Physical Review Letters Research Articles

LIGO backstory delights and displeases

Robert Garisto tells us (Physics Today, August 2016, page 10) of the secrecy he maintained at Physical Review Letters prior to the announcement that a “chirp” had been detected at the Laser Interferometer Gravitational-Wave Observatory (LIGO). On sabbatical at Caltech, I had the pleasure of joining local astronomers to watch the press conference from the astronomy and astrophysics auditorium (whose street number, 1216, is the Lyman-alpha wavelength in angstroms). But as we left after the dazzling announcement, with music in our ears, they gave out coffee cups and bumper stickers each with the data already emblazoned on it. I should have hung out in the print shop days before!

In search for “magic” nuclei, theory catches up to experiments

The bundle of 78 nucleons in a single nickel-78 nucleus are infinitesimal. And yet, calculating that nucleus’s structure entailed an enormous computing effort: 5 million CPU hours on the most powerful supercomputer in the United States. The results could offer key insights into the potential existence of the long-sought “island of stability”: ultraheavy but unusually stable nuclei. The most powerful supercomputer in the United States, Titan at Oak Ridge National Laboratory, needed 5 million CPU hours to calculate the nickel nucleus's structure. Image courtesy of the Oak Ridge National Laboratory and US Department of Energy. In October, three scientists at Oak Ridge National Laboratory and the University of Tennessee in Knoxville published the results of this nickel-78 calculation in Physical Review Letters (1). The researchers demonstrated that the nucleus’s combination of protons and neutrons formed a very stable structure, what physicists call a doubly magic nucleus. It was no small feat: the finding involved solving a quantum mechanical system, including the strong nuclear force acting between 28 protons and 50 neutrons. “The immensity of these calculations are way beyond anything you can think about doing on a laptop or desktop or small cluster,” says Gaute Hagen of Oak Ridge, the study’s first author. It was the latest example of a supercomputing trend that is shaking up the field of nuclear physics. For decades, scientists have sought to find the “magic numbers” of protons and neutrons that form these especially stable nuclei. But although experimentalists have forged heavier and heavier such magic nuclei in the beams of their accelerators, theorists have lacked the computational power to keep up. Although theoretical calculations of the structure and stability of nuclei with small numbers of nucleons have been tractable, there has simply been no way to perform the calculations necessary to accurately predict and …

High-energy physics to become open access in three APS journals

A new agreement ensures that results from the field will be freely available in the high-impact-factor Physical Review Letters.

The state of open access

On page 24 you’ll find David Kramer’s in-depth report on the current state of open-access publishing. Open access and its place in the landscape of academic journals have changed since November 2012, when Physics Today last covered the topic. Besides authors, publishers, and policy makers, other actors are now on the open-access stage, among them charitable foundations, scholarly collaboration networks, and, yes, pirates who post unauthorized copies of papers on Russian servers.CYNTHIA CUMMINGSPPT|High resolutionMy attitude toward open access is conflicted. On the one hand, I agree that the fruits of publicly funded research should be freely available, especially to scientists in poor countries and to scientists employed by companies and colleges that can’t afford journal subscriptions. On the other hand, I’m well aware that Physics Today is funded in part by the profits that AIP’s publishing subsidiary makes from selling subscriptions to its 19 journals. If Physics Today had to rely solely on advertising and subscription revenue, it would have to shrink and change format.Regardless of where you, I, or anyone else stands on open access, there are forces in play that are hard for publishers to resist. One of those forces arises from the nature of the principal end product of scholarly research, a paper that’s usually in the form of a PDF. The P in PDF stands for portable, which is what PDFs all too easily are. For Physics Today’s August 2009 issue, I wrote a feature article about iron-based superconductors, which had been discovered just two years earlier. Google Scholar lists 16 unauthorized PDFs of the article, 13 of which are on Chinese websites. (I couldn’t find the article on Sci-Hub, the pirate website founded by a Kazakhstani grad student.)Portability isn’t the only disrupting force at play. University library budgets have not kept up with inflation or with the growth in the number of the world’s scientists and their output. The cash crunch is forcing librarians to scrutinize journals based on price and usage. Subscriptions to those that don’t meet increasingly stringent criteria are not renewed.Despite those trends, some aspects of scholarly publishing remain the same. It’s just as hard now as it was in the 19th century to conceive of an experiment or theory that is both original and significant enough to be worth publishing in a scientific journal. Reviewing your peers’ papers before publication continues to be an unpaid yet valuable duty. And a paper’s final version of record still needs to be archived, online if not in bound volumes on library shelves.When I ask physicists and other scientists how they choose where to publish their work, I tend to get the same answers. Scientists want their papers to be read, so they publish in journals that their peers read. A physicist told me once that he regretted publishing in the prestigious Proceedings of the Royal Society because his fellow fluid dynamicists didn’t read that journal. Physics of Fluids, he mused, would have been a better choice.Some physicists tell me that if they have a hot result, they’ll go for a journal with a high impact factor, such as Physical Review Letters, Nature, or Science. But in the digital age, as George Lozano, Vincent Larivière, and Yves Gingras discovered in an extensive bibliometric study, the correlation between a journal’s impact factor and a paper’s citations is weakening.11. G. A. Lozano, V. Larivière, Y. Gingras, J. Am. Soc. Inf. Sci. Tec. 63, 2140 (2012). https://doi.org/10.1002/asi.22731One of the findings in David’s report in this issue is that open-access papers in the physical sciences currently make up just 10–12% of the total. That modest proportion likely reflects the continuing appeal and reputation of traditional journals. But as any marketing guru will tell you, appeal and reputation are intangible components of a brand. The contest for the best papers in physics will likely be won by the publishers who nurture those intangibles, regardless of access model.ReferencesSection:ChooseTop of pageReferences <<CITING ARTICLES1. G. A. Lozano, V. Larivière, Y. Gingras, J. Am. Soc. Inf. Sci. Tec. 63, 2140 (2012). https://doi.org/10.1002/asi.22731, Google ScholarCrossref© 2017 American Institute of Physics.

(Invited) MoS2 Field-Effect Transistors Gated with a Two-Dimensional Electrolyte

Two dimensional (2D) materials are being explored for power efficient electronics at the limit of scaling. The 2D semiconductor, molybdenum disulfide (MoS2), has a high electron mobility (200 cm2V-1s-1) and large direct bandgap (1.9 eV) in single layer form.1,2 However, doping methods are required to create transistors and other electronic devices with 2D materials. Different from irreversible substitutional or charge-transfer doping, electrostatic ion doping relies on the formation of an electric double layer (EDL) formed by mobile ions that accumulate at the surface of the 2D semiconductor and induce image charge. The doping can be reconfigured by changing the polarity of the bias, and high capacitance densities have been demonstrated (~4 µF/cm2).3 However, commonly used electrolytes such as ionic liquids are liquid phase, and solid polymer electrolytes cannot be scaled to nanometer thickness. Our group has developed a 2D electrolyte that is a single monolayer thick and can electrostatically dope the surface of 2D semiconductors. The 2D electrolyte comprises cobalt crown ether phthalocyanine (CoCrPc) and lithium perchlorate (LiClO4) (Fig.1 (a)). CoCrPc is an atomically thin, flat-laying and electrically insulating material (band gap ~1.34 eV).4 An ordered array of CoCrPc can be deposited on a 2D material by simple drop-casting and annealing.4 Each of the four crown ethers in a molecule can solvate one Li+.5 In this study, we demonstrate that the Li+ location with respect to the crown ether can be modulated by a gate bias to induce image charges in MoS2, which leads to n-type doping with sheet carrier density of ~1012 cm-2. Back-gate MoS2 FETs were fabricated by electron beam lithography (EBL) and a monolayer of CoCrPc was deposited by drop-casting and annealing (Fig.1 (b)). Atomic force microscopy (AFM) was used to confirm the thickness of the electrolyte as 0.5 ~ 0.7 nm, corresponding to a monolayer. Because a single monolayer of 2D electrolyte must be deposited on the channel surface, it is critical for the channel to be free of EBL resist residue, otherwise the residue will interfere with the packing arrangement of the 2D electrolyte. Contact-mode AFM was used to remove the residue before electrolyte deposition; surface roughness after the cleaning equals that of the freshly exfoliated flakes (Rq ~0.23 nm). Importantly, the cleaning does not degrade the device performance as indicated by transfer measurements (IDS-VBG) taken before and after cleaning. FET transfer characteristics after 2D electrolyte deposition showed bistability of the 2D electrolyte (Fig 1. (c) and (d)), with the extent of n-type doping depending on the magnitude of the applied bias, and the direction of the doping (i.e., more or less n-type) depending on the polarity of the applied bias. The threshold voltage shift of ~10 V corresponds to a sheet carrier density of 3.2×1012 cm-2 at a CE: Li+ ratio of 5:1, which is about 2 orders of magnitude greater than the intrinsic MoS2 carrier density (~1×1010 cm-2).6 The measurement also show that the channel resistance can be maintained at two distinct values after the bias is removed for at least the timescale of the transfer measurement. DFT calculations by Kyeongjae Cho group at UT Dallas predict that the gate bias required for Li+ to pass through the crowns is sub-volt, which is desirable for power efficient electronics.7 However, the back-gate MoS2 devices require a large gate bias to modulate the location of the Li+because of electric field loss through the 90 nm back-gate oxide. Therefore, a future goal is to demonstrate sub-volt operation in top-gate FETs doped by the 2D electrolyte. In summary, this study demonstrates that an electrolyte can be scaled to 2D and used for the adjustable doping of 2D semiconductors with state retention in the absence of an applied gate bias. Acknowledgments This work was supported by NSF-ECCS/GOALI 1408425 and by the Center for Low Energy Systems Technology (LEAST), a STARnet Semiconductor Research Corporation program sponsored by MARCO and DARPA. References Radisavljevic, B., et al. Nature nanotechnology 6.3 (2011): 147-150.Mak, K. F., et al. Physical Review Letters 105.13 (2010): 136805.Xu, H., et al. ACS nano 9.5 (2015): 4900-4910.Lu, H., et al. The Journal of Physical Chemistry C 119.38 (2015): 21992-22000.De, S., et al. Journal of Molecular Structure: THEOCHEM 941.1 (2010): 90-101.Wang, Han, et al. Nano letters 12.9 (2012): 4674-4680.Wang, W.-H., et al. "Energetics of metal ions adsorption on and diffusion through the crown ethers: first principles study on 2D electrolyte” submitted. Figure 1

Non-commuting two-local Hamiltonians for quantum error suppression

Physical constraints make it challenging to implement and control many-body interactions. For this reason, designing quantum information processes with Hamiltonians consisting of only one- and two-local terms is a worthwhile challenge. Enabling error suppression with two-local Hamiltonians is particularly challenging. A no-go theorem of Marvian and Lidar [Physical Review Letters 113(26), 260504 (2014)] demonstrates that, even allowing particles with high Hilbert-space dimension, it is impossible to protect quantum information from single-site errors by encoding in the ground subspace of any Hamiltonian containing only commuting two-local terms. Here, we get around this no-go result by encoding in the ground subspace of a Hamiltonian consisting of non-commuting two-local terms arising from the gauge operators of a subsystem code. Specifically, we show how to protect stored quantum information against single-qubit errors using a Hamiltonian consisting of sums of the gauge generators from Bacon-Shor codes [Physical Review A 73(1), 012340 (2006)] and generalized-Bacon-Shor code [Physical Review A 83(1), 012320 (2011)]. Our results imply that non-commuting two-local Hamiltonians have more error-suppressing power than commuting two-local Hamiltonians. While far from providing full fault tolerance, this approach improves the robustness achievable in near-term implementable quantum storage and adiabatic quantum computations, reducing the number of higher-order terms required to encode commonly used adiabatic Hamiltonians such as the Ising Hamiltonians common in adiabatic quantum optimization and quantum annealing.

Half-Quantum Vortices in Superfluid Helium

This is the manuscript version of the Physics ViewPoint article introducing the paper "Observation of half-quantum vortices in topological superfluid $^3$He", by S. Autti et al., which appeared in Physical Review Letters, December 14, 2016.

Commentary: A biology journal provides a lesson in peer review

This is a Commentary in $Physics~Today$ on the novel review process developed by the biology journal $eLife$, with the suggestion that it be adopted by physics journals.

In-Situ Microfluidic Study with Kinetic-Monte Carlo Simulations to Investigate Zn Electroplating Morphology at High Overpotentials

Despite the low cost and high energy density, use of Zinc anode in secondary batteries is limited due to the associated shape change of Zn during cycling. Vast literature on morphological studies of Zn in alkaline electrolyte indicates formation of varied structures ranging from mossy, to boulder-like and dendritic morphologies,1 primarily depending on the plating potential. Recently, Zinc plating at extremely high overpotentials 2 is shown to form a highly porous, conductive, ramified foam like morphology, called Hyper Dendritic Zinc (HD Zn). HD Zn has been demonstrated to act as an efficient secondary anode, with improved cycle life and kinetics 3. The fine (~60 nm) needle-like crystallite core microstructure that forms the dendrite makes this morphology unique. An important distinguishing feature from the previously known morphologies is that it grows in conformal layers, giving it an appearance of dense branching morphology, but instead of DLA like motifs it has Dendritic motifs. In this work, in-situ microfluidic studies coupled with Kinetic-Monte Carlo simulations are used to investigate plating and cycling behavior of HD Zn. While Monte Carlo simulations have been implemented in the past 4 to show growth of DLA like structures, we extend these to incorporate effect of crystal anisotropy in electrochemical systems. We hypothesize that growth at high overpotentials leads to the formation of a space charge region at the electrolyte/electrode interface due to high potential gradient. This space charge region is where migration becomes important. The migration length along with high concentration gradient built at the growth overpotentials gives rise to the HD Zn morphology.1. Naybour, R. D. et al. Electrochimica Acta 13.4 (1968): 763-769. 2. M. Chamoun et al., NPG Asia Materials, 7, e178 (2015). 3. T. Gupta et al., J. Power Sources, 305, 22–29 (2016). 4. Erlebacher, J. et al. Physical review letters 71.20 (1993): 3311.

The Role of Temperature on Salt Removal Using Capacitive Deionization

Current technologies utilized for seawater desalination, reverse osmosis (RO) and Membrane distillation (MD), are energy intensive because they operated by separating the main component water (H2O) from the salt (NaCl). Capacitive deionization (CDI), an emerging separations based technology, operates by extracting the minority component (NaCl). CDI is similar to a supercapacitors[1], where ions adsorb to the high surface area activated carbon once an electric potential is applied across the electrochemical cell (ion separation process)[2-5]. However, in place of traditional non-aqueous based electrolytes is a electrolyte comprised of sea, brackish or wastewater. More recent theoretical based studies have emphasized the role heat transfer has on ion adsorption dynamics within CDI cells[6].Traditional CDI cells operate in a cyclic process where the capacitive electrodes are brought in contact with a concentrated salt solution (e.g. brackish water) and charged. Once the charged electrodes are fully saturated with salt ions, the electrodes are regenerated through discharging the electrodes in a brine solution. Analogous to a P-V diagram for traditional heat engines, the enclosed area of the charge versus voltage represents the energy consumed during this charging-discharging process. Here we explore the effect of temperature on salt removal in a CDI cycle. Experimentally, we use traditional electrochemical characterization methods, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), to evaluate the capacitance and resistance changes with temperature. Specifically the salt adsorption capacity is shown to decrease from 13.82±1.13, to 6.58±1.01 milligram NaCl/mg carbon as the cell temperature is increased from 25oC to 45oC. 1. Hatzell, K.B., M. Boota, and Y. Gogotsi. Chemical Society Reviews, 2015. 44(23): p. 8664-8687. 2. Porada, S., R. Zhao, A. Van Der Wal, V. Presser, and P. Biesheuvel.Progress in Materials Science, 2013. 3. Hatzell, K.B., M.C. Hatzell, K.M. Cook, M. Boota, G.M. Housel, A. McBride, E.C. Kumbur, and Y. Gogotsi. Environmental science & technology, 2015. 49(5): p. 3040-3047. 4. Ren, C.E., K.B. Hatzell, M. Alhabeb, Z. Ling, K.A. Mahmoud, and Y. Gogotsi. The journal of physical chemistry letters, 2015. 6(20): p. 4026-4031. 5. Hatzell, K.B., E. Iwama, A. Ferris, B. Daffos, K. Urita, T. Tzedakis, F. Chauvet, P.-L. Taberna, Y. Gogotsi, and P. Simon. Electrochemistry Communications, 2014. 43: p. 18-21. 6. Janssen, M., A. Härtel, and R. Van Roij. Physical review letters, 2014. 113(26): p. 268501.

Adhesion Energy and Bonding Wave Velocity Measurements

Direct bonding is now widely used in microelectronics for SOI elaboration or 3D integration. One of its main characterizations is the adherence energy, also called bonding energy, which estimates the strength of the bonded structure and its evolution with the different process parameters (annealing temperature, plasma activation…). The double cantilever beam (DCB) technique described by Maszara et al. [1] is the most common technic to measure the adherence energy. During the bonding another key characterization, the adhesion energy, deserves to be studied. This quantity gives information about the attractive forces involved when contacting the two surfaces and helps to understand the bonding wave velocity. Rieutord et al. [2] suggested an analytical model based on air flow dynamics between the two wafers and showed an analytical relation between the adhesion energy and the bonding wave velocity. In this work, a simple measurement apparatus derived from the DCB technique has been developed to measure the adhesion energy and the bonding wave velocity. Beams cut in <001> bonded silicon wafers are opened at the bonding interface by a blade insertion; then the blade is suddenly partially removed allowing the structure to be bonded again. Recording multiple infra-red pictures one can follow the rebonding wave propagation and measure its velocity. The blade allows an easy and long debonded area in order to be sure to detect a stable rebonding wave speed. As a part of the blade is not totally removed, one can also determine the remaining debonded length when the wave propagation stops due to the known blade thickness. The energy associated to this length and calculated using El Zein [3] equation is the adhesion energy. In this experiment, upper and lower substrates of the bonded structure are allowed to be deformed. We also check that measurements performed on 2 cm wide beams are equivalent to larger beams in order to prevent any fluid edge effect as described by Radisson et al. [4]. So according to these considerations, we assume that the apparatus well describe the Rieutord’s hypothesis of infinite wide beams free to deform in the perpendicular direction and we can then compare our measures to his analytical predictions. We will show in this paper a very good correlation between the adhesion energy and the bonding wave speed. The surface energy has been varied by changing the surface roughness. Surprisingly, an interesting evolution of the adhesion energy after the blade stop will be presented. During 90 minutes, a slow increase of the bonding energy is observed at room temperature and 50% Relative Humidity. A mechanism will be proposed to explain this long time evolution mainly based on a slow kinetics of capillary condensation between the rough surfaces [5]. We will then discuss the choice of the energy adhesion value and show that long time values combined to measured velocities well agree with Rieutord’s model (cf. figure). REFERENCES [1] W. P. Maszara, G. Goetz, A. Caviglia and J. B. McKitterick, “Bonding of silicon wafers for silicon on insulator”, J. Appl. Phys., 64 p 4943 (1988) [2] F. Rieutord, B. Bataillou, and H. Moriceau, “Dynamics of a bonding front”, Physical Review Letters, vol. 94, pp. 236101, (2005). [3] M. S. El-Zein and K. L. Reijsnider, “Evaluation of GIC of a DCB Specimen Using an Anisotropic Solution”, Journal of Compo. Tech. & Research, 10(4), pp.151-155, (1988) [4] D. Radisson, “Direct bonding on patterned surfaces”, PhD thesis, Grenoble Univ., France (2014) [5] F. Fournel, C. Martin-Cocher, D. Radisson, V. Larrey, E. Beche, C. Morales, P. A. Delean, F. Rieutord, and H. Moriceau, “Water Stress Corrosion in Bonded Structures”, ECS Journal of Solid State Science and Technology, 4 (5) P124-P130 (2015) Figure 1

Talented 12 class of 2015: Where are they now?

TALENTED 12 Talented 12 class of 2015: Where are they now?Changing the world takes a while. We asked our inaugural class what they’ve been up to this past year. ShareShare onFacebookTwitterWechatLinked InRedditEmail C&EN, 2016, 94 (33), p 50August 22, 2016Cite this:C&EN 94, 33, 50Here, Erb (left) celebrates the feat with grad student Thomas Schwander. “Put your helmets on, we are going to cycle CO2!” (Credit: Erb Lab )Figure1of2Balskus, a microbial metabolism expert, poses with Hitomi Nakamura (left) and Smaranda Bodea (right). (Credit: Courtesy of Emily Balskus)Figure1of2 Brad OlsenMIT Olsen reports that his group published its first paper on loop defects in polymer networks in Physical Review Letters (DOI: 10.1103/physrevlett.116.188302). Tobias ErbMax Planck Institute for Terrestrial Microbiology Erb’s team successfully engineered enzymes to pull CO2 from the atmosphere and efficiently convert it into useful carbon-based compounds. Luke LavisHoward Hughes Medical Institute’s Janelia Research Campus “After a year of heavy traveling and writing papers, I finally got back into the lab and made some dyes with my own hands.” Matt MacDonaldAir Products & Chemicals MacDonald tells us he’s been whipping up new silicon-based compounds to build microelectronic devices with three-dimensional memory technology. Troy ListerSpero Therapeutics Lister disclosed his company’s lead drug candidate, SPR741, for the first time at a meeting in Boston. SPR741 is a molecule that disrupts the outer membrane of resistant bacteria so that antibiotics can sneak in and attack. Denis MalyshevTop secret start-up “I got a job at a biotech company that I’m super stoked about.” The firm is still in stealth mode, though, so Malyshev wouldn’t name names. Kami HullUniversity of Illinois, Urbana-Champaign Hull reports that her lab has “successfully done both directed and undirected anti-Markovnikov-selective amination” this year. (Translation for nonorganickers: They’ve achieved both tight and loose control over a reaction that adds amines to the most crowded carbon in a carbon-carbon double bond.) Hosea NelsonUCLA “My lab ran its first experiment. It worked!” Nelson says. The organic chemist adds that he also taught his first classes ever. “The second class was 100 times better than the first.” Karen HavenstriteTangible Science Havenstrite says her firm was issued two patents and received U.S. Food & Drug Administration clearance for its contact lens technology, which helps treat dry eye. Emily BalskusHarvard “I graduated my first class of Ph.D. students this year!” Jacob HookerHarvard Medical School Hooker celebrated his first graduate student getting her Ph.D. And the radiochemist will soon celebrate the birth of his second child, in mid-September. Matt KananStanford Kanan pointed us to a paper his team published in Nature on a reaction that uses simple molten salts to convert greenhouse gas CO2 into building blocks for making a type of polyester plastic (DOI: 10.1038/nature17185).

Commentary: How gravitational waves went from a whisper to a shout

Commentary: How gravitational waves went from a whisper to a shout

Stabilization of the vertical instability by non-axisymmetric coils

In a published Physical Review Letter (Reiman 2007 Phys. Rev. Lett. 99 135007), it was shown that axisymmetric (or vertical) stability can be improved by placing a set of parallelogram coils above and below the plasma oriented at an angle to the constant toroidal planes. The physics of this stabilization can be understood as providing an effective additional positive stability index. The original work was based on a simplified model of a straight tokamak and is not straightforwardly applicable to a finite aspect ratio, strongly shaped plasma such as in DIII-D. Numerical calculations were performed in a real DIII-D -like configuration to provide a proof of principal that 3-D fields can, in fact raise the elongation limits as predicted. A four field period trapezioid-shaped coil set was developed in toroidal geometry and 3D equilibria were computed using trapezium coil currents of , , and . The ideal magnetohydrodynamics growth rates were computed as a function of the conformal wall position for the symmetry-preserving family. The results show an insignificant relative improvement in the stabilizing wall location for the two lower coil current cases, of the order of 10−3 and less. In contrast, the marginal wall position is increased by 7% as the coil current is increased to , confirming the main prediction from the original study in a real geometry case. In DIII-D the shift in marginal wall position of 7% would correspond to being able to move the existing wall outward by 5 to 10 cm. While the predicted effect on the axisymmetric stability is real, it appears to require higher coil currents than could be provided in an upgrade to existing facilities. Additional optimization over the pitch of the coils, the number of field periods and the coil positions, as well as plasma parameters, such as the internal inductivity , , and would mitigate this but seem unlikely to change the conclusion.

Jim Dungey, The Open Magnetosphere, and Space Weather

AbstractIn 1961, James W. Dungey published a remarkable two‐paged paper in Physics Review Letters that revolutionized our understanding of the Earth's magnetosphere. In it, he used his concept of “magnetic reconnection” to introduce the open magnetosphere model. Dungey died in 2015, but his idea does a great deal more than just live on in the literature. At the same time as making sense of the magnetosphere, it has established key applications in astrophysics, planetary physics, solar and heliospheric physics, and fusion energy research—in fact, any area involving ionized gases threaded by magnetic fields. It is now the basis of our understanding and prediction of space weather phenomena.

Systematic Grant and Funding Body Acknowledgment Data for Publications: An Examination of New Dimensions and New Controversies for Bibliometrics

Bibliographic databases are beginning to provide systematic grant and funding body acknowledgement data for the publications they index. This paper considers how this new data might be used for policy purposes and the key issues that are likely to arise in its use. While the provision of systematic funding data is at a relatively early stage, there is already sufficient in the Web of Science information within the WOS database to begin tentatively to examine a number of controversies in science studies. This paper considers one such issue, namely the relationship between the number of funding sources acknowledged and the citation impact of publications where a positive relationship has been assumed to exist. Analyses of sets of publications from 2009 from the journals Cell and Physical Review Letters give contrasting results, suggesting that our understanding of the issue of the relationship between the impact of a publication and the number of funding sources which it acknowledges is not fully understood and may be more complicated that previously considered. It is proposed that scientific research findings are packaged by researchers into papers in a variety of ways for a wide variety of purposes. Individual funding quanta from whatever source are not therefore inputs to papers directly; rather, such funding supports a process that has amongst its outcomes, the production of papers.

The correlation between editorial delay and the ratio of highly cited papers in Nature, Science and Physical Review Letters

Ideally, in a reviewing process, it is generally easier for referees to make faster and more reliable decisions for high quality papers, which ideally and on average will later attract more citations. Therefore, it is possible that the editorial delay time--the time between dates of submission and acceptance or publication--is correlated to the number of received citations, as has been weakly confirmed by previous studies. In this study, we propose a different measure for this correlation. Instead of directly calculating the correlation coefficient between the editorial delay and the number of citations, we define a ratio of above median highly cited papers and perform correlation analysis between editorial delay and that ratio for all academic papers published in Nature, Science and Physical Review Letters. Using this alternative measure, we find that on average papers with shorter editorial delay do have larger probabilities of becoming highly cited papers.

The COMPASS Measurement of the Pion Polarizability

The COMPASS experiment at CERN reported in a 2015 Physical Review Letter the first precise measurement of the electromagnetic polarizability of the charged pion. After a short introduction of the experiment, we will underline the basic aspects of the measurement of the polarizability performed by COMPASS and the impact of the result.

From Einstein's general theory of relativity to gravitational‐wave astronomy

In his 1916 article [1] predicting the existence of gravitational waves, Einstein wrote that they were too weak to be of any consequence. A century later, the world’s attention was captured by the February 11th announcement, demonstrating how wrong this was. In a landmark publication in Physical Review Letters [2], an international team reports the first direct detection of the gravitational waves emitted by a pair of black holes (29 and 36 solar masses) during their final few orbits before merging to form a single 62 solar-mass black hole. Physicists love extremes, because pushing the limits leads to insight and understanding. This discovery, a short chirp lasting about a quarter-second (see Fig. 1, adapted from [2]), pushes the limits in many different directions. Let’s start with the human side. The first unsuccessful attempts to detect gravitational waves were smallinvestigator experiments made about fifty years ago. In contrast, the discovery paper had about 1000 authors (20% are from the Max Planck Institute for Gravitational Physics, for which I am the Managing Director). Some of these authors have worked towards the discovery for more than forty years. The detector technology also pushes the limits. The advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) instruments are located 3000 km apart, in Hanford, Washington and Livingston, Louisiana. The effect of the gravitational waves is to distort the effective path length between pairs of mirrors hanging 4 km apart in a seismically-isolated high-vacuum system. At the peak of the signal the measured length change in each detector arm is about 0.002 femtometers, 1/1000 the diameter of a hydrogen nucleus. This is a fractional precision of a part in 1021; analogous to measuring the distance to the nearest star (Proxima Centuri) to an accuracy of 40 μm. I don’t know of any other measurement done with comparable precision. The binary system we observed was about one billion light years distant from earth; over some tens of milliseconds it converted about three solar masses of gravitational binding energy into gravitational waves. During that brief time, the system emitted more power than the optical luminosity of every star in every galaxy in the visible universe. My kids, jaded by generations of Star Wars movies, were unimpressed until I told them that in comparison with this, the “Death Star”, capable of vaporizing entire planets, is child’s toy, a harmless plaything. Three solarmasses is enough energy to vaporize every planet in many galaxies! Binary black hole systems like this one could not have been detected in any other way, because (being black!) they do not emit any light or electromagnetic energy. But there are intriguing reports [3] that a team analyzing data from the Gamma-ray Burst Monitor (GBM) detector on board NASA’s Fermi satellite observed a gammaray burst 0.4 seconds after the merger. So Nature might still surprise us. Could such systems be surrounded by clouds of gas or dust? We can’t be sure now, but within a few years, I am confident that we will know the answer to this and to many other questions. The rate at which our knowledge will now increase is breathtaking. In their first observing run the advanced LIGOdetectors were a factor of three below their final design sensitivity. That doesn’t seem like much, but keep in mind that the expected number of sources/detections is proportional to the observable volume of space, which scales like the cube of the sensitivity. So the second observing run, starting this September and lasting six months, should observe about a dozen black hole mergers, and the third observing run, starting in 2017, should see about one hundred. It’s going to be quite a ride – a golden age of gravitational wave astronomy. By the end of it, we’ll know themass distribution and spatial density of these stellarmass black hole binary systems. And perhaps our catalog of observations will include new extremes, such as systemswith high spin, or neutron-star/black-hole binaries, or other surprises.

Carbon Nanotube Array Field Effect Transistors with High Current Density and On/Off Ratio

Single walled carbon nanotubes (SWCNTs) exhibit extraordinarily high current carrying capacity and suitable band gaps for logic and thin film field-effect transistors (FETs). Progress in honing the exceptional properties of SWCNTs at the multi-tube level, however, has been dampened by incremental advances in the materials science of electronic type sorting and assembly of SWCNTs. To address these challenges we leveraged the exceptional semiconducting sorting fidelity of polyfluorene polymers and we pioneered an alignment technique known as Floating Evaporative Self-Assembly (FESA).1 Recently, we demonstrated individually placed and uniformly pitched purely semiconducting SWCNT arrays using these techniques, allowing for negligible current lost to scaling when the arrays were implemented as the channel in FETs. The SWCNT array FETs exhibited the highest on-state conductance of 261 μS/μm with a simultaneous on/off conductance ratio exceeding 105 for a multi-tube SWCNT FET.2 Here we present our recent optimization of the contact resistance at the palladium-SWCNT interface, which enables a substantial increase in device on-current density compared to our previous report. For SWCNTs, the quality of the contact-semiconductor interface is highly dependent on the SWCNT packing density, film cleanliness, and surface energy, where any non-idealities may lead to poor palladium film adhesion, or even complete film delamination.3 To address the contact challenge we perform surface treatments on the SWCNT array prior to depositing palladium contacts, which involves rinsing the SWCNT arrays in specific solvents and annealing the films in vacuum. In XPS and optical absorbance spectra, we observe significant mass reduction of the polyfluorene wrapper while maintaining the quality and alignment of the SWCNT array. AFM height maps of the palladium contacts deposited on top of the surface treated SWCNTs demonstrate nearly ideal conformation of the palladium on the SWCNT array. The surface-treated SWCNT array FETs exhibit more than 10-fold improvement in the device on-conductance compared to non-treated samples. [1] Y. Joo, G. J. Brady, M. S. Arnold, and P. Gopalan, Langmuir 30 (12), 3460 (2014). [2] G. J. Brady, Y. Joo, M. Y. Wu, M. J. Shea, P. Gopalan, and M. S. Arnold, ACS Nano 8 (11), 11614 (2014). [3] V. Perebeinos and J. Tersoff, Physical Review Letters 114 (8), 4 (2015).