9,845 research outputs found
Transient intensity changes of cosmic rays beyond the heliospheric termination shock as observed at Voyager 1
This paper continues our studies of temporal variations of cosmic rays beyond the heliospheric termination shock (HTS) using Voyager 1 (V1) data when V1 was beyond 94 AU. This new study utilizes cosmic ray protons and electrons of several energies. Notable transient decreases of 5–50% are observed in galactic cosmic ray nuclei and electrons at V1 shortly after similar decreases are observed at Voyager 2 (V2) still inside the HTS. These decreases at V1 appear to be related to the large solar events in September 2005 and December 2006 and the resulting outward moving interplanetary shock. These two large interplanetary shocks were the largest observed at V2 after V1 crossed the HTS at the end of 2004. They were observed at V2 just inside the HTS at 2006.16 and 2007.43 providing timing markers for V1. From the timing of the intensity decreases observed at V1 as the shocks first reach the HTS and then later reach V1 itself, we can estimate the shock speed beyond the HTS to be between 240 and 300 km s^(−1) in both cases. From the timing of the decreases observed when the shock first reaches the HTS and then several months later encounters the heliopause, we can estimate the heliosheath thickness to be 31 ± 4 and 37 ± 6 AU, respectively, for the two sequences of three decreases seen at V1. These values, along with the distances to the HTS that are determined, give distances from the Sun to the heliopause of 121 ± 4 and 124 ± 6 AU, respectively
At Voyager 1 Starting on about August 25, 2012 at a Distance of 121.7 AU From the Sun, a Sudden Disappearance of Anomalous Cosmic Rays and an Unusually Large Sudden Increase of Galactic Cosmic Ray H and He Nuclei and Electron Occurred
At the Voyager 1 spacecraft in the outer heliosphere, after a series of
complex intensity changes starting at about May 8th, the intensities of both
anomalous cosmic rays (ACR) and galactic cosmic rays (GCR) changed suddenly and
decisively on August 25th (121.7 AU from the Sun). The ACR started the
intensity decrease with an initial e-folding rate of intensity decrease of ~1
day. Within a matter of a few days, the intensity of 1.9-2.7 MeV protons and
helium nuclei had decreased to less than 0.1 of their previous value and after
a few weeks, corresponding to the outward movement of V1 by ~0.1 AU, these
intensities had decreased by factors of at least 300-500 and are now lower than
most estimates of the GCR spectrum for these lower energies and also at higher
energies. The decrease was accompanied by large rigidity dependent anisotropies
in addition to the extraordinary rapidity of the intensity changes. Also on
August 25th the GCR protons, helium and heavier nuclei as well as electrons
increased suddenly with the intensities of electrons reaching levels ~30-50%
higher than observed just one day earlier. This increase for GCR occurred over
~1 day for the lowest rigidity electrons, and several days for the higher
rigidity nuclei of rigidity ~0.5-1.0 GV. After reaching these higher levels the
intensities of the GCR of all energies from 2 to 400 MeV have remained
essentially constant with intensity levels and spectra that may represent the
local GCR. These intensity changes will be presented in more detail in this,
and future articles, as this story unfolds.Comment: 13 Pages, 5 Figure
Termination shock particle spectral features
Spectral features of energetic H ions accelerated at the termination shock may be evidence of two components. At low energies the energy spectrum is ~E^(–1.55), with break at ~0.4 MeV to E^(–2.2). A second component appears above ~1 MeV with a spectrum of E^(–1.27) with a break at ~3.2 MeV. Even though the intensities upstream are highly variable, the same spectral break energies are observed, suggesting that these are durable features of the source spectrum. The acceleration processes for the two components may differ, with the lower energy component serving as the injection source for diffusive shock acceleration of the higher energy component. Alternatively, the spectral features may result from the energy dependence of the diffusion tensor that affects the threshold for diffusive shock acceleration
Voyager observations of galactic and anomalous cosmic rays in the helioshealth
Anomalous cosmic rays display large temporal variations at the time and location where Voyager 1 (V1) crossed the heliospheric termination shock (2004.86) (94AU, 34°N). On a short time scale (3 months) there was a large decrease produced by a series of merged interaction regions (MIR), the first of which was associated with the intense Oct./Nov. 2003 solar events. On a longer time scale there is a remarkable correlation between changes in the galactic cosmic ray (GCR) intensity and those of 10–56 MeV/n ACR He and 30–56 MeV H extending over a 4.3 year period with the GCRs exhibiting their expected behavior over this part of the 11 and 22 year solar activity and heliomagnetic cycle. The relative changes in the ACR and GCR are the same for both the short term and long term variations. The comparative V1/V2 ACR and GCR spectra in the foreshock and heliosheath indicate that at this time most of the higher energy ACRs are not being accelerated near V1 but must have their source region elsewhere — possibly near the equatorial region of the TS as was suggested in our first paper on the TS crossing (1)
Large periodic time variations of termination shock particles between ~0.5-20 mev and 6-14 mev electrons measured by the crs experiment on Voyager 2 as it crossed into the heliosheath in 2007: An example of freshly accelerated cosmic rays?
We have examined features in the structure of the heliosheath using the fine scale time variations of termination shock particles (TSP) between ~0.5 - 20 MeV and electrons between 2.5-14 MeV measured by the CRS instrument as the V2 spacecraft crossed the heliospheric termination shock in 2007. The very disturbed heliosheath at V2 is particularly noteworthy for strong periodic intensity variations of the TSP just after V2 crossed the termination shock (2007.66) reaching a maximum between 2007.75 and 2008.0. A series of 42/21 day periodicities was observed at V2 along with spectral changes of low energy TSP and the acceleration of 6-14 MeV electrons. Evidence is presented for the acceleration of TSP and electrons at the times of the 42/21 day periodicities just after V2 crossed the HTS. Spectra for TSP between 2-20 MeV and electrons between 2.5-14 MeV are derived for three time periods including the time of the HTS crossing. The energy spectra of TSP and electrons at these times of intensity peaks are very similar above ~3 MeV, with exponents of a power law spectrum between -3.0 and -3.6. The ratio of TSP intensities to electron intensities at the same energy is ~500. The electron intensity peaks and minima are generally out of phase with those of nuclei by ~1/2 of a 42 day cycle. These charge dependent intensity differences and the large periodic intensity changes could provide new clues as to a possible acceleration mechanism
Design Methodology for Unmanned Aerial Vehicle (UAV) Team Coordination
Unmanned Aerial Vehicle (UAV) systems, despite having no onboard human pilots, currently
require extensive human involvement to accomplish successful mission operations. Further,
successful operations also require extensive colalboration between mission stakeholders,
including operators, mission commanders, and information consumers (e.g. ground troops relying
on intelligence reports in their area).
Existing UAV system interfaces provide little to no support for collaboration between remote
operators or for operators to collaborate with information consumers. As reliance on UAVs
continues to increase in military and civilian operations, this lack of support for collaboration will
likely become a substantial limitation of existing UAV systems.
In order to introduce effective collaboration support to UAV system interfaces, it is essential to
understand, and be able to derive system design requirements that address, the necessary group
interactions that occur in UAV task enviroments. However, few collaborative requirements
analysis methods exist, and to our knowledge, no method exists that captures design requirements
for collaborative decision making in complex, time-critical environments.
This report describes the development of a new design requirements analysis method for deriving
information and functional requirements that address the collaboration needs of UAV (and other
complex task) operators, and the needs of stakeholders interacting with these operators. More
specifically, theis method extends a recently developed requirements analysis method, called the
Hybrid Cognitive Task Analysis (CTA) method, which enables the generation of information and
functional requirements for futuristic UAV system interfaces. The original Hybrid CTA method
focused on deriving single user system interface requirements. This work extends this method by
introducing analytic steps to identify task and decision-making dependencies between different
UAV operations collaborators.
This collaborative extension to the Hybrid CTA utilizes the notion of boundary objects, an
analytic construct commonly used in the study of group work. Boundary objects are physical or
information artifacts that cross the task boundaries between members of distinct groups.
Identifying boundary objects in complex task operations help the analyst to identify task and
decision-making dependencies between local and remote collaborators. Understanding these
dependencies helps to identify information sharing requirements that the UAV system should
support.
This report describes the analytic steps of the collaborative extension, and provides background
information on the original Hybrid CTA method and the boundary object construct. The report
also describes a project in which the new design requirements method was used to revise a
proposed set of UAV operator displays.Prepared For Boeing Phantom Work
Designing Decision and Collaboration Support Technology for Operators in Multi-UAV Operations Teams
Effective team collaboration and timely decision-making significantly influence the outcome of
time-sensitive military operations. The increasing complexity introduced by the recent move
towards network centric operations (NCO) in U.S. military operations provides additional
challenges for efficient decision-making. Future operations will include co-located and
distributed teams composed of operators from difference services, often at different global
locations. Military operations which require extremely quick decisions, such as operations
dealing with time-sensitive targets (TST) like improvised explosive devices (IEDs), are
particularly challenging in NCO teaming environments. Operators in TST environments not
only have to manage overwhelming amounts of target-related information, but also have the
overhead of communicating and coordinating with co-located and distributed team members.
Given the increasing trend for modern hostile forces to employ unconventional weapons such as
IEDs and suicide bombs, the success of TST operations are becoming critical to current and
future military operations. Providing TST teams with effective tools for communicating and
coordinating their efforts is key to enabling their success.Prepared For Boeing, Phantom Work
Acceptability, feasibility and challenges of implementing an HIV prevention intervention for people living with HIV/AIDS among healthcare providers in Mozambique: Results of a qualitative study
Despite the Mozambique government’s efforts to curb human immunodeficiency virus (HIV)/acquired immune deficiency syndrome (AIDS), national prevalence is 11.5% and support is needed to expand HIV-related services and improve program quality. Positive prevention (PP) programs, which prioritize HIV prevention with people living with HIV and AIDS (PLHIV), have been recognized as an important intervention for preventing new HIV infections. To address this, an evidence-based PP training intervention was implemented with HIV healthcare providers in Mozambique. This study focuses on the acceptability and feasibility of a PP intervention in HIV clinics from the healthcare provider perspective. In depth interviews were conducted with 31 healthcare providers from three provinces who participated in PP trainings in Mozambique. Interview data were coded using content analysis. Study data suggest that healthcare providers found PP acceptable, feasible to implement in their HIV work in clinic settings, and valued this strategy to improve HIV prevention. The PP training also led providers to feel more comfortable counseling their patients about prevention, with a more holistic approach that included HIV testing, treatment and encouraging PLHIV to live positively. While overall acceptance of the PP training was positive, several barriers to feasibility surfaced in the data. Patient-level barriers included resistance to disclosing HIV status due to fear of stigma and discrimination, difficulty negotiating for condom use, difficulty engaging men in testing and treatment, and the effects of poverty on accessing care. Providers also identified work environment barriers including high patient load, time constraints, and frequent staff turnover. Recognizing PP as an important intervention, healthcare providers should be trained to provide comprehensive prevention, care and treatment for PLHIV. Further work is needed to explore the complex social dynamics and cultural challenges such as gender inequalities, stigma and discrimination which hinder the full impact of PP interventions in this context.Keywords: positive prevention, feasibility and acceptability, healthcare provider, HIV/AID
Anomalous cosmic rays in the heliosheath
We report on Voyager 1 and 2 observations of anomalous cosmic rays in the outer heliosphere. The energy spectrum of anomalous cosmic ray helium as each spacecraft crossed the solar wind termination shock into the heliosheath remained modulated. Assuming the intensity gradient between the two spacecraft is purely radial, we find that radial gradients in the heliosheath of He with 11.6–22.3 MeV/nuc and with ∼61–73MeV/nuc∼61–73 MeV/nuc are 4.9±1.2%/AU4.9±1.2%/AU and 0.0±0.5%/AU,0.0±0.5%/AU, respectively. Strong temporal variations of the 11.6–22.3 MeV/nuc He intensity at both spacecraft were observed in 2005 just after Voyager 1 crossed the termination shock and while Voyager 2 was upstream. After 2006.0, the intensity variations are more moderate and likely due to a combination of spatial and temporal variations. As of early 2008, the anomalous cosmic ray He energy spectrum has unfolded to what may be a source spectrum. The spectrum at Voyager 2 remains modulated. We examine three recent models of the origin of anomalous cosmic rays in light of these observations
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