Friday, July 03, 2020

Simple, Basic, COVID-19 Math

This is highly elementary for most of you. But I've learned a long time ago that what I consider to be obvious and trivial, is not the case for many members of the public. This is one such case because I've heard this uttered in the media, in print, and among some people.

There is a large increase in the number of positive COVID-19 cases being reported in many states in the US. A lot of people, who shall remain nameless, make the excuse that this is due to the increase in testing, and that it shouldn't be alarming. The more you test, the more you find, they argued.

So I'll illustrate this with simple, basic math.

Let's say you have a population of 1000 people. And let's say that 200 of them has COVID-19. This means that 20% of the population has the virus.

If you randomly test 100 people, you'll get 20 people who is positive.
If you randomly test 200 people, you'll get 40 people who is positive.
If you randomly test 300 people, you'll get 60 people who is positive.

So yes, in terms of absolute numbers, the more people you test, the more number of positive results that you will get. HOWEVER, look at the percentage of positive test. No matter how many people you test, the percentage will still be 20%. The absolute number will increase with increasing number of tests, but the percentage (some people call it positive rate) does not change considerably. This is what a lot of people appear to not fully comprehend.

Of course, in real life, the percentage won't be exact, but if we keep having these tests, it will hover around some value and not change systematically or monotonically over time if there is no change in the number of people infected. So what you need is not the absolute number but also the overall percentage of positive result per day, let's say. That is of more importance if you are trying to see if things are getting better, or worse.

The situation, of course, is more complex than this. But the point in all of this is that you simply can't dismiss the increase in numbers by claiming that it is due to an increase in the number of testing. That is not the whole picture. What if you do the above exercise again and instead, you get 50 out of 200 being positive one week, and 90 out of 300 being positive the week after that? Can you still attribute that to increase in testing only?


Monday, June 29, 2020

Building PIP-II at Fermilab

PIP-II is being built at Fermilab as a new linear proton accelerator for its needs in years to come.


Wednesday, June 24, 2020

Lightest Known Blackhole, Or Largest Known Neutron Star?

I tell ya, after years and years of searching for gravitational waves, and then finally discovering it several years ago, the LIGO-Virgo gravitational waves detector has become an amazing astronomical/astrophysical observatory, making one amazing discovery after another. The existence of such gravitational waves are no longer in doubt that they are now being used as a means to detect other astronomical events.

This is one such case where it appears that a 2.6 solar-mass unknown object collided with a 23 solar-mass blackhole.[1] If this 2.6 solar-mass object is a blackhole, it will be the lightest known blackhole. If it is a neutron star, it will be the heaviest known neutron star. Both scenario will require a reworking of current theories, because a blackhole that light, or a neutron star that heavy, was thought to be unlikely.

Neutron stars and stellar black holes are the final stages of evolution for large stars – with black holes being more massive than neutron stars. In theory, the maximum mass of a neutron star is about 2.1 solar masses. However, there is some indirect evidence that more massive neutron stars could exist. There is little evidence for the existence of black holes smaller than about 5 solar masses, leading to a mass gap in our observations of these compact objects.

What is intriguing about the August 2019 merger – dubbed GW190814 – is the mass of the smaller object, which appears to fall within this gap. “Whether any objects exist in the mass gap has been an ongoing mystery in astrophysics for decades,” says Charlie Hoy of the UK’s Cardiff University, who played a key role in analysing data from the detection and writing the paper that describes the observation, which has been published in The Astrophysical Journal Letters. “What we still don’t know is whether this object is the heaviest known neutron star or the lightest known black hole, but we do know that either way it breaks a record.”

The actual paper is available to be read for free here since it is an open access article.

Like I had said to the students in my astronomy classes, this is going to go down as the golden age of astronomy. Since the beginning of human history, we only had light as our only detector of the heavens. Now, we have not only neutrinos and high-energy cosmic rays, but also gravitational waves as our means to look at the heavens. We have three different and separate ways to look at our sky!


[1] R. Abbott et al., The Astrophysical Journal Letters,896:L44(20pp), 2020.

Tuesday, June 23, 2020

The Physics Of N95 Masks

Many, if not most, of us have heard of N95 masks when the pandemic first appeared, especially when there were reports of their shortages. Why are they so in high demand? This MinutePhysics video tells you why they are the ones that front-line health care workers need to be wearing.


Monday, June 22, 2020

Back To Remote Learning In Fall 2020

While there has been no official word yet, there are strong indications that come Fall 2020, my classes will go back to totally remote learning once more, continuing what happened during the second half of Spring 2020.

It is not surprising to me. I've been expecting it, and in some ways, I've been preparing for it. I mentioned earlier that I've enrolled in Quality Matters courses to give me formal training and credentials in running online and hybrid courses. I just finished the first workshop, and I have one more to do with them before I do the last required course with my own institution.

I must say that the one course that I've completed so far was more useful than I initially expected. There were a few "eye-opener" moments that I never realized before. It is one thing to anticipate and guess what a student needs from an online course, it is another when one actually goes through it, and are shown some of the best-practice methods of online education from the point of view of the student.

At the end of the first course, I realize that what I've learned was not only useful for the next time I have to teach a remote or online course, which will be this Fall most likely, but I'm going to take what I've learned to also improve my face-to-face courses, whenever I get to teach one. I know that many of the things I put on the Learning Management Systems can be reorganized better, because if it is suitable for online students, then it certainly is appropriate for face-to-face students.

But of course, one of the unique challenges with teaching a science course is labs, and how one can effectively do such a thing with a remote class. I've been looking at material put out by Pivot Interactives, which looks promising. I attended one of their webinars, and I like the way they show the experiments. I intend to sign up for the instructor trial version during the next week or so to check them out further. Do you have any experience with using them, either as a student or as an instructor? If you do, I'd love to hear from you.

There are more challenges unique to teaching math and science online, and I'm going to explore them during the next few weeks. I'll post them here whenever I encounter them, and maybe you might have an idea on the best-practice way to tackle them.


Friday, June 12, 2020

More Experimental Verification of General Relativity

This is another one of those "The more they test it, the more convincing it becomes."

New "free fall" measurement in extreme high gravitational field has upheld one of the foundations of General Relativity. This time the measurement comes from a white dwarf orbiting a neutron star (a pulsar). A neutron star is a star that has huge gravitational field, so this is an amazing testing ground for GR under extreme condition.

"Above all, it is the unique configuration of that system, akin to the Earth-Moon-Sun system with the presence of a second companion (playing the role of the Sun) towards which the two other stars 'fall' (orbit) that has allowed to perform a stellar version of Galileo's famous experiment from Pisa's tower. Two bodies of different compositions fall with the same acceleration in the gravitational field of a third one."

"The pulsar emits a beam of radio waves which sweeps across space. At each turn this creates a flash of radio light which is recorded with high accuracy by Nançay's radio telescope. As the pulsar moves on its orbit, the light arrival time at Earth is shifted. It is the accurate measurement and mathematical modeling, down to a nanosecond accuracy, of these times of arrival that allows scientists to infer with exquisite precision the motion of the star," says Dr. Guillaume Voisin.

You can get free access to the actual paper here.


Thursday, June 11, 2020

BEC In Space

 Not as amusing as Pigs In Space, but still quite impressive.

The ISS is useful after all! :) Physicists have created the first controlled Bose-Einstein condensate in low earth orbit, thus eliminating the issue of gravitational effects[1] that affects the stability of the condensate.

A review of the work can be found here.

As discussed, Bose–Einstein condensation requires low temperatures, at which atoms hardly move. However, when a BEC is released from a magnetic trap so that experiments can be carried out, repulsive interactions between the atoms cause the cloud to expand. Within a few seconds, the BEC becomes too dilute to be detected. The expansion rate can be reduced by decreasing the depth of the trap, and, thereby, the density of atoms in the trap.

On Earth, the planet’s gravitational pull restricts the shape of possible magnetic traps in such a way that a deep trap is needed to confine a BEC (Fig. 1a,b). By contrast, Aveline and colleagues found that the extremely weak gravity (microgravity) on the International Space Station allowed rubidium BECs to be created using shallow traps. As a result, the authors could study the BECs after about one second of expansion, without needing to manipulate the atoms further.

But this is more than just an achievement on the scientific level. It is also a technological feat because of the numerous requirements that are needed to be able to have an experiment on the ISS, as stated in the review:

Aveline and colleagues’ technological achievement is remarkable. Their apparatus needed to satisfy the strict mass, volume and power-consumption requirements of the International Space Station, and be robust enough to operate for years without needing to be serviced. The authors’ Earth-orbiting BECs provide new opportunities for research on quantum gases, as well as for atom interferometry, and pave the way for missions that are even more ambitious.

If you have ever designed an experiment, you know of all the issues involved, not just the scientific ones. This includes engineering, robustness, economics/costs, etc. So I can't imagine what they had to come up with to be able to send something up there and basically run this with very little to no involvement from the astronauts onboard.

Very well done indeed!


[1] D.C. Aveline et al. Nature v.582, p.193 (2020).

Thursday, June 04, 2020

DESI Begins

A new eye on the sky is about to add to our knowledge of dark energy.

It's interesting that in the list of funding agencies, NASA is absent. This goes to show you that many of these research activities that seem to be "astronomy-related" are not the sole domain of NASA. In fact, the area of particle-astrophysics is more closely related to particle physics than astronomy.

The video didn't clarify explicitly that in looking at the "spectrum" of light from each of these celestial bodies, one gets the radial velocity of these bodies with respect to us (i.e. via the amount of redshift), not its distance from us. That last piece of information can only be "deduced" using the radial velocity and the Hubble equation, i.e. the Hubble constant, a number that is still being refined.

Still, this new telescope is going to be quite exciting in revealing more of the mysteries of dark energy.


Thursday, May 21, 2020

Transition to Online Teaching

The June 2020 issue of Physics Today has an article on various physics instructors' effort in dealing with the migration to online teaching in physics courses. I notice a few similar issues I had to deal with, such as this:

During in-person lectures, says Greco, the instructor would pose a question every 10 minutes or so. The students would discuss the question with their neighbors for a few minutes and then submit their answers. “If most of them get the right answer, I move on,” says Greco. “If not, I adjust the live lecture.” That doesn’t work as well online: Student discussion is harder to facilitate and web-based interactions are much slower. In person, he adds, “you can tell if someone is paying attention, but that’s hard to do virtually.”

I use "clickers" in class to do a quick snapshot if the students understood the concept that was presented. And certainly, student-to-student discussion is a part of it especially if the first round of in-class question didn't produce a correct response. This can't be done during a Zoom session even though it has a Poll feature. Student discussion was almost non-existent, and we had to revert back to almost passive learning, which killed me since I'm a strong advocate for active learning.

I did resorted to giving them at-home projects as part of the material where they used simulations and virtual experiments to investigate something that was relevant to the topic of that week. But it isn't the same, obviously.

The other similar thing that I read was this:

Other instructors chose to teach asynchronously, sometimes in a flipped mode, with students watching lectures before attending virtual discussions. Some instructors, including Dubson, embed questions in their video lectures such that students can’t continue until they commit to an answer. “This allows us to require that they think,” he says.

Luckily, all my classes have these "pre-lecture" videos or documents that the students had to view or read, and then answer a few questions. These were meant to introduce to them the concepts related to the topic of that week before the come to class. So I was already doing the "flipped" mode. When we went totally remote, I expanded the pre-lecture videos and material so that the students had a bit more to view because now it became a major source of the material.

It's nice to read that many other instructors were doing the same thing, and that we could all learn from one another on how to do this better next time.


Thursday, May 14, 2020

Goodbye Spring Semester 2020

It's been close to a week since I submitted the final grades for my students. I'm still giving my sigh of relief that the crazy semester is finally over, and I'm sure the students felt the same way too.

For someone who has had a bit of training on how to run blended or hybrid classes, it was still a huge challenge to modify an existing on-site classes to run 100% online. And as someone who is a strong advocate of active learning, it is an even bigger disappointment that all the meticulous planning and in-class activities along this line of learning had to be thrown out of the window. But as they say, life happens while you're making plans!

After this whole debacle, I'm taking the entire summer off. I was planning on going to Hawaii at the end of May and fulfill one of the items on my bucket list, which is to view a sunrise or sunset on Mauna Kea. But of course, all of that had to be cancelled.

Still, I won't be just sitting on my rear end doing nothing throughout the summer. This whole pandemic thing has force me to get more official training on the best-practice way to run online classes and lessons, especially for a course that requires labs, etc. I've signed up for several accredited training courses, with the hope of improving my online lessons and presentations. I'm very much interested in the best ways to minimize online cheating during exams, etc., because I consider that to be a major issue and why I am skeptical of the skill and understanding of students taking online classes. Other faculty members who had taken such courses mentioned that it also helped with their in-person classes, so it definitely sounds like a positive thing to do. We shall see.

I've also realized that I've been consuming more than my usual amount of wine during this stay-at-home order. Not sure if that's good or bad.... :)😁


Friday, April 17, 2020

Simple Electric Motor Experiment

This was the last lab that my students managed to do before all in-person classes were cancelled due to the coronavirus. They had to build a simple electric motor, making use of the concept of magnetic field created by a loop of wire, the concept of magnetic moment, and magnetic torque.

The final "proof" that they had successfully built the motor is to show that it will spin continuously, which looks like this:

It's a common experiment done in many General Physics labs, but it is still a cool exercise. The students certainly had fun doing it and they felt a sense of accomplishment when they see the spinning coil in motion.

I was just glad we managed to do it just before the shutdown.