lipids - Does a reduction in stem cells mean possible earlier death?

The basis of this question relies on my understanding of these 2 facts:

1) A person has a certain number of stem cells from birth 
2) Stem cells are the basis of all cells and are used to repair and replenish

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I read an article about stem cells being found in fat removed by lipsuction and that the trials that has been done on using these stem cells for repair elsewhere in the body.

My question is, if stem cells are used for repair in the body and you have a certain amount of them, if you "lose" some via liposuction, does this then mean you have less stem cells and therefore less chance of repair and could then theoretically die sooner?

It's more than likely my lack of knowledge on the subject but I would like to understand why.

teaching - What is the benefit of writing lecture notes for an introductory course vs using a textbook?

Background: I am a junior university staff member, and I will teach an introductory course in linear algebra for the first time in a few months.

I see that many teachers devote time to writing lecture notes. To me, this looks odd. Whatever I can write will not be half as good as a well-written textbook. so my first choice would be looking for a good book, recommend it to the students, and stick with it as much as possible for my lectures. "Everyone writes their own notes" looks like a model in which there is a lot of needless duplication of work.

Why do people write detailed lecture notes for basic courses? What is the advantage with respect to following closely a textbook?

Are the two approaches really alternative, or am I misunderstanding the role of lecture notes? Should I do both?

Answer

As someone who's tried to do both, there are some very valid reasons to prepare "formal" lecture notes.

The primary reason why you'd want to create your own notes is that for many courses, a single good text is not available, and as a result, the instructor has to cobble together material from a number of different sources to produce a coherent set of lecture notes—or recommend that students work with multiple source texts. (Given the out-of-control nature of textbook prices, the latter alternative is unlikely to work out well.)

If you have a single-text class, it may not be necessary to provide students an additional set of notes, provided your lectures stick to the main text material. However, if you bring in alternative or additional topics into your lectures, you may want to include notes for those topics, and refer students to the textbook for places where you follow the "standard" outline.

teaching - During recitation sections, should I ask students for help in coming up with the answer?

Typically when teaching recitation sections (in lower level applied math classes), I bring a problem or two, and ask students to fill in the steps in the solution. Usually 4 or 5 people (out of 10-15) are engaged in this process.

On the one hand, I think the engaged students benefit from the class discussion, and enjoy it more than listening to a lecture.

On the other hand, I worry that the students who don't participate in the discussion will find it boring, or get confused (because sometimes the other students suggest wrong approaches, and I humor them a bit before explaining why it's wrong). It also makes the problem-solving process longer than it could be, and in that time I could cover more types of problems or just let students go home early.

What do you think is the best practice? (And is it different in regular lectures than in recitation sections?)

Answer

I really like working problems with students, because I think that actually working a problem is a very good way to engage more deeply with the material. That said, you've put your finger on two very important problems: engaging the whole class, and dealing with incorrect solutions.

My approaches to these two problems:

• 
  
  

  Engaging the whole class: you don't have to have everybody talk, but you have to give an opportunity for everybody to talk. In fact, I think it's often better not to call on individual students, and thereby put them on the spot. But you can promote engagement by calling on subsets of the class, e.g., "Let's hear from somebody who hasn't spoken yet", "somebody on the left side of the room", "one of you folks in the back". This gives you ways to make sure the confident students don't dominate and allow less confident students space to step forward.

  
  


• 
  

  Dealing with incorrect solutions: Honest mistakes are golden, for every one highlights a way in which a student is misunderstanding the material. Depending on the nature of the mistake, you can take a number of different approaches. With some mistakes, you can just follow through to illustrate how things go wrong, then use that as a contrast. With others, you can go Socratic and ask the student questions that lead them to understand the correct answer more deeply. Yet others give you a chance to segue into an explanation of common misunderstandings. I say, cherish the mistakes, give the student positive feedback for speaking and thinking even as you tell them they are wrong, and turn them into opportunities for deeper understanding.

  
  

To me, the flip side of the problems you highlight are, in fact, the best reasons to ask students to help work problems in small recitations. Solved well, they can present students with some of the best guided learning opportunities in an entire course.

neuroscience - Do people with colorblindness have less cones or no cones of a certain type?

https://en.wikipedia.org/wiki/Color_blindness#Red.E2.80.93green_color_blindness

Protanopia (1% of males): Lacking the long-wavelength sensitive retinal cones,

Deuteranopia (1% of males): Lacking the medium-wavelength cones,

Do they lack all those cones, or are they just (severely) short?

Answer

This is a complicated case, as it can have multiple causes. The genes which are coding for the long (L, yellow) and medium (M, green) wavelength photopigments are located head-to-tail on the X chromosome. This is the reason why this colors are affected much more and especially in men (which only have one copy of this chromosome).

What seems to happen mostly is that the photopigment of one type of cone cells (and their neuronal connectivity) is missing, while the density of the cone cells is still the same. This means that the cells are they, but are not functioning. See these publications (when you have problems getting the articles, let me know in the comments, I can help):

What can additionally happen in some cases is that these cones have a different pigment than they should have. See the third paper above for details.

phd - Could you get a doctorate based solely on a thesis written in your free time?

I am a very enthusiastic person academically and I love to gather new (sometimes irrelevant but useful) knowledge about my field in my free time. I am now at the point where I would like to start writing a paper on something in my field of interest and based on my own research.

If my paper is credible, contributes to my field and fulfills the standards that apply to any PhD thesis, would I be awarded a doctorate if I applied for the degree and publish the paper?

As an undergraduate, I don't know much about a PhD program. From what I know, it's simply you and your research that counts. I understand that, in the last analysis, it is the contribution to your field that counts. Am I missing anything?

Answer

Just write your paper, as long as the writing does not distract you from your undergrad studies. If the paper has merit, you may be able to present it at a colloquium of your university, at a workshop, or even at a conference. If you put some more work into it and are lucky, you might eventually be able to publish it in a journal. Certainly, your paper will open up more questions than it answers. Now you have a research trajectory that you can follow up and that may lead to a PhD thesis, based on but surely not limited to your first paper.

In other words: There is no reason why you should not start to work on your PhD topic already as an undergraduate, but it seems to me that you underestimate the time and work it takes to finish the PhD. And since PhDs require a lot of work, there are PhD programs, which facilitate the process and in which most PhDs are actually produced. In that sense, writing your PhD outside of the designated framework is a bit like digging a well with a spoon. It can be done, but it is not too efficient. On top of that (as others have said already), at many institutions, the written thesis is only one requirement among others to be awarded a title.

genetics - How are epigenetic marks transmitted during cell division?

As far as I know, this is one of the biggest questions in the epigenetic field: how are the epigenetic marks like histone modifications propagated through cell division? A lot is already known about DNA methylation (e.g. as in How does “inheritance of methylation” of DNA and/or histones work?), but very little about histone modifications. What is the current state of knowledge?

physiology - Fast standing and the heart's insufficient accommodation of the increased venous return

Assume you are 45 minutes on the supine position. Furthermore: you stand all of a sudden and fast and without sympaticus activity. The venous return (smooth musculature of vessels) accommodates faster to the change (decrease of venous return) so returns blood to the heart before the sympaticus has accommodated for increased cardiac output. This creates a significant increase in the blood volume entering the heart. In pathological situation where systemic vasoconstriction not occurring normally, the heart is not capable of handling the overdistension; resulting in a pain during the second cardiac cycle.

I am interested in knowing which phase the heart is most vulnerable:

• filling,


• isovolumetric contraction


• ejection


• isovelumetric relaxation

or more explicitly (from my answer here)

• Atrial systole



• Isovolumetric ventricular contraction


• Rapid ventricular ejection


• Reduced ventricular ejection


• Isovolumetric ventricular relaxation


• Rapid ventricular filling

I think filling can happen normally, but not with the sudden isovolumetric contraction (most sympathetic innervations here, so therefore I think this is the weak link). When there is too much blood in the ventricles, some of the blood is reflected back from the ventricles into the atria causing a painful sensation and possibly tachycardia (as well as an possible increased risk of atrial fibrillation if such events happen regularly).

Is the isovolumetric contraction (systole of ventricles) of the cardiac cycle the possible weak link in accommodating a sudden increased venous return?