Archive for nuclear weapons

75 years later, it is more than time for full nuclear disarmament!

Posted in Kids with tags , , , , , , , , , on August 6, 2020 by xi'an

radioactive ant fiction [in J. Hymenoptera Research]

Posted in Books, Kids, pictures, University life with tags , , , , , , , , , on November 30, 2019 by xi'an

Following a link in Nature, I read a short communication in the Journal of Hymenoptera Research [which I confess I rarely peruse!], which sounded more like a B movie from the 1950s than a scientific article. Starting with the title “Ants trapped for years in an old bunker; survival by cannibalism“! (This is actually the second episode in the series.) While the bunker was intended for storing Soviet nuclear weapons, no radioactivity impacted on the ants and they (the colony) survived in the dark at the bottom of the bunker for 22 years, with no source of food but their own, with new ants falling into the bunker on a regular basis. Hence the title. What I found most surprising in the paper is the fact that it is a sheer description of an observation (with field pictures) and of an intervention (we set a 3m vertical boardwalk to allow for escape) that reminded me more of my childhood fascination with ants (involving radical interventions) than of a typical science paper!

and it only gets worse…

Posted in Kids, pictures, Travel with tags , , , , , , , , , , , , , on February 21, 2019 by xi'an

” A recent survey by found that just 40% of US households have enough money to cover a $1,000 in emergency expenses.” The Guardian, Feb 2, 2019

““Until we heard those cheers coming from Albany, we thought states were moving beyond such barbaric practices.” Mr. Pence offered his argument as a litmus test of morality; he described the new abortion legislation as a “shameless embrace of a culture of death.” But among conservatives, the White House’s outrage was also greeted as a clear and shrewd political strategy” The New York Times, Feb 1, 2019

“When Senator Elizabeth Warren formally announced her 2020 presidential bid this weekend, President Trump responded with a familiar line of attack. He mocked Ms. Warren for her claims to Native American ancestry, again calling her by the slur “Pocahontas.” Mr. Trump then appeared to refer to the Trail of Tears, the infamously cruel forced relocation of Native Americans in the 19th century that caused thousands of deaths.” The New York Times, Feb 10, 2019

“The United States is suspending one of the last major nuclear arms control treaties with Russia after heated conversations between the two powers recently failed to resolve a long-running accusation that Moscow is violating the Reagan-era treaty. Mr. Pompeo acknowledged a risk of a new arms race if the treaty is ultimately scrapped after the six-month window.” The New York Times, Feb 1, 2019

“In some states, lawmakers have sought to pass laws that would ban or severely restrict abortion in the event that Roe v. Wade is eventually overturned or effectively gutted (…) The court is likely to confront other abortion cases, too, as several state legislatures have recently enacted laws that seem calculated to try to force the Supreme Court to consider overruling Roe v. Wade, the 1973 decision that established a constitutional right to abortion.” The New York Times, Feb 8, 2019

“Mr. Trump’s willingness to invoke emergency powers to circumvent Congress is likely to go down as an extraordinary violation of constitutional norms — setting a precedent that future presidents of both parties may emulate to unilaterally achieve their own policy goals.” The New York Times, Feb 15, 2019

and it only gets worse…

Posted in Books, pictures, Travel with tags , , , , , , , , , , , , , , , , , on February 9, 2018 by xi'an

““Why are we having all these people from shithole countries come here?” Trump said, after being presented with a proposal to restore protections for immigrants from those countries [African nations].” The Guardian, Jan 12, 2018

“The Trump administration is creating an office to protect the religious rights of medical providers, including those who may oppose abortion or transgender rights.” The Guardian, Jan 18, 2018

“Nuclear experts are warning, using some of their most urgent language since President Trump took office, that Hawaii’s false alarm, in which state agencies alerted locals to a nonexistent missile attack, underscores a growing risk of unintended nuclear war with North Korea.” NYT, Jan 15, 2018

““I don’t know if the president is clinically off his rocker. I do know, from what I saw and what I heard from people around him, that Donald Trump is deeply unpredictable, irrational, at times bordering on incoherent, self-obsessed in a disconcerting way, and displays all those kinds of traits that anyone would reasonably say, ‘What’s going on here, is something wrong?’” [Michael Wolff]” The Guardian, Jan 15, 2018

“Mr. Trump received a score of 30 out of 30 on the Montréal Cognitive Assessment, a well-known test regularly used at hospitals. It asks patients to repeat a list of spoken words, identify pictures of animals like a lion or a camel, draw a cube or draw a clock face set to a particular time.” NYT, Jan 17, 2018

““Through statistical analysis, video evidence, and personal experience, our team has uncovered a disturbing reality. In the majority of cases, US border patrol agents are responsible for the widespread interference with essential humanitarian efforts. The practice of destruction of and interference with aid is not the deviant behavior of a few rogue border patrol agents, it is a systemic feature of enforcement practices in the borderlands.” [No More Deaths]” The Guardian, Jan 18, 2018

““We’ll save a lot. We don’t care. But this isn’t like it used to be where they could vote against you and then you pay them hundreds of millions of dollars,” [Trump] said. “We’re not going to be taken advantage of any longer.”” The Guardian, Dec 21, 2017

Monte Carlo calculations of the radial distribution functions for a proton-electron plasma

Posted in Books, pictures, Statistics, University life with tags , , , , , , , , on October 11, 2017 by xi'an

“In conclusion, the Monte Carlo method of calculating radial distribution functions in a plasma is a feasible approach if significant computing time is available (…) The results indicate that at least 10000 iterations must be completed before the system can be considered near to its equilibrium state, and for a badly chosen starting configuration, the run would need to be considerably longer (…) for more conclusive results a longer run is needed so that the energy of the system can settle into an equilibrium pattern and steady-state radial distribution functions can be obtained.” A.A. Barker

Looking for the history behind Barker’s formula the other day made me look for the original 1965 paper. Which got published in the Australian Journal of Physics at the beginning of Barker’s PhD at the University of Adelaide.

As shown in the above screenshot, the basis  of Barker’s algorithm is indeed Barker’s acceptance probability, albeit written in a somewhat confusing way since the current value of the chain is kept if a Uniform variate is smaller than what is actually the rejection probability. No mistake there! And more interestingly, Barker refers to Wood and Parker (1957) for the “complete and rigorous theory” behind the method. (Both Wood and Parker being affiliated with Los Alamos Scientific Laboratory, while Barker acknowledges support from both the Australian Institute of Nuclear Science and Engineering and the Weapons Research Establishment, Salisbury… This were times when nuclear weapon research was driving MCMC. Hopefully we will not come back to such times. Or, on the pessimistic side, we will not have time to come back to such times!)

As in Metropolis et al. (1953), the analysis is made on a discretised (finite) space, building the Markov transition matrix, stating the detailed balance equation (called microscopic reversibility). Interestingly, while Barker acknowledges that there are other ways of assigning the transition probability, his is the “most rapid” in terms of mixing. And equally interestingly, he discusses the scale of the random walk in the [not-yet-called] Metropolis-within-Gibbs move as major, targetting 0.5 as the right acceptance rate, and suggesting to adapt this scale on the go. There is also a side issue that is apparently not processed with all due rigour, namely the fact that the particles in the system cannot get arbitrarily close from one another. It is unclear how a proposal falling below this distance is processed by Barker’s algorithm. When implemented on 32 particles, this algorithm took five hours to execute 6100 iterations. With a plot of the target energy function that does not shout convergence, far from it! As acknowledged by Barker himself (p.131).

The above quote is from the conclusion and its acceptance of the need for increased computing times comes as a sharp contrast with this week when one of our papers was rejected based on this very feature..!