A cash flow diagram is a financial diagram that shows incomes and expenses for a given period, as arrows. 

But, 

How can one produce a cash flow in a computer, to place in a report, for example?

The Squares Problem is a purely mathematical problem. Although interesting, it has no known practical application.

Imagine that you have a square grid made out of cells, like a chessboard. Each cell has a probability p of being either black (associated with the number 1) or white (associated with the number 0). Every start of the game, the board is filled randomly with either white or black cells. It can form continuous regions of black cells, when cells share a black neighbor to either one of the directions up, down, left or right.   

A continuous black area with 5 cells has an area of 5. We are interesting in finding out what is the distribution of areas, how many of them are isolated (area 1), of area 2, area 3, and so forth. 

How does the area distribution varies with p? 

Can you solve the problem analytically, and verify the results with the use of a computer?

When I was young, I remember making a a white flower absorb ink and turn into some color. I don't recall if this was actually a true memory or not. 

The idea here is much more permanent, it is to develop a business that breeds or modifies genetically flowers so that they have unusual and unexpected colors. 

This may exist already.

It is a simple modification to the scroll bar of a PDF reader, so that it shows in a color scale the parts of the document that were more accessed than others, in the history of the file.

This is so that for example, when you open up a book PDF, you know instantly what are the sections that deserve more attention. 

I've seen this done in websites, but not in PDFs. 

Dengue fever, Yellow fever, Zika, Chikungunya, all baddies transmitted by the same fellow: Aedes aegypti.

The idea is to create an artificial flesh, a lure that can fool this mosquito into biting it, instead of us! Just think about it, if you had one lure in your bedroom, and it worked, you would reduce the bites in 50%. Two lures, that goes to 33%. Personally, I like those odds. 

Just spread around enough lures to make the job of this guy a lot harder. Giving it more targets might not be so easy to do, in practice. I'd have reservations about making the lures deadly to the mosquito, however, as they might play some role in the biological networks that I'm unaware.

This could either build a multi-billion corporate empire or fail completely. 

The idea is to measure traffic, using devices that would be placed at key locations on the road network of a city. Then, one would use this data to guide real-estate investments. 

It would not be just counting the number of vehicles travelling. You would use pattern recognition to identify specific car models. By knowing for example, that more luxury cars are commuting to a part of the city, you would get an indication that this region is booming. You would reposition the traffic meters until you can pinpoint exactly where is the sweet spot. You see, it is very hard to tell if region A or B is better for an investment, in practice, and this would aid the decision process. 

There are legal issues involved. The city hall need to issue a sort of permit I suppose, and should you start collecting individual nameplates and track people all hell would break loose. 

Additionally, should your company buy a lot, you could install some solar panels for as long as it takes for the land to gain value, and profit with renewables.

Assume that energy-to-matter conversion is possible, somehow.

How fast could a solar park grow, if it reinvested 100% of its production into growing larger and larger?

There are some people that argue that the next major conflict on the planet will be for this: potable, drinking water. This already affects 2 billion people around the World, according to this UNESCO report. It is not possible to neglect this issue. 

The idea is actively search for means to assure that there will be water for the future generations. 

This can be achieved by increasing the water supply (improvements in water treatment, desalinization techniques, rain collection, protection of water streams) and decrease the losses with water usage. Ideally, one would start with the activities that are more responsible for waste, then move on to more marginal gains. 

Here are some suggestions:

• First, from now on make a spreadsheet where you will note, every month, how many m3 of water does your household uses. Search online to see what is an average water usage for your location and number of family members, and compare your value to this. This will increase your awareness and raise an alert for any unchecked water leaks.

• If you don't have the phone number of a good plumber, make a list of phone numbers for emergencies, so that you can respond more quickly when there is a problem. Correct leaks promptly. 

• Consider changing your habits. Every 20 days or so, start enforcing one of these positive habits: 

  • Cut 2 minutes of your shower time; Just 2 minutes, you can do it. Make long relaxing showers and exception rather than the rule. Listen to music while you shower, so you know how long has it been. It is also fun;

  • Brush your teeth and shave without a running faucet; 

  • Take more time between car washes; 

  • Only wash clothes and laundry on full loads and use the proper water level; 

  • Dry clean with a broom driveways and sidewalks most of the time, 

  • Watering grass, If you step on grass and it lifts back when you remove the foot, it does not need water. Also, when watering, make sure to deep-soak the grass, or else water will just evaporate - do this on morning rather than dusk to prevent fungus; 

  • Get a mug instead of plastic cups for your office.

• It is important not to try to change all your habits at once, but gradually. Change takes time. You should also naturally inspire your children to do the same, but don't force habits into them. Just do your part. 

• If you have issues changing your ways, but have some money to spare, invest on a rain collector for your toilets. The idea is to flush your toilet with rainwater. You can save many gallons of water in this fashion. There are also dual-flush options that flush less water, for say, Number 1 and Number 2. 

• Experimental Projects - these experiments were never tested by me:

  • Change the faucets in you home to electronic faucets with electro mechanical valves and ARDUINO. Control precisely the flow, prevent a leaking faucet after use. 

  • Put a plastic bottle with sand inside the water compartment of your flush, if possible. That will rise the level of water and fool the level sensor conserving water. Check if the efficiency of the flush is still OK, or if you are just repeating the flushes over and over.

  • Upgrade your garden with an ARDUINO watering system that measures moisture from the dirt. There are inexpensive sensors for this purpose. This will even save you time and make sure your plants get more consistent watering. You can also opt for dry-resistant species.   

• Advanced and Demanding Projects

  • Prepare a cost-effective and easy-to-install project of rain collection for rural homes.

  • Learn how to use and install small wind generators to pump water. Share this expertise with small communities. 

  • Study extensively how people spend water in their homes to come up with real suggestions to save water that actually rank water saving measures from best to worse. Publish your findings. Make pamphlets for your community. 

  • If you have a chemistry flare, delve into desalinization, until you can figure out how to contribute on the development of those technologies.

  • Study effective ways to reduce water waste in agriculture.  

  • Focus on an industrial process that consumes a lot of water, study it, and try to improve upon it or replace the product it produces.

In Idea #119, we proposed to filter atoms used slabs of a material that expand very little with temperature. The idea here has the same goal, to produce an atomic filter, but uses a different approach. 

Imagine that you have a flat paper surface. Then you take an ultra-sharp pencil, or rather a graphite rod, and start drawing a trajectory into the paper, without lifting the carbon rod. A random trajectory, it can be a zig-zag pattern bouncing off the edges of the paper or circles with various radii, or just a curly random line. 

The paper starts to get filled with carbon. The white areas start to slowly disappear, and become smaller and smaller.

If you keep this process for a long time, do you end up with a filter of atomic sizes?

Is this filter dense in holes enough to be useful?

By the way, you are supposed to dissolve the paper after it has been drawn to. 

You can also try this by pouring on the surface a trickle of something that solidifies in contact with a surface, like a polymer, and moving the container you are pouring. I suppose you could also use droplets, anything to fill most of the surface.