618 research outputs found
Eyes in the sky: Interactions between AGB winds and the interstellar magnetic field
We aim to examine the role of the interstellar magnetic field in shaping the
extended morphologies of slow dusty winds of Asymptotic Giant-branch (AGB)
stars in an effort to pin-point the origin of so-called eye shaped CSE of three
carbon-rich AGB stars. In addition, we seek to understand if this pre-planetary
nebula (PN) shaping can be responsible for asymmetries observed in PNe.
Hydrodynamical simulations are used to study the effect of typical interstellar
magnetic fields on the free-expanding spherical stellar winds as they sweep up
the local interstellar medium (ISM). The simulations show that typical Galactic
interstellar magnetic fields of 5 to 10 muG, are sufficient to alter the
spherical expanding shells of AGB stars to appear as the characteristic eye
shape revealed by far-infrared observations. The typical sizes of the simulated
eyes are in accordance with the observed physical sizes. However, the eye
shapes are of transient nature. Depending on the stellar and interstellar
conditions they develop after 20,000 to 200,000yrs and last for about 50,000 to
500,000 yrs, assuming that the star is at rest relative to the local
interstellar medium. Once formed the eye shape will develop lateral outflows
parallel to the magnetic field. The "explosion" of a PN in the center of the
eye-shaped dust shell gives rise to an asymmetrical nebula with prominent
inward pointing Rayleigh-Taylor instabilities.
Interstellar magnetic fields can clearly affect the shaping of wind-ISM
interaction shells. The occurrence of the eyes is most strongly influenced by
stellar space motion and ISM density. Observability of this transient phase is
favoured for lines-of-sight perpendicular to the interstellar magnetic field
direction. The simulations indicate that shaping of the pre-PN envelope can
strongly affect the shape and size of PNe.Comment: Accepted for publication in A&A. Final version will contain animated
result
Elliptic flow in transport theory and hydrodynamics
We present a new direct simulation Monte-Carlo method for solving the
relativistic Boltzmann equation. We solve numerically the 2-dimensional
Boltzmann equation using this new algorithm. We find that elliptic flow from
this transport calculation smoothly converges towards the value from ideal
hydrodynamics as the number of collisions per particle increases, as expected
on general theoretical grounds, but in contrast with previous transport
calculations.Comment: 5 pages, 3 figures, revise
Vascular disease in HIV/AIDS patients
Objectives. An ongoing prospective clinical survey to determine the spectrum of vascular disease in HIV/AIDS patients and the risk factors affecting clinical outcome in order to formulate a management protocol for future use.
Methods. Comprehensive screening for risk factors for vascular disease as well as HIV/AIDS-related conditions. Disease pattern and presentation are noted and patients treated accordingly. Vascular emergencies are managed regardless of HIV status because this information is usually not available at the time of presentation. Elective management is based on immune status and risk stratification.
Results. 42 patients tested positive for HIV. The majority of patients presented with occlusive disease (57%), followed by anearysms (21%) and vascular trauma (19%). A variety of vascular surgical procedures were performed on 36 patients. There was no surgical mortality and 10 patients developed complications, including 2 amputations and 7 cases of minor wound sepsis. The 3 patients who received preoperative antiretroviral therapy showed a marked reduction in viral count and a significant improvement in CD4 T-cell count.
Conclusion. Surgery can be safe and effective in HIV-positive patients provided the necessary precautions are taken to reduce surgical morbidity.
(South African Medical Journal: 2002 92(12): 974-977
The Environments around Long-Duration Gamma-Ray Burst Progenitors
Gamma-ray burst (GRB) afterglow observations have allowed us to significantly
constrain the engines producing these energetic explosions. Te redshift and
position information provided by these afterglows have already allowed us to
limit the progenitors of GRBs to only a few models. The afterglows may also
provide another observation that can place further constraints on the GRB
progenitor: measurements telling us about the environments surrounding GRBs.
Current analyses of GRB afterglows suggest that roughly half of long-duration
gamma-ray bursts occur in surroundings with density profiles that are uniform.
We study the constraints placed by this observation on both the classic
``collapsar'' massive star progenitor and its relative, the ``helium-merger''
progenitor. We study several aspects of wind mass-loss and find that our
modifications to the standard Wolf-Rayet mass-loss paradigm are not sufficient
to produce constant density profiles. Although this does not rule out the
standard ``collapsar'' progenitor, it does suggest a deficiency with this
model. We then focus on the He-merger models and find that such progenitors can
fit this particular constraint well. We show how detailed observations can not
only determine the correct progenitor for GRBs, but also allow us to study
binary evolution physics.Comment: 44 pages including 11 figure
The use of an automated flight test management system in the development of a rapid-prototyping flight research facility
An automated flight test management system (ATMS) and its use to develop a rapid-prototyping flight research facility for artificial intelligence (AI) based flight systems concepts are described. The ATMS provides a flight test engineer with a set of tools that assist in flight planning and simulation. This system will be capable of controlling an aircraft during the flight test by performing closed-loop guidance functions, range management, and maneuver-quality monitoring. The rapid-prototyping flight research facility is being developed at the Dryden Flight Research Facility of the NASA Ames Research Center (Ames-Dryden) to provide early flight assessment of emerging AI technology. The facility is being developed as one element of the aircraft automation program which focuses on the qualification and validation of embedded real-time AI-based systems
On the hyperbolicity and causality of the relativistic Euler system under the kinetic equation of state
We show that a pair of conjectures raised in [11] concerning the construction
of normal solutions to the relativistic Boltzmann equation are valid. This
ensures that the results in [11] hold for any range of positive temperatures
and that the relativistic Euler system under the kinetic equation of state is
hyperbolic and the speed of sound cannot overcome .Comment: 6 pages. Abridged version; full version to appear in Commun. Pure
Appl. Ana
Pharmacy fall prevention services for the community-dwelling elderly:Patient engagement and expectations
Medication use is an important risk factor for falls. Community pharmacists should therefore organise fall prevention care; however, little is known about patients' expectations of such services. This qualitative study aims to explore the expectations of community-dwelling older patients regarding fall prevention services provided by community pharmacies. Telephone intakes, followed by three focus groups, were conducted with 17 patients, who were aged ≥75 years, used at least one fall risk-increasing drug (FRID) and were registered at a community pharmacy in Amsterdam, the Netherlands. Some time of the focus groups was spent on playing a game involving knowledge questions and activities to stimulate discussion of topics related to falling. Data were collected between January 2020 and April 2020, and all focus groups were audiotaped and transcribed verbatim. The precaution adoption process model (PAPM) was applied during data analysis. Patients who had already experienced a fall more often mentioned that they took precautions to prevent falling. In general, patients were unaware that their medication use could increase their fall risk. Therefore, they did not expect pharmacists to play a role in fall prevention. However, many patients were interested in deprescribing. Patients also wanted to be informed about which medication could increase fall risk. In conclusion, although patients initially did not see a role for pharmacists in fall prevention, their perception changed when they were informed about the potential fall risk-increasing effects of some medications. Patients expected pharmacists to focus on drug-related interventions to reduce fall risk, such as deprescribing
Community pharmacists' perceptions on providing fall prevention services:A mixed-methods study
Background Pharmacists may contribute to fall prevention particularly by identifying and deprescribing fall risk-increasing drugs (FRIDs) in patients with high fall risk. Objective To assess community pharmacists’ perceptions on providing fall prevention services, and to identify their barriers and facilitators in offering these fall prevention services including deprescribing of FRIDs. Setting A mixed-methods study was conducted with Dutch pharmacists. Method Quantitative (ranking statements on a Likert scale, survey) and qualitative data (semi-structured interviews) were collected. Out of 466 pharmacists who were invited to participate, 313 Dutch pharmacists ranked statements, about providing fall prevention, that were presented during a lecture, and 205 completed a survey. To explore pharmacists’ perceptions in-depth, 16 were interviewed. Quantitative data were analysed using descriptive statistics. All interviews were audiotaped and transcribed verbatim. The capability opportunity motivation-behaviour model was applied to interpret and analyse the findings of qualitative data. Main outcome measure Community pharmacists’ views on providing fall prevention. Results Pharmacists stated that they were motivated to provide fall prevention. They believed they were capable of providing fall prevention by FRID deprescribing. They perceived limited opportunities to contribute. Major barriers included insufficient multidisciplinary collaboration, patient unwillingness to deprescribe FRIDs, and lack of time. Facilitators included goal-setting behaviour, financial compensation, and skilled communication. Conclusion Despite the complex decision-making process in medication-related fall prevention, community pharmacists are motivated and feel capable of providing fall prevention. Opportunities for pharmacists to provide fall prevention services should be enhanced, for example by implementing multidisciplinary agreements. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s11096-021-01277-4
Linking the hydrodynamic and kinetic description of a dissipative relativistic conformal theory
We use the entropy production variational method to associate a one particle
distribution function to the assumed known energy-momentum and entropy currents
describing a relativistic conformal fluid. Assuming a simple form for the
collision operator we find this one particle distribution function explicitly,
and show that this method of linking the hydro and kinetic description is a non
trivial generalization of Grad's ansatz. The resulting constitutive relations
are the same as in the conformal dissipative type theories discussed in J.
Peralta-Ramos and E. Calzetta, Phys. Rev. D {\bfseries 80}, 126002 (2009). Our
results may prove useful in the description of freeze-out in ultrarelativistic
heavy-ion collisions.Comment: v2: 23 pages, no figures, accepted in Phys. Rev.
Integrating Neuroscience in Criminal Law: The Dutch Situation as an Example
Empirical findings demonstrate that neuroscientific expertise is increasingly prevalent in
courtrooms. This suggests that both “territorial conflicts” between law and neuroscience—-
for example about how to conceptualize concepts like culpability—and questions regarding
the integration of neuroscience and law, which both have long been present in theoretical
discussions, are now finding their way to legal practice. As jurisdictions around the globe
differ on multiple dimensions (e.g., on how concepts like culpability are conceptualized,
embedded in legal doctrine, and how integration of neuroscience takes place within (procedural) legal frameworks) analyses on a national level are needed next to universal endeavors. In this article, the Dutch situation will be addressed. First, we will assess whether the
theoretical notions underlying Dutch criminal law are compatible with the theore
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