Institute of Advanced Study
Institute of Advanced Study
News Article | April 17, 2017
Bernard Degrange, emeritus director of research at CNRS, has been awarded the 2016 André Lagarrigue Prize in acknowledgement of his exemplary career in experimental particle physics. Co-financed by the CNRS, the University Paris Sud, Linear Accelerator Laboratory (LAL), Eʹcole Polytechnique, CERN and CEA, with the support of the French Physical Society, the prize was created in 2005 in honour of André Lagarrigue. Director of LAL from 1969 to 1975, Lagarrigue played a leading role in the discovery of weak neutral currents in the Gargamelle bubble-chamber experiment at CERN, thus paving the way for electroweak theory. After completing his thesis in 1969, Degrange joined the Gargamelle collaboration where he contributed to the first measurement of the ratio of the neutrino and antineutrino cross-sections on nucleons and studied exclusive channels produced in neutral or charged-current interactions. In the early 1980s he moved into the study of cosmic rays and high-energy gamma-ray astronomy, helping to discover several “blazars” in the Crab Nebula with the CAT experiment. For the simultaneous observation of gamma and X-rays during the major bursts of these extragalactic sources, Degrange was awarded the silver medal of the CNRS in 1997. Anticipating the detection power of stereoscopy associated with fast high-granularity imagery, he made major contributions to the design and the results of the HESS experiment. The Czech Republic’s Academia Film Olomouc has decided to give its 2017 Award for Contribution to Science Communication to CERN, for its “long-lasting commitment not only to research in the edge of science but also to communication of its results and science in general to broader public”. The committee described CERN as a pioneer in developing new ways to communicate science via social media, film, traditional media and events such as CineGlobe. The award ceremony will take place on 29 April at Palacký University Interactive Science Centre in Olomouc. On 2 March, in collaboration with CERN and 20th Century Fox, the Pathé cinema in Geneva hosted an advance screening of the film Hidden Figures, followed by a debate on the position of women in science. The film tells the story of three African-American female scientists who played key roles in the US space conquest, contributing in particular to the preparations for putting astronaut John Glenn into orbit. After the film, Maite Barroso Lopez of CERN’s IT department, Stéphanie Beauceron and Anne-Marie Magnan from CMS, and Andry Rakotozafindrabe from ALICE shared their experiences of science careers with the audience in a debate. They answered questions about the alleged rivalry among women, about whether there is a link between CERN and NASA as pictured in the film, and about their mentors. The 2017 Rencontres de Moriond conference took place in La Thuile, Italy, from 18 March to 1 April, with around 270 participants attending the two-week-long event. The four main LHC experiments presented many fresh results, ranging from precise measurements of the Standard Model (SM) to searches for new physics, including the first obtained with the full 13 TeV data set collected during 2016. Numerous results from experiments outside CERN were also presented, especially in the neutrino field, and participants heard some of the latest developments in theory. Analyses of the Higgs boson presented by CMS included a precise new measurement of the Higgs mass. CMS also showed results from searches for associated Higgs-top production in final states with multiple leptons, which provides direct evidence for the existence of a top-quark Higgs coupling with a measured signal strength consistent with the SM. Both CMS and ATLAS showed new measurements of total and differential cross-sections of the Higgs boson decaying into four leptons or two photons, which agree with the SM. ATLAS also showed preliminary results from searches for the rare Higgs-boson decay to two muons, which are now approaching the sensitivity required to observe a signal. Concerning other SM particles, ATLAS presented its first measurement of the mass of the W boson with similar precision to the previous best result from a single experiment. The D0 and CDF collaborations at the former Tevatron collider, meanwhile, presented precise measurements of the top-quark mass. Among the highlights of searches for physics beyond the SM were new limits on supersymmetric particles from ATLAS, which now exclude models with particle masses above 2 TeV (see "ATLAS pushes SUSY beyond 2 TeV"). ATLAS also showed searches for new heavy particles decaying to jets of hadron particles, excluding non-elementary quarks with masses as large as 6 TeV. Both ATLAS and CMS are also looking for new heavy resonances decaying to a vector and a Higgs boson: ATLAS sees a 3.3 standard deviation local excess for a W´ → WH decay at masses around 3 TeV, whereas CMS sees a similar local excess but at a lower mass. Exotic searches from CMS using the full 2016 data sample place new limits on many scenarios including dark matter, new types of quarks, vector bosons and gravitons. No significant deviations from SM predictions have been observed so far by CMS and ATLAS. Results of searches for bottonium states at the Belle experiment and charmonium-like states at BESIII were also shown. In particular, the analysis of the Y(4260) appears to be inconsistent with a single peak at more than seven standard deviations. The heavy-flavour field also saw several new results presented by LHCb. Besides an update of the measurement of the rarest decay of a particle containing a b quark ever observed, and the recent observation of a new system of five particles all in a single analysis, LHCb presented the most precise single measurement of the CP-violating phase φ . The LHCb collaboration is also putting in place new analyses to shed light on two flavour anomalies: R(D*) and R(K), which remain around three standard deviations away from their SM values. A measurement of the angular coefficient P ´ in the flavour-changing neutral current decay of B mesons was also presented by ATLAS, CMS and Belle, and was found to be compatible with previous LHCb results. In the dedicated heavy-ion session, ALICE showed recent results from large samples of proton–proton, lead–lead, and proton–lead collisions collected in 2015 and 2016. One of the new results, concerning the azimuthal asymmetry of the production of J/ψ mesons, shows that heavy quarks directly “feel” the shape and size of the asymmetric quark–gluon plasma produced in the interaction region. With LHC Run 2 about to get under way with a similar integrated-luminosity target as achieved in 2016, the search for new physics is in full swing at CERN and elsewhere. The 8th High-Energy Physics (HEP) Madagascar International Conference (HEPMAD 2016) was held in Antananarivo, Madagascar, from 13 to 18 October. It was the event’s 15th anniversary and some 50 participants – including 15 invited high-energy physicists from abroad – were present. It is the only conference series in high-energy physics and indeed across all science held in sub-Saharan countries, and aims to be both pedagogical and topical, reviewing the latest experimental and theoretical results in high-energy physics. Recent results from the LHC, including precision tests of the Standard Model, Higgs properties and searches for new physics, were presented by ATLAS and CMS. Theory talks, meanwhile, covered topics including the status of the muon anomalous magnetic moment and determinations of the masses and couplings of charmonium and bottomium states using QCD spectral sum rule. The high-energy physics talks were complemented by national contributions about climate science and sustainable technologies for energy. The next HEPMAD event will take place in Antananarivo on 21–27 September 2017. In the digital era, where we are surrounded by ever more technological innovations, it is interesting to reflect on the enormous progress that modern physics has made following the quantum-mechanics revolution 90 years ago. The story began in 1900, with Max Planck’s suggestion that light is quantised, which Albert Einstein was the first to fully comprehend and exploit. Then, in the mid 1920s, a revolution in physics took place: quantum mechanics was formulated by Werner Heisenberg, Erwin Schrödinger, Paul Dirac and a handful of other young geniuses under the supervision of Niels Bohr and with Einstein as a critical voice. At the famous Fifth Solvay Conference in 1927, where 17 of the participants either already were or were to be Nobel laureates, much of the basic elements of quantum mechanics were ready and discussed. Never in the history of physics has so much been achieved by so few in such a short time. To commemorate the beginning of this revolution and its impact on the modern world, a special conference titled 90 Years of Quantum Mechanics was held at the Institute of Advanced Study at Nanyang University in Singapore on 23–26 January. The event gathered leading experts in the foundations of quantum mechanics, quantum cosmology, quantum gravity, quantum field theory, quantum condensed matter, quantum optics, quantum information and technology, and quantum chemistry. Altogether there were 30 talks, with six speakers being Nobel laureates. Some 300 participants attended from all over the world, with a strong emphasis on South East Asia and China. The Standard Model of particle physics has proved to be a consistent description of natureʼs fundamental constituents and their interactions, and its predictions have been confirmed by numerous experiments, most recently with the discovery of the Higgs boson at the LHC. However, the model fails to explain several phenomena in particle physics, astrophysics and cosmology, and it is expected that yet unknown particles or interactions are needed to explain these puzzles. Our inability to observe new particles possibly lies in their extremely feeble interactions. If true, this would imply that experiments are needed not just at the high-energy frontier but also at the “intensity frontier”, by increasing the number of collisions to search for rare events. In 2016, CERN created a Physics Beyond Colliders study group with a mandate to explore opportunities offered by the CERN accelerator complex to address outstanding questions in particle physics through projects complementary to high-energy colliders (CERN Courier November 2016 p28). A two-week-long “theory institute” took place at CERN from 20 February to 3 March to discuss the theory and phenomenology of possible new physics at low energy scales. More than 100 participants from 21 countries discussed the theoretical landscape, predicting new light particles and “dark forces”. The potential for the new physics reach of existing and planned intensity-frontier experiments – SHiP, NA62, DUNE, MATHUSLA and many others – was discussed. These future experiments are at different stages today, ranging from the preparation of a comprehensive design report (SHiP) to a letter of intent (MATHUSLA). The time is therefore ripe to ensure that any necessary changes to the experiment designs can still be made to the physics reach of intensity-frontier experiments. The annual Compact Linear Collider (CLIC) workshop took place at CERN on 6–10 March, attracting 220 collaborators from 26 countries to discuss the latest status of the CLIC accelerator and detector studies. CLIC is a future multi-TeV electron–positron linear collider at CERN envisaged for the era beyond the High-Luminosity LHC (HL-LHC). First beams in CLIC could be foreseen in 2035 and be the starting point of a 20–25 year-long physics programme. During the workshop particular focus was placed on the recently published updated staging scenario for the CLIC accelerator, where construction and operation are pursued in three stages with collision energies of 0.38, 1.5 and 3 TeV, respectively (CERN Courier November 2016 p20). At its initial energy, CLIC is optimised for Higgs and top measurements and enables a scan at the top-quark pair-production threshold, while the higher-energy stages provide the best sensitivity to new physics through direct and indirect searches. High-energy operation also provides access to rare processes such as double Higgs production, which is sensitive to the important Higgs self-coupling. CLIC week 2017 hosted a variety of sessions with 150 speakers, covering the activities of both the accelerator and detector-and-physics studies. The workshop also included meetings among the CLIC accelerator institutes and the detector-and-physics institutes. In both meetings the focus was on the steps necessary to submit a project-implementation plan in time for the European Strategy update in 2019–2020. Particular priority is given to the studies where cost and power can be reduced, presenting the initial CLIC project and further upgrades as a realistic option that is compatible with the level of resources available at CERN. Another highlight was the summary of the successful demonstration of key CLIC concepts obtained by the recently completed CTF3 test programme at CERN. Part of the CFT3 facility has now been approved for conversion into an electron accelerator facility called CLEAR (CERN Linear Electron Accelerator for Research), providing an open user facility for accelerator R&D, irradiation and training. The future CLEAR programme will include CLIC high-gradient and instrumentation studies. The successful operation of high-gradient accelerating structures and experience with advanced beam-dynamics techniques, developed for the small dimensions of these structures, have inspired a growing number of applications outside of particle physics. Applications of high-gradient and X-band technology include compact linacs and advanced diagnostics for photon sources, as well as medical applications. Many of the technologies under study for the CLIC detector are also of interest to the HL-LHC, where the high granularity and time-resolution needed for CLIC are equally crucial. Other communities also benefit: for example, software reconstruction techniques developed for particle flow at linear colliders have been applied to current and next-generation neutrino experiments. For many years the biennial Russian conference on accelerator physics and technology, RuPAC, was viewed by the international accelerator community as an internal event for representatives of the Soviet accelerator school. Although representatives of the latter have actively been working in accelerator centres around the world since the beginning of perestroika in the late 1980s, it is indeed rare to see a foreign specialist invited to a prominent position in Russia. But that situation is changing, and RuPAC16 held at St Petersburg State University (SPbSU) in November last year saw the worldʼs largest accelerator projects represented and more than 60 reports by participants from outside Russia. For the first time, the event also provided simultaneous translation from Russian to English. Today, RuPAC has become an excellent platform for information exchange between researchers working in accelerator science and technology and related issues. More than 40 reports from SPbSU students were presented at RuPAC16, and the geographical reach of the event extended to 260 participants from 67 institutions in 13 countries. In addition to traditional participants Ukraine, Belarus and Armenia, the event was attended by experts from China, South Africa, UK, Germany, Italy, Canada, US, Japan, Poland, Sweden and Switzerland. CERN’s High-Luminosity LHC and Future Circular Collider projects were presented, and several other reports were devoted to mutual research between Russian and European scientists. A particular focus was the FAIR-NICA collaboration concerning production and testing of superconducting accelerator magnets. Two new facilities have been commissioned at the Joint Institute for Nuclear Research (JINR) in Dubna for the international FAIR and NICA projects in Germany and Russia, respectively. The first is a high-tech assembly and testing hall for superconducting magnets, while the second is a heavy-ion linear accelerator that accelerates ions up to Au31+ to an energy of 3.2 MeV per nucleon. Status reports from all accelerator facilities of JINR were presented, as were activities at other major accelerator centres. The National Research Centre Kurchatov Institute carries out a broad range of activities, among them the development of a synchrotron radiation source and operation of the U-70 facility, Russiaʼs largest accelerator complex, with its new facility for carbon-beam medical applications and plans to attain high-power neutron fluxes. Important work also continues at the Institute for Nuclear Research of the Russian Academy of Sciences and the Budker Institute of Nuclear Physics (BINP). The latter facility has established itself as a manufacturer and supplier of high-tech accelerator facilities to the international market, such as electronic cooling systems, electron accelerators for industrial applications, components and synchrotron systems, magnetic systems and power systems, for example for the European X-FEL. BINP is also actively involved in the construction of FAIR and NICA, while continuing to develop domestic projects including a free electron laser, two electron–positron colliders (VEPP 2000 and VEPP4M) and facilities for radioisotope analysis. The conference concluded with a satellite meeting devoted to NICA, for which most Russian accelerator centres are already involved in manufacturing elements. Backed by the Russian government since 2016, NICA is a major factor driving current trends in the country’s accelerator science and technology. The success of this project will influence government support of other accelerator projects, such as the super C-tau factory project at BINP. Although Russia has a highly developed scientific infrastructure and potential to design complex accelerator facilities, the corresponding market is underestimated. Applied research projects such as medical beams for Russia’s first proton-therapy facility, along with the Russian “mega-science” projects, are thus a vital factor for accelerating Russian industry. As is clear, such projects are reinforcing the international outlook of Russian accelerator science and technology. The next RuPAC event will be held in autumn 2018. Marianne Thyssen, MEP and European commissioner for employment, social affairs, skills and labour mobility, toured CERN on 10 March, during which she visited CMS, ISOLDE and the new MEDICIS facility. She is pictured signing the guestbook with CERN Director-General Fabiola Gianotti. Enrique Cabrero Mandoza, director-general of CONACYT in Mexico, visited CERN on 23 March, immediately following the 9th CERN–Latin American School held in San Juan del Rio. He visited the ALICE experiment and the LHC tunnel before signing the guestbook with CERN’s head of relations with associate members and non-Member States, Emmanuel Tsesmelis, and director of international relations Charlotte Warakaulle. UK minister of state for universities, science, research and innovation Jo Johnson (top) came to CERN on 29 March, during which he visited the underground area at CMS. Two days later, chief scientific adviser to the UK government Mark Walport (bottom) also visited CERN, taking in the computing centre, ATLAS and the Antiproton Decelerator.
Menard B.,University of Toronto |
Scranton R.,University of California at Davis |
Fukugita M.,University of Tokyo |
Fukugita M.,Institute of Advanced Study |
Richards G.,Drexel University
Monthly Notices of the Royal Astronomical Society | Year: 2010
We present a simultaneous detection of gravitational magnification and dust reddening effects due to galactic haloes and large-scale structure. The measurement is based on correlating the brightness of ~85 000 quasars at z > 1 with the position of 24 million galaxies at z ~ 0.3 derived from the Sloan Digital Sky Survey and is used to constrain the galaxy-mass and galaxy-dust correlation functions up to cosmological scales. The presence of dust is detected from 20 kpc to several Mpc, and we find its projected density to follow: Σdust ~ r-0.8 p , a distribution similar to mass. On large scales, its wavelength dependence is described by RV ≃ 4.9 ± 3.2, consistent with interstellar dust. This, in turn, implies a cosmic dust density of Ωdust ≃ 5 × 10-6, roughly half of which comes from dust in haloes of ~L* galaxies. We estimate the resulting opacity of the Universe for various evolutionary models and find (AV) ~ 0.03mag up to z = 0.5. We present magnification measurements, corrected for dust extinction, from which the galaxy-mass correlation function is inferred to give the mean surface mass density profile around galaxies Σ ~ 30 (θ/1 arcmin)-0.8 hM pc-2 up to a radius of 10 Mpc, in agreement with gravitational shear estimates. © 2010 The Authors. Journal compilation © 2010 RAS.
News Article | December 5, 2016
The flashy Breakthrough Awards ceremony, organized by billionaires and hosted by some A-list celebrities, made two dozen scientists a bit wealthier Sunday night. Eight prizes, more lucrative than even the Nobels, were awarded to 12 elite scientists for work ranging from astrophysics to DNA and cell biology. Six physicists and four mathematicians at the beginnings of their career reaped New Horizons awards, and two teenagers won Breakthrough Junior Challenge distinctions. “Science is universal,” said Yuri Milner, the Russian billionaire who founded the Breakthroughs, in a statement Sunday. “Tonight it brought together some of the world’s greatest actors, sportsmen, musicians, academics, entrepreneurs, astronauts and, last but not least, scientists, to celebrate what the human mind can achieve.” The Special Breakthrough Prize was awarded in May. The three founders of the Laser Interferometer Gravitational-Wave Observatory (LIGO), which made a watershed breakthrough in observing gravitational waves last year, split $1 million: Ronald W.P. Drever and Kip S. Thorne, both emeritus professors at Caltech and Rainer Weiss, an emeritus professor from the Massachusetts Institute of Technology. The remaining $2 million will be split between the 1,012 contributors to the experiment. The split is nearly $2,000 for each of the scientists. The Breakthrough Prize in Life Sciences was split between five people from separate fields. Stephen J. Elledge of Harvard Medical School was included for his investigations into DNA’s natural repair process. Harry F. Noller of the University of California – Santa Cruz was honored for his discovery of some of the function of the ribosome, a kind of protein factor in the cell that translates form to function. Roeland Nusse of Stanford University was recognized for his discovery of the Wnt signaling pathway, which has been shown as a major waypoint for the development of some cancers. Yoshinori Ohsumi of the Tokyo Institute of Technology, fresh off a Nobel win in October, won for his discoveries in understanding autophagy, the process in which cells break down and recycle cellular material. Huda Yahya Zoghbi was included for her look into the genetics and workings of spinocerebellar ataxia and Rett syndrome. The Breakthrough Prize in Fundamental Physics was split by Joseph Polchinski, of the University of California – Santa Barbara, and Andrew Strominger and Cumrun Vafa, both of Harvard. All three won for their contributions to string theory, quantum gravity, and particularly how string theory applies to black holes. The Breakthrough Prize in Mathematics was given to the only sole winner. Jean Bourgain of the Institute of Advanced Study in Princeton, N.J., was acknowledged for transforming the state of partial differential equations, high-dimensional geometry, number theory, and other analytical pursuits. Three New Horizons in Physics prizes (each $100,000) were split between Asimina Arvanitaki, Peter W. Graham, Surjeet Rajendran, Simone Giombi, Xi Yin, and Frans Pretorius. Three New Horizons in Mathematics prizes (each $100,000) were split between Mohammed Abouzaid, Hugo Deuminil-Copin, Benjamin Elias, and Geordie Williamson. The Breakthrough Junior Challenge was won by two teenagers from Peru and Singapore. The total awarded to all was more than $25 million. After an awards ceremony that was hosted by Morgan Freeman, some of the honorees appeared still shocked by the recognition during panels. “It is a little bit unreal,” Nusse said. “I would say the experience has been surreal,” said Deanna See, 17, from Singapore. “The goal was to celebrate intellectual achievement – and these amazing people who make it happen,” added Milner. Founded in 2012, the Breakthrough Prizes have awarded nearly $200 million total.
Barak B.,Microsoft |
Gopalan P.,Microsoft |
Hastad J.,KTH Royal Institute of Technology |
Meka R.,Institute of Advanced Study |
And 2 more authors.
Proceedings - Annual IEEE Symposium on Foundations of Computer Science, FOCS | Year: 2012
The long code is a central tool in hardness of approximation, especially in questions related to the unique games conjecture. We construct a new code that is exponentially more efficient, but can still be used in many of these applications. Using the new code we obtain exponential improvements over several known results, including the following: 1) For any ε > 0, we show the existence of an n vertex graph G where every set of o(n) vertices has expansion 1-ε, but G's adjacency matrix has more than exp(logδ n) eigenvalues larger than 1 - ε, where δ depends only on ε. This answers an open question of Arora, Barak and Steurer (FOCS 2010) who asked whether one can improve over the noise graph on the Boolean hypercube that has poly(log n) such eigenvalues. 2) A gadget that reduces unique games instances with linear constraints modulo K into instances with alphabet k with a blowup of Kpolylog(K), improving over the previously known gadget with blowup of 2Ω(K). 3) An n variable integrality gap for Unique Games that survives exp(poly(log log n)) rounds of the SDP + Sherali Adams hierarchy, improving on the previously known bound of poly(log log n). We show a connection between the local testability of linear codes and small set expansion in certain related Cayley graphs, and use this connection to derandomize the noise graph on the Boolean hypercube. © 2012 IEEE.
News Article | November 24, 2016
COVENTRY, 24-Nov-2016 — /EuropaWire/ — To celebrate Coventry’s bid for the City of Culture in 2017 Dr Emma Parfitt, Sociology Researcher at the University of Warwick and Fargo village are bringing 17 artists and academics together for an exhibition of local artists’ work that aims to bridge the art-science divide. Artist-researcher collaborations have resulted in pieces of work that will be exhibited for one day only, on Saturday 26 November 10am-6pm at the Fargo Village Box Gallery. A collection of Warwickshire artists were given the challenge to communicate research in creative ways. On display will be unique and visually stunning hand crafted jewellery, photography, sculpture, charcoal sketches, models, paintings, 2D and 3D drawings, illustrations, stained glass, and more created by local artists to help communicate cutting edge research to a wider audience. Visitors will be given the opportunity to vote for their favourite collaboration, and be able to chat to the researchers and the artists about what they think of the work. The event is family friendly, even offering free yoga sessions at 3pm and 4pm. Visitors will also have the chance to purchase the artists’ work thereby supporting local art and culture. Dr Emma Parfitt who created and organised the event said: “I am a storytelling researcher so I am always thinking of new ways to communicate that research to people. The basic idea was that knowledge, like art, should be accessible to all. We call it an exhibition, but it is really an event crafted for people that may not have been in a traditional exhibition space before and are not sure whether it is for them or not. Of course, I hope that people who enjoy art already will also find the idea one that they would like to explore.” “This exciting exhibition is a chance to bring people together with the aim of closing the art-science divide. It opens the academic world to the community, from an internationally diverse set of students and subjects.” Lorella Medici of Arty Folks said: “This is something that has never been done before in Coventry. It’s an exciting new way to communicate important issues and cutting edge research through an incredible mix of artistic mediums that everyone can enjoy.” Visitors to the exhibition will experience a centre piece sculpture entitled ‘Twixt Nature and Nurture’ influenced by Rebecca Noble’s research into madness and by artists Francisco Goya and Hieronymus Bosch. This piece of work will measure 6m long x 2m wide x 2.5-3.0m high and will be made predominantly of paper. Rebecca Noble PhD Researcher in the Centre for History of Medicine at the University of Warwick said: “Arty Folks has made a fantastic exhibition piece in response to my work on madness in eighteenth-century Mexico. The artwork is the result of creative conversations about mental health inspired by the past and I hope it will be thought provoking for others.” This event has been supported by the Sociology Department and the Institute of Advanced Study, at Warwick University. This exhibition has also been made possible by the generosity of Warwick Alumni.
Kobayashi K.,Institute of Advanced Study |
Kawabata M.,Institute of Advanced Study |
Hisano K.,Kyushu University |
Kazama T.,Tohoku University |
And 6 more authors.
Nucleic Acids Research | Year: 2012
The expressions of chloroplast and mitochondria genes are tightly controlled by numerous nuclear-encoded proteins, mainly at the post-transcriptional level. Recent analyses have identified a large, plant-specific family of pentatricopeptide repeat (PPR) motif-containing proteins that are exclusively involved in RNA metabolism of organelle genes via sequence-specific RNA binding. A tandem array of PPR motifs within the protein is believed to facilitate the RNA interaction, although little is known of the mechanism. Here, we describe the RNA interacting framework of a PPR protein, Arabidopsis HCF152. First, we demonstrated that a Pfam model could be relevant to the PPR motif function. A series of proteins with two PPR motifs showed significant differences in their RNA binding affinities, indicating functional differences among PPR motifs. Mutagenesis and informatics analysis putatively identified five amino acids organizing its RNA binding surface [the 1st, 4th, 8th, 12th and 'ii'(-2nd) amino acids] and their complex connections. SELEX (Systematic evolution of ligands by exponential enrichment) and nucleobase preference assays determined the nucleobases with high affinity for HCF152 and suggested several characteristic amino acids that may be involved in determining specificity and/or affinity of the PPR/RNA interaction. © 2011 The Author(s).
Lovett S.,Institute of Advanced Study |
Viola E.,Northeastern University
Proceedings of the Annual IEEE Conference on Computational Complexity | Year: 2011
We study a variant of the classical circuit-lower-bound problems: proving lower bounds for sampling distributions given random bits. We prove a lower bound on the statistical distance between (i) the output distribution of any small constant-depth (a.k.a. AC0) circuit, and (ii) the uniform distribution over any code that is "good", i.e. has constant relative distance and rate. This seems to be the first lower bound of this kind. We give two simple applications of this result: (1) any data structure for storing codewords of a good code requires an additive logarithmic redundancy, if each bit of the codeword can be retrieved by a small AC0 circuit; (2) for some choice of the underlying combinatorial designs, the output distribution of Nisan's pseudorandom generator against AC0 circuits of depth d cannot be sampled by small AC0 circuits of depth less than d. © 2011 IEEE.
Torquato S.,Princeton University |
Torquato S.,Institute of Advanced Study |
Stillinger F.H.,Princeton University
Reviews of Modern Physics | Year: 2010
Understanding the characteristics of jammed particle packings provides basic insights into the structure and bulk properties of crystals, glasses, and granular media and into selected aspects of biological systems. This review describes the diversity of jammed configurations attainable by frictionless convex nonoverlapping (hard) particles in Euclidean spaces and for that purpose it stresses individual-packing geometric analysis. A fundamental feature of that diversity is the necessity to classify individual jammed configurations according to whether they are locally, collectively, or strictly jammed. Each of these categories contains a multitude of jammed configurations spanning a wide and (in the large system limit) continuous range of intensive properties, including packing fraction φ, mean contact number Z, and several scalar order metrics. Application of these analytical tools to spheres in three dimensions (an analog to the venerable Ising model) covers a myriad of jammed states, including maximally dense packings (as Kepler conjectured), low-density strictly jammed tunneled crystals, and a substantial family of amorphous packings. With respect to the last of these, the current approach displaces the historically prominent but ambiguous idea of "random close packing" with the precise concept of "maximally random jamming." Both laboratory procedures and numerical simulation protocols can and, frequently, have been used for creation of ensembles of jammed states. But while the resulting distributions of intensive properties may individually approach narrow distributions in the large system limit, the distinguishing varieties of possible operational details in these procedures and protocols lead to substantial variability among the resulting distributions, some examples of which are presented here. This review also covers recent advances in understanding jammed packings of polydisperse sphere mixtures, as well as convex nonspherical particles, e.g., ellipsoids, "superballs," and polyhedra. Because of their relevance to error-correcting codes and information theory, sphere packings in high-dimensional Euclidean spaces have been included as well. Some remarks are also made about packings in (curved) non-Euclidean spaces. In closing this review, several basic open questions for future research to consider have been identified. © 2010 The American Physical Society.
Hatami H.,McGill University |
Lovett S.,Institute of Advanced Study
Proceedings of the Annual ACM Symposium on Theory of Computing | Year: 2011
Recently there has been much interest in Gowers uniformity norms from the perspective of theoretical computer science. This is mainly due to the fact that these norms provide a method for testing whether the maximum correlation of a function f: double-struck Fpn ← double-struck F p with polynomials of degree at most d ≤ p is non-negligible, while making only a constant number of queries to the function. This is an instance of correlation testing. In this framework, a fixed test is applied to a function, and the acceptance probability of the test is dependent on the correlation of the function from the property. This is an analog of proximity oblivious testing, a notion coined by Goldreich and Ron, in the high error regime. We study in this work general properties which are affine invariant and which are correlation testable using a constant number of queries. We show that any such property (as long as the field size is not too small) can in fact be tested by the Gowers uniformity test, and hence having correlation with the property is equivalent to having correlation with degree d polynomials for some fixed d. We stress that our result holds also for non-linear properties which are affine invariant. This completely classifies affine invariant properties which are correlation testable. The proof is based on higher-order Fourier analysis, where we establish a new approximate orthogonality for structures defined by linear forms. In particular, this resolves an open problem posed by Gowers and Wolf. Another ingredient is a nontrivial extension of a graph theoretical theorem of Erdos, Lovasz and Spencer to the context of additive number theory. © 2011 ACM.
Holt G.C.,Institute of Advanced Study
Nanotechnology Perceptions | Year: 2012
The protagonists of Great Britain's Industrial Revolution were, famously, typically men without a formal education. Nevertheless, the development of ultrahigh technologies such as nanotechnology seems to demand a high level of higher education. This essay appraises the appropriate level of graduate education using the concept of the J-value. Education is discussed in the context of other government services. It is concluded that higher education is an excellent national investment provided the number of graduates is maintained at an affordable level. © 2012 Collegium Basilea.