Confronting Observations and Modeling: The Role of the Interstellar Magnetic Field in Voyager 1 and 2 Asymmetries

Magnetic effects are ubiquitous and known to be crucial in space physics and astrophysical media. We have now the opportunity to probe these effects in the outer heliosphere with the two spacecraft Voyager 1 and 2. Voyager 1 crossed, in December 2004, the termination shock and is now in the heliosheath. On August 30, 2007 Voyager 2 crossed the termination shock, providing us for the first time in-situ measurements of the subsonic solar wind in the heliosheath. With the recent in-situ data from Voyager 1 and 2 the numerical models are forced to confront their models with observational data. Our recent results indicate that magnetic effects, in particular the interstellar magnetic field, are very important in the interaction between the solar system and the interstellar medium. We summarize here our recent work that shows that the interstellar magnetic field affects the symmetry of the heliosphere that can be detected by different measurements. We combined radio emission and energetic particle streaming measurements from Voyager 1 and 2 with extensive state-of-the art 3D MHD modeling, to constrain the direction of the local interstellar magnetic field. The orientation derived is a plane ～60°–90° from the galactic plane. This indicates that the field orientation differs from that of a larger scale interstellar magnetic field, thought to parallel the galactic plane. Although it may take 7–12 years for Voyager 2 to leave the heliosheath and enter the pristine interstellar medium, the subsonic flows are immediately sensitive to the shape of the heliopause. The flows measured by Voyager 2 in the heliosheath indicate that the heliopause is being distorted by local interstellar magnetic field with the same orientation as derived previously. As a result of the interstellar magnetic field the solar system is asymmetric being pushed in the southern direction. The presence of hydrogen atoms tend to symmetrize the solutions. We show that with a strong interstellar magnetic field with our most current model that includes hydrogen atoms, the asymmetries are recovered. It remains a challenge for future works with a more complete model, to explain all the observed asymmetries by V1 and V2. We comment on these results and implications of other factors not included in our present model.     

Biodosimetry of heavyions by interphase chromosome painting

We report measurements of chromosomal aberrations in peripheral blood lymphocytes from cancer patients undergoingradiotherapy treatment. Patients with cervix or esophageal cancer were treated with 10 MV X-rays produced at a LINAC accelerator, or high-energy carbon ions produced at the HIMAC accelerator at the National Institute for Radiological Sciences (NIRS) in Chiba. Blood samples were obtained before, during, and after the radiation treatment. Chromosomes were prematurely condensed by incubation in calyculin A. Aberrations in chromosomes 2 and 4 were scored after fluorescence in situ hybridization with whole-chromosome probes. Pre-treatment samples were exposed in vitro to X-rays, individual dose-response curves for the induction of chromosomal aberrations were determined, and used as calibration curves to calculate the effective whole-body dose absorbed during the treatment. This calculated dose, based on the calibration curve relative to the induction of reciprocal exchanges, has a sharp increase after the first few fractions of the treatment, then saturates at high doses. Although carbon ions are 2–3 times more effective than X-rays in tumor sterilization, the effective dose was similar to that of X-ray treatment. However, the frequency of complex-type chromosomal exchanges was much higher for patients treated with carbon ions than X-ray.     

Track segment association, fine-step IMM and initialization with Doppler for improved track performance

In this work we present a new track segment association technique to improve track continuity in large-scale target tracking problems where track breakages are common. A representative airborne early warning (AEW) system scenario, which is a challenging environment due to highly maneuvering targets, close target formations, large measurement errors, long sampling intervals, and low detection probabilities, provides the motivation for the new technique. Previously, a tracker using the interacting multiple model (IMM) estimator combined with an assignment algorithm was shown to be more reliable than a conventional Kalman filter based approach in tracking similar targets but it still yielded track breakages due to the difficult environment. In order to combine the broken track segments and improve track continuity, a new track segment association algorithm using a discrete optimization approach is presented. Simulation results show that track segment association yields significant improvements in mean track life as well as in position, speed, and course rms errors. Also presented is a modified one-point initialization technique with range rate measurements, which are typically ignored by other initialization techniques, and a fine-step IMM estimator, which improves performance in the presence of long revisit intervals. Another aspect that is investigated is the benefit of "deep" (multiframe or N-dimensional, with N > 2) association, which is shown to yield significant benefit in reducing the number of false tracks.     

Genomic instability and tumorigenic induction in immortalized human bronchial epithelial cells by heavy ions

Carcinogenesis is postulated to be a progressive multistage process characterized by an increase in genomic instability and clonal selection with each mutational event endowing a selective growth advantage. Genomic instability as manifested by the amplification of specific gene fragments is common among tumor and transformed cells. In the present study, immortalized human bronchial (BEP2D) cells were irradiated with graded doses of either 1GeV/nucleon ⁵⁶Fe ions or 150 keV/μm alpha particles. Transformed cells developed through a series of successive steps before becoming tumorigenic in nude mice. Tumorigenic cells showed neither ras mutations nor deletion in the p16 tumor suppressor gene. In contrast, they harbored mutations in the p53 gene and over-expressed cyclin D1. Genomic instability among transformed cells at various stage of the carcinogenic process was examined based on frequencies of PALA resistance. Incidence of genomic instability was highest among established tumor cell lines relative to transformed, non-tumorigenic and control cell lines. Treatment of BEP2D cells with a 4 mM dose of the aminothiol WR-1065 significantly reduced their neoplastic transforming response to ⁵⁶Fe particles. This model provides an opportunity to study the cellular and molecular mechanisms involved in malignant transformation of human epithelial cells by heavy ions.     

Observations in the South Atlantic geomagnetic anomaly with intercosmos-Bulgaria-1300 during a geomagnetic storm

The region of South Atlantic Geomagnetic Anomaly (SAGA) was investigated by the Intercosmos-Bulgaria-1300 satellite, launched on August 7, 1981. On the basis of data obtained from 15 orbits during increased geomagnetic activity in August 1981, a map of the Anomaly was elaborated. Two centres of activity were identified. By means of the EMO-5 electrophotometer on board the Intercosmos-Bulgaria-1300 satellite, the atmosphere glow in lines λ 5577 Å, λ 6300 Å and λ 4278 Å was studied.     

Current status and future plans for the general antiparticle spectrometer (GAPS)

We discuss current progress and future plans for the general antiparticle spectrometer experiment (GAPS). GAPS detects antideuterons through the X-rays and pions emitted during the deexcitation of exotic atoms formed when the antideuterons are slowed down and stopped in targets. GAPS provides an exceptionally sensitive means to detect cosmic-ray antideuterons. Cosmic-ray antideuterons can provide indirect evidence for the existence of dark matter in such form as neutralinos or Kaluza–Klein particles. We describe results of accelerator testing of GAPS prototypes, tentative design concepts for a flight GAPS detector, and near-term plans for flying a GAPS prototype on a balloon.     

Implication of multiple dipolarization event near 9 RE for the physics of substorms

In 2001, 2002 and 2003, the Polar spacecraft probed the near equatorial plasma sheet at 9 R_E near local midnight. Using the magnetic field observations, the signatures at substorm onsets are studied. Close to the flux pile-up region, the Polar spacecraft readily detects the dipolarization front, especially for pseudo onsets. An event with two distinct onsets has been examined. The signatures are found to be consistent with the multiple-onset model suggested by Russell [Russell, C.T. How northward turnings of the IMF can lead to substorm expansion onsets. Geophys. Res. Lett. 27, 3257–3259, 2000] which is a modified Near-Earth Neutral Line (NENL) model. Another similar event is also examined showing the effects of different Interplanetary Magnetic Field (IMF) conditions upon substorms. Moreover, ground effects can be very weak compared to in situ observations, especially for pseudo onsets, because these signatures appear to be localized and not global.     

Do we understand the inner magnetotail dynamics during substorms?

Substorm evolution of the near-Earth (|X|<15 R_E) plasma sheet has been emphasized recently because the inner tail is thought to link closely to the substorm auroral activity in the ionosphere during the early stage of substorms. In this paper, we discuss how the inner tail substorm phenomena during the late substorm growth phase and early expansion phase are accounted for by the two prevailing substorm models, namely, the near-Earth neutral line model and the current disruption model. We find that the late growth phase features are more satisfactorily accounted for by the current disruption model than by the near-Earth neutral line model. In addition, detailed observations on current disruption show evidence inconsistent with the proposed idea of dipolarization being due to plasma flow braking from reconnection in the mid-tail region, which poses a difficulty to the near-Earth neutral line model as well.     

Viscoelastic behaviour of pumpkin balloons

The lobes of the NASA ULDB pumpkin-shaped super-pressure balloons are made of a thin polymeric film that shows considerable time-dependent behaviour. A nonlinear viscoelastic model based on experimental measurements has been recently established for this film. This paper presents a simulation of the viscoelastic behaviour of ULDB balloons with the finite element software ABAQUS. First, the standard viscoelastic modelling capabilities available in ABAQUS are examined, but are found of limited accuracy even for the case of simple uniaxial creep tests on ULDB films. Then, a nonlinear viscoelastic constitutive model is implemented by means of a user-defined subroutine. This approach is verified by means of biaxial creep experiments on pressurized cylinders and is found to be accurate provided that the film anisotropy is also included in the model. A preliminary set of predictions for a single lobe of a ULDB is presented at the end of the paper. It indicates that time-dependent effects in a balloon structure can lead to significant stress redistribution and large increases in the transverse strains in the lobes.     

Simulation experiments of the cosmic ray isotope telescope on ETS VI

A computer simulation was carried out to evaluate the basic characteristics of a Δ E×E cosmic ray telescope consisting of 23 solid state detectors including 3 position sensitive detectors with large effective area. Based on the simulation, the geometric factor of the telescope is deduced to be as large as 22.5 cm²sr, almost independent of charge and energy concerned. The energy ranges to be covered by the telescope are, for example, 18–98 MeV/n for Li and 56–339 MeV/n for Fe. By analyzing simulated data, the mass resolution for iron in the overall energy range covered by the telescope is estimated as about 0.22 amu in standard deviation. The expected counting rates and mass-histograms are simulated for Galactic cosmic rays and solar energetic particles.