Archive for the The Universe and Stuff Category

The Joy of Penguin Faeces

Posted in The Universe and Stuff with tags , , , on July 4, 2020 by telescoper

Last night my attention was drawn to an important article on the ArXiv in the domain of biophysics. The title is Projectile Trajectory of Penguin’s Faeces and Rectal Pressure Revisited*.

Here is the abstract:

We discuss a trajectory of penguins’ faeces after the powerful shooting due to their strong rectal pressure. Practically, it is important to see how far faeceses reach when penguins expel them from higher places. Such information is useful for keepers to avoid the direct hitting of faeceses. We estimate the upper bound for the maximum flight distance by solving the Newton’s equation of motion. Our results indicate that the safety zone should be 1.34 meters away from a penguin trying to poop in typical environments. In the presence of the viscous resistance, the grounding time and the flying distance of faeces can be expressed in terms of Lambert W function. Furthermore, we address the penguin’s rectal pressure within the hydrodynamical approximation combining Bernoulli’s theorem and Hagen-Poiseuille equation for viscosity corrections. We found that the calculated rectal pressure is larger than the estimation in the previous work.

That is amusing enough (though admittedly the English isn’t great) but the diagrams are an absolute joy!

*In case you’re wondering about the “revisited” at the end of the title, the authors of the present work present a critique of earlier work by Meyer-Rochow & Gal (2003) in which “the projectile trajectory of the faeces is not taken into account”. This previous paper was awarded the Ignobel Prize in 2005.

One should not pooh-pooh research on this topic and now that we have got to Number Two I for one hope for the speedy production of further outputs in this area.

The Open Journal of Astrophysics & INSPIRE

Posted in Open Access, The Universe and Stuff with tags , , , , on July 1, 2020 by telescoper

After a busy morning I’ve got time for an update or two about the Open Journal of Astrophysics.

As well as the NASA Astrophysics Data System (ADS) many papers in astrophysics are also indexed by INSPIRE HEP the analogous information management system for high energy physics. Here is the logo for the latter:

Being indexed in INSPIRE  is particularly relevant for authors of papers in astroparticle physics and cosmology, but papers in other areas of astrophysics are also listed on INSPIRE HEP. I am given to understand that, e.g., postdoc selection committees often look at INSPIRE for bibliometric information about applications so this is potentially important for early career researchers.

I am very grateful to staff at Inspire for ensuring that all our papers are now fully indexed in INSPIRE HEP as refereed articles with metadata fully consistent with NASA/ADS. The back catalogue having been dealt with manually we can now set up a feed to ensure that future papers are indexed automatically by NASA/ADS and Inspire HEP.

It is worth noting that because our papers are only published online we do not use the standard referencing style of volumes and pages. We have volumes: Volume 3 is 2020, Volume 2 is 2019, and everything before that is Volume 1. Each paper published in a given year is allocated an numerical id which is just an integer.

For an example of this style, see here.

The main thing for proper cross-referencing and citation is the Digital Object Identifier, which is displayed on the overlay for each paper.

The final thing I wanted to say is that I’m now reliably informed that the correct name to be use for the form of Open Access Publishing offered by the Open Journal of Astrophysics is not Green (which has come to mean author self-archiving of papers) but Diamond Open Access, which means that neither authors nor readers are charged.

Watch “Why the Universe is quite disappointing really – Episode 6” on YouTube

Posted in The Universe and Stuff, YouTube with tags , , on June 30, 2020 by telescoper

I had to suspend the production of these videos for a month or so while I dealt with examination matters, but after that short hiatus, here is Episode 6 during which I explain just how weak and feeble the force of gravity really is. Combined with the fact that the Universe has such a low density (see Episode 5), the weakness of gravity means that the cosmos evolves extremely slowly.

R.I.P. Olivier Le Fèvre (1960-2020)

Posted in The Universe and Stuff with tags , , , , , on June 29, 2020 by telescoper

Olivier Le Fèvre (1960-2020)

The international cosmological community was deeply saddened last week to hear of the death on 25th June after a long illness of Olivier Le Fèvre. He was 59 years old.

Olivier was a specialist in astronomical spectroscopy and as such he made important contributions to cosmology through galaxy redshift surveys. He was Director of the Laboratoire d’Astrophysique de Marseille from 2004 to 2011. In latter years he was involved, among many other things, in the Euclid space mission.

You can find a full obituary and appreciation of Olivier’s life and work here. His funeral takes place this morning and there is an online book of condolence here to send messages of condolence and support to his family, friends and colleagues at this difficult time.

Rest in peace, Olivier Le Fèvre (1960-2020).

Another Open Day Preview – General Science at Maynooth

Posted in Education, Maynooth, The Universe and Stuff with tags , , , on June 26, 2020 by telescoper

I thought I’d put up another post following on from yesterday’s post about Open Day at Maynooth coming up on Saturday 27th June which, owing to Covid-19 restrictions still being in place,  is once again a virtual event. It will take place between 10am and 2pm and be online for that period to answer queries about Theoretical and Mathematical Physics at Maynooth University. You can sign up for the event here.

Yesterday’s post was about our denominated degree programme in Theoretical Physics and Mathematics, but I also recorded a separate video for students interested in studying Mathematical Physics  (or Theoretical Physics – we use the terms interchangeably) through our General Science programme, MH201, so here’s a little presentation about how to study Mathematical physics at Maynooth that way:

Currently, most students doing Science subjects here in Maynooth enter on the General Science programme (codename)  a four-year Omnibus science course that involves doing four subjects in the first year, but becoming increasingly specialised thereafter. That’s not unlike the Natural Sciences course I did at Cambridge, except that students at Maynooth can do both Mathematical Theoretical Physics and Experimental Physics in the first year as separate choices. Other possibilities include Chemistry, Computer Science, Biology, etc.

In Year 1 students do four subjects (one of which has to be Mathematics). That is narrowed down to three in Year 2 and two in Year 3. In their final year, students can stick with two subjects for a Joint Honours (Double Major) degree, or specialise in one, for Single Honours.

I like this programme very much because it does not force the students to choose a specialism before they have had a taste of the subject, and that it is flexible enough to accommodate Joint Honours qualifications in, e.g., Theoretical Physics and Mathematics. It also allows us to enrol students onto Physics degrees who have not done Physics or Applied Mathematics as part of the Leaving Certificate.

I think Mathematical Physics has a particular value in the first year of this course, even for students who do now wish to continue with beyond that level. The material we present in the first year focusses on Mechanics, which is perfect for students to learn how to apply concepts from the Mathematics courses in calculus and linear algebra (especially vectors). It obviously complements Experimental Physics and I would recommend all students who want to do Experimental Physics to do Mathematical Physics too, but  basic mechanics comes up in a wide range of contexts in science, including Biology and Chemistry, so it is relevant for students taking a wide range of pathways through this very flexible programme.

 

 

New Publication at the Open Journal of Astrophysics!

Posted in Open Access, The Universe and Stuff with tags , , , , , , on June 25, 2020 by telescoper

Proving further the point that the The Open Journal of Astrophysics is definitely fully open we have published yet another paper. This one was actually published yesterday, which means that we had two in two days..

This one is in the Cosmology and Nongalactic Astrophysics section and is entitled Source Distributions of Cosmic Shear Surveys in Efficiency Space. The authors are Nicolas Tessore and Ian Harrison, both from the University of Manchester. The paper is concerned with the extraction of cosmological information from cosmic shear surveys.

Here is a screen grab of the overlay:

You can find the arXiv version of the paper here.

What kind of thing is GW190814?

Posted in The Universe and Stuff with tags , , , , , , , on June 24, 2020 by telescoper

There’s been a lot of interest in the past day or two over an event that occurred in the LIGO detectors last August, entitled GW190814. A paper has appeared declaring this to be “the observation of a compact binary coalescence involving a 22.2–24.3 M  black hole and a compact object with a mass of 2.50–2.67 M “. That would be interesting of course because the smaller object is smaller than the black holes involved in previous detections and its mass suggests the possibility that it may be a neutron star, although no electromagnetic counterpart has yet been detected.  It’s a mystery.

I was quite excited when I saw the announcement about this yesterday but my enthusiasm was dampened a bit when I saw the data from the two LIGO detectors at Hanford and Livingston in the USA and the Virgo detector in Italy.

Visually, the Livingston detection seems reasonably firm, but the paper notes that there were thunderstorms in the area at the time of  GW190814 which affected the low-frequency data. There doesn’t look like anything at all but noise in the Virgo channel. The Hanford data may show something but, according to the paper, the detector was “not in nominal observing mode at the time of GW190814” so the data from this detector require special treatment. What you see in the Hanford channel looks rather similar to the two (presumably noise) features seen to the left in the Livingston plot.

I know that – not for the first time – I’m probably going to incur the wrath of my colleagues in the gravitational waves community but I have to sound a note of caution. Before asking whether the event involves a black hole or a neutron star you have to be convinced that the event is an event at all.  Fortunately, at least some of the data relating to this have been released and will no doubt be subjected to independent scrutiny.

Now I’m going to retreat into my bunker and hide from the inevitable comments…

New Publication at the Open Journal of Astrophysics!

Posted in Open Access, The Universe and Stuff with tags , , , , on June 23, 2020 by telescoper

Well, Maynooth University may well be still (partially) closed as a result of the Covid-19 pandemic but the The Open Journal of Astrophysics is definitely fully open.

In fact we have just published another paper! This one is in the Astrophysics of Galaxies section and is entitled A Bayesian Approach to the Vertical Structure of the Disk of the Milky Way. The authors are Phillip S Dobbie and Stephen J Warren of Imperial College, London.

Here is a screen grab of the overlay:

 

You can find the arXiv version of the paper here.

I’d like to take this opportunity to thank the Editorial team and various referees for their efforts in keeping the Open Journal of Astrophysics going in these difficult times.

The Summer Solstice 2020

Posted in The Universe and Stuff with tags , , , , , , on June 20, 2020 by telescoper

The Summer Solstice in the Northern hemisphere happens this evening, Saturday 20th June 2020, at 22:43 Irish Time (21.43 UTC). Among other things, this means that today is the longest day of the year. This is an earlier day in June than you might expect, primarily because 2020 is a leap year.

Days will get shorter from today until the Winter Solstice in December, although this does not mean that sunset will necessarily happen earlier tomorrow than it does today. In fact it is a little later. This is because there is a difference between mean solar time (measured by clocks) and apparent solar time (defined by the position of the Sun in the sky), so that a solar day does not always last exactly 24 hours. A description of apparent and mean time was given by Nevil Maskelyne in the Nautical Almanac for 1767:

Apparent Time is that deduced immediately from the Sun, whether from the Observation of his passing the Meridian, or from his observed Rising or Setting. This Time is different from that shewn by Clocks and Watches well regulated at Land, which is called equated or mean Time.

The discrepancy between mean time and apparent time arises because of the Earth’s axial tilt and the fact that it travels around the Sun in an elliptical orbit in which its orbital speed varies with time of year (being faster at perihelion than at aphelion).

Using a rapid calculational tool (Google), I found a table of the local mean times of sunrise and sunset for Dublin around the 2020 summer solstice. This shows that today is indeed the longest day (with a time between sunrise and sunset of 17 hours and 10 seconds), but sunset on 21st June is actually a bit later than this evening, but sunrise is also bit later so the day is indeed (slightly) shorter.

In fact if you plot the position of the Sun in the sky at a fixed time each day from a fixed location on the Earth you get a thing called an analemma, which is a sort of figure-of-eight curve whose shape depends on the observer’s latitude. Here’s a photographic version taken in Edmonton, with photographs of the Sun’s position taken from the same position at the same time on different days over the course of a year:

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The summer solstice is the uppermost point on this curve and the winter solstice is at the bottom. The north–south component of the analemma is the Sun’s declination, and the east–west component is the so-called equation of time which quantifies the difference between mean solar time and apparent solar time. This curve can be used to calculate the earliest and/or latest sunrise and/or sunset.

Varun Sahni on Dark Matter & Dark Energy

Posted in The Universe and Stuff with tags , , , , on June 17, 2020 by telescoper

I’m very happy to be able to share a couple of lectures by esteemed cosmologist and erstwhile co-author Varun Sahni of the Inter University Centre for Astronomy & Astrophysics (IUCAA) in Pune, India. They’re at an introductory level appropriate for a summer school so I think quite a lot of students will find them interesting and informative!