The time-dependent modulation of galactic cosmic rays in the heliosphere is studied by computing intensities using a time-dependent modulation model. By introducing recent theoretical advances in the ...transport coefficients in the model, computed intensities are compared with
Voyager 1
,
International Monitoring Platform
(IMP)
8
, and
Ulysses
proton observations in search of compatibility. The effect of different modulation parameters on computed intensities is also illustrated. It is shown that this approach produces, on a global scale, realistic cosmic-ray proton intensities along the
Voyager 1
spacecraft trajectory and at Earth up to ≈ 2004, whereafter the computed intensities recover much more slowly towards solar minimum than observed in the inner heliosphere. A modified time dependence in the diffusion coefficients is proposed to improve compatibility with the observations at Earth after ≈ 2004. This modified time dependence led to an improved compatibility between computed intensities and the observations along the
Voyager 1
trajectory and at Earth even after ≈ 2004. An interesting result is that the cosmic-ray modulation during the current polarity cycle is not determined only by changes in the drift coefficient and tilt angle of the wavy current sheet, but is also largely dependent on changes in the diffusion coefficients.
•First detailed CFD model of a hybrid counter/parallel- solar air heater.•Inclusion of a solar load model in contrast to the commonly used constant heat flux boundary condition.•Validation of the CFD ...model.•Experimental and computational discussion of the efficiency of the hybrid solar air heater.
Solar air heaters may be used in a variety of applications such as space heating, pre-heating for industrial applications, drying of various materials and pre-heating for solar water desalinators. This research is aimed at evaluating a unique solar air heater design in terms of its thermal efficiency and temperature distributions within the solar air heater. The solar heater is unique as it combines parallel- and counter flows inside the heater in order to reduce mass and improve overall heat transfer. Current modelling techniques are not suitable to this type of SAH, as they apply to SAHs with simpler geometries, like counterflow heaters or parallel flow heaters. The solar air heater is evaluated using computational fluid dynamics and experiment. The computational models are validated experimentally. The computational models account for the solar load, surface to surface radiation, conduction, convection and turbulence. A screening of turbulence models is performed. The average conversion efficiency ranges between 23% and 83% and the average collector efficiency between 11% and 44%. The thermal efficiency values predicted by the computational models show good agreement with the experimentally derived values. The computational models over-predict the thermal efficiency by between 6.75% and 9.01% of the measured quantity, depending on the solar radiative power input used. The model predictions of temperatures show good qualitative agreement with the measured temperatures but do not compare well quantitatively for all points of comparison. The average error between predicted temperature and experimental results for the various points of comparison is 9.165 K.
ABSTRACT The PAMELA space experiment, in orbit since 2006, has measured cosmic rays (CRs) through the most recent period of minimum solar activity with the magnetic field polarity as A < 0. During ...this entire time, galactic electrons and protons have been detected down to 70 MV and 400 MV, respectively, and their differential variation in intensity with time has been monitored with unprecedented accuracy. These observations are used to show how differently electrons and protons responded to the quiet modulation conditions that prevailed from 2006 to 2009. It is well known that particle drifts, as one of four major mechanisms for the solar modulation of CRs, cause charge-sign-dependent solar modulation. Periods of minimum solar activity provide optimal conditions in which to study these drift effects. The observed behavior is compared to the solutions of a three-dimensional model for CRs in the heliosphere, including drifts. The numerical results confirm that the difference in the evolution of electron and proton spectra during the last prolonged solar minimum is attributed to a large extent to particle drifts. We therefore present new evidence of charge-sign-dependent solar modulation, with a perspective on its peculiarities for the observed period from 2006 to 2009.
This paper summarizes the results obtained by the team “Heliosheath Processes and the Structure of the Heliopause: Modeling Energetic Particles, Cosmic Rays, and Magnetic Fields” supported by the ...International Space Science Institute (ISSI) in Bern, Switzerland. We focus on the physical processes occurring in the outer heliosphere, especially at its boundary called the heliopause, and in the local interstellar medium. The importance of magnetic field, charge exchange between neutral atoms and ions, and solar cycle on the heliopause topology and observed heliocentric distances to different heliospheric discontinuities are discussed. It is shown that time-dependent, data-driven boundary conditions are necessary to describe the heliospheric asymmetries detected by the
Voyager
spacecraft. We also discuss the structure of the heliopause, especially due to its instability and magnetic reconnection. It is demonstrated that the Rayleigh–Taylor instability of the nose of the heliopause creates consecutive layers of the interstellar and heliospheric plasma which are magnetically connected to different sources. This may be a possible explanation of abrupt changes in the galactic and anomalous cosmic ray fluxes observed by
Voyager 1
when it was crossing the heliopause structure for a period of about one month in the summer of 2012. This paper also discusses the plausibility of fitting simulation results to a number of observational data sets obtained by
in situ
and remote measurements. The distribution of magnetic field in the vicinity of the heliopause is discussed in the context of
Voyager
measurements. It is argued that a classical heliospheric current sheet formed due to the Sun’s rotation is not observed by
in situ
measurements and should not be expected to exist in numerical simulations extending to the boundary of the heliosphere. Furthermore, we discuss the transport of energetic particles in the inner and outer heliosheath, concentrating on the anisotropic spatial diffusion diffusion tensor and the pitch-angle dependence of perpendicular diffusion and demonstrate that the latter can explain the observed pitch-angle anisotropies of both the anomalous and galactic cosmic rays in the outer heliosheath.
A perspective is given of the solar modulation of galactic cosmic rays in the heliosphere during the extraordinary quiet solar minimum period from 2006 to 2009. This is done in the context of the ...total modulation of cosmic rays in a global heliosphere. Such an approach has become possible since the observation of galactic cosmic rays made beyond the heliopause by Voyager 1 so that together with very precise observations at higher energies at the Earth, more reliable local interstellar spectra can be established. Combined with the results from comprehensive modeling, a global view unfolds. The requirements for such an approach to the modeling of solar modulation are discussed. Computed, modulated spectra for protons and electrons are shown, for 2006–2009 together with computed radial and latitudinal gradients for protons, in comparison with observations where available. Predictions are made for the energy ranges not covered by the 2006–2009 observations. Respectively, the modulation factor for protons, electrons and positrons are given for energies as low as 5MeV for the mentioned period. The computed electron to positron ratio is presented as applicable to solar minimum modulation conditions. The differences in the modulation of protons, electrons and positrons are illustrated for such conditions and the main contributions to this global process, including particle drifts, are discussed.
We present a newly developed numerical code that integrates Fokker–Planck type transport equations in four to six spatial dimensions (configuration plus momentum space) and time by means of ...stochastic differential equations. In contrast to other, similar approaches our code is not restricted to any special configuration or application, but is designed very generally with a modular structure and, moreover, allows for Cartesian, cylindrical or spherical coordinates. Depending on the physical application the code can integrate the equations forward or backward in time. We exemplify the mathematical ideas the method is based upon and describe the numerical realisation and implementation in detail. The code is validated for both cases against an established finite-differences explicit numerical code for a scenario that includes particle sources as well as a linear loss term. Finally we discuss the new possibilities opened up with respect to general applications and newly developed hardware.
► SDE code for multidimensional Fokker–Planck-type equations. ► Transport equation includes source terms and sinks. ► Applicable to heliospheric as well as galactic problems. ► Code may be applied also to other fields of research. ► Designed also to run on GPUs.
Abstract
Simultaneous and continuous observations of galactic cosmic-ray electrons (
e
−
) and positrons (
e
+
) from the PAMELA and AMS02 space experiments are most suitable for numerical modeling ...studies of the heliospheric modulation of these particles below 50 GeV. A well-established comprehensive three-dimensional modulation model is applied to compute full spectra for
e
−
and
e
+
with the purpose of reproducing the observed ratio
e
+
/
e
−
for a period that covers the previous long and unusual deep solar minimum activity and the recent maximum activity phase, including the polarity reversal of the solar magnetic field. For this purpose, the very local interstellar spectra for these particles were established first. Our study is focused on how the main modulation processes, including particle drifts, and other parameters, such as the three major diffusion coefficients, evolved and how the corresponding charge-sign dependent modulation subsequently occurred. The end result of our effort is the detailed reproduction of
e
+
/
e
−
from 2006 to 2015, displaying both qualitative and quantitative agreement with the main observed features. Particularly, we determine how much particle drift is needed to explain the time dependence exhibited by the observed
e
+
/
e
−
during each solar activity phase, especially during the polarity reversal phase, when no well-defined magnetic polarity was found.
Global gradients for cosmic-ray (CR) protons in the heliosphere are computed with a comprehensive modulation model for the recent prolonged solar minimum of Cycle 23/24. Fortunately, the PAMELA (
...Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics
) and
Ulysses
/KET (
Kiel Electron Telescope
) instruments simultaneously observed proton intensities for the period between July 2006 and June 2009. This provides a good opportunity to compare the basic features of the model with these observations, including observations from
Voyager
-1 in the outer heliosphere, beyond
50
AU
. Radial and latitudinal gradients are calculated from measurements, with the latter possible because
Ulysses
changed its position significantly in the heliocentric meridional plane during this period. The modulation model is set up for the conditions that prevailed during this unusual solar-minimum period to gain insight into the role that particle drifts played in establishing the observed gradients for this period. Four year-end PAMELA proton spectra were reproduced with the model, from 2006 to 2009, followed by corresponding radial profiles that were computed along the
Voyager
-1 trajectory, and compared to available observations.
It is found that the computed intensity levels are in agreement with solar-minimum observations from
Voyager
-1 at multiple energies. The model also reproduces the steep intensity increase observed when
Voyager
-1 crossed the heliopause region. Good agreement is found between computed and observed latitudinal gradients, so that we conclude that the model gives a most reasonable representation of modulation conditions from the Earth to the heliopause for the period from 2006 to 2009. As a characteristic feature of CR drifts, the most negative latitudinal gradient is computed for 2009, with a value of
−
0.15
%
degree
−
1
around
600
MV
. The maximum radial gradient in the inner heliosphere (as covered by
Ulysses
) also occurs in this range, with the highest value of
4.25
%
AU
−
1
in 2009.
The recent 2009 solar-minimum period was characterized by a record-setting high Galactic cosmic-ray flux observed at Earth. This, along with the unexpected low heliospheric magnetic-field magnitude, ...caused this period to be characterized as unusual compared with previous minimum epochs. In this work, selected solar-activity proxies and corresponding cosmic-ray observations for the past five solar cycles are compared with each other, and we identify those that showed unusual behaviour during the 2009 solar-minimum modulation period. Using a state-of-the-art numerical-modulation model, the proton-intensity spectra for the past solar minima are reproduced to establish which of the transport processes might be considered the main cause of this unusually high cosmic-ray flux. It is found that diffusion was more prominent during 2009 so that drift effects on the modulation of cosmic rays in the heliosphere were less evident than during previous solar-polarity epochs. However, particle drifts still occurred and because of these drift effects, the proton spectrum is predicted to be even higher during the coming
A
>0 solar-minimum period.
Background. South Africa (SA) and other countries worldwide are experiencing extreme drought conditions. Since the start of the drought in SA, many ways of saving water have been proposed and ...innovative water-saving mechanisms have become part of the lives of communities. We investigated water use during surgical scrubbing procedures and possible interventions to reduce water consumption.Objectives. To compare water use during surgical hand preparation before and after the implementation of specific water-saving interventions.Methods. This was a non-randomised controlled study, following a before-and-after design, of orthopaedic theatre personnel scrubbing for surgical cases at Tygerberg Hospital, Cape Town. A control (CON) group (n=32) was established to observe standard practice for baseline measurements including total amount of water used, wash time and water flow rate during surgical hand preparation. After this, three interventions were randomly assigned to a single theatre each, where the same variables were measured. Intervention AS entailed using an alcohol scrub (n=18), intervention SN (n=12) had a dedicated assistant to open and close taps during scrubbing, and intervention SW (n=12) made use of adjusted tap levers to allow the surgeon to open and close taps more easily. Analysis of variance was used to detect global differences between groups, and Tukey’s post hoc test was performed to detect differences between groups.Results. Significant differences in water use (pConclusions. Water use during surgical hand preparation can easily be reduced by implementing easy and effective interventions. The practicality of interventions may differ between institutions, and their acceptance by surgical staff is important to ensure compliance. However, ensuring that alternative scrubbing options are available to surgical staff would equate to substantial savings over time.
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