Group items matching

in title, tags, annotations or url

Progress in atomic, optical and quantum science1, 2 has led to rapid improvements in atomic clocks. At the same time, atomic clock research has helped to advance the frontiers of science, affecting both fundamental and applied research. The ability to control quantum states of individual atoms and photons is central to quantum information science and precision measurement, and optical clocks based on single ions have achieved the lowest systematic uncertainty of any frequency standard3, 4, 5. Although many-atom lattice clocks have shown advantages in measurement precision over trapped-ion clocks6, 7, their accuracy has remained 16 times worse8, 9, 10. Here we demonstrate a many-atom system that achieves an accuracy of 6.4 × 10−18, which is not only better than a single-ion-based clock, but also reduces the required measurement time by two orders of magnitude. By systematically evaluating all known sources of uncertainty, including in situ monitoring of the blackbody radiation environment, we improve the accuracy of optical lattice clocks by a factor of 22. This single clock has simultaneously achieved the best known performance in the key characteristics necessary for consideration as a primary standard-stability and accuracy. More stable and accurate atomic clocks will benefit a wide range of fields, such as the realization and distribution of SI units11, the search for time variation of fundamental constants12, clock-based geodesy13 and other precision tests of the fundamental laws of nature. This work also connects to the development of quantum sensors and many-body quantum state engineering14 (such as spin squeezing) to advance measurement precision beyond the standard quantum limit.

There has been much recent interest in accelerating materials discovery. High-throughput calculations and combinatorial experiments have been the approaches of choice to narrow the search space. The emphasis has largely been on feature or descriptor selection or the use of regression tools, such as least squares, to predict properties. The regression studies have been hampered by small data sets, large model or prediction uncertainties and extrapolation to a vast unexplored chemical space with little or no experimental feedback to validate the predictions. Thus, they are prone to be suboptimal. Here an adaptive design approach is used that provides a robust, guided basis for the selection of the next material for experimental measurements by using uncertainties and maximizing the 'expected improvement' from the best-so-far material in an iterative loop with feedback from experiments. It balances the goal of searching materials likely to have the best property (exploitation) with the need to explore parts of the search space with fewer sampling points and greater uncertainty.

Can AI create the next wonder material? http://www.nature.com/news/can-artificial-intelligence-create-the-next-wonder-material-1.19850?WT.ec_id=NATURE-20160505&spMailingID=51301208&spUserID=MTEzODM0NjYzMzgS1&spJobID=920498312&spReportId=OTIwNDk4MzEyS0

Although it may seem like the above two experiments violate the uncertainty principle because the results show a smaller-than-required degree of uncertainty, Shih and his coauthors explain that no violation has occurred due to the fact that the experiments involve photon pairs rather than individual photons. The scientists argue that Popper's original thought experiment was based on a misunderstanding of the proper context of the uncertainty principle: it governs the behavior of single particles only, not the "correlation" of two particles.

can't read the full paper from here but this looks really interesting!! Pacome, Luzi I am sure you will like it ...

triggered from the other posts, just to show the uncertainty

Latest update: the European Space Agency says their experts "confirm there is no link between the meteor incidents in Russia and asteroid 2012DA14 flyby tonight". How did they find this? As they did not see this one coming, how could they come to that conclusion that early!

yes, now i get my 100% certainty with the reconstructed orbits nothing else (http://wiki.nasa.gov/cm/blog/Watch%20the%20Skies/posts/post_1361037562855.html) ... I still think that esa anouncemement was highly premature but with a high probability of being right...

Some more results on the topic (link to an arxiv article inside): http://www.bbc.co.uk/news/science-environment-21579422

The researchers used a global climate model to show that if an extreme emissions pathway -- RCP8.5 -- is followed up until 2035, allowing temperatures to rise 1°C above the 1970-1999 mean, and then SRM (Solar Radiation Management) is implemented for 25 years and suddenly stopped, global temperatures could increase by 4°C in the following decades.

Nice quantitative study. They treat the problem within the full uncertainty range of climate sensitivity parameter (much uncertain), very complete. However, at SRM ceasing, after an initial positive spike of Radiative Forcing, the rate of warming seems to return to rates predicted for the non-geoengineering case: "The 20-year temperature trends following SRM cessation are 0.2−0.6 °C/decade for the range of climate sensitivities (figure 5), comparable to those trends that occur under the RCP8.5 scenario without any SRM." I am actually working on a similar idea for deliberate Mars terraforming: aiming to cool the planet down before we introduce a positive Temperature raising feedback with greenhouse gases, maybe could be more efficient than warming itself.

This is becoming a mess :)

I see your point, and I agree that funding was also promoted through the energy players and their political influence. A coincident parallel interest which is irrelevant to the fact that the question remains vital. How do we affect climate and how does it respond. Huge complex system to analyse which responds in various time scales which could obscure the trend. What if we made a conceptual parallelism with the L Ácquila case : Is the scientific method guilty or the interpretation of uncertainty in terms of societal mobilization? Should we leave the humanitarian aspect outside any scientific activity?

I do not think there is anyone arguing that the question is not interesting and complex. The debate, instead, addresses the predictive value of the models produced so far. Are they good enough to be used outside of the scientific process aimed at improving them? Or should one wait for "the scientific method" to bring forth substantial improvements to the current understanding and only then start using its results? One can take both stand points, but some recent developments will bring many towards the second approach.

CliSAP: Mr. Held, several hundred researchers worked for several years on preparing the recently published third part of the Assessment Report, without pay and on top of their normal duties. The result was a work over two thousand pages long. Was it worth it? An overview of the uncertainties when it comes to estimating investments in low carbon. Maybe there is room for computational management projects in there?

Here we go: we might not need liquid water after all on mars to get some nice flowering plants there! ... and terraform ? :-) Thirsty plants can extract water from the crystalline structure of gypsum, a rock-forming mineral found in soil on Earth and Mars.

Some plants grow on gypsum outcrops and remain active even during dry summer months, despite having shallow roots that cannot reach the water table. Sara Palacio of the Pyrenean Institute of Ecology in Jaca, Spain, and her colleagues compared the isotopic composition of sap from one such plant, called Helianthemum squamatum (pictured), with gypsum crystallization water and water found free in the soil. The team found that up to 90% of the plant's summer water supply came from gypsum.

The study has implications for the search for life in extreme environments on this planet and others.

Nature Commun 5, 4660 (2014)

Very interesting indeed. Attention is to be put on the form of calcium sulfate that is found on Mars. If it is hydrated (gypsum Ca(SO4)*2(H2O)) it works, but if it is dehydrated there is no water for the roots to take in. The Curiosity Rover tries to find out, but has uncertainty in recognising the hydrogen presence in the mineral: Copying : "(...) 3.2 Hydration state of calcium sulfates Calcium sulfates occur as a non-hydrated phase (anhydrite, CaSO4) or as one of two hydrated phases (bassanite, CaSO4.1/2H2O, which can contain a somewhat variable water content, and gypsum, CaSO4.2H2O). ChemCam identifies the presence of hydrogen at 656 nm, as already found in soils and dust [Meslin et al., 2013] and within fluvial conglomerates [Williams et al., 2013]. However, the quantification of H is strongly affected by matrix effects [Schröder et al., 2013], i.e. effects including major or even minor element chemistry, optical and mechanical properties, that can result in variations of emission lines unrelated to actual quantitative variations of the element in question in the sample. Due to these effects, discriminating between bassanite and gypsum is difficult. (...)"

forgot the reference http://www.msl-chemcam.com/doc/documents/577/Nachon%20et%20al%20Calcium%20sulfate%20veins%20characterized%20by%20ChemCam%20Curiosity%20at%20Gale%20Crater%20Mars_2013.pdf