https://ufarasuntalk.home.blog/definitions/physics-definitions-according-to-field-or-subject/2024-01-03T10:15:10+00:00weekly0.6https://ufarasuntalk.home.blog/definitions/physics-definitions/2024-01-03T10:03:06+00:00weekly0.6https://ufarasuntalk.home.blog/about/2024-01-02T12:50:46+00:00weekly0.6https://ufarasuntalk.home.blog/2023/08/05/life-update-im-a-doctor-now/https://ufarasuntalk.home.blog/wp-content/uploads/2023/08/img_3308-copy.jpgIMG_3308 - Copy2024-01-02T11:11:11+00:00monthlyhttps://ufarasuntalk.home.blog/2019/02/08/hello-world/2024-01-02T10:29:20+00:00monthlyhttps://ufarasuntalk.home.blog/definitions/2023-12-26T19:32:08+00:00weekly0.6https://ufarasuntalk.home.blog/contact/2023-12-26T10:26:39+00:00weekly0.6https://ufarasuntalk.home.blog/2023/09/02/book-review-ryder-carrolls-the-bullet-journal-method/2023-08-27T11:13:13+00:00monthlyhttps://ufarasuntalk.home.blog/blog/categories/2023-08-27T10:32:29+00:00weekly0.6https://ufarasuntalk.home.blog/2021/09/03/not-knowing-part-2-dealing-with-ignorance/2021-09-03T07:13:39+00:00monthlyhttps://ufarasuntalk.home.blog/2021/08/06/not-knowing-part-1-feeling-stupid-but-being-fine-with-it/2021-08-06T08:58:48+00:00monthlyhttps://ufarasuntalk.home.blog/2021/04/30/ensemble-forecasting-of-predicted-recipes/2021-04-23T17:53:04+00:00monthlyhttps://ufarasuntalk.home.blog/2021/04/03/modelling-an-infection-outbreak-like-a-physicist-part-3-modelling-south-africas-infections-recoveries-and-deaths/https://ufarasuntalk.home.blog/wp-content/uploads/2021/04/zacoronabestinjectparameters.pngZACoronaBestInjectParametershttps://ufarasuntalk.home.blog/wp-content/uploads/2021/04/zacoronabestinject.pngZACoronaBestInjecthttps://ufarasuntalk.home.blog/wp-content/uploads/2020/07/zacoronadata.pngZACoronaDataFigure 1. The total number of COVID-19 infections, recoveries, and deaths on each day for South Africa from 5 March until 31 May. The number of active infections is just the total number of infections with the recoveries and deaths subtracted. A three day running average is used to remove variability and highlight trends. Dashed vertical lines indicate important events.2021-04-03T13:45:24+00:00monthlyhttps://ufarasuntalk.home.blog/2021/02/12/being-more-childlike/https://ufarasuntalk.home.blog/wp-content/uploads/2021/02/pencilsketch20170820.pngPencilSketch20170820A pencil sketch of my left hand made on 2017-08-20.2021-02-12T13:59:16+00:00monthlyhttps://ufarasuntalk.home.blog/2020/05/18/modelling-an-infection-outbreak-like-a-physicist-part-2-calculating-infection-recovery-and-death-rates-from-data/https://ufarasuntalk.home.blog/wp-content/uploads/2020/05/recoverydeathrate.pngRecoveryDeathRateFigure 5. The number of COVID-19 recoveries and deaths per day as a function of the number of active infections for South-Africa from 5 March until 17 May. The slope of these graphs gives the recovery and death rates needed for the SIS model. The lines fitted to the data to extract the slope are also shown.https://ufarasuntalk.home.blog/wp-content/uploads/2020/05/rates.pngRatesFigure 6. The temporal dependence of the infection (red), recovery (green), and death (grey) rate calculated from Figures 4-5 for South Africa from 5 March until 17 May. The shaded region surrounding each line, indicates the range of uncertainty of the value. The exact temporal profiles and values are indicated in the legend.https://ufarasuntalk.home.blog/wp-content/uploads/2020/05/percentagepositivetest.pngPercentagePositiveTestFigure 3. The percentage of positive test (the number of new COVID-19 cases on a given day divided by the number of tests conducted on that day times a hundred) on each day for South Africa from 5 March until 17 May. A three day running average removes variability and highlights trends. The average percentage before lockdown, during the hard lockdown, and during the easing of the hard lockdown are also indicated.https://ufarasuntalk.home.blog/wp-content/uploads/2020/05/newvaluesvsdays.pngNewValuesVsDaysFigure 1. The number of new COVID-19 infections, recoveries, and deaths per day as a function of time for South Africa from 5 March until 17 May. A three day running average is used to remove variability and highlight trends. Recoveries were not reported on a daily basis and had to be reworked into a daily number. Dashed vertical lines indicate events of importance.https://ufarasuntalk.home.blog/wp-content/uploads/2020/05/lockdownworked.jpgLockdownWorkedFigure 7. The percentage daily increase in new positive cases (the number of new COVID-19 infections on a given day divided by the number of existing cases times a hundred) per day for South Africa from 5 March until 13 May. This graph was used by president Cyril Ramaphosa during his speech on 13 May 2020.https://ufarasuntalk.home.blog/wp-content/uploads/2020/05/infectionrate.pngInfectionRateFigure 4. The number of new COVID-19 infections per day as a function of the number of active infections times the number of susceptibles for South-Africa from 5 March until 17 May. The time before the lockdown, during the hard lockdown, and during the easing of the lockdown is indicated with different colours. The slope of this graph gives the infection rate needed for the SIS model. The lines fitted to the data to extract the slope are also shown.https://ufarasuntalk.home.blog/wp-content/uploads/2020/05/correlation.pngCorrelationFigure 2. The number of new COVID-19 infection per day as a function of the number of test did per day for South Africa from 5 March until 17 May. The data is coloured for certain times of interest. It is clear to see that more cases are found if more tests are done.2020-05-18T20:27:04+00:00monthlyhttps://ufarasuntalk.home.blog/2020/05/10/modelling-an-infection-outbreak-like-a-physicist-part-1-the-sis-model/https://ufarasuntalk.home.blog/wp-content/uploads/2020/05/basicsis.pngBasicSISFigure 1. A solution of the SIS model showing the average (red) and most probable (orange) number of infections as a function of time. The average and most probable values tend to the maximum number of infections which will be reached when the new infections and recoveries are balanced. The red band shows the standard deviation from the mean. The green background represents the logarithm of the (unnormalised) probability distribution with dark green representing a higher probability than white.2020-05-10T19:34:32+00:00monthlyhttps://ufarasuntalk.home.blog/2020/02/07/what-do-phd-students-do/https://ufarasuntalk.home.blog/wp-content/uploads/2020/02/yourstillastudent.gifYourStillAStudent2020-02-07T07:26:52+00:00monthlyhttps://ufarasuntalk.home.blog/2019/10/25/what-are-galactic-cosmic-rays/https://ufarasuntalk.home.blog/wp-content/uploads/2019/10/gcrabundance.pngGCRAbundanceFigure 2. The relative abundances of elements in galactic cosmic rays and the solar system. The elemental abundances are normalised with respect to silicon. This figure was taken from Schlaepfer [2003].2019-10-24T08:49:32+00:00monthlyhttps://ufarasuntalk.home.blog/2019/11/08/the-my-philosophy-of-physics-ask-why/2019-10-11T10:29:08+00:00monthlyhttps://ufarasuntalk.home.blog/2019/10/11/why-part-2-why-does-nature-work-the-way-it-does/2019-10-10T16:20:42+00:00monthlyhttps://ufarasuntalk.home.blog/2019/09/27/what-are-anomalous-cosmic-rays/https://ufarasuntalk.home.blog/wp-content/uploads/2019/09/v1acrs.pngV1ACRsFigure 2. Top panels: Proton, helium, and oxygen spectra for termination shock particles, anomalous cosmic rays, and galactic cosmic rays observed by Voyager 1 in the inner heliosheath (Voyager 1 crossed the termination shock on 16 December 2004) during the days of 2005 as indicated (about two months after the termination shock crossing). The termination shock particles' spectra are broken power laws and the helium and oxygen spectra are dominated by anomalous cosmic rays at mid-energies and by galactic cosmic rays at higher energies. Computed anomalous cosmic ray spectra at the termination shock, assuming diffusive shock acceleration for a strong shock (dashed line) and a weak shock (dotted line), are shown for comparison. Bottom panel: Evolution of the anomalous helium spectrum as Voyager 1 crossed the termination shock and moved into the inner heliosheath. The estimate contributions of termination shock particles and galactic cosmic rays have been subtracted. The black filled triangles are for days 313 to 350 of 2014 just before the termination shock crossing, the red open circles are for days 352 of 2014 to 52 of 2005 in the inner heliosheath, the green crosses are for days 53 to 104 of 2005 and the blue filled circles are for days 105 to 156 of 2005. This figure was taken from Stone et al. [2005].https://ufarasuntalk.home.blog/wp-content/uploads/2019/09/acracceleration.pngACRAccelerationFigure 1. The processes resulting in the production of anomalous cosmic rays: Neutral atoms (dotted lines with open arrows) in the local interstellar medium, enter the heliosphere. Some neutral species (mainly hydrogen and oxygen) experience a filtration (1) in the inner heliosheath due to charge exchange with solar wind protons. An element-specific fraction of those neutrals entering the heliosphere gets ionized by charge-exchange, photo-ionization, or electron impact ionization (open circles). The resulting pick-up ions are pre-accelerated while they are advected with the solar wind (2) towards the termination shock. There, a certain fraction of pick-up ions gets injected (3) into the process of diffusive shock acceleration and are accelerated into anomalous cosmic rays. During their acceleration (solid lines repeatedly crossing the shock) the anomalous cosmic rays modify the structure of the termination shock (4). Eventually, after sufficient energization, the anomalous cosmic rays diffuse and drift (Pesses et al. [1981] showed that drift effects are important to explain observations of anomalous cosmic rays) either back into the heliosphere towards the Sun (5) or into the inner heliosheath (6) where they, like those pick-up ions not being accelerated at the shock, serve as a source distribution of so-called energetic neutral atoms. This figure was taken from Fichtner [2001].2019-09-26T05:25:56+00:00monthlyhttps://ufarasuntalk.home.blog/2019/09/13/so-why-do-i-do-physics-part-3-skill-building/2019-09-09T09:07:38+00:00monthlyhttps://ufarasuntalk.home.blog/2019/08/30/what-are-cosmic-rays/https://ufarasuntalk.home.blog/wp-content/uploads/2019/08/crspectra.pngCRSpectraFigure 2. Energy spectrum of cosmic rays at Earth. See the text for details. This figure was taken from Schlaepfer [2003].https://ufarasuntalk.home.blog/wp-content/uploads/2019/08/protonshower.jpgProtonShowerFigure 1. Simulation of a cosmic ray shower created by a TeV proton hitting the atmosphere 20 km above the Earth. This figure was taken from https://en.wikipedia.org/wiki/Air_shower_(physics).2019-09-02T08:55:53+00:00monthlyhttps://ufarasuntalk.home.blog/2019/08/16/so-why-do-i-do-physics-part-2-the-ancient-greek-law-of-motion/2019-09-09T08:58:29+00:00monthlyhttps://ufarasuntalk.home.blog/2019/07/26/what-is-the-heliosphere/https://ufarasuntalk.home.blog/wp-content/uploads/2019/07/solarcycle.pngSolarCycleFigure 6. Contour plots of the proton density in the meridional plane through the solar cycle. The local interstellar medium is flowing from the right, the Sun is at the centre, and the interstellar magnetic field is directed from the upper-right corner. This figure was taken from Pogorelov et al. [2011].https://ufarasuntalk.home.blog/wp-content/uploads/2019/07/mhdhmf.pngMHDHMFFigure 5. Left panel: Contour plot of the logarithm of the magnitude of the heliospheric and interstellar magnetic field in the meridional plane. The approximate trajectories of the Voyager 1 and 2 spacecraft are indicated by the solid and dashed lines, respectively. Right panel: Contour plot of the logarithm of the magnitude of the heliospheric and interstellar magnetic field in the meridional (vertical) and equatorial (horizontal) plane with two heliospheric magnetic field lines (blue and green) and a single interstellar magnetic field line (red). The local interstellar medium is flowing from the right, the Sun is at the centre and the interstellar magnetic field is directed from the upper-right corner. This figure was taken from Strauss [2013].https://ufarasuntalk.home.blog/wp-content/uploads/2019/07/hdpuidensity.pngHDPUIDensityFigure 3. Similar to Fig. 1 but for pick-up ions. The streamlines of the pick-up ions are the same as the streamlines of the protons inside the heliosphere in Fig. 1. Outside the heliosphere, pick-up ions do not exist and the pick-up ions outside the heliosphere in the tail region is an artificial result of the numerical procedure. This figure was taken from Fahr et al. [2000].https://ufarasuntalk.home.blog/wp-content/uploads/2019/07/hdprotondensity.pngHDProtonDensityFigure 1. Contour plot of the logarithm of the proton density and stream lines of the protons (white dashed lines) for interactions between protons, neutral hydrogen, and pick-up ions in the meridional plane. The local interstellar medium is flowing from the right and the Sun is at the centre (notice that the heliosphere is symmetric around the x-axis). The termination shock (closest to the Sun), heliopouse, and bow shock (furthest from the Sun) are indicated with solid white lines. This figure was taken from Fahr et al. [2000].https://ufarasuntalk.home.blog/wp-content/uploads/2019/07/hdneutraldensity.pngHDNeutralDensityFigure 2. Similar to Fig. 1, but for the neutral hydrogen density. Note that the bumpy structure of the bow shock is an artificial result of the numerical procedure. This figure was taken from Fahr et al. [2000].https://ufarasuntalk.home.blog/wp-content/uploads/2019/07/hdacrdensity.pngHDACRDensityFigure 4. Similar to Fig. 1. but for the anomalous cosmic ray energy density. The bumpy structure of the bow shock is an artificial result of the numerical procedure. This figure was taken from Fahr et al. [2000].2019-07-26T09:56:03+00:00monthlyhttps://ufarasuntalk.home.blog/2019/07/12/so-why-do-i-do-physics-part-1-the-light-bulb-moment/2019-07-04T18:24:48+00:00monthlyhttps://ufarasuntalk.home.blog/2019/06/28/what-is-the-heliospheric-magnetic-field-part-2/https://ufarasuntalk.home.blog/wp-content/uploads/2019/06/hmfzprojection.pngHMFzProjectionhttps://ufarasuntalk.home.blog/wp-content/uploads/2019/06/hmfxyprojection.pngHMFxyProjectionFigure 2. Projections of the magnetic field lines in Fig. 1 starting at θ = 30° on the xz- (top left panel), yz- (top right panel), and xy-plane (bottom panel). From the top panels it is clear that the field line of Parker [1958] (black lines) and Smith and Bieber [1991] (green lines) lay on cones of constant opening angle, while the field lines of Jokipii and Kóta [1990] (red lines) and Fisk [1996] (blue and magenta lines) do not. From the bottom panel it can be seen that the field lines of Smith and Bieber [1991] are more tightly wound.https://ufarasuntalk.home.blog/wp-content/uploads/2019/06/hmf.pngHMFFigure 1. A representation of the Parker [1958] (top left panel), Jokipii and Kóta [1990] (top right panel), Smith and Bieber [1991] (bottom left panel), and Fisk [1996] (bottom right panel; β = 10° and $\omega (\theta) = \omega_{\odot} / 4$) heliospheric magnetic field lines at polar angles of θ = 90° (blue; in the equatorial plane), θ = 60° (red), and θ = 30° (green) for a constant solar wind speed of 400 km/s. The Sun is at the origin represented by a yellow dot. In the bottom right panel both the green and cyan field lines originates at the same latitude (θ = 30°) but are separated in longitude by 180°.2019-06-25T16:27:27+00:00monthlyhttps://ufarasuntalk.home.blog/2019/06/14/so-why-do-we-do-physics-part-3-overcoming-friction/2019-06-07T14:58:15+00:00monthlyhttps://ufarasuntalk.home.blog/2019/05/31/what-is-the-heliospheric-magnetic-field-part-1/https://ufarasuntalk.home.blog/wp-content/uploads/2019/05/hmfparker.pngHMFParkerFigure 5. A representation of the Parker [1958] heliospheric magnetic field lines at polar angles of $\theta = 90^{\circ}$ (in the equatorial plane), $\theta = 60^{\circ}$, and $\theta = 30^{\circ}$ for a constant solar wind speed of 400 km/s. The Sun is at the origin represented by a yellow dot.https://ufarasuntalk.home.blog/wp-content/uploads/2019/05/hcstan.pngHCSTanFigure 4. A schematic representation of the heliospheric current sheet at solar minimum (left panel; ɑ=10º) and maximum (right panel; ɑ=45º), with the Sun located in the centre. The sheet separates oppositely directed open magnetic field lines originating from the Sun.https://ufarasuntalk.home.blog/wp-content/uploads/2019/05/sc_hcs.pngSC_HCSFigure 3. Temporal variations of the averaged sunspot number and number of spotless days per year, the solar polar magnetic field strength, the heliospheric magnetic field strength at Earth, and the heliospheric current sheet tilt angle (the angle between the Sun’s rotational and magnetic axis). The vertical dashed lines indicate times of approximate solar maximum activity. Sunspot number data obtained from http://sidc.be/silso/, number of spotless days per year obtained from https://www.spaceweatherlive.com/en/solar-activity/solar-cycle, solar polar magnetic field strength and heliospheric current sheet tilt angle obtained from http://wso.stanford.edu/, heliospheric magnetic field strength data obtained from http://cohoweb.gsfc.nasa.gov.https://ufarasuntalk.home.blog/wp-content/uploads/2019/05/coronafield.pngCoronalFieldFigure 2. Magnetic field lines in the corona during solar minimum (left panel; beginning of 1996) and solar maximum (right panel; 2000). The photospheric (the Sun’s visible surface) radial field strength is represented by the grayscale, with white/black indicating positive/negative polarity. The blue lines represent closed field lines and the green/red lines represent positive/negative polarity (outwards/ inwards directed) field lines. This figure was taken from Petrie [2015].2019-06-07T14:36:08+00:00monthlyhttps://ufarasuntalk.home.blog/2019/05/10/so-why-do-we-do-physics-part-2-the-law-of-inertia/2019-05-09T15:40:45+00:00monthlyhttps://ufarasuntalk.home.blog/2019/04/26/what-is-the-solar-wind/https://ufarasuntalk.home.blog/wp-content/uploads/2019/04/sw.pngSWFigure 2. The latitudinal (top panel) and radial (bottom panel) dependence of the solar wind speed. Top panel: The first and third fast latitude scans (FLS) of Ulysses, represented by the blue and green lines, respectively, show a clear latitudinal dependence of the solar wind during solar minimum. The second fast latitude scan, represented by the purple line, shows no such dependence during solar maximum conditions (although the increase of the solar wind speed to solar minimum of the third FLS can be seen above $70^{\circ}$). The red lines (solid for solar minimum and dashed for solar maximum) represents the modelled solar wind for $\alpha = 10^{\circ}$. Bottom panel: The solar wind speed measured by Helios 1 during its second orbit and Helios 2 during its first orbit (one year following Helios 1's second orbit), represented by the blue and purple lines, respectively, are the closest measurements of the solar wind to the Sun, excluding the new Parker Solar Probe measurements which are not released yet. The solar wind speed measured by Voyager 2, represented by the green line, clearly show the decrease of the solar wind speed at the termination shock. The red lines (solid for slow and dashed for fast solar wind speeds) represent the modelled solar wind for $r_{TS} = 84$ AU. Data obtained from http://cohoweb.gsfc.nasa.gov.2019-04-26T10:09:54+00:00monthlyhttps://ufarasuntalk.home.blog/2019/04/12/so-why-do-we-do-physics-part-1-the-potential-well/https://ufarasuntalk.home.blog/wp-content/uploads/2019/04/potentialwell.pngPotentialWellFigure 1. Example of gravitational (blue), centrifugal (red), and effective (green) potential energies. The centrifugal potential is, for example, due to the angular momentum of the object about the origin. If there are more than one potential acting on the object, the object will experience an effective potential.2019-04-12T09:10:26+00:00monthlyhttps://ufarasuntalk.home.blog/2019/03/22/what-is-the-solar-cycle/https://ufarasuntalk.home.blog/wp-content/uploads/2019/03/dk1osqlvsaaltje.jpgSolarCycleInFlaresFigure 3. Temporal variations of the averaged sunspot number, number of solar flares, latitudinal position of solar flares, latitudinal SDO/AIA 193 Å density, and latitudinal line of sight magnetic field strength. In the first three panels green, blue, and red refers to C-, M-, and X-class flares, respectively. This figure was taken from <a href="https://twitter.com/swmcintosh/status/1030595026361802752">https://twitter.com/swmcintosh/status/1030595026361802752</a>.https://ufarasuntalk.home.blog/wp-content/uploads/2019/03/sc.pngSolarCycleFigure 2. Temporal variations of the averaged sunspot number and number of spotless days per year, the solar polar magnetic field strength, the heliospheric magnetic field strength at Earth, the yearly number of solar flares, and various neutron monitor counting rates (normalized to 100 for March 1987). The vertical dashed lines indicate times of approximate solar maximum activity. Notice that a logarithmic scale was used for the number of solar flares per year. Sunspot number data obtained from <a href="http://sidc.be/silso/">http://sidc.be/silso/</a>, solar polar magnetic field strength and heliospheric magnetic field strength data obtained from <a href="http://cohoweb.gsfc.nasa.gov">http://cohoweb.gsfc.nasa.gov</a>, yearly number of solar flares and number of spotless days per year obtained from <a href="https://www.spaceweatherlive.com/en/solar-activity/solar-cycle">https://www.spaceweatherlive.com/en/solar-activity/solar-cycle</a>, and neutron monitor data obtained from <a href="http://natural-sciences.nwu.ac.za/neutron-monitor-data">http://natural-sciences.nwu.ac.za/neutron-monitor-data</a>.2019-03-20T10:49:34+00:00monthlyhttps://ufarasuntalk.home.blog/2019/03/08/why-part-1-why-do-we-do-physics/2019-03-08T09:22:41+00:00monthlyhttps://ufarasuntalk.home.blog/2019/02/22/what-is-a-plasma/https://ufarasuntalk.home.blog/wp-content/uploads/2019/02/debey.pngDebeyFigure 4. Left: Potential difference as a function of distance in the presence of Debye shielding. Middle and right: Behaviour of the Debye length as a function of the electron temperature (middle panel) and plasma number density (right panel). Each trend is described in the text. Notice that these two behaviours combine together to yield the Debye length.https://ufarasuntalk.home.blog/wp-content/uploads/2019/02/collectivebehaviourminusbox.pngCollectiveBehaviourFigure 2. The geometrical setup to explain why collective behaviour occurs. It might seem that the $\latex \Delta r$ subtending the two angles is not equal to the $\latex \Delta r$ extending $\latex r$, but this is simply due to the range of the y- and z-axis in comparison to the x-axis. This figure was adapted from Chen [1984].https://ufarasuntalk.home.blog/wp-content/uploads/2019/02/saha.pngSahaFigure 2. Behaviour of the ionization of a gas as a function of the ion number density (left panel), ionization energy (middle panel), and temperature (right panel). Each trend is described in the text. Notice that these three behaviours combine together to yield the total amount of ionization.2019-02-22T10:47:11+00:00monthlyhttps://ufarasuntalk.home.blog/blog/2019-01-31T11:03:07+00:00weekly0.6https://ufarasuntalk.home.blogdaily1.02024-01-03T10:15:10+00:00