# hitmankratos

Senior Members

88

1. ## Proof of elementary row operation for matrices?

Hey everyone, I'm taking a Linear Algebra course, and we just started talking about matrices. So we were introduced to the elementary row operations for matrices which say that we can do the following: 1. Interchange two rows. 2. Multiply a row with a nonzero number. 3. Add a row to another one multiplied by a number. Now I understood from the lecture in class how to use these and all, but I want to understand the logic behind number 2 and 3? Is there a mathematical proof that shows that by adding row R1 to row R2 we are not changing the system of equation? Same thing with number 2, how can we just multiply a row without changing the solution set? Thanks in advance,
2. ## Mechanism of a reaction

yes you're right, it can't be the last step. But in my case it cannot be the first step.
3. ## Mechanism of a reaction

Hi, We've had this chem assignement at school, and I'm stuck! I've tried everything but it just doesn't work. I don't even think anyone here can help me, but meh, might as well just give it a try. So we have this reaction : 2NH3 ---> N2 + 3H2 So we're asked to find a plausible mechanism (basically invent one!) that can give the following rate law: Rate = k[NH3] / [H2] I've spent about 3 hours trying diffrent mechanisms that take in account the balanced equation, but it never gives the right rate law. For example. I'Ve had this mechanism (the * means radical): NH3] --> NH2* + H* NH2* --> N* + H2 N* + NH3 --> N2H* + H2 N2H* + H* --> N2 + H2 When I take the last step for the slow step (as the rate law depends only on the slow step), I get something like Rate = k[NH3]² / [H2]² ... AND I ALWAYS GET SOMETHING SIMILAR! So any ideas?
4. ## Question concerning the roles of dopamine

Hi everyone, I am reading about parkinson's disease and all, and obviously there is dopamine. So after what I read, dopamine is an inhibitory neurotransmitter, which means that it stops the impulse. So by having a balance between acethylcolin and dopamine, the movement can be controlled (correct me if I said something wrong). Now my question is, dopamine has this role in movement, however, I read that it also has a role in motivation and all that stuff. So what is the diffrence between these two types of dopamine? Are both "types" made in the substantia nigra? Do they both go to the striatum? Thanks in advance.
5. ## How does a lack of dopamine affect movement (PD)?

Hi, I am doing a science fair project on a Parkinson's disease and I am wondering how can a lack of dopamine affect movement, as such to cause Parkinson's Disease? Doesn't dopamine affect desire and motivation? So why does someone start shaking when there's a lack of dopamine? Thanks,
6. ## Any INTERESTING gas-forming reactions?

Hi, So for our next lab this week in chemistry, we were asked to look around and find out about gas-forming reactions. Our teacher said that we can do pretty much any reactions (even those that smell bad or "explode", as long as it is done in very small quantities in a controlled envriomment), so I was wondering if anyone knows any gas forming reactions like that? It's ok if they don't smell, or explode or anything, any gas-forming reaction is welcome. I just want to get as many as I can before the lab. Thanks in advance for any help whatsoever.
7. ## How to calculate the fraction of elements with diffrent oxidation states within a compound?

I just don't get it for some reason... Basically, the equation is : LaH2 + LaH3 --> LaH2.90 I'm just comparing the hydrogens...so 2.9 = H3(x) + H2(y)....this equation cannot be solved as i don't have a second equation.... Any other clues?
8. ## How to calculate the fraction of elements with diffrent oxidation states within a compound?

Hi There is a chemistry problem that I'm really not able to do. It's basically the reaction of Lanthanum with Hydrogen to produce the nonstochiometric compound LaH2.90 . So, if we know that the compound contains Hˉ, La⁺² and La⁺³ (yeah its a little 3 there), how can we know the fraction of La⁺² and La⁺³ present in the compound? I know that the answer will be 10.9% La+2 and 90%La+3....but I have NO IDEA on how to get that... I'm not asking for HOW to do it completely, but just clues that can guide me into finding the answer... Thanks in advance,
9. ## What diffrenciates totipotent, pluripotent, multipotent and unipotent stem cells?

Hi, I know that there are several stem cells that can become several types of cells. However, I was wondering what characterises these stem cells - meaning, what is the diffrence in their metabolisms that make them totipotent, pluripotent, multipotent or just unipotent (is it how they are made, or is it some enzymes...or what?) thanks in advance,
10. ## Why don't nerospheres adhere to the bottom of the petri?

oooh okkay I see.... thank you very much. Very clear.
11. ## Why don't nerospheres adhere to the bottom of the petri?

hmm seems like no one knows.... can anyone prove me wrong? xD
12. ## Why don't nerospheres adhere to the bottom of the petri?

Hi, I was wondering how come neurospheres (generated by neural stem cells) don't adhere to the bottom of the petri dish? I thought all of the cells when they weren't clung to the petri dish meant the cells were dead...why isn't the case with stem cells? Thanks in advance to all those of you who can answer !
13. ## Neurofibrillary tangles in Alzheimer's

Hi, I'm a little confused... Are Neurofibrillary tangles directly made up out of hyperphosphorylated Tau, or is it their formation that is CAUSED by the hyperphosphorylation of Tau? If so, then why is it that a more phosphate on Tau causes these tangles?
14. ## What is phosphorylation?

Hi, I'm working on a science fair project on Alzheimer's and it's basically all about the protein Tau being hyperphosphorylated... I know in this particular case, that phosphorylation is used to activate this protein (tau), and that kinases and phosphatases that add and take awat those phosphates. Now my question : How come phosphorylation activates proteins? Does phosphorylation have another purpose? What else is important to know about phosphorylation?
15. ## Is there a link between tau protein and amyloid plaques in alzeihmer's disease?

Hi, I was wondering if there is a link between the hyperphosphorylation of tau protein and amyloid plaques in alzeihmer's disease? Are both present in Alzeihmer's?
16. ## Optical Physics question concerning mirrors and observers !

OK ! First take a look at this picture : Basically, what I want to know is, how can I determine the minimal mirror's length so that the observer (blue smiley) can see the whole reflected image (reversed moon)?
17. ## Light on a mirror question...

Hi, I was wondering on the way light reacts with mirrors when the mirror is thick... Is it the image on the left or the image on the right?

Anyone?
19. ## Alzeihmer disease: inhibition of amyloid plaques?

Hi everyone, Ive heard that one reason of the Alzeihmer's disease is the formation of amyloid plaques in the brain. Ive also heard that - according to in vitro tests - some natural stuff such as garlic and cranberry could inhibit them. I have 2 questions: If someone just ate garlic for example, would it reach the brain and specifically the amyloid plaques automatically (would it pass the blool brain barrier (sorry if im completly off-topic). If this works, would this help cure alzeihmer's disease or prevent it? Thanks.
20. ## How are alzeihmer tests done on rats?

How can they tell is the rat is getting any better?
21. ## How are alzeihmer tests done on rats?

Hey everyone, I was wondering, with all the alzeihmer research going on, how can they test something on rats? Is it by injecting them whatever they want with a special technique? How does it work for these kind of tests?
22. ## How are proteins used in lab?

Can you give me an example on something you've worked on or seen? Anything ! I just want to get an idea
23. ## How are proteins used in lab?

Hi, I'm going to start my science-fair project for next year soon, and I have some questions in relation with proteins and experiments in lab... 1- Can a protein be extracted from something? What kind of material is used for that? 2- In lab tests, how can proteins be tested on cells? What kind of material again? I am particularly interested in the protein TRAIL (TNF related apoptosis induced ligand) and their potential in destroying tumors when being carried by stem cells (http://www.medicinenet.com/script/main/art.asp?articlekey=100521). Can anyone tell me about these sorts of proteins? Thanks.
24. ## Is it true that the human body is better off with 2 sets of 4 hours of sleep?

Allrighty. Very informative. Thank you !
25. ## Is it true that the human body is better off with 2 sets of 4 hours of sleep?

I've read somewhere the human body is better off with 2 sets of 4 hours of sleep rather than 8 hours of sleep and was wondering if it was true. Are there any studies that can prove that? Thanks !
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