# Search results

1. ### Testing gradient against a value

Homework Statement I have 25 pairs of values. I have a gradient and want to test if this gradient is significantly different from 1. Which stats test do I use? I thought of using a one-sample t-test, but how are you meant to put 25 gradients in the test!??? thanks...

how do they improve high-frequency transmission (and not low-frequency?) ? I'm a biologist... Thanks
3. ### Mass moment of inertia of an irregular area

Hi. Please help. I'm struggling to find the mass moment of inertia of an area. Please see picture. I already have the centroid of the area, and the exact area. How would I find the mass moment of inertia of this area about its centroid? I tried using AutoCAD, but it gives you the...
4. ### MathCAD - separation of real and imaginary parts of a complex variable

Hi guys, just wondering whether you could help. I've got a complex number in terms of a lot of variables, and need to separate it into its real and imaginary parts. How do I do that? I spent past hour trying to look for tutorials, unfortunately none tells you how to do it...
5. ### Bag of coffee bean

Recently I bought a bag of coffee beans from abroad on a plane, now the bag is very inflated. I want to take the bag on a plane again, would it burst?
6. ### Irreducible complexities

we had a lecture on intelligent design (or should I say - one against ID). the lecturer went into great detail as to how some complex systems that are apparently irredicubly complex can actually be taken apart, and the system still works. e.g. the blood clotting system. what I don't...
7. ### Donnan Equation

How do you adapt the Donnan Equation to 3 difffusible ions?
8. ### Medical OBEs/Astral Projections

Is there ANY scientific basis of OBEs or Astral Projections, or remote viewing?:confused: and whether it is possible or not to project astrally?
9. ### Medical Action Potential

This is about voltage clamping: When Hodgkin and Huxley voltaged clamped a nerve - when hyperpolarised there was a small inward current, why is that? and when they used a depolarising clamp, there is firstly a brief capacitative current - this current is outwards, why?:confused:
10. ### GABA(A) Receptors

In the lecture handout it says "When cells are hyperpolarised the result is a depolarisation towards threshold." What does this mean?:confused:
11. ### Medical Chemical and Electrical transmission

Signal propagation along motor nerves or fibres of muscles is electrochemical (or electrical)l, whereas transmission at the neuromuscular junction is chemical, Why is that?
12. ### Medical Membrane potentials in a nerve membrane

This is about membrane potentials in a nerve membrane. I've already studied the Nernst equation and the Goldmann equation, but I have found its significance in explaining the resting potential. The Nernstian potential occurs at equlibrium, when concentration gradient = opposing electric...
13. ### Glycogen synthesis and lysis

How are signals form insulin integrated with those from adrealine and contraction to regulate the breakdown or synthesis of glycogen in muscle? I know that adrenaline stimulates the conversion of ATP to cyclic AMP by activating adenyl cyclase, and I think insulin does the opposite. But how are...
14. ### Medical Sodium Channels in refractory period

After an action potential has passed the localised region enters its refractory period, and during the absolute refractory period a second impulse cannot be conducted regardless of the size of the stimulation. This is because the sodium channels cannot open immediately after closing, why is that?
15. ### Electricity and Magnetism

1) A horizontal metal rod of 1.5m long is aligned in and East-West direction and dropped from rest from the top of a high building. Calculate the e.m.f. induced across the falling rod 2.5s after release. The horizontal component of Earths magnetic field is 2x10^5 T. Surely you need the area...
16. ### Refractory Period for Neurone

The absolute refractory period: is there any reason for this period (the cause)?
17. ### Relay Neurones

Are they bipolar? I cant find it anywhere :( Thanks
18. ### Activation Energy

Is activation energy dependent? I think it isn't, but if you rearrange the Arrhenius equation you get: Ea - activation energy Ea = RT(lnA - lnk) so as temperature Ea can change. But I am thinking that k will also change in relation so Ea is constant?
19. ### Titrations and pH indicators

quote from http://www.chem.ubc.ca/courseware/pH/section15/content.html [Broken] Intuition may suggest that the endpoint of the titration will occur at the equivalence point if we choose an indicator whose pKa is equal to the pH of the equivalence point. If such an indicator was chosen, the...
20. ### Zinc Carbon Cell

The hydrogen liberated at the cathode would coat the electrode so polarises the cell. And manganse (IV) oxide is used as a depolariser. I got an equation in my notes: 2MnO2 + 3H2 --> 2MHO(OH) + 2H2O. But evidently the oxygen doesn't balance. I tried looking on the internet but still no...
21. ### Hydrogen Peroxide

What do you get if you use KMnO4 to oxidise hydrogen peroxide? and what happens to hydrogen peroxide if it is used as an oxidiser? Surely the second one there are two possibilities: 1) H2O2 + 2e- --> 2OH- 2) H2O2 + 2H+ + 2e- --> 2H2O
22. ### Ester be separated from other liquids using fractional distillation?

After esterification, can the ester be separated from other liquids using fractional distillation?
23. ### Reducing Sugar

Fructose is a reducing sugar, and the ketone acts as a reducing centre, which reduces Cu2+ --> Cu+. Therefore fructose itself becomes oxidised. However, how can a ketone group be oxidised? I thought: aldehyde becomes oxidised to carboxylic acid ketone: cannot be oxidised.
24. ### How come the three layers of retina are so awkwardly arranged?

How come the three layers of retina are so awkwardly arranged? Light has to pass through the inner and intermediate layers before reaching the photoreceptor layer, was there any evolutionary advantage by having this arrangement?
25. ### Microbiology Practical

I used a white tray to work on for my antibiotics investigation. What is the tray called? :frown:
26. ### H+ concentration gradient Photosynthesis

FOr the light dependent reaction, In the textbook it says that the H+ concentration gradient across the thylakoid membrane is maintained by: 1) photolysis 2) transport of electrons from photosystem II along carriers 3) formation of NADPH. I can understand 1) and 3), but I have no idea...
27. ### Bubble Chamber

Why don't neutral particles leave tracks in the bubble chamber? How is the bubble formed, is it condensation around ionised hydrogen, or around the particles?
28. ### Reducing agents

I have got some problems on reducing agents, can someone explain why: 1) LiAlH4 and NaBH4 both reduce carboxylic acids / ketones, but only LiAlH4 reduces a nitro group? Why doesn't NaBH4 reduce the Nitro group? 2) How come H2/Nickel reduces C=C bond but LiAlH4 doesnt? 3) Similarly, why...
29. ### Different antibiotics on Gram positive and Gram negative bacteria

Hi. I am doing an investigation on the effects of different antibiotics on Gram positive and Gram negative bacteria. 1) Can you say that antibiotics and bacteria form a chaotic system? Can a very small change in concentration of antiboitics, or a small variation in pH, change the diameter of...
30. ### Comparing effects of antibiotics on Gram +ve and -ve bacteria

I am doing an investigation on: comparing effects of antibiotics on Gram +ve and -ve bacteria. I have used 8 antibiotics and I have measured the diameter of killing zones. I am a bit unsure of how to carry out the analysis. I will be using Mann Whitney U Test, but what about graphical...