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1. ### Excel - linest function with blanks help

Hi, Ive been trying to use the linest function with blanks but I can't get it to work... (specifically =INDEX(LINEST(E6:E16,A6:A16^{1,2,3}),1). Here A6:A16 is a number increasing in increments of 1 between 25 to 35, and E6:E16 is only filled if the corresponding measurment is made. Does anyone...
2. ### Determine the uncertainties

Great thanks :) any idea why it is the same as the uncertainty in a single measurement... Just doesn't seem right to me! Xxx
3. ### Determine the uncertainties

Homework Statement what is the uncertainty of \frac{a+b}{c+d} if a=b=c=d and σ_a = σ_b =σ_c=_d Homework Equations σ_{a+b}=√(σ_a^2+σ_b^2) σ_{\frac{a}{b}}=√((\frac{σ_a}{a})^2+(\frac{σ_b}{b}^2)) The Attempt at a Solution since a=b=c=d σ_{a+b}=√2 σ_a σ_{\frac{a}{b}}=√2...
4. ### Statistics: detectibility of two objects, with 95% confidence

Homework Statement Apologies if this is not meant to go into homework area; this is not a homework or coursework question, but more to convince myself that what I am reading is correct I have attached the diagram I am pondering over... How can I prove that if I want to differentiate...
5. ### Area under v vs t sinusoidal trace

if I have a sinusoidal trace on an oscilloscope (v vs t) and I wanted to find the area under the wave form squared graph I could integrate the sqaured waveform with respect to t. but since i don't have the integration facility... is it fair to say that the area under the graph is proprtional...
6. ### Impedence and reflection

why does a change in impedance causes reflection? I know that R=(Z2-Z1)/(Z1+Z2), but what is it that makes the wave be reflected? thanks
7. ### If i have a=exp x, and i know that my uncertainty in a is 3% ( at all

so dx = da/a? so the absolute uncertainty in x is equal to the percentage uncetainty in a?
8. ### If i have a=exp x, and i know that my uncertainty in a is 3% ( at all

if i have a=exp x, and i know that my uncertainty in a is 3% ( at all points). At a point where a=2, how do we calculate the uncdrtainty in x. is the absolute value = (3% of ln 2)/ln 2, which equals 0.03mm, which equals 1% (if x is 3mm) thanks
9. ### Trying to calcualte the uncertainty

Thanks :) is this just differentiation? So delta F(A) = da times dF/da ?
10. ### Trying to calcualte the uncertainty

if i have two repeat measuremetns, A and B, is the following correct? I am trying to calcualte the uncertainty... I know there are easier ways to do this but i need to have the uncertainty of the mean in terms of δ(A-B). from pairs of measurements A and B at each setting we have...
11. ### Percetnage by volume of propanol from original volumes

if i had 500ml of water and added 250ml of propanol, how would I go about working out its percentage by volume? thanks
12. ### P-value calculation

Homework Statement This isn't a homework question but figured this is the best place to ask :) what I have done is measure doses from an x-ray tube at various positions using two different methods, method1 and method2. I would like to say if they are statistically significant or not by using...
13. ### What affects the speed of sound - does viscosity?

Ive just noticed all these posts - thank you! (sorry for the delay!)
14. ### LaTeX Latex - graphs closer together

ive got to give a hard copy... They have lots of rules incl fig size, margin size, font size etc etc :( thanks ill have a play!
15. ### LaTeX Latex - graphs closer together

the graphics size is fine, and the white box is too. i have know idea why this is happening! :(
16. ### LaTeX Latex - graphs closer together

Hi thanks for your response. However my graphs have to be this size. and they don't go side by side unless smaller. Its the vertical space inbetween them I don't want. so instead of having 6cm between them on the page i want only one cm. if tried eg \vspace{-50mm} but that doesn't shift it...
17. ### LaTeX Latex - graphs closer together

There was not enough room to fit my graphs in the text where they were supposed to go so latex put them in the next page. This meant that this page only has these two graphs and the text begins again on the page after that. There is a lot of space between (see attached). How do i make it take up...
18. ### Angular momentum - length of day change if drive on other side of road

but would one increase the angular momentum and the other decrease the angular momentum? I think I am missing something that is staring me in the face...
19. ### Angular momentum - length of day change if drive on other side of road

This is a question that I remember hearing a few years ago: If the law were changed so that traffic in Great Britain traveled on the righthand side of the road instead of on the left, would the length of the day increase, decrease or be unaltered? I remember the answer was increase...
20. ### 95% confidence interval - median

can you do that in excel?
21. ### 95% confidence interval - median

To calculate the 95% confidence interval of the mean of a normal distribution you calculate 1.96 χ standard error on the mean. what do you do if you want to calculate the 95% confidence interval on the median of the distribution, for a distribution that is most definitely skewed and not...
22. ### Calculating RMS Value for Unequal Peak Amplitudes

If I have a wave that looks pretty much sinusoidal but the peak positive amplitide is greater than the peak negative applitude how do I calcualte the rms vlaue - is it still the peak positive amplitude divided by root 2? Thanks :)
23. ### Medical Open heart surgery

replacing the aortic valve
24. ### Medical Open heart surgery

In an open heart surgery, blood is diverted to a heart-lung bypass machine by means of cannulae. A patient had previous CABG so the line was put into his leg, and the other in the right ventricle I think. Why would you put it in the leg? and would it be the right ventrical that the other cannula...
25. ### Common-mode rejection ratio and Instrumentation and difference amplifiers

s youd agree that the answer is -66dB?
26. ### Common-mode rejection ratio and Instrumentation and difference amplifiers

thats what i thought i was doing 1/0.05 = 20/1 or am i misunderstanding it? thanks
27. ### Common-mode rejection ratio and Instrumentation and difference amplifiers

Homework Statement 1. a) If we wish to record an ECG of amplitude 1mV in the presence of interference that causes a common-mode voltage of 100mV to appear on the inputs of the amplifier, then what common-mode rejection ratio (CMRR) do we need require if we need a signal to noise ratio better...
28. ### Confusion with dB equation - 10 or 20?

i meant in other situations. like if you arent measuring the voltage or the power. but instead some other quantity. how do i know what one to use?
29. ### Confusion with dB equation - 10 or 20?

how do you know when to use dB= 20log(ratio of input/output quantities) or dB=10log(ratio of output and inout). voltage seems to be 20, power seems to be 10... but how about when doing Fourier transforms and you want to find out 3dB of maximum, for example? thanks
30. ### Fast Fourier Transform in excel

thats what I was following. It only works for a constant sampling rate...
31. ### Fast Fourier Transform in excel

I really need your help - i can't work out how to do a FFT in excel. The main problem is I don't have a constant sampling rate - I recorded the time and then the corresponding magnitude of the wave. I have followed everything oneline but I can't seem to get anything to work as I can't fill the...
32. ### Speed of sound - why does adding ethanol to water increase the speed of sound

wow - thanks everyone! glad I am not missing something really obvious! your help is much appreciated!

thanks :)
34. ### Attenuation coefficient of water

I have read that the attenuation of water (for ultrasound) is 0.0472 Np m–1 (MHz)–2. What is this in dB/cm/MHz^-2 ? What is Np? thanks
35. ### What affects the speed of sound - does viscosity?

yes. I can't find viscosity anywhere. that is the parameter I was wondering. I was just wondering if there was any less obvious parameters...
36. ### Speed of sound - why does adding ethanol to water increase the speed of sound

Kevin Martin, David Spinks, Measurement of the speed of sound in ethanol/water mixtures,Ultrasound in Medicine & Biology, Volume 27, Issue 2, February 2001, Pages 289–291 If you google image speed of sound in ethanol solution the image is actually on the second line...
37. ### What affects the speed of sound - does viscosity?

What factors affect the speed of sound besides the temperature? Does viscosity affect the speed of sound? Thanks
38. ### Speed of sound - why does adding ethanol to water increase the speed of sound

If you have a tank of water then the speed of sound is 1482 m/s. If you add ethanol, the speed of sound increases. This seems to be pretty linear with the % concentration of ethanol. why does ethanol (or propanol) increase the speed of sound? thanks
39. ### Percentage errors

ah great :) thanks :)
40. ### Percentage errors

i understand the money analogy, but not when talking about the areas - sorry! :S we are only subtracting once
41. ### Percentage errors

How can you get positive and negative errors to be different in magnitude? for example - when calculating the error of the area of an annulus from two circular areas (ie subtracting one from the other, why is the positive error greater than the negative error Thanks
42. ### General uncertainties question - type B

Homework Statement i am trying to quanify uncertainties.. Homework Equations The Attempt at a Solution For type B uncertainties I have calibration of the oscilloscope, scale reading of the ocilloscope and the uncertaninty of the setup, with associated percentage errors of 2.5%...
43. ### Speed of sound in water at 16 degrees celsius

Homework Statement How do you calculate the speed of sound in water at 16 degrees celsius? Homework Equations Speed at 20 degrees is 1482m/s The Attempt at a Solution I need help getting started... I don't know how to go about trying to work this out (this isn't a homework...
44. ### LaTeX Latex - tables taking up too much room

what do you mean by float the tables?
45. ### LaTeX Latex multicolumn problem

also how to I insert my text properly?!
46. ### LaTeX Latex multicolumn problem

Can anyone tell me what is wrong with what I've written here - its coming up with lots of errors (inlcuded below). I have the \usepackage{multirow} at the beginning. Thanks [tex] \begin{table}[h] \caption{Investigation of interleaf leakage using ion chamber} \begin{center}...
47. ### LaTeX Latex - tables taking up too much room

Fantastic! this works exactly how i wanted it to! thanks :)
48. ### LaTeX Latex - tables taking up too much room

i didnt include all the info but you appear to see what my probem in anyway... Do you mean do this: \begin{table}[htp] \caption{Caption goes here} \begin{center} \begin{tabular}{c c c c c c} \hline\hline Plan (\%) & 1 & 2& 3 & 4 & 5\\ \hline Max & 108.7 & 108.1 & 109.2...
49. ### LaTeX Latex - tables taking up too much room

Okay thanks. here is an example of a table: \begin{table}[htp] \caption{Caption goes here} \begin{center} \begin{tabular}{c c c c c c} \hline\hline Plan (\%) & 1 & 2& 3 & 4 & 5\\ \hline Max & 108.7 & 108.1 & 109.2 & 108.7 & 109 \\ Min & 86.2 & 88.4 & 91.6 & 92.3 & 89.6 \\...
50. ### LaTeX Latex - tables taking up too much room

Hi, when i have multiple tables together the spacing between them is large and takes up unnecessary room. I have 5 tables which span the entire width and are one ontop of the other. If i was to put these tables into word they would fit into the one page. However, on latex the are spread over...