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Short description of the experiment.
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MBobrik Offline
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Post: #1
Short description of the experiment.
We had a lot of talk about the experiment itself, this thread here is to sum it all up so that it for example can ber presented to a biologist we ask for feedback/recomendations.
The description of the experiment itself :

Goal.
To observe gravitropism of p. patens in hypogravity 0 < g < 1 G, and to find a gravity level where the growth becomes indistinguishable from 1G.

Procedure.
  • There will be N batches , each consisting of M samples, due placement constraints N * M <= 18 ( we are currently planing to use 6 batches, 3 samples per batch ).
  • All batches are initially in dormant state, and will be activated sequentially, each observed for 25 days, during which artificial gravity is maintained at a given level.
  • To set the gravity values of the batches, following algorithm has been proposed ( EDIT: this is already version 2, the final algorithm of how we choose the G values is up to debate ) :

    Start :
    • use 0.3 G first
    • If the growth is significantly altered
      • use 0.6 G,
      • If the growth is significantly altered
        • use folowing values for the rest 0.9 G, 0.75 G, 0.45 G, 0.15 G
      • Else
        • use folowing values for the rest 0.5 G, 0.4 G, 0.2 G, 0.1 G
    • Else
      • use 0.1 G,
      • If the growth is significantly altered
        • use folowing values for the rest 0.25 G, 0.2 G, 0.15 G, 0.05 G
      • Else
        • use folowing values for the rest 0.08 G, 0.06 G, 0.04 G, 0.02 G
    We will thus have four possible sequences :
    1. If even 0.6 G still affect growth, we will have ....................{ 0.90, 0.75, 0.60, 0.45, 0.30, 0.15 }.
    2. If 0.3 G affects growth but 0.6 G doesn't, we will have .......{ 0.60, 0.50, 0.40, 0.30, 0.20, 0.10 }.
    3. If 0.3 G doesn't affect growth but 0.1 G does, we will have .{ 0.30, 0.25, 0.20, 0.15, 0.10, 0.05 }.
    4. If even 0.1 G doesn't affect growth, we will have ...............{ 0.30, 0.10, 0.08, 0.06, 0.04, 0.02 }.
    .
  • Growth conditions
    • Gravity variable, set per batch.
    • Temperature : constant 23 +-0.5 deg C.
    • Zero light to enhance the gravitropism. As a consequence the plant won't photosynhetise, won't need atmospheric CO2, and will get energy from glucose in the growth medium.
    • Growth medium : a 15x15x2 mm patch of gelatinous growth medium. The composition is yet to be decided, but our most probable choice will be the BCDAT medium with glucose added as a source of carbon and energy, enhanced by all other trace elements used by other compositions to be on the safe side.
    • Atmospheric conditions :
      • Initial 21 % O2, we will allow drop to a value yet to be determined.
      • Either we will absorb all CO2 chemically, leaving us with constant zero concentration through the experiment, or we will allow build-up up to a maximum level (value yet to be determined).
      • Pressure 1 Atm, we wil allow drop/increase to a value yet to be determined.
      • 100 % humidity.
  • The growth will be evaluated by taking photograph of each sample hourly at fixed zoom. It is yet to be determined if the short flash of light during photographing will suppress the gravitropic response, and we have to take only IR photographs, or we can afford normal visible light photos.

EDIT: continuosly fixing typos and stuff
(This post was last modified: 02-19-2015 05:13 PM by MBobrik.)
02-16-2015 11:47 PM
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HenryRasia Offline
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Post: #2
RE: Short description of the experiment.
Great plan, man, a few questions:

After each batch's 25 days are over, will we still be able to film previous batches? Just in case something interesting happens, or is that completely worthless? We could even reduce picture taking to one a day.

About the dormant/awakening thing, are we positive this can be achieved reliably and cheaply (money and mass/volume-wise?). If so what would that be?

This experiment has the objective of finding the minimum g level at which the moss grows well, is that correct? I thought that we were going to create a graph of g level versus growth speed and discover if it is linear, exponential, or what have you. Also, we were going to see, besides arbitrary g increments, how growth is like at exactly 0.16 and 0.38 g (the gravity of the Moon and Mars, respectively). This would be our real-life application as Moon/Mars colonies may have to use centrifuges to grow crops, and NASA hasn't even considered this yet (as far as we know, could be wrong). What do you have to say about that?

We choose to go to the Moon and do the other things not because they are easy but because they are hard. -JFK
02-17-2015 12:41 AM
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Nicholander Offline
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Post: #3
RE: Short description of the experiment.
I agree with HenryRasia, we should also do 0.16 and 0.38 g levels, but that will bring us down to having just 4 batches for the arbitrary gs. Would 4 batches be enough for finding the minimum g level that the moss grows properly? Or would we have to redesign the moss container to include 8 batches?
02-17-2015 02:03 AM
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MBobrik Offline
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Post: #4
RE: Short description of the experiment.
(02-17-2015 12:41 AM)HenryRasia Wrote:  After each batch's 25 days are over, will we still be able to film previous batches? Just in case something interesting happens, or is that completely worthless? We could even reduce picture taking to one a day.

Sure. We may check how long they will last as the oxygen levels keep falling.

(02-17-2015 12:41 AM)HenryRasia Wrote:  About the dormant/awakening thing, are we positive this can be achieved reliably and cheaply (money and mass/volume-wise?). If so what would that be?

No water = spores dormant. Water, spores active. The only question is, whether we keep the spores in dehydrated growth medium and then just add water, or we have to keep the medium moist and spores separated and dry, and then add the two together.

(02-17-2015 12:41 AM)HenryRasia Wrote:  This experiment has the objective of finding the minimum g level at which the moss grows well, is that correct? I thought that we were going to create a graph of g level versus growth speed and discover if it is linear, exponential, or what have you.

Maybe we should ask the biologists. At any rate, we should avoid results like 0.3G normal, 0.25G normal, 0.2G normal, 0.15G normal, 0.1G normal, 0.05G zero growth. So we should do the bisection thing at least with the first two samples, and then perhaps proceed linearly to zero.

(02-17-2015 12:41 AM)HenryRasia Wrote:  Also, we were going to see, besides arbitrary g increments, how growth is like at exactly 0.16 and 0.38 g (the gravity of the Moon and Mars, respectively).

The division would bring us very close to those values if the turning point happens to be there. For example, the values could be 0.15625G and 0.1625G, and 0.375G and 0.3875G respectively. And I personally don't think that if the moss grows normally at 0.1625G, it will fail at 0.1600G. But then again, someone who researched gravithropism his entire life knows probably better.
02-17-2015 02:30 AM
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Newt Offline
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Post: #5
RE: Short description of the experiment.
(02-17-2015 02:03 AM)Nicholander Wrote:  I agree with HenryRasia, we should also do 0.16 and 0.38 g levels, but that will bring us down to having just 4 batches for the arbitrary gs. Would 4 batches be enough for finding the minimum g level that the moss grows properly? Or would we have to redesign the moss container to include 8 batches?

It seems that, if we get the other measurements well, we will be able to construct a reasonable estimate for what it should be like at those g levels, if there is so much deviation as to make us need to specifically do Mars/Lunar gravity, we may well not be able to get our sat to spin at the precise right speed. Not to mention the fact that over the course of the few cm that the moss is thick, there may be relatively large difference in the psuedogravitation.

As a quick calculation of that, if we have r=.04m, and we spin at 80rpm, we will have a=2.8m/s^2 (0.286g).
If we have r=.045, still spinning at 80rpm, a=3.158m/s^2, or.322g; in half a centimeter, we just added more than .3g's.

I do not think we can really justify caring about getting more precise than what Mbobrik already had.
(This post was last modified: 02-17-2015 03:46 AM by Newt.)
02-17-2015 03:44 AM
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MBobrik Offline
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Post: #6
RE: Short description of the experiment.
Thinking about it again, you guys are true, we will have a G difference of 11 % between root and tip, so it is pointless to make G increments that small. And the growth change will most probably be continuous, not sharp on/off behavior. So it is pointless to search for its edge, and a more or less linear grapth is preferred. On the other hand, we don't know where the 'interesting' part starts, so it would be wise to change the G steps at least according to the results of the first batches. So I came to the following algorithm.

Start :
  • use 0.3 G first
  • If the growth is significantly altered
    • use 0.6 G,
    • If the growth is significantly altered
      • use folowing values for the rest 0.9 G, 0.75 G, 0.45 G, 0.15 G
    • Else
      • use folowing values for the rest 0.5 G, 0.4 G, 0.2 G, 0.1 G
  • Else
    • use 0.1 G,
    • If the growth is significantly altered
      • use folowing values for the rest 0.25 G, 0.2 G, 0.15 G, 0.05 G
    • Else
      • use folowing values for the rest 0.08 G, 0.06 G, 0.04 G, 0.02 G

We will thus have four possible sequences :
  1. If even 0.6 G still affect growth, we will have { 0.90, 0.75, 0.60, 0.45, 0.30 0.15 }.
  2. If 0.3 G affects growth but 0.6 G doesn't, we will have { 0.60, 0.50, 0.40, 0.30, 0.20 0.10 }.
  3. If 0.3 G doesn't affect growth but 0.1 G does, we will have { 0.30, 0.25, 0.20, 0.15, 0.10 0.05 }.
  4. If even 0.1 G doesn't affect growth, we will have { 0.30, 0.10, 0.08, 0.06, 0.04 0.02 }.

This way, we are not likely to miss the G range where the behavior changes, but we still have evenly spaced values to create a nice graph from.
(This post was last modified: 02-18-2015 01:25 AM by MBobrik.)
02-17-2015 06:33 PM
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HenryRasia Offline
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Post: #7
RE: Short description of the experiment.
What I mean is that moss growth isn't a binary normal/no growth as you put it. Maybe the moss will grow faster at around 0.6 g, but then lose its bearings below 0.4 g. Maybe it just grows faster and faster as you decrease g force (linearly? exponentially?). These are questions that cannot be answered with an experiment that assumes a threshold.

Also, we should consider forcing a 0.38 g and 0.16 match, and have the increments be done with that in mind. Finally, do we need to test the moss at 0 g? Or do we suggest an ISS experiment for that very particular moss?

We choose to go to the Moon and do the other things not because they are easy but because they are hard. -JFK
02-18-2015 01:26 AM
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MBobrik Offline
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Post: #8
RE: Short description of the experiment.
(02-18-2015 01:26 AM)HenryRasia Wrote:  These are questions that cannot be answered with an experiment that assumes a threshold.

Well, that's why I changed the algorithm so that it uses the first two batches to determine where the first difference from 1 G behavior occurs, and then proceeds down from there ina a linear fashion.

(02-18-2015 01:26 AM)HenryRasia Wrote:  Finally, do we need to test the moss at 0 g? Or do we suggest an ISS experiment for that very particular moss?

I believe that 0 G on the ISS has been already done.
(This post was last modified: 02-18-2015 02:07 AM by MBobrik.)
02-18-2015 01:52 AM
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Nicholander Offline
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Post: #9
RE: Short description of the experiment.
If we decide to do 0.16 and 0.38 g, would it be possible to change the moss container so it has 8 batches, instead of 6? (So we wouldn't loose 2 batches for finding the lowest gravity that it grows well in)
02-18-2015 06:35 AM
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MBobrik Offline
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RE: Short description of the experiment.
(02-18-2015 06:35 AM)Nicholander Wrote:  If we decide to do 0.16 and 0.38 g, would it be possible to change the moss container so it has 8 batches, instead of 6? (So we wouldn't loose 2 batches for finding the lowest gravity that it grows well in)

one sample is 15 mm wide. the sample holder will have diameter cca 90 mm (external diameter will be bigger because of wall thickness and and growth medium layer ), so that makes 282.74 mm of lenght, or 18.85 sample widths, taking into account separation between samples, we will have place for 18 samples at most. If we want to have at least 3 samples per batch, that makes at most 6 batches.
.
And also, as Newt pointed out the gravity won't be uniform, if the roots are at 0.4 g, the tip of the plant will have only 0.356 G. so there is little point to try to have 0.38 G or 0.16 G sharp.
(This post was last modified: 02-18-2015 08:40 AM by MBobrik.)
02-18-2015 08:35 AM
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