One of the better proposals to fix whatever market structure issues we have is to move to "frequent batch auctions", in which a micro-auction would occur every 30 seconds or minute, which would amount to a similar thing. I'm not aware of any research that discusses whether such a system would be workable in the presence of the existing continuous trading market.
So lets say at tick one 1 see that only 50% of the buy orders were filled.
At tick 2 I want to buy 100 shares. But maybe I'll guess that only 50% will be filled this tick too, so maybe I should submit a buy order for 200 shares instead? This kind of game playing can lead to highly unstable outcomes.
If you think time priority orders are viewed as unfair, think what random matching would mean. It would mean that you could put in an order 6 months ago and watch it repeatedly never get filled as your price point was hit over and over again.
That chart understates the cumulative return of McDonalds by 20%, since it is just a graph of price appreciation and does not include the effect of reinvesting dividends. The proper cumulative return for McDonalds over that time period is actually 64.7%, assuming reinvestment of dividends.
I found this book helpful: The HIPAA Roadmap for Business Associates ( http://www.amazon.com/gp/product/1484067010/ref=oh_aui_searc... ). It goes through some of the basics of HIPAA, what kinds of policies you need to have and why, and includes some example policy templates similar to the ones being graciously provided in this article.
Saying that we're due for another pandemic is quite simply the gambler's fallacy: http://en.wikipedia.org/wiki/Gambler's_fallacy . The odds of a pandemic may well be higher than recent experience would indicate, but pandemics still occur randomly.
On the other hand, there's a very good reason why HFT liquidity has evaporated in previous crashes (such as the 2010 Flash Crash) -- the exchanges broke trades in an unpredictable fashion, so that any attempt at market-making would have opened the market maker to considerable risk.
Let's say you step in during a major market crash and buy AAPL when it's trading at $200/share. Let say it then rises some more to $300/share and you sell, only to see the price recover to $500/share. What happens if the exchange breaks your original buy at $200? Then you end up being short on the way from $300 up to $500, even though you were right about the direction of trading and contributed liquidity during market distress.
They've theoretically instituted a fix for this ( http://en.wikipedia.org/wiki/2010_Flash_Crash#Trading_curb ) which will make it clear in advance what trades will be broken, so we'll have to see how HFT and market making responds in the next crash. Bid-ask spreads tend to widen significantly during market distress, which should actually increase the profitability of being a market maker during a crash.
"Because Ripple’s new architecture does not require mining [to reach consensus], the creators of Ripple faced a choice: exclusively distribute XRP via mining or diversify distribution methods to include useful mining, business development, funding third-party developers, and hiring talent at Ripple Labs, the company responsible for improving upon and promoting the Ripple protocol."
XRP is currently distributed via the "Computing for Good" program:
"We’re giving away XRP in exchange for donating computing power to scientific research via World Community Grid. Anyone with an Internet-connected computer or Android device can participate."
Ripple is actually a generalized network flow problem, in which the flow through an edge can be multiplied by an exchange rate when converting between currencies. As a result, regular network flow algorithms don't apply. There's also another issue with using a minimum cost criterion, since the costs are in different currencies and it's not clear how to put them on the same footing.