Density Disturbances Research Articles

An investigation of the double layers caused by space vehicles moving through the ionosphere

On the basis of non-steady-state nonlinear coupling equations of high-frequency field, density disturbance and potential, the evolution of double layers in the wake region of space vehicles moving through the ionosphere is numerically simulated in the non-static limit case. The results show that the interactions among plasmas, the vehicle and high-frequency electromagnetic waves radiated from the antenna system of the vehicle can lead to the formation of double layers. It is shown that the double layer is a nonlinear entity-caviton. Potential disturbance far away from the vehicle and the peak value of potential near the vehicle in the double layer are obvious. This is very important for detecting space vehicles with a stealth characteristic and preventing space vehicles from being harmed by double layers.

Amphibian pathogen Batrachochytrium dendrobatidis prevalence is correlated with season and not urbanization in central Virginia

The global amphibian pathogen Batrachochytrium dendrobatidis (Bd) has been documented among many species throughout the United States, though cases of chytridiomycosis, the resulting disease, have occurred mostly on the west coast. We conducted a 2 yr survey of amphibians along an urban gradient in Virginia, U.S.A., to test whether Bd prevalence among the amphibians sampled varied with urbanization and/or season. A total of 867 adult amphibians from 13 species and 49 tadpoles from 3 species were tested for Bd. The level of urbanization was based on surrounding human population density and anthropogenic disturbance. Bd was detected in 6 species. Bd prevalence was not found to vary with increases in urbanization, but did vary with season. Prevalence peaked in the spring at 45%, when temperatures were between 14 and 25 degrees C, and dropped to below 2% in the autumn. Results from this survey support the hypothesis that Bd is endemic to the studied sites in Virginia. The present study, in concurrence with previous research by other investigators, shows that Bd is affected strongly by weather patterns. Urbanization, defined by human population density, appeared to have minimal impact on the prevalence of Bd. In addition to understanding the geographic distribution of Bd, it is important to understand factors that affect its prevalence if we are to develop approaches to managing this emerging disease.

Two‐dimensional frequency domain modeling of lightning EMP‐induced perturbations to VLF transmitter signals

The lightning electromagnetic pulse creates observable modifications to the overlying D region ionosphere, exhibited optically as elves. Recent work, both experimental and theoretical, has shown that elves are accompanied by considerable electron density disturbances of up to a factor of 2 increase in local density. We investigate the possibility that these density disturbances are observed by subionospheric VLF transmitter signals as the so‐called early VLF events. We use a finite difference frequency domain model to simulate the VLF transmitter signal propagating subionospherically to a VLF receiver, under ambient conditions and through a disturbed region. We show that modeled electron density disturbances, consistent with optical observations of elves, yield small but detectable perturbations to the VLF transmitter signal and may explain at least some observed early VLF events. We further show that sequences of in‐cloud lightning pulses, as in spider lightning, may yield considerably higher density disturbances and similarly more prominent VLF transmitter perturbations. In this way, the model herein supports previously reported correlations between sferic bursts and early VLF events.

Substorm-related thermospheric density and wind disturbances derived from CHAMP observations

Abstract. The input of energy and momentum from the magnetosphere is most efficiently coupled into the high latitude ionosphere-thermosphere. The phenomenon we are focusing on here is the magnetospheric substorm. This paper presents substorm related observations of the thermosphere derived from the CHAMP satellite. With its sensitive accelerometer the satellite can measure the air density and zonal winds. Based on a large number of substorm events the average high and low latitude thermospheric response to substorm onsets was deduced. During magnetic substorms the thermospheric density is enhanced first at high latitudes. Then the disturbance travels at an average speed of 650 m/s to lower latitudes, and 3–4 h later the bulge reaches the equator on the night side. Under the influence of the Coriolis force the travelling atmospheric disturbance (TAD) is deflected westward. In accordance with present-day atmospheric models the disturbance zonal wind velocities during substorms are close to zero near the equator before midnight and attain moderate westward velocities after midnight. In general, the wind system is only weakly perturbed (Δvy<20 m/s) by substorms.

Satellite monitoring of anomalous effects in the ionosphere related to the great Wenchuan earthquake of May 12, 2008

In this paper, we present an investigation into plasma density disturbances and electric field perturbations associated with China, Sichuan, Wenchuan earthquake of magnitude M = 7.9 that occurred on May 12, 2008, at 06:28:01 UTC. The DEMETER (Detection of Electromagnetic Emissions Transmitted from Earthquake Regions) satellite was launched on June 29, 2004. The orbit of DEMETER is polar, circular with an altitude of 710 km and its main scientific objective is the study of ionospheric perturbations linked to seismic activity. For satellite orbits near the epicenter region, some ionospheric effects are investigated, which can be considered as possible earthquake precursors. The paper discusses anomalous effects in the ionosphere associated with the Wenchuan earthquake, which cannot be explained by factors of solar-magnetospheric origin. For satellite orbits eight to four days before the main shock, fluctuations in ion density and increase in horizontal and vertical components of electric field are observed near the epicenter. Post-effect is observed too. The observations suggest a coupling between the lithosphere-atmosphere-ionosphere and can be associated with the earthquake growing processes in the lithosphere and troposphere zones above the source. The results of ionospheric anomalous effects are presented and discussed. The results obtained are important because they are observed very near to epicenter.

Obstacle and predator avoidance in a model for flocking

The modeling and investigation of the dynamics and configurations of animal groups is a subject of growing attention. In this paper, we present a deterministic continuum model of flocking and use it to investigate the linearized response of an infinite extent flock to an obstacle or an attacking predator. We show that the steady-state flock response is in the form of density disturbances that resemble Mach cones whose configuration is determined by the anisotropic propagation of waves through the flock. We analytically and numerically test relations that predict the Mach wedge angles, disturbance heights, and wake widths. We find that these expressions are insensitive to many of the parameters of the model.

Scaling Behavior of Electronic Excitations in Assemblies of Molecules with Degenerate Ground States

The behavior of long space-time excitations in many-electron systems with ground state degeneracy is explored via multiscale analysis. The analysis starts with an ansatz for the wave function's dual dependence on the N-electron configuration (i.e., both by direct means and by indirect means via a set of order parameters). It is shown that a Dirac-like equation form of the wave equation emerges in the limit where the ratio epsilon (of the average nearest-neighbor distance to the characteristic length of the long-scale phenomenon of interest) is small. Examples of the long scale are the size of a quantum dot, nanotube, or wavelength of a density disturbance. The velocities in the Dirac-like equation are the transition moments of the single-particle momentum operator connecting degenerate ground states. While detailed band structure and the independent quasi-particle picture could underlie the behavior of some systems (as commonly suggested for graphene), the present scaling law results show it is not necessarily the only explanation. Rather, it can follow from the scaling properties of low-lying, long spatial scale excitations and ground state degeneracy, even in strongly interacting systems. The generality of our findings suggests graphene may be just one of many examples of Dirac-like equation behavior. A preliminary validation of our quantum scaling law for molecular arrays is presented. As our scaling law constitutes a coarse-grained wave equation, path integral or other methods derived from it hold great promise for calibration-free, long-time simulation of many-particle quantum systems.

Riparian vegetation assessment of Cauvery River Basin of South India

The Cauvery river basin of South India has a large phyto-floristic wealth, rightfully enough to constitute a separate phyto-geographic unit. Increase in the anthropogenic pressures within the river basin and surrounding landscapes have persistently stressed the riparian ecosystem structure adversely, besides altering its composition. The objective of this study was to examine the present status of riparian vegetation along the Cauvery river basin, in response to anthropogenic pressures. For vegetation analysis, the riparian forest coming in the middle stretch of Cauvery river was categorized into two zones, viz., forest zone covering ~54km stretch and agroecosystem zone covering ~80km stretch. In each zone, tree species were quantified using transects at 8-km interval. Overall tree species accounting for both forest and agroecosystem were recorded and compared. The results indicate that the mean density and basal area of trees per plot were higher in the forest zone than agroecosystem zone. The Shannon-Weiner diversity of forest zone is 4.6, which is higher than agroecosystem. In addition, species composition indicated a relatively low or poor similarity between the two zones. The vegetation density and site disturbance scores for all the study sites reveals that sand mining and grazing areas have exerted negative impact on riparian forest. The results of the present study clearly brought out the need for preparing and implementing site-specific conservation plans for riparian ecosystem.

Method for studying the spatial-temporal structure of wave-like disturbances in the ionosphere

The method for studying the spatial-temporal structure and propagation characteristics of traveling ionospheric disturbances, using the spectral and cross-correlation analysis of electron density disturbances at different altitudes, obtained with the incoherent scatter radar and vertical sounding ionosonde, is considered. Different algorithms for detecting traveling ionospheric disturbances and calculating the total vector of the disturbance propagation velocity are presented. The results of the method application have been considered in detail, using September 11, 2005, as an example.

Pharmacogenetic Risk Factors for Altered Bone Mineral Density and Body Composition in Pediatric Acute Lymphoblastic Leukemia.

Abstract 3071Poster Board III-8 IntroductionAs the survival of pediatric acute lymphoblastic leukemia (ALL) improves, research on treatment-related morbidity, like disturbance of body composition and bone mineral density (BMD), is required. This study investigates pharmacogenetic risk factors for BMD and body composition in pediatric ALL. MethodsWe determined the influence of SNPs in 4 genes (vitamin-D receptor (VDR: BsmI/ ApaI/ TaqI and Cdx-2/ GATA), collagen type I alpha 1 (SpI), estrogen receptor 1 (ESR1: PvuII/ XbaI) and the glucocorticoid receptor (BclI)) on body composition, BMD and fracture risk during dexamethasone-based pediatric ALL treatment. Anthropometry data of 69 patients (mean age 7.4 (range: 1.6-16.8) year) treated according to the DCOG-ALL9 protocol were evaluated. In patients aged >4 years body composition and BMD of the total body (BMD-TB) and the lumbar spine (BMD-LS) were measured repeatedly using dual energy X-ray absorptiometry. To correct for bone size we calculated bone mineral apparent density of the lumbar spine (BMAD-LS) with the model BMAD-LS = BMD-LS x (4/ (n × width)). All values were expressed as standard deviation scores (SDS). Repeated measurements analysis (ANOVA) was used. ResultsNon-carriers of VDR 5'-end (Cdx-2/ GATA) haplotype 3 revealed a significant larger fat gain than carriers (Δ%fat: non-carriers: +1.76 SDS, carriers: +0.77 SDS, p<0.001). At diagnosis and during therapy, BMD-LS was significant higher in non-carriers of VDR 5'-end (Cdx-2/ GATA) haplotype 3 than in carriers. The other SNPs did not influence BMD or fracture risk during or after treatment. The year after treatment discontinuation, lean body mass increased in non-carriers of ESR1 (PvuII/ XbaI) haplotype 3 and decreased in carriers (Δ lean body mass: non-carriers: +0.28 SDS, carriers: -0.55 SDS, p<0.01). ConclusionThis is the first study investigating the influence of genetic variation of the VDR, COLIA1, ESR1 and GR on body composition, BMD and fracture risk in pediatric ALL. We found the VDR 5'-end (Cdx-2/GATA) haplotype 3 as a protective factor for excessive fat gain during therapy. Moreover, this haplotype 3 of the VDR 5'-promoter was determined as risk factor for a lower BM(A)D-LS at diagnosis that remained during ALL treatment. Carriage of ESR1 (PvuII/XbaI) haplotype 3 negatively influenced recovery of lean body mass after treatment discontinuation. DisclosuresNo relevant conflicts of interest to declare.

Direct observation of the two-phase flow in the air channel of a proton exchange membrane fuel cell and of the effects of a clogging/unclogging sequence on the current density distribution

A small single-channel fuel cell prototype was built with the objective of monitoring the appearance and transport of water droplets in the gas channels in usual operating conditions. It allows the simultaneous observation of droplets and of their local effects on current density. The first results show that the air flow rate seems to control the transition between two different water removal mechanisms: a plug flow when the air stoichiometry is low, with significant disturbances in the local current density, pressure drop and fuel cell performance, and a more conventional flow with steadier removal of smaller droplets when the stoichiometry is higher.

Alteration in Bone Mineral Metabolism in Children with Acute Lymphoblastic Leukemia (ALL): A Review

In recent years there has been a significant increase in event free survival (EFS) and overall survival in children with cancer. As survival rates for childhood cancer have radically improved, late effects associated with the successful but highly intensive chemotherapy and/or radiotherapy have dramatically increased. Many possible late effects of cancer treatment are recognized in pediatric cancer patients as infertility, endocrine deficiency, renal failure, pulmonary and cardiac toxicity, obesity and osteopenia/osteoporosis. Decreased bone mineral density (BMD) and bone metabolism disturbances have been recognized and reported in literature. Osteopenia/osteoporosis skeletal abnormalities, osteonecrosis and pathological fractures are known to occur frequently in childhood acute lymphoblastic leukemia (ALL) at diagnosis, during and after treatment with chemotherapy. Various studies have revealed different metabolic alterations related to ALL. Some suggestions have been made about their relationship with the disease process. Various metabolic abnormalities may be encountered in the newly diagnosed ALL patients. It includes decreased and increased serum levels of calcium and phosphate. Hypercalcemia may result from leukemic infiltrations of bone and release of parathormone like substance from lymphoblast. Elevated serum phosphate can occur as a result of leukemic cell lysis and may induce hypocalcemia. It has been postulated by other authors that leukemic cells may directly infiltrate bone and produce parathroid hormone related peptides, prostaglandin E and osteoblast inhibiting factors. Hypomagnesemia, hypocalcaemia and hypothyroidisum have been demonstrated in patients with ALL. Some patients may have poor nutrition and decreased physical activities during treatment. However postulations have also been made that chemotherapy may play a role in creating metabolic alterations in children with ALL. Corticosteroid, methotraxate and cranial irradiations have all been assumed as a cause of loss of bone mass. Continuing chemotherapy in children with ALL was assumed with normal growth and normal or high collagen turnover and reduced alkaline phosphatase or impaired osteoblastic activity on mineralization of bone. Considering the derangements in bone mineral metabolism in ALL at diagnosis or with chemotherapy, it is imperative that specific attention and therapeutic measures should be considered.DOI: 10.3329/bsmmuj.v1i1.3695 BSMMU J 2008; 1(1): 29-32

Variations in the parameters of scattered signals and the ionosphere connected with plasma modification by high-power radio waves

We describe the results of using the incoherent scatter technique to observe time-altitude variations in regular parameters of the ionospheric plasma and wave disturbances, which accompanied periodic modification of the near-Earth plasma by radio waves emitted by the “Sura” facility. A distinctive feature of the experiments was that the processes in the ionosphere were diagnosed at a distance of about 1000 km from the facility. It was found that the spectrum composition of wave disturbances in the electron density was changing noticeably during the active experiment. Quasi-periodic processes in the ionosphere were observed with a delay of about 40–60 min. The relative amplitude of wave disturbances was equal to 0.02–0.10, and the periods were equal to 30, 60, 120, and 150–180 min. The observed effect can be explained by the generation and/or amplification of traveling ionospheric disturbances. The results of theoretical estimations agree well with the observational data.

DEMETER and DMSP satellite observations of the disturbed H +/O + ratio caused by Earth’s seismic activity in the Sumatra area during December 2004

In the present paper, plasma probe data taken from DEMETER and DMSP-F15 satellites were used to study the ion density and temperature disturbances in the morning topside ionosphere, caused by seismic activity at low latitudes. French DEMETER (Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions) micro-satellite mission had been especially designed to provide global scale observations in the topside ionosphere over seismically active regions. Onboard the DEMETER satellite, the thermal plasma instrument called “Instrument Analyser de Plasma” (IAP) provides ion mass and densities, ion temperature, three component ion drift and ion density irregularities measurements. As a part of “Defense Meteorological Satellite Program”, DMSP-F15 satellite is on orbit operation since 1999. It provides ionospheric plasma diagnostics by means of the “Special Sensor-Ion, Electron and Scintillations” (SSIES-2) instrument. We examined few examples of possible seismic effects in the equatorial ionosphere, probably associated with seismic activity during December month in the area of Sumatra Island, including main shock of giant Sumatra event. It is found that the localized topside ionospheric disturbances appear close to the epicenters of certain earthquakes in the Sumatra region. In two cases, ion H +/O + ratio rises more than one hour before the main shock, due to the O + density decrease at the winter side of the geomagnetic equator, with longitudinally closest location to the epicenter of the earthquakes. These anomalous depletions in O + density do exist in all cases of SSIES-2 data. Particularly for Sumatra main event, more than one hour after the main shock, we observe large-scale depletion in O + density northward of the geomagnetic equator at winter side hemisphere. Associated with O + depletion, ion temperature latitudinal profile around the geomagnetic equator shows enhanced asymmetry with minimum at the summer side and maximum in positive Ti deviation from mean value at the winter side. This disturbance lasted for more than three hours, later in time observed at the same place by IAP/DEMETER.

Spectrum of quasi-wave disturbances in the topside daytime ionosphere according to the data of radiosounding onboard the Intercosmos-19 satellite

Quasi-wave disturbances in the topside daytime ionosphere, related to auroral activity, have been detected using the data of radiosounding onboard the Intercosmos-19 satellite on April 28, 1979. A disturbance was caused by an abrupt enhancement of the eastward electrojet, which was not reflected in the variations in the AE and AU indices. According to the estimates, the period of electron density disturbances was about 0.5 h, the velocity was 350 m/s, and the length along the meridian was several hundreds of kilometers, which corresponds to medium-scale traveling ionospheric disturbances (TIDs). The disturbance amplitude was only 30 km in the hmF2 variations and 0.20–0.25 MHz in the foF2 variations but increased to 0.25–0.30 MHz in the plasma frequency variations at satellite altitudes of 520–580 km with increasing altitude. It is impossible to register so weak short-period variations during ground-based sounding. The method for detecting disturbance spatial characteristics has been proposed. The disturbance spectrum including three quasiperiodic structures has been revealed using this method. The optimal estimates have been made for the trend, described by the polynomial of the third degree, and for the expansion of the residuals in terms of three harmonics.

The effect of Poisson noise on SPH calculations

A simple algorithm is presented which generates a lattice-like, regular spacing of smoothed particle hydrodynamics (SPH) particles in discs, with any prescribed density gradient. Using this for comparison we demonstrate the effect of Poisson noise on SPH estimates of density, pressure and viscous forces when calculated using randomly distributed particles. The standard deviation of density and pressure is typically increased by greater than an order of magnitude. In a disc with a Keplerian velocity profile, the effectiveness of the Balsara switch in reducing the shear component of SPH artificial viscosity is greatly enhanced when the particles are properly spaced, reducing the magnitude of viscosity by two orders of magnitude. Noise problems are exacerbated, not removed, by increasing the numbers of SPH particles, if the number of neighbours used is kept constant. However, comparison of the evolution of a disc created using perfectly spaced particles and a disc with identical parameters but randomly placed particles, reveals very similar results. Although there are subtle differences in the evolution, and the smooth disc takes longer to begin developing structure, in both cases the identical number of objects is created by gravitational collapse. SPH disc simulations do not depend on initial density disturbances to evolve objects by gravitational collapse, which gives added credence to the validity of the results. It also appears that complicated disc settling procedures are unnecessary.

Optical study of prebreakdown cathode processes in deionized water

The initial stage of prebreakdown cathode processes is studied with the help of the shadow method and electrooptical Kerr effect with laser light exposure of ≈ 3 ns. Experiments are performed by using triangular voltage pulses with time rise of ≈ 1 μs, time decay of μ 0.1 μs and total width of < 2 μs. The distance between electrodes 50 mm in diameter is 3 - 5 mm. Field strength varies from 275 kV/cm up to 500 kV/cm. Initial separate optical heterogeneities of size of 50-100 μm are registered at E ≥ 380 kV/cm. Spherical density disturbances with epicenter placed over the cathode are registered when the cathode "bush" reaches the size of ≥ 100 μm. In front of the "bush" the enhancement of electric field exceeding the average field several times in the gap is registered. However, fast discharge is developed from anode. Experiments performed without restriction of voltage pulse duration at E ≈ 300 kV/cm show that within 6 - 8 μs cathode disturbances increase up to the size of 2 - 4 mm and initiate the breakdown. The EHD model of subsonic cathode streamer development is considered.

Observations of the Heating Experiments in the Polar Winter Ionosphere

AbstractAccording to the analysis of the ISR observation data, the heating effects in polar winter ionospheric modification experiments carried out in January 2008 at Tromsø, Norway were studied. A clear disturbance effect is present under the O‐mode over‐dense heating conditions. The enhancement of the electron temperature is up to 60%~120%, extending from 150 km to 400 km. The disturbance of the electron density is not obvious, with a 12% maximum decrease. An 1~2 kHz increase at the acoustic frequency can be observed, and an enhancement in the peak‐to‐valley ratio of the ion line and sometimes its high‐order harmonics can be seen as well. The power of the ion line and plasma line has shown an overshoot effect, single‐humped, double‐humped and triple‐humped structures have appeared in the power profile of plasma line, and the enhancement in power amplitude of the plasma line decreases exponentially as the frequency increases.

Multiscale theory of finite-size Bose systems: Implications for collective and single-particle excitations

Boson droplets (i.e., dense assemblies of bosons at low temperature) are shown to mask a significant amount of single-particle behavior and to manifest collective, droplet-wide excitations. To investigate the balance between single-particle and collective behavior, solutions to the wave equation for a finite size Bose system are constructed in the limit where the ratio $\ensuremath{\epsilon}$ of the average nearest-neighbor boson distance to the size of the droplet or the wavelength of density disturbances is small. In this limit, the lowest order wave function varies smoothly across the system, i.e., is devoid of structure on the scale of the average nearest-neighbor distance. The amplitude of short range structure in the wave function is shown to vanish as a power of $\ensuremath{\epsilon}$ when the interatomic forces are relatively weak. However, there is residual short range structure that increases with the strength of interatomic forces. While the multiscale approach is applied to boson droplets, the methodology is applicable to any finite size Bose system and is shown to be more direct than field theoretic methods. Conclusions for $^{4}\mathrm{He}$ nanodroplets are drawn.

One Analysis on the Rocket Detection of Polar Mesosphere Summer Echoes

利用仅发生极区中层夏季回波 (Polar Mesosphere Summer Echoes, PMSE) 现象时的ECT-02 火箭探空数据, 反演出电子数密度和尘埃电荷数密度. 这些典型的极区中层顶的基本参量为研究PMSE提供了良好的数据基础. 通过分析得出了极区中 层顶区域属于弱电离、弱耦合尘埃等离子体的结论. 根据电子数密度数扰动分析PMSE现象发现, 电子数密度的扰动与PMSE有密切的联系, 扰动强烈的地方回波就强, 扰动弱的地方回波就弱, 或者不发生PMSE 现象.