive activity on the East Rift Zone of Kilauea volcano allows dikes to exist within the rift zone for extended periods of time. Leakage of magma from the summit storage region into the rift zone can cause inflation of a rift zone dike. Inflation raises the excess pressure at the dike centre and increases the stress intensity at the dike edges. If the inflation is sufficiently large, the stress intensity may exceed the fracture toughness of the country rocks and allow vertical or lateral dike emplacement to occur. Theoretical modelling can be used to predict the conditions under which vertical or lateral dike propagation and hence eruptive or intrusive activity may occur. Over typical ranges of dike half height and regional tension gradient, vertical propagation and hence eruption are favored by high fracture toughness, relatively low dike half heights, and low regional tension gradients. Lateral propagation can occur when the fracture toughness is low, when dike half height is higher, and when the regional tension gradient is high. The results of from the model constrain the fracture toughness within the East Rift Zone to be 100–110 MPa m½ and the regional tension gradient to be ≪ 1000 Pa/m.
Determination of Saharan dust radiance and chlorophyll from CZCS imagery
Authors: Carder K. L. , Gregg W. W. , Costello D. K. , Haddad K. , Prospero J. M.
Published: February 2008

An atmospheric correction algorithm is derived for oceanic areas of low chlorophyll a plus phaeophytin a concentrations (〈C〉 ≤ 0.25 mg/m3). The algorithm simultaneously corrects for the radiance effects of two different aerosol types observed in coastal zone color scanner (CZCS) imagery. The algorithm, called the two‐component method, is applied to data from a time series of CZCS orbits during which both Saharan dust and a bluish haze were present. The method is evaluated by comparing the ocean chlorophyll concentrations after atmospheric correction to those measured in situ and to those determined by single‐component methods from CZCS imagery. Reasonable agreement is found between the chlorophyll values estimated by the two‐component method and in situ values, and the derived chlorophyll values for a Sargasso Sea region varied by less than 6% during a major influx of Saharan dust to the region. Aerosol and chlorophyll fields appeared confounded in imagery derived using single‐component methods when multiple aerosol types were present, but no confounding was observed for imagery generated by the two‐component method. The time series of aerosol radiance values due to Saharan dust was consistent with the changes in dust concentration and particle size measurements from an adjacent aerosol collection site on the Florida coast.
Nonresonant absorption of shear AlfvÉn waves
Authors: Strauss H. R.
Published: February 2008

Resonant absorption of shear Alfvén waves is thought to be a likely candidate to explain heating of the solar corona and acceleration of the solar wind. A difficulty with the theory is that the absorption process is slow. It takes a long time ∼ S⅓τA, where S ≫ 1 is the magnetic Reynolds number, and τA a typical Alfvén wave propagation time, for wave fronts to steepen sufficiently for absorption to occur. Moreover, heating occurs in a very thin layer whose width scales as S−⅓. A faster absorption mechanism is nonresonant absorption by compressional viscosity, in a curved magnetic field. Heating is nonresonant and is not localized to a narrow layer. The effect could be quite important where the solar coronal magnetic field is strongly curved, in the chromosphere. It could also be important on open field lines in the upper corona, where the compressional viscosity is large. It might imply that a significant part of outgoing Alfvén waves are absorbed in the corona.
Measurement of the volatile component in particles emitted from an ice/dust mixture
Authors: Mauersberger K. , Michel H.‐J. , Krankowsky D. , Lämmerzahl P. , Hesselbarth P.
Published: February 2008

A set of novel instruments has been developed to measure the volatile component of solid particles emitted from the surface of an insolated ice/dust mixture (“sample”). To detect such particles a pressure gauge is mounted inside a volume which has a narrow tube placed on top for particles to enter. The experiments are positioned about 0.5 m away from and below the sample. Particles, after falling through the tube are collected in a heated cup, ices evaporate and produce a gas pulse inside the volume. The pressure, registered by the gauge, will decrease with a time constant of about 0.4 s. In some instruments the single cup is replaced by a multiple cup collector. In recent comet simulation experiments (KOSI 5 and KOSI 6) with ice/dust mixtures over 1200 gas pulses were observed. They fall into two categories: (a) short pressure pulses with a fast rising amplitude followed by the expected exponential decay, and (b) long pulses with rise times of about one second and several tens of seconds decay times. The former pulses are associated with ice particles, whereas the latter pulses are attributed to skeleton silicate grain agglomerates which have ice imbedded in them. The estimated mass distribution ranges from 2 × 10−10 g to 10−5 g of volatile material. Ice particles are emitted at maximum rate immediately at turn‐on of the artificial sun and drop to much lower frequencies within less than one hour. “Mineral” particles, in contrast, reach their maximum frequency later, with their abundance also decreasing but less pronounced. Since gas emission varies very little while the ice particle frequency drops rapidly, it appears that the particle rate is not controlled by the gas flux's drag force, but by the availability of particles suited for acceleration at the surface of the sample.
Evidence of anisotropic temperatures of molecular ions in the auroral ionsphere
Authors: Lathuillere C. , Hubert D. , La Hoz C. , Kofman W.
Published: February 2008

Using incoherent scatter measurements obtained from Kiruna and Sodankylä EISCAT remote stations, and corresponding to different aspect angles, we show, for the first time, anisotropic temperatures of molecular ions. The electric field obtained for the 5 hours period of the 2nd February 1990 experiment presented here range from 20 to 50 mV/m. We show that the line of sight ion temperature deduced from Kiruna incoherent scatter spectra is larger than the one deduced from Sodankylä spectra which correspond to a smaller aspect angle. A statistical approach has been chosen to evaluate a βs parameter for Sodankylä measurements which describes the anisotropy. We found a value of 0.60 ± 0.02 which compares very well with values inferred from theoretical studies.
On the temperature dependence of polar stratospheric clouds
Authors: Fiocco Giorgio , Fuà Daniele , Cacciani Marco , Girolamo Paolo Di , De Luisi John
Published: February 2008

Polar stratospheric clouds were frequently observed by lidar at the Amundsen‐Scott South Pole Station during May–October 1988. The dependence of the bakscattering cross section on the temperature can be referred to transitions of the HNO3/H2O system: it appears possible to distinguish the pure trihydrate from the mixed ice‐trihydrate phase in the composition of the aerosol and, in some cases, to bracket the HNO3 and H2O content of the ambient gas, and to provide indications on the size of the particles.
The Jovian ionospheric E region
Authors: Kim Y. H. , Fox J. L.
Published: February 2008

We have constructed a model of the Jovian ionosphere that includes direct photoionization of hydrocarbon molecules. A high resolution solar spectrum was synthesized from Hinteregger's solar maximum spectrum (F79050N) and high resolution cross sections for photoabsorption by H2 bands in the range 842 to 1116 Å were constructed. Two strong solar lines and about 30% of the continuum flux between 912 and 1116 Å penetrate below the methane homopause despite strong absorption by CH4 and H2. We find that hydrocarbons (mainly C2H2) are ionized at a maximum rate of 55 cm−3 sec−1 at 320 km above the ammonia cloud tops. The hydrocarbon ions produced are quickly converted to more complex hydrocarbon ions through reactions with CH4, C2H2, C2H6, and C2C4. We find that a hydrocarbon ion layer is formed near 320 km that is about 50 km wide with a peak density in excess of 1 × 104 cm−3.
Dust emission of mineral/ice mixtures: residue structure and dynamical parameters
Authors: Thiel K. , Kölzer G. , Kohl H.
Published: February 2008

In a series of experiments the particle emission from ice/dust mixtures under insolation at space conditions was investigated using an array of particle collectors and Piezo impact detectors. The dust data provide an estimate of the ratio of ice containing to ice free particles for different size ranges, indicating a decrease in the frequency of ice free particles with increasing particle size. The measurement of the main dynamical parameters of the particle emission reveals a significant interrelation of particle size, starting angle and velocity of the emission process. The near surface particle stream exhibits an internal structure of a low‐speed central core of large grains superimposed by a high‐speed background of small grains. Possible implications for the dynamics of a dust jet emanating from a comet nucleus are discussed.
The reaction of gaseous N2O5 with solid NaCl at 298 K: Estimated lower limit to the reaction probability and its potential role in tropospheric and stratospheric chemistry
Authors: Livingston F. E. , Finlayson‐Pitts B. J.
Published: February 2008

Gaseous N2O5/air mixtures were flowed over solid NaCl at 298 K and the gaseous product ClNO2 measured using FTIR. With excess NaCl, one ClNO2 was produced per N2O5 in the initial mixture, and from the contact time between N2O5 and the salt, a lower limit to the fraction of collisions leading to reaction was estimated to be 2.5 × 10−3. This reaction is sufficiently rapid that it may lead to the formation of ppb levels of ClNO2 overnight in polluted marine urban areas. The ClNO2 will photolyze at dawn to give chlorine atoms which initiate the photooxidation of organics in a manner analogous to OH. This reaction may also play a role in remote Arctic chemistry if the reaction is significantly faster than our lower limit. This supports the hypothesis of Michelangeli et al. (1990) that the N2O5(g) + NaCl(s) reaction may contribute significantly to stratospheric chemistry after the eruption of alkalic volcanoes such as El Chichon.
Dual polarization radar observation of thunderclouds on the coast of the Sea of Japan in the winter season
Authors: Fukao Shoichiro , Maekawa Yasuyuki , Sonoi Yasuo , Yoshino Fumio
Published: February 2008

A C‐band dual polarization radar has observed wintertime thunderclouds peculiar to the coast area of the Sea of Japan. At the moment of lightning, graupel identified by low ZDR and high ZH is seen to be rapidly lifted up to 3 km height, corresponding to the −10°C level. In addition, the graupel encounters small ice crystals with high ZDR and low ZH above this height. This situation satisfies the recent thunderstorm electrification theory. The PPI radar display reveals a band‐like structure for this type of wintertime thunderclouds. In this structure, the small ice crystals are primarily seen on the windward side of the clouds. Part of the ice crystals mixed with the graupel seems to be brought from the back of an adjacent cloud, which precedes the thundercloud carrying the graupel.
Asymmetries in the location of the Venus and Mars bow shock
Authors: Zhang T‐L. , Schwingenschuh K. , Russell C. T. , Luhmann J. G.
Published: February 2008

An examination of observations of the position of the terminator bow shock at Venus and Mars shows that the terminator bow shock varies with the angle between the local bow shock normal and the upstream magnetic field, θBN. The part of the shock on the quasi‐parallel side is closer to the planet than the part on the quasi‐perpendicular side, a result which had been suggested by an earlier computer simulation by Thomas and Winske [1990]. This bow shock asymmetry is observed to be larger at Mars than at Venus.
Changes in the solar forced tides caused by stratospheric ozone depletion
Authors: Ross Martin N. , Walterscheid Richard L.
Published: February 2008

Depletion of stratospheric ozone by anthropogenic trace gases reduces the thermal forcing of the solar‐driven atmospheric tides. We examine changes that have occurred in the diurnal and semidiurnal upward propagating tides since the onset of stratospheric ozone depletion. Estimated reductions in tide amplitudes since circa 1960 vary among the different modes but are generally less than about 10%. The most accurate measure of tidal strength for the main symmetric semidiurnal mode, the tropical semidiurnal surface pressure oscillation, has decreased about 3% since the beginning of ozone depletion, an amount that might be detected in the barometric record. Reductions in upper atmospheric tidal momentum fluxes are generally less than about 20%. The amplitudes of the solar forced tides will continue to decrease as ozone depletion continues.
Polarization of Jovian hectometric emission
Authors: Ortega‐Molina Arturo , Lecacheux Alain
Published: February 2008

We have studied the polarization properties of the Jovian hectometric (HOM) emission observed in the low‐frequency band 1.2–1326 kHz by the planetary radio astronomy (PRA) experiment aboard the Voyager spacecraft. We have shown that the complex morphology of HOM can be explained by simultaneous radiations from two independent 100% oppositely polarized sources. Analysis of data recorded under different antenna‐source configurations indicates that the existence of a linear component in HOM is very unlikely. We show that the apparent degree of circular polarization measured by the PRA instrument, which practically ranges from −1 to +1, is the result of fluctuations in the relative intensities of the two HOM circular components. The observed distribution of the degree of circular polarization is accurately reproduced by assuming that the intensity distribution of each individual HOM circular component follows an exponentially decreasing probability law. The emission mode, source location, and beaming of the HOM components are inferred from the polarization properties of the emission. A global model for the hectometric and decametric (DAM) Jovian emissions in which the left and right HOM components are identified with the left and right non‐Io DAM components, respectively, is outlined.
Langmuir wave growth and electron bunching: Results from a wave‐particle correlator
Authors: Ergun R. E. , Carlson C. W. , McFadden J. P. , Clemmons J. H. , Boehm M. H.
Published: February 2008

Recent measurements of auroral electrons and intense Langmuir waves on a high‐altitude sounding rocket show that these waves were produced by dispersive bursts of low‐energy electrons. The sounding rocket was launched northward into the evening auroral zone during a substorm expansion and crossed several discrete auroral arcs having electron energy peaks greater than 25 keV. The large‐amplitude Langmuir waves, which appeared in ∼ 100‐ms bursts and had amplitudes greater than 200 mV/m, were seen only during periods of enhanced low‐energy (0.3–3.0 keV), field‐aligned electron precipitation. The enhanced electron flux displayed a dispersive signature in which the higher‐energy electrons arrived before the lower‐energy electrons. A wave‐particle correlator, a new instrument that performed a direct correlation of the arrival times of electrons with the phase of the high‐frequency wave field, detected electron bunching at the wave frequency during the bursts of intense Langmuir waves. The electron bunching events, which had amplitudes of a few percent, provided a direct identification of the energy (velocity) of the resonant electrons and therefore established the parallel wavelength (∼15 m). The electron bunching events were detected at or near the energy at which a positive slope in the electron distribution function was seen. During a dispersive burst, the phase velocity (or wavelength) of the Langmuir waves changed in response to the changing velocity at which the positive slope occurred. We conclude that the velocity dispersion in the low‐energy, field‐aligned electrons created the unstable electron distribution that was responsible for Langmuir wave growth. The proposed growth mechanism is similar to that suggested for Langmuir wave growth during solar type III radio bursts.
Quasi‐perpendicular/quasi‐parallel divisions of Earth's bow shock
Authors: Greenstadt E. W.
Published: February 2008

Computer‐drawn diagrams of the boundaries between quasi‐perpendicular and quasi‐parallel areas of Earth's bow shock are displayed for a few selected cone angles of static interplanetary magnetic field (IMF). The effect on the boundary of variable IMF in the foreshock is also discussed and shown for one nominal case. The boundaries demand caution in applying them to the realistic, dynamic conditions of the solar wind and in interpreting the effects of small cone angles on the distributions of structures at the shock. However, the calculated, first‐order boundaries are helpful in defining areas of the shock where contributions from active structures inherent in quasi‐parallel geometry may be distinguishable from those derived secondarily from upstream reflected ion dynamics. The boundaries are also compatible with known behavior of daytime ULF geomagnetic waves and pulsations according to models postulating that cone angle‐controlled, time‐dependent ULF activity around the subsolar point of the bow shock provides the source of geomagnetic excitation.
World Day observations at Arecibo: 1985 to 1989
Authors: Burnside R. G. , Tepley C. A. , Sulzer M. P.
Published: February 2008

In the past 5 years, simultaneous incoherent scatter and optical observations have been obtained at Arecibo, Puerto Rico, during fourteen World Day campaigns with an average duration of 3 or more days. Here we present the period average values of important F layer parameters such as the peak electron density and the height of the layer peak. We have compared our electron density measurements with those given by the international reference ionosphere and generally find a reasonable agreement. The meridional neutral wind velocity is calculated for a height of 300 km from the incoherent scatter measurements. The period average values of the vertical gradient in the meridional wind velocity is derived. A maximum positive gradient in this quantity and the vertical gradient in the vertical ion velocity are found to occur near to 0600 AST in most of the months we have examined. We find that these vertical gradients are some three times larger for solar cycle minimum conditions than they are at solar cycle maximum. This is a new result that, as far as we are aware, has not been reported before. The period average values of the southward and eastward ion velocities are also derived from the measured radar line‐of‐sight velocities and show no obvious solar cycle dependence. We have used an ion energy balance method to infer atomic oxygen densities and exospheric temperatures at Arecibo. The temperatures show a fair agreement with the mass spectrometer/incoherent scatter model. The neutral densities also agree fairly well for all the years up to 1989 but then are consistently less than those predicted by the model.
Different FTE signatures generated by the bursty single X line reconnection and the multiple X line reconnection at the dayside magnetopause
Authors: Ding D. Q. , Lee L. C. , Ma Z. W.
Published: February 2008

Magnetic signatures associated with the time‐dependent magnetic reconnection processes at the dayside magnetopause are studied based on two‐dimensional compressible MHD simulations. In the simulations, magnetic and plasma signatures resemblant to the observed flux transfer events (FTEs) can be generated either by the magnetic bulges formed during the bursty single X line reconnection (BSXR) or by the magnetic islands (flux tubes) formed during the multiple X line reconnection (MXR). It is found that the FTE magnetic signatures are not exhibited on the magnetospheric side if the FTEs are due to the BSXR process and Bm/Bs ≥ 1.7, where Bm and Bs are the magnetic field strength in the magnetosheath and in the magnetosphere, respectively. On the other hand, the bipolar FTE signatures can be detected on both the magnetosphere and magnetosheath sides if the FTEs are caused by the MXR process and Bm/Bs ≤ 2.6. When Bm/Bs > 2.6, the bipolar FTE signatures in the magnetosphere site become too small to be detected even if magnetic islands are formed during the MXR process. Furthermore, for Bm/Bs > 1, the region for the detection of FTE signatures in the magnetospheric side is smaller than that in the magnetosheath side. Since at the dayside magnetopause the typical value of Bm/Bs is 1–3, the simulation results indicate that more FTE signatures can be detected in the magnetosheath side than in the magnetosphere. It is also found that the MXR process often generates a clear bipolar Bn signature while the BSXR process tends to produce FTEs with a monopolar Bn signature near the reconnection region and a highly asymmetric bipolar Bn signature away from the reconnection region.
On the spatial relationship between lightning discharges and propagation paths of perturbed subionospheric VLF/LF signals
Authors: Yip Wai‐Yeung , Inan Umran S. , Orville Richard E.
Published: February 2008

A study has been made of the spatial relationship between propagation paths of subionospheric VLF/LF signals exhibiting sudden amplitude perturbations (Trimpi events) and time correlated cloud‐to‐ground lightning flashes. On each of the 4 days examined the storm centers were located close to the signal path from the NAU transmitter (28.5‐kHz) in Puerto Rico to Stanford (SU) and were at large distances from the propagation path of the 48.5‐kHz transmitter signal from Nebraska to SU. Nevertheless, no Trimpi events were observed on the former path, while many were seen on the latter. Furthermore, the detected Trimpi perturbations of the 48.5‐kHz signal received at Stanford were found to be associated with the lightning activity in the distant storm centers. Since the NAU‐SU path lies entirely at L < 2 and the 48.5‐SU path is located mostly at 2 < L < 3, the L dependent magnetospheric conditions which determine the level of lightning‐induced electron precipitation are different along the two paths. Thus we postulate that the observed difference in Trimpi occurrence on the two paths was due to the different magnetospheric conditions. Hence the occurrence of Trimpi events over the geographical region corresponding to L < 3 may be more dominantly controlled by magnetospheric conditions than the source lightning distribution.
Mean zonal acceleration and heating of the 70‐ to 100‐km region
Authors: Miyahara S. , Portnyagin Yu. I. , Forbes J. M. , Solovjeva T. V.
Published: February 2008

The dynamical interactions which occur in the atmospheric region around the mesopause (∼90 km) determine the boundary characteristics for the thermospheric region above. A significant data base of radar wind measurements exists which characterizes the global circulation at altitudes between 70 and 110 km. In the present work, using an empirical model of Eulerian‐mean meridional motions based on monthly climatological winds from these radar data, the net vertical motions in this atmospheric regime are derived from the continuity equation. Assuming empirical prescriptions of the mean density and temperature fields, mean heat flux divergences and momentum flux divergences are estimated which exhibit very specific characteristics in the height versus latitude domain for winter, summer, and equinox conditions in both hemispheres. A numerical circulation model including gravity wave/mean flow and tide/mean flow interactions is utilized to examine possible origins of these heat and acceleration sources. At low latitudes (≤30°), it is evident that atmospheric tides represent the primary wave source contribution to zonal mean acceleration and heating of this region of the atmosphere; similarly, at middle and high latitudes (≥30°) below about 90 km, dissipation of vertically propagating gravity waves appears to provide the dominant momentum source for the mean zonal circulation. However, above approximately 90 km and between about 40° and 70° latitude, very significant regions of mean heating and acceleration exist which are not accounted for by the effects of vertically propagating gravity waves and tides. The possible origins of these effects are examined. We suggest that the two most likely candidates to explain these observed features are (1) obliquely propagating gravity waves and/or (2) planetary scale waves.
Simulations of pulsed electron beam injection during active experiments
Authors: Winglee R. M.
Published: February 2008

During electron beam injection the spacecraft can become positively charged, reaching potentials as high as the beam energy, particularly at currents exceeding about 100 mA. After beam turnoff the spacecraft can become negatively charged and the current system around the spacecraft can be strongly modified. The dynamics of such an alternating current system are of particular importance in understanding results from pulsed beam injection. Two‐dimensional electromagnetic particle simulations are used to investigate the characteristics of the spacecraft charging, particle acceleration, and wave emissions during beam injection, turnoff and subsequent pulsing of the beam. It is shown that during beam injection the beam current is neutralized by a spatially separate return current region extending several tens of meters from the beam region, with the currents being closed across the field lines by the perpendicular acceleration of ambient plasma ions into the beam region. After beam turnoff this current system reverses after a time lag of about an ion plasma period. The current reversal is accompanied by (1) prolonged electron collection by the spacecraft near the beam region, (2) preferential ion collection by sections of the spacecraft magnetically connected to the initial return current regions, and (3) the creation of hot plasma extending well into the return current regions. Because of the time lag, the currents induced in the plasma during periodic beam injection can be strongly modified from the imposed beam current. The resultant wave spectrum is dominated by (1) the fundamental pulsing frequency if the pulse frequency ωp is much greater than the ion plasma frequency ωpi, (2) odd harmonics if ωp ≳ ωpi, and (3) even harmonics if ωp ≲ ωpi. This dependence on ωp/ωpi is proposed as the reason for the different spectra during VLF pulsing of an electron beam during the shuttle STS‐3 experiments.
On open and closed field line regions in Tsyganenko's field model and their possible associations with horse collar auroras
Authors: Birn J. , Hones E. W. , Craven J. D. , Frank L. A. , Elphinstone R. D. , Stern D. P.
Published: February 2008

Using the empirical Tsyganenko (1987) long model as a prime example of a magnetospheric field model, we have attempted to identify the boundary between open and closed field lines. We define as “closed” all field lines that are connected with the Earth at both ends and cross the equatorial plane earthward of x = −70RE, the tailward validity limit of the Tsyganenko model. We find that the form of the open/closed boundary at the Earth's surface, identified with the polar cap boundary, can exhibit the arrowhead shape, pointed toward the Sun, observed in “horse collar auroras” (Hones et al., 1989). The “polar cap” size in the Tsyganenko model increases with increasing Kp values, and it becomes rounder and less pointed. The superposition of a net By field, which is the expected consequence of an IMF By, rotates the polar cap pattern and, for larger values, degrades the arrowhead shape, resulting in polar cap configurations consistent with known asymmetries in the aurora. The pointedness of the polar cap shape also diminishes or even completely disappears if the low‐latitude magnetopause is assumed open and located considerably inside of the outermost magnetic flux surface in the Tsyganenko model. The arrowhead shape of the polar cap is found to be associated with a strong increase of Bz from midnight toward the tail flanks, which is observed independently, and is possibly related to the NBZ field‐aligned current system, observed during quiet times and strongly northward IMF Bz. The larger Bz values near the flanks of the tail cause more magnetic flux to close through these regions than through the midnight equatorial region. Since field lines at the flanks primarily map to the dayside polar regions, it becomes plausible that the closed field line region extends to higher latitudes on the dayside than on the nightside, when the increase of Bz becomes more pronounced. By comparison with a different field model we demonstrate that this association is not unique to the Tsyganenko model. The similarity of the quiet symmetric polar cap pattern to “horse collar” auroras suggests that the bright “bars,” observed at the sides of the arrowhead shaped polar cap, are connected with the separatrix layers (or plasma sheet boundary layers) extending to the distant X line or separator, while the adjacent “web” regions, located between the bars and the main auroral oval, are connected with the low‐latitude boundary regions along the flanks of the magnetotail.
Response of the polar cap F region convection direction to changes in the interplanetary magnetic field: Digisonde measurements in northern Greenland
Authors: Cannon Paul S. , Reinisch Bodo W. , Buchau Jurgen , Bullett Terence W.
Published: February 2008

Results of ionospheric drift measurements with a Digisonde 256 digital ionospheric sounder located at Qaanaaq, Greenland (87°N, corrected geomagnetic latitude), are presented. Digisonde drift data have been related to the interplanetary magnetic field (IMF) measured by the IMP 8 satellite for 32 days during 1986, 1987, and 1988. Extremely good statistical agreement between these measurements and convection directions derived from satellite instrumentation is demonstrated when the IMF z component is negative. For Bz negative and By negative the daily average convection direction is centered on −12° (anticlockwise) from the antisunward direction. When Bz is negative but By is positive, the convection direction is centered on +36°. These directions differ by 3° and 9°, respectively, from the models of Heppner and Maynard (1987). The variation about these values is ∼ ±20°. The excellent agreement between the Digisonde measurements and models derived from satellite measurements demonstrates the utility of the Digisonde for making ground‐based measurements of the convection direction in the polar cap F region when Bz is south. The convection directions under conditions of positive Bz have also been examined, and we have measured three types of temporal variation in azimuth, namely, an ordered and slowly (OS) varying change in direction, an ordered and quickly (OQ) varying change in direction, and disordered (D) variations in direction. The latter are believed to result from a breakdown of the analysis technique due to velocity shears in the vicinity of polar cap arcs, and we estimate that they account for ∼25% of the measurements when Bz > 0. When Bz is positive and By is negative, our small subset of OS measurements supports the distorted two‐cell model of Heppner and Maynard (1987). The remainder of the measurements show no well‐defined daily average convection direction or diurnal variation. Likewise for Bz positive and By positive, no well‐defined convection direction can be discerned, nor can any diurnal variation. The existence of OQ variations when Bz > 0 suggests that meaningful average statistical convection patterns may be much harder to synthesize than similar patterns when Bz < 0.