Large Hardon Collider

[Lochnessmonster]

Q is the energy released. Q1, Q2, Q3, describe the individual contributions each reaction yields.

I had the same reaction to the energy rates and I have to believe he slipped up on that. The equations are balanced and he's provided the total energy produced as being Qtotal = 2*Q1+2*Q2+Q3 = 26.731 MeV. (Q1 and Q2 occur twice for every Q3.) This isn't accounting the loss of neutrinos which he approximates as being 2*(0.263 MeV) which would occur during the first reaction. The net Q would be 26.205 MeV. I'm coming up with a initial result of 25.71 MeV. I feel that my Q2=5.4935 MeV and Q3=12.8596 MeV are accurate....

>>While typing this up, I decided to do some algebra to figure out what my Q1 should be. Interestingly enough, I found out the electron mass is the difference. Would this be the result of annihilation? Or should I have not included it in the first place? Either way, thanks for guiding me along. I'll be hitting the sack now.. Tired of looking at 10 sig fig coefficients.

[Lochnessmonster]

[Removed]- Double Post.

[Kaylia]

Q is the energy released. Q1, Q2, Q3, describe the individual contributions each reaction yields.

I had the same reaction to the energy rates and I have to believe he slipped up on that. The equations are balanced and he's provided the total energy produced as being Qtotal = 2*Q1+2*Q2+Q3 = 26.731 MeV. (Q1 and Q2 occur twice for every Q3.) This isn't accounting the loss of neutrinos which he approximates as being 2*(0.263 MeV) which would occur during the first reaction. The net Q would be 26.205 MeV. I'm coming up with a initial result of 25.71 MeV. I feel that my Q2=5.4935 MeV and Q3=12.8596 MeV are accurate....

>>While typing this up, I decided to do some algebra to figure out what my Q1 should be. Interestingly enough, I found out the electron mass is the difference. Would this be the result of annihilation? Or should I have not included it in the first place? Either way, thanks for guiding me along. I'll be hitting the sack now.. Tired of looking at 10 sig fig coefficients.

Would you mind posting PP-I equation for me, I could check if there is anything wrong with them.

Let's say the first equation is:
1H + 1H → Deuterium + e+ + νe + 0,42 MeV
It means that
2 proton (no electron)--> 1 proton 1 neutron 1 positron 1 neutrino
or, if you want to remove anti matter out of the last equation
2 proton +1 electron --> 1 proton 1 neutron 1 neutrino

Are you sure you're not including any electron with the hydrogen and deuterium, than counting it again as a positron..or something like that. It's a dumb mistake that I remember doing a while back, but it could make the difference.

[Eliseos]

Man that is a tough decision.

In your gut which job sounds more fun to you? If you were offered both which one would you take? (Assuming both paid exactly the same.)

I faced a similar situation though not exactly the same, when I interviewed for my current job the same company also interviewed me for a different position, they ended up offering me both positions at the exact same starting salary and I had to decide which one I wanted to take. That situation was a little bit easier than yours but it did take some thought. Ironically later on they merged both jobs together so now I perform the duties of both.

I am inclined to say go for the sure thing but it is kinda weird they are making you decide so fast. I have to assume it is because you told them you have another interview coming up and they want to pressure you into accepting before you run off to a different job.

It would also suck to accept the offer then do the Boeing interview and get an offer for that job that is better. Sorry I don't have a concrete answer for what you should do but I would sit down with a loved one/family/parent/mentor and get some guidance or an opinion from someone that you really trust.

Honestly, the Boeing job sounds more fun, but I'm pretty sure I won't know what I'll be doing until the phone interview. The Boeing position also gives me the chance to relocate, which I've sort of wanted to do at graduation. And yeha, I'm pretty sure they gave me the short deadline due to my other interview. I think what I'm going to do is ask them for another week, if they really want me they'd give me that at least. A couple of friends have told me to accept the position now, then if I get the Boeing job, cancel on the offer I accepted, but I don't really want to burn bridges like that. Thanks for the advice anyways though, this is going to be a tough decision either way.

[Lochnessmonster]

Would you mind posting PP-I equation for me, I could check if there is anything wrong with them.

Let's say the first equation is:
1H + 1H → Deuterium + e+ + νe + 0,42 MeV
It means that
2 proton (no electron)--> 1 proton 1 neutron 1 positron 1 neutrino
or, if you want to remove anti matter out of the last equation
2 proton +1 electron --> 1 proton 1 neutron 1 neutrino

Are you sure you're not including any electron with the hydrogen and deuterium, than counting it again as a positron..or something like that. It's a dumb mistake that I remember doing a while back, but it could make the difference.

Thanks for the advice again. I ended up over-thinking it. The first question wanted the energy assuming no electron annihilation which was what I calculated. The second part wanted me to figure it out assuming electron annihilation which was the value in my notes. Then calculate it again assuming kinetic energy loss due to neutrinos.

[Tristam]

Stem cells getting shit done.

http://www.nature.com/news/2011/1104....2011.215.html

A retina made in a laboratory in Japan could pave the way for treatments for human eye diseases, including some forms of blindness.

Created by coaxing mouse embryonic stem cells into a precise three-dimensional assembly, the 'retina in a dish' is by far and away the most complex biological tissue engineered yet, scientists say.

"There's nothing like it," says Robin Ali, a human molecular geneticist at the Institute of Ophthalmology in London who was not involved in the study. "When I received the manuscript, I was stunned, I really was. I never though I'd see the day where you have recapitulation of development in a dish."

If the technique, published today in Nature, can be adapted to human cells and proved safe for transplantation — which will take years — it could offer an unlimited well of tissue to replace damaged retinas. More immediately, the synthetic retinal tissue could help scientists in the study of eye disease and in identifying therapies.

The work may also guide the assembly of other organs and tissues, says Bruce Conklin, a stem-cell biologist at the Gladstone Institute of Cardiovascular Disease in San Francisco, who was not involved in the work. "I think it really reveals a larger discovery that's coming upon all of us: that these cells have instructions that allow them to self-organize."

In hindsight, previous work had suggested that, given the right cues, stem cells could form eye tissue spontaneously, Ali says. A cocktail of genes is enough to induce frog embryos to form form eyes on other parts of their body2, and human embryonic stem cells in a Petri dish can be coaxed into making the pigmented cells that support the retina, sheets of cells that resemble lenses and light-sensing retinal cells themselves3.

However, the eye structure created by Yoshiki Sasai at the RIKEN Center for Developmental Biology in Kobe and his team is much more complex.

The optic cup is brandy-snifter-shaped organ that has two distinct cell layers. The outer layer — that nearest to the brain — is made up of pigmented retinal cells that provide nutrients and support the retina. The inner layer is the retina itself, and contains several types of light-sensitive neuron, ganglion cells that conduct light information to the brain, and supporting glial cells.

To make this organ in a dish, Sasai's team grew mouse embryonic stem cells in a nutrient soup containing proteins that pushed stem cells to transform into retinal cells. The team also added a protein gel to support the cells. "It's a bandage to the tissue. Without that, cells tend to fall apart," Sasai says.

At first, the stem cells formed blobs of early retinal cells. Then, over the next week, the blobs grew and began to form a structure, seen early in eye development, called an optic vesicle. Just as it would in an embryo, the laboratory-made optic vesicle folded in on itself over the next two days to form an optic cup, with its characteristic brandy-snifter shape, double layer and the appropriate cells.

Even though the optic cups look and develop like the real thing, "there may be differences between the synthetic retina and what happens normally," Ali says.

Sasai's team has not yet tested whether the optic cups can sense light or transmit impulses to the mouse brain. "That's what we are now trying," he says. However, previous studies have suggested that embryonic retinas can be transplanted into adult rodents4, so Sasai is hopeful.

Sasai, Ali and others expect that human retinas, which develop similarly to those of mice, could eventually be created in the lab. "In terms of regenerative medicine, we have to go beyond mouse cells. We have to make human retinal tissue from human embryonic stem cells and investigation is under way," Sasai says.
The eyes have it

Synthetic human retinas could provide a source of cells to treat conditions such as retinitis pigmentosa, in which the retina's light-sensing cells atrophy, eventually leading to blindness. In 2006, Ali's team found that retinal cells from newborn mice work when transplanted into older mice5. Synthetic retinas, he says, "provide a much more attractive, more practical source of cells".

David Gamm, a stem-cell biologist at the University of Wisconsin, Madison, says that transplanting entire layers of eye tissue, rather than individual retinal cells, could help people with widespread retinal damage. But, he adds, diseases such as late-stage glaucoma, in which the wiring between the retina and brain is damaged, will be much tougher to fix.

When and whether such therapies will make it to patients is impossible to predict. However, in the nearer term, synthetic retinas will be useful for unpicking the molecular defects behind eye diseases, and finding treatments for them, Sasai says. Retinas created from reprogrammed stem cells from patients with eye diseases could, for instance, be used to screen drugs or test gene therapies, Ali says.

Robert Lanza, chief scientific officer of the biotechnology company Advanced Cell Technology, based in Santa Monica, California, says the paper has implications far beyond treating and modelling eye diseases. The research shows that embryonic stem cells, given the right physical and chemical surroundings, can spontaneously transform into intricate tissues. "Stem cells are smart," Lanza says. "This is just the tip of the iceberg. Hopefully it's the beginning of an important new phase of stem-cell research."

[Chun Liroy]

That's really cool, but I thought that they were already bladders that were grown using stem cells?

[Tristam]

That's really cool, but I thought that they were already bladders that were grown using stem cells?

Pretty sure that was in a graft, the big thing here is that they just took a blob of ES cells in a dish with a chemical environment that supported growth, as opposed to a physical environment that provides a huge amount of other cues. Additionally, an eye is a hugely complicated developmental process and a very specialized organ, and if these retinas are actually functional, again from such a minimal framework, then ES cells in this case perform better than most would have hoped.

Put another way, it's been shown that putting ES cells in a complicated scaffold can direct the cells according to the information provided in that scaffold (weakly functioning rat hearts have been developed via es cells similarly).

http://www1.umn.edu/news/features/20...7_REGION1.html

But the key here is that a photosensitive organ has been created *without* any of those complicated scaffolds, they just plain grew it in a dish. Also, the development seems to have progressed in a manner very close to how it would have within the embryo, which is not necessarily the case with grafted cells. So this is better empirical evidence that the instructions for organization and development in this case are mostly intrinsic to the ES cells.

[Chun Liroy]

Yeah, I also thought the bladders were grown in the same manner, but apparently that was only a theoretical application. Good to see that it has finally been able to be proven possible then.

[Kaylia]

Thanks for the advice again. I ended up over-thinking it. The first question wanted the energy assuming no electron annihilation which was what I calculated. The second part wanted me to figure it out assuming electron annihilation which was the value in my notes. Then calculate it again assuming kinetic energy loss due to neutrinos.

Overthinking is probably your worst enemy in undergrade physics. I don't know how many time I turned a simple problem into something overly complicate, only to realize after 20 hours that all I did was pointless.

[Eliseos]

Watched both semesters of his intro physics classes on MIT's open course-ware. God damn if he isn't the best teacher I've ever seen.

http://www.sciencedump.com/content/i...r-walter-lewin

[Kaylia]

Watched both semesters of his intro physics classes on MIT's open course-ware. God damn if he isn't the best teacher I've ever seen.

http://www.sciencedump.com/content/i...r-walter-lewin

I don't know what to think bout this. I can't deny this sort of class would be entertaining to watch, but if that's what draw a person toward sciences, someone will have to break his bubble eventually.

You won't be doing fancy thing in the labs, and you won't reinvent newton mechanics or relativity every days. Instead, you will spend 20 hours recalibrating something only to get crap result, you will waste half a week on a stupid integral...thats what sciences is like. It's boring...mostly, but there is always a reward at the end that make it worthwhile.

[Woozie]

I think he's good. Physics needs better PR. Physics' reputation is almost as bad as math these days. I can't remember the last time I told someone I do physics without getting a response along the lines of "yuck". And, as you already know, we're bringing in more physicists from overseas every year for work and teaching than we hire. I think that anything that gets people interested in physics is good.

Besides, this is MIT. Every student there is destined to go into some career doing what you just described anyways. Maybe a few people will now choose to frustrate the hell out of themselves in a physics lab instead of a chemistry lab. I know that you're just trying to say that this will give people a false impression, but I'm not sure if I believe students watching this will get any more of a false impression about physics than they have about other fields (this isn't exactly what I want to say, but I can't figure out how to say what I'm trying to say, and my previous sentence is the closest I can do right now. The point is, I don't think there's anything bad or wrong with teaching that way. After all, most sciences either have in-class demonstrations or have tons of demonstrations on youtube that many students may have seen before, like alkali metals in water or turning supercooled water into ice, etc).

[Kaylia]

I agree that physics needs betters PR, but at the same time, a teachers should always show both side of the coins. I don't think they would be be sincere with their students if they turned every classes into a show like this without preparing for what is coming. I'm not particularly worried about these MIT students, I was mostly thinking about high school/college teachers who decide to take that route.

Meh...w/e work I guess. It can't hurt if more people try a degree in physics. It just depress me when I see 75% of the people quit after a few years.

[Yugl]

Question: How do intervals between sleep work? Conventional wisdom suggests eight hours of sleep last I recall, but how many hours of activity needs to go between those eight hours before they will qualify? To give an example of what I mean, I highly doubt I can tell someone to sleep for 80 hrs so they can stay up for 10 dys. If the question isn't clear, I'll try to rephrase it.

[Kaylia]

Question: How do intervals between sleep work? Conventional wisdom suggests eight hours of sleep last I recall, but how many hours of activity needs to go between those eight hours before they will qualify? To give an example of what I mean, I highly doubt I can tell someone to sleep for 80 hrs so they can stay up for 10 dys. If the question isn't clear, I'll try to rephrase it.

I'm not sure I can answer this questions, all I know is that sleep is an inverse function of the distance between now and the next exam/deadline.

The shorter this distance is, the less sleep you need.



[edit]
More seriously, I'm confident that the real answer would be "8 hours on a 24 hours schedule". Our body function are usually regulated around that 24 hours clocks. Doing anything else is most likely harmful to some extent.

[Chun Liroy]

Question: How do intervals between sleep work? Conventional wisdom suggests eight hours of sleep last I recall, but how many hours of activity needs to go between those eight hours before they will qualify? To give an example of what I mean, I highly doubt I can tell someone to sleep for 80 hrs so they can stay up for 10 dys. If the question isn't clear, I'll try to rephrase it.

Uh I'm unsure, but I do know that the way that we sleep is pretty inefficient and the best way to sleep is about 5 times a day or something. I don't think there's really any "conversion" for time asleep to time awake. Because it not only depends on length awake, but what you do during those periods so I would say it's probably hard to tell. I do know that you can "make up" for lost sleep as well. For example, normally sleep 8 hours, pull all nighter, go to sleep at your traditional time except sleep longer than your normal 8 hours, and if you don't then that sleep will still need to be made up etc.

[Chun Liroy]

I'm not sure I can answer this questions, all I know is that sleep is an inverse function of the distance between now and the next exam/deadline.

The shorter this distance is, the less sleep you need.



[edit]
More seriously, I'm confident that the real answer would be "8 hours on a 24 hours schedule". Our body function are usually regulated around that 24 hours clocks. Doing anything else is most likely harmful to some extent.

Our internal body clocks actually operate on 25 hour days.

[Tristam]

Question: How do intervals between sleep work? Conventional wisdom suggests eight hours of sleep last I recall, but how many hours of activity needs to go between those eight hours before they will qualify? To give an example of what I mean, I highly doubt I can tell someone to sleep for 80 hrs so they can stay up for 10 dys. If the question isn't clear, I'll try to rephrase it.

I don't think there's really a solid answer to this question yet. Some ideas I've read are that we tend to stay awake during times when we are most likely to be able to find food, we need to eat every day, so we need to stay awake for some length of time to find and eat that food. We also need to consolidate memories learned each day. But there's tons of variation in sleep cycles among different mammals, so no obvious evolutionary things jump out (e.g. dolphins sleep in 10 hour cycles w/ 0.2hr REM, Ferrets sleep in 14.5 hr cycles with 6hr REM). We know that REM cycles are important for some reason, and are more important early in life, and only exist in mammals and birds. The timing of REM is important for some reason, if you stay awake too long after learning a task, REM won't help with certain types of nondeclarative memory consolidation.

Our internal body clocks, as a slight correction, operate on 24.2 hour cycles, but under artificial light (which we all are exposed to after dusk) our body tends towards the 25 hour cycle Silentleroy mentioned. This is because the maximum shift our body allows over a one day period is one hour.

I'm paraphrasing heavily in all this from David Linden's "The Accidental Mind". He has a great description in Chapter 7 of what we know about sleep cycles, REM, and what parts of the brain are active during particular dreams and points in sleep cycles. He spends alot of time on why REM might be important, and why we need cycles and what might be going on at a molecular level to time everything, but no clear answer as to why our cycle is a certain length. I've also read in other books that an 8 hour sleep cycle is a recent invention due to how we organize our workdays in modern life. I seem to recall, if left to our own devices and were jobless, we would revert to shorter cycles more frequently. But I can't remember where I read that so take it with a grain of salt.

edit: On rereading a bit, REM for memory consolidation works best 4-8 hours after learning a task, so maybe there is something biasing towards multiple shorter intervals of sleep during the day? I dunno. Interesting question though.

[Yugl]

Thanks for the information (All three; especially, the REM part). I don't get much intimacy with this topic (Nor the subject of this topic), so I felt it was something I could safely ask here. I would like to test that 4-8 hour idea though.