| 1. |
- Aartsen, M. G., et al.
(författare)
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Very high-energy gamma-ray follow-up program using neutrino triggers from IceCube
- 2016
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Ingår i: Journal of Instrumentation. - 1748-0221. ; 11
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Tidskriftsartikel (refereegranskat)abstract
- We describe and report the status of a neutrino-triggered program in IceCube that generates real-time alerts for gamma-ray follow-up observations by atmospheric-Cherenkov telescopes (MAGIC and VERITAS). While IceCube is capable of monitoring the whole sky continuously, high-energy gamma-ray telescopes have restricted fields of view and in general are unlikely to be observing a potential neutrino-flaring source at the time such neutrinos are recorded. The use of neutrino-triggered alerts thus aims at increasing the availability of simultaneous multi-messenger data during potential neutrino flaring activity, which can increase the discovery potential and constrain the phenomenological interpretation of the high-energy emission of selected source classes (e. g. blazars). The requirements of a fast and stable online analysis of potential neutrino signals and its operation are presented, along with first results of the program operating between 14 March 2012 and 31 December 2015.
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| 2. |
- Arndt, D. S., et al.
(författare)
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STATE OF THE CLIMATE IN 2017
- 2018
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Ingår i: Bulletin of The American Meteorological Society - (BAMS). - : American Meteorological Society. - 0003-0007 .- 1520-0477. ; 99:8, s. S1-S310
-
Forskningsöversikt (refereegranskat)
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| 3. |
- Arndt, D. S., et al.
(författare)
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State of the Climate in 2016
- 2017
-
Ingår i: Bulletin of The American Meteorological Society - (BAMS). - 0003-0007 .- 1520-0477. ; 98:8, s. S1-S280
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Tidskriftsartikel (refereegranskat)abstract
- In 2016, the dominant greenhouse gases released into Earth's atmosphere-carbon dioxide, methane, and nitrous oxide-continued to increase and reach new record highs. The 3.5 +/- 0.1 ppm rise in global annual mean carbon dioxide from 2015 to 2016 was the largest annual increase observed in the 58-year measurement record. The annual global average carbon dioxide concentration at Earth's surface surpassed 400 ppm (402.9 +/- 0.1 ppm) for the first time in the modern atmospheric measurement record and in ice core records dating back as far as 800000 years. One of the strongest El Nino events since at least 1950 dissipated in spring, and a weak La Nina evolved later in the year. Owing at least in part to the combination of El Nino conditions early in the year and a long-term upward trend, Earth's surface observed record warmth for a third consecutive year, albeit by a much slimmer margin than by which that record was set in 2015. Above Earth's surface, the annual lower troposphere temperature was record high according to all datasets analyzed, while the lower stratospheric temperature was record low according to most of the in situ and satellite datasets. Several countries, including Mexico and India, reported record high annual temperatures while many others observed near-record highs. A week-long heat wave at the end of April over the northern and eastern Indian peninsula, with temperatures surpassing 44 degrees C, contributed to a water crisis for 330 million people and to 300 fatalities. In the Arctic the 2016 land surface temperature was 2.0 degrees C above the 1981-2010 average, breaking the previous record of 2007, 2011, and 2015 by 0.8 degrees C, representing a 3.5 degrees C increase since the record began in 1900. The increasing temperatures have led to decreasing Arctic sea ice extent and thickness. On 24 March, the sea ice extent at the end of the growth season saw its lowest maximum in the 37-year satellite record, tying with 2015 at 7.2% below the 1981-2010 average. The September 2016 Arctic sea ice minimum extent tied with 2007 for the second lowest value on record, 33% lower than the 1981-2010 average. Arctic sea ice cover remains relatively young and thin, making it vulnerable to continued extensive melt. The mass of the Greenland Ice Sheet, which has the capacity to contribute similar to 7 m to sea level rise, reached a record low value. The onset of its surface melt was the second earliest, after 2012, in the 37-year satellite record. Sea surface temperature was record high at the global scale, surpassing the previous record of 2015 by about 0.01 degrees C. The global sea surface temperature trend for the 21st century-to-date of +0.162 degrees C decade(-1) is much higher than the longer term 1950-2016 trend of +0.100 degrees C decade(-1). Global annual mean sea level also reached a new record high, marking the sixth consecutive year of increase. Global annual ocean heat content saw a slight drop compared to the record high in 2015. Alpine glacier retreat continued around the globe, and preliminary data indicate that 2016 is the 37th consecutive year of negative annual mass balance. Across the Northern Hemisphere, snow cover for each month from February to June was among its four least extensive in the 47-year satellite record. Continuing a pattern below the surface, record high temperatures at 20-m depth were measured at all permafrost observatories on the North Slope of Alaska and at the Canadian observatory on northernmost Ellesmere Island. In the Antarctic, record low monthly surface pressures were broken at many stations, with the southern annular mode setting record high index values in March and June. Monthly high surface pressure records for August and November were set at several stations. During this period, record low daily and monthly sea ice extents were observed, with the November mean sea ice extent more than 5 standard deviations below the 1981-2010 average. These record low sea ice values contrast sharply with the record high values observed during 2012-14. Over the region, springtime Antarctic stratospheric ozone depletion was less severe relative to the 1991-2006 average, but ozone levels were still low compared to pre-1990 levels. Closer to the equator, 93 named tropical storms were observed during 2016, above the 1981-2010 average of 82, but fewer than the 101 storms recorded in 2015. Three basins-the North Atlantic, and eastern and western North Pacific-experienced above-normal activity in 2016. The Australian basin recorded its least active season since the beginning of the satellite era in 1970. Overall, four tropical cyclones reached the Saffir-Simpson category 5 intensity level. The strong El Nino at the beginning of the year that transitioned to a weak La Nina contributed to enhanced precipitation variability around the world. Wet conditions were observed throughout the year across southern South America, causing repeated heavy flooding in Argentina, Paraguay, and Uruguay. Wetter-than-usual conditions were also observed for eastern Europe and central Asia, alleviating the drought conditions of 2014 and 2015 in southern Russia. In the United States, California had its first wetter-than-average year since 2012, after being plagued by drought for several years. Even so, the area covered by drought in 2016 at the global scale was among the largest in the post-1950 record. For each month, at least 12% of land surfaces experienced severe drought conditions or worse, the longest such stretch in the record. In northeastern Brazil, drought conditions were observed for the fifth consecutive year, making this the longest drought on record in the region. Dry conditions were also observed in western Bolivia and Peru; it was Bolivia's worst drought in the past 25 years. In May, with abnormally warm and dry conditions already prevailing over western Canada for about a year, the human-induced Fort McMurray wildfire burned nearly 590000 hectares and became the costliest disaster in Canadian history, with $3 billion (U.S. dollars) in insured losses.
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| 4. |
- Mayer, Manuel, et al.
(författare)
-
Constraints on particle acceleration in SS433/W50 from MAGIC and HESS observations
- 2018
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 612
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Tidskriftsartikel (refereegranskat)abstract
- Context. The large jet kinetic power and non-thermal processes occurring in the microquasar SS 433 make this source a good candidate for a very high-energy (VHE) gamma-ray emitter. Gamma-ray fluxes above the sensitivity limits of current Cherenkov telescopes have been predicted for both the central X-ray binary system and the interaction regions of SS 433 jets with the surrounding W50 nebula. Non-thermal emission at lower energies has been previously reported, indicating that efficient particle acceleration is taking place in the system. Aims. We explore the capability of SS 433 to emit VHE gamma rays during periods in which the expected flux attenuation due to periodic eclipses (P-orb similar to 13.1 days) and precession of the circumstellar disk (P-pre similar to 162 days) periodically covering the central binary system is expected to be at its minimum. The eastern and western SS 433/W50 interaction regions are also examined using the whole data set available. We aim to constrain some theoretical models previously developed for this system with our observations. Methods. We made use of dedicated observations from the Major Atmospheric Gamma Imaging Cherenkov telescopes (MAGIC) and High Energy Spectroscopic System (H.E.S.S.) of SS 433 taken from 2006 to 2011. These observation were combined for the first time and accounted for a total effective observation time of 16.5 h, which were scheduled considering the expected phases of minimum absorption of the putative VHE emission. Gamma-ray attenuation does not affect the jet/medium interaction regions. In this case, the analysis of a larger data set amounting to similar to 40-80 h, depending on the region, was employed. Results. No evidence of VHE gamma-ray emission either from the central binary system or from the eastern/western interaction regions was found. Upper limits were computed for the combined data set. Differential fluxes from the central system are found to be less than or similar to 10(-12)-10(-13) TeV-1 cm(-2) s(-1) in an energy interval ranging from similar to few x 100 GeV to similar to few TeV. Integral flux limits down to similar to 10(-12)-10(-13) ph cm(-2) s(-1) and similar to 10(-13)-10(-14) ph cm(-2) s(-1) are obtained at 300 and 800 GeV, respectively. Our results are used to place constraints on the particle acceleration fraction at the inner jet regions and on the physics of the jet/medium interactions. Conclusions. Our findings suggest that the fraction of the jet kinetic power that is transferred to relativistic protons must be relatively small in SS 433, q(p) <= 2.5 x 10(-5), to explain the lack of TeV and neutrino emission from the central system. At the SS 433/W50 interface, the presence of magnetic fields greater than or similar to 10 mu G is derived assuming a synchrotron origin for the observed X-ray emission. This also implies the presence of high-energy electrons with E-e up to 50 TeV, preventing an efficient production of gamma-ray fluxes in these interaction regions.
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| 5. |
- Aleksic, J., et al.
(författare)
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Measurement of the Crab Nebula spectrum over three decades in energy with the MAGIC telescopes
- 2015
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Ingår i: Journal of High Energy Astrophysics. - : Elsevier BV. - 2214-4048 .- 2214-4056. ; 5-6, s. 30-38
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Tidskriftsartikel (refereegranskat)abstract
- The MAGIC stereoscopic system collected 69 hours of Crab Nebula data between October 2009 and April 2011. Analysis of this data sample using the latest improvements in the MAGIC stereoscopic software provided an unprecedented precision of spectral and night-by-night light curve determination at gamma rays. We derived a differential spectrum with a single instrument from 50 GeV up to almost 30 TeV with 5 bins per energy decade. At low energies, MAGIC results, combined with Fermi-LAT data, show a flat and broad Inverse Compton peak. The overall fit to the data between 1 GeV and 30 TeV is not well described by a log-parabola function. We find that a modified log-parabola function with an exponent of 2.5 instead of 2 provides a good description of the data (chi(2)(red) = 35/26). Using systematic uncertainties of the MAGIC and Fermi-LAT measurements we determine the position of the Inverse Compton peak to be at (53 +/- 3(stat)+ 31(syst)-13(syst)) GeV, which is the most precise estimation up to date and is dominated by the systematic effects. There is no hint of the integral flux variability on daily scales at energies above 300 GeV when systematic uncertainties are included in the flux measurement. We consider three state-of-the-art theoretical models to describe the overall spectral energy distribution of the Crab Nebula. The constant B-field model cannot satisfactorily reproduce the VHE spectral measurements presented in this work, having particular difficulty reproducing the broadness of the observed IC peak. Most probably this implies that the assumption of the homogeneity of the magnetic field inside the nebula is incorrect. On the other hand, the time-dependent 1D spectral model provides a good fit of the new VHE results when considering a 80 mu G magnetic field. However, it fails to match the data when including the morphology of the nebula at lower wavelengths.
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| 6. |
- Ahnen, M. L., et al.
(författare)
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Limits to dark matter annihilation cross-section from a combined analysis of MAGIC and Fermi-LAT observations of dwarf satellite galaxies
- 2016
-
Ingår i: Journal of Cosmology and Astroparticle Physics. - : IOP Publishing. - 1475-7516. ; :2
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Tidskriftsartikel (refereegranskat)abstract
- We present the first joint analysis of gamma-ray data from the MAGIC Cherenkov telescopes and the Fermi Large Area Telescope (LAT) to search for gamma-ray signals from dark matter annihilation in dwarf satellite galaxies. We combine 158 hours of Segue 1 observations with MAGIC with 6-year observations of 15 dwarf satellite galaxies by the Fermi-LAT. We obtain limits on the annihilation cross-section for dark matter particle masses between 10 GeV and 100 TeV - the widest mass range ever explored by a single gamma-ray analysis. These limits improve on previously published Fermi-LAT and MAGIC results by up to a factor of two at certain masses. Our new inclusive analysis approach is completely generic and can be used to perform a global, sensitivity-optimized dark matter search by combining data from present and future gamma-ray and neutrino detectors.
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| 7. |
- Coll, M., et al.
(författare)
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Towards Oxide Electronics: a Roadmap
- 2019
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Ingår i: Applied Surface Science. - : Elsevier BV. - 0169-4332 .- 1873-5584. ; 482, s. 1-93
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Tidskriftsartikel (refereegranskat)abstract
- At the end of a rush lasting over half a century, in which CMOS technology has been experiencing a constant and breathtaking increase of device speed and density, Moore’s law is approaching the insurmountable barrier given by the ultimate atomic nature of matter. A major challenge for 21st century scientists is finding novel strategies, concepts and materials for replacing silicon-based CMOS semiconductor technologies and guaranteeing a continued and steady technological progress in next decades. Among the materials classes candidate to contribute to this momentous challenge, oxide films and heterostructures are a particularly appealing hunting ground. The vastity, intended in pure chemical terms, of this class of compounds, the complexity of their correlated behaviour, and the wealth of functional properties they display, has already made these systems the subject of choice, worldwide, of a strongly networked, dynamic and interdisciplinary research community. Oxide science and technology has been the target of a wide four-year project, named Towards Oxide-Based Electronics (TO-BE), that has been recently running in Europe and has involved as participants several hundred scientists from 29 EU countries. In this review and perspective paper, published as a final deliverable of the TO-BE Action, the opportunities of oxides as future electronic materials for Information and Communication Technologies ICT and Energy are discussed. The paper is organized as a set of contributions, all selected and ordered as individual building blocks of a wider general scheme. After a brief preface by the editors and an introductory contribution, two sections follow. The first is mainly devoted to providing a perspective on the latest theoretical and experimental methods that are employed to investigate oxides and to produce oxide-based films, heterostructures and devices. In the second, all contributions are dedicated to different specific fields of applications of oxide thin films and heterostructures, in sectors as data storage and computing, optics and plasmonics, magnonics, energy conversion and harvesting, and power electronics.
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| 8. |
- Berntsson, Oskar, 1989, et al.
(författare)
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Sequential conformational transitions and alpha-helical supercoiling regulate a sensor histidine kinase
- 2017
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 8
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Tidskriftsartikel (refereegranskat)abstract
- Sensor histidine kinases are central to sensing in bacteria and in plants. They usually contain sensor, linker, and kinase modules and the structure of many of these components is known. However, it is unclear how the kinase module is structurally regulated. Here, we use nano- to millisecond time-resolved X-ray scattering to visualize the solution structural changes that occur when the light-sensitive model histidine kinase YF1 is activated by blue light. We find that the coiled coil linker and the attached histidine kinase domains undergo a left handed rotation within microseconds. In a much slower second step, the kinase domains rearrange internally. This structural mechanism presents a template for signal transduction in sensor histidine kinases.
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| 9. |
- Berntsson, Oskar, 1989, et al.
(författare)
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Time-Resolved X-Ray Solution Scattering Reveals the Structural Photoactivation of a Light-Oxygen-Voltage Photoreceptor
- 2017
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Ingår i: Structure. - : Elsevier BV. - 0969-2126. ; 25:6
-
Tidskriftsartikel (refereegranskat)abstract
- Light-oxygen-voltage (LOV) receptors are sensory proteins controlling a wide range of organismal adaptations in multiple kingdoms of life. Because of their modular nature, LOV domains are also attractive for use as optogenetic actuators. A flavin chromophore absorbs blue light, forms a bond with a proximal cysteine residue, and induces changes in the surroundings. There is a gap of knowledge on how this initial signal is relayed further through the sensor to the effector module. To characterize these conformational changes, we apply time-resolved X-ray scattering to the homodimeric LOV domain from Bacillus subtilis YtvA. We observe a global structural change in the LOV dimer synchronous with the formation of the chromophore photoproduct state. Using molecular modeling, this change is identified as splaying apart and relative rotation of the two monomers, which leads to an increased separation at the anchoring site of the effector modules.
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| 10. |
- Björling, Alexander, 1983, et al.
(författare)
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Structural photoactivation of a full-length bacterial phytochrome
- 2016
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Ingår i: Science Advances. - : American Association for the Advancement of Science (AAAS). - 2375-2548. ; 2:8
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Tidskriftsartikel (refereegranskat)abstract
- Phytochromes are light sensor proteins found in plants, bacteria, and fungi. They function by converting a photon absorption event into a conformational signal that propagates from the chromophore through the entire protein. However, the structure of the photoactivated state and the conformational changes that lead to it are not known. We report time-resolved x-ray scattering of the full-length phytochrome from Deinococcus radiodurans on micro-and millisecond time scales. We identify a twist of the histidine kinase output domains with respect to the chromophore-binding domains as the dominant change between the photoactivated and resting states. The time-resolved data further show that the structural changes up to the microsecond time scales are small and localized in the chromophore-binding domains. The global structural change occurs within a few milliseconds, coinciding with the formation of the spectroscopic meta-Rc state. Our findings establish key elements of the signaling mechanism of full-length bacterial phytochromes.
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| 11. |
- Takala, H., et al.
(författare)
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On the (un)coupling of the chromophore, tongue interactions, and overall conformation in a bacterial phytochrome
- 2018
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Ingår i: Journal of Biological Chemistry. - 0021-9258. ; 293:21, s. 8161-8172
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Tidskriftsartikel (refereegranskat)abstract
- Phytochromes are photoreceptors in plants, fungi, and various microorganisms and cycle between metastable red light-absorbing (Pr) and far-red light-absorbing (Pfr) states. Their light responses are thought to follow a conserved structural mechanism that is triggered by isomerization of the chromophore. Downstream structural changes involve refolding of the so-called tongue extension of the phytochrome-specific GAF-related (PHY) domain of the photoreceptor. The tongue is connected to the chromophore by conserved DIP and PRXSF motifs and a conserved tyrosine, but the role of these residues in signal transduction is not clear. Here, we examine the tongue interactions and their interplay with the chromophore by substituting the conserved tyrosine (Tyr(263)) in the phytochrome from the extremophile bacterium Deinococcus radiodurans with phenylalanine. Using optical and FTIR spectroscopy, X-ray solution scattering, and crystallography of chromophore-binding domain (CBD) and CBD-PHY fragments, we show that the absence of the Tyr(263) hydroxyl destabilizes the -sheet conformation of the tongue. This allowed the phytochrome to adopt an -helical tongue conformation regardless of the chromophore state, hence distorting the activity state of the protein. Our crystal structures further revealed that water interactions are missing in the Y263F mutant, correlating with a decrease of the photoconversion yield and underpinning the functional role of Tyr(263) in phytochrome conformational changes. We propose a model in which isomerization of the chromophore, refolding of the tongue, and globular conformational changes are represented as weakly coupled equilibria. The results also suggest that the phytochromes have several redundant signaling routes.
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| 12. |
- Bartel, T., et al.
(författare)
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Investigations on enhanced Fischer–Burmeister NCP functions : application to a rate-dependent model for ferroelectrics
- 2019
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Ingår i: Archive of Applied Mechanics. - : Springer Science and Business Media LLC. - 0939-1533 .- 1432-0681. ; 89:6, s. 995-1010
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Tidskriftsartikel (refereegranskat)abstract
- This contribution deals with investigations on enhanced Fischer–Burmeister nonlinear complementarity problem (NCP) functions applied to a rate-dependent laminate-based material model for ferroelectrics. The framework is based on the modelling and parametrisation of the material’s microstructure via laminates together with the respective volume fractions. These volume fractions are treated as internal-state variables and are subject to several inequality constraints which can be treated in terms of Karush–Kuhn–Tucker conditions. The Fischer–Burmeister NCP function provides a sophisticated scheme to incorporate Karush–Kuhn–Tucker-type conditions into calculations of internal-state variables. However, these functions are prone to numerical instabilities in their original form. Therefore, some enhanced formulations of the Fischer–Burmeister ansatz are discussed and compared to each other in this contribution.
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| 13. |
- Baust, A., et al.
(författare)
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Ultrastrong coupling in two-resonator circuit QED
- 2016
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Ingår i: Physical Review B. - 2469-9969 .- 2469-9950. ; 93:21, s. Art. no. 214501-
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Tidskriftsartikel (refereegranskat)abstract
- We report on ultrastrong coupling between a superconducting flux qubit and a resonant mode of a system comprised of two superconducting coplanar stripline resonators coupled galvanically to the qubit. With a coupling strength as high as 17.5% of the mode frequency, exceeding that of previous circuit quantum electrodynamics experiments, we observe a pronounced Bloch-Siegert shift. The spectroscopic response of our multimode system reveals a clear breakdown of the Jaynes-Cummings approximation. In contrast to earlier experiments, the high coupling strength is achieved without making use of an additional inductance provided by a Josephson junction.
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| 14. |
- Biermann, D., et al.
(författare)
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Modelling and simulation of thermal effects in internal traverse grinding of hardened bearing steel
- 2016
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Ingår i: CIRP Annals - Manufacturing Technology. - : Elsevier BV. - 0007-8506. ; 65:1, s. 321-324
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Tidskriftsartikel (refereegranskat)abstract
- Internal traverse grinding with electro-plated cBN wheels combines the advantages of both internal hard turning and internal grinding, enabling a high material removal rate along with a high surface quality. The drawback, however, is a high thermal load on the workpiece, resulting in shape and dimension errors of the finished part. This paper deals with the compensation of these manufacturing errors with a hybrid simulation system. It combines thermo-mechanically coupled finite element models on both meso- and macro-scale with a scale-bridging kinematic simulation system, enabling the prediction of the resulting temperatures and the development of corresponding simulation-based compensation strategies.
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| 15. |
- Holtermann, R., et al.
(författare)
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Numerical Determination of Process Values Influencing the Surface Integrity in Grinding
- 2016
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Ingår i: 3rd CIRP Conference on Surface Integrity. - : Elsevier BV. - 2212-8271. - 9781510824621 ; 45, s. 39-42
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Konferensbidrag (refereegranskat)abstract
- Internal traverse grinding with electroplated cBN wheels using high-speed process conditions combines high material removal rates and a high surface quality of the workpiece in one single grinding stroke. In order to capture the macroscopic and mesoscopic thermo-mechanical loads onto the workpiece during internal traverse grinding, numerical simulations are conducted at the two scales. This results in a hybrid approach coupling two finite element models with a geometric kinematic simulation. The article focuses on the influence of multiple grain engagements onto a surface layer region using a two-dimensional chip formation simulation.
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| 16. |
- Junker, Robert R., et al.
(författare)
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Covariation and phenotypic integration in chemical communication displays : Biosynthetic constraints and eco-evolutionary implications
- 2018
-
Ingår i: New Phytologist. - : Wiley. - 0028-646X .- 1469-8137. ; 220:3, s. 739-749
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Tidskriftsartikel (refereegranskat)abstract
- Chemical communication is ubiquitous. The identification of conserved structural elements in visual and acoustic communication is well established, but comparable information on chemical communication displays (CCDs) is lacking. We assessed the phenotypic integration of CCDs in a meta-analysis to characterize patterns of covariation in CCDs and identified functional or biosynthetically constrained modules. Poorly integrated plant CCDs (i.e. low covariation between scent compounds) support the notion that plants often utilize one or few key compounds to repel antagonists or to attract pollinators and enemies of herbivores. Animal CCDs (mostly insect pheromones) were usually more integrated than those of plants (i.e. stronger covariation), suggesting that animals communicate via fixed proportions among compounds. Both plant and animal CCDs were composed of modules, which are groups of strongly covarying compounds. Biosynthetic similarity of compounds revealed biosynthetic constraints in the covariation patterns of plant CCDs. We provide a novel perspective on chemical communication and a basis for future investigations on structural properties of CCDs. This will facilitate identifying modules and biosynthetic constraints that may affect the outcome of selection and thus provide a predictive framework for evolutionary trajectories of CCDs in plants and animals.
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| 17. |
- Maniprakash, S., et al.
(författare)
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Experimental investigation, modelling and simulation of rate-dependent response of 1-3 ferroelectric composites
- 2016
-
Ingår i: Mechanics of Materials. - : Elsevier BV. - 0167-6636. ; 94, s. 91-105
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Tidskriftsartikel (refereegranskat)abstract
- Further development and design of piezoelectric composites enhances the improved use of piezoelectric materials and devices by overcoming their brittleness. In order to engineer this class of materials and to predictably simulate its behaviour, a computationally efficient constitutive model is established in this paper. This contribution deals with the development of a model for piezoelectric composites to capture their effective behaviour. We first discuss a three-dimensional fully coupled electromechanical rate-dependent model for the response of ferroelectric ceramics. Secondly, a simple homogenisation approach is applied to capture the behaviour of composites for various volume fractions of PZT fibres under different loading frequencies. Following this, a finite element formulation is applied in order to study the behaviour of composites. Finally, these two approaches are compared with experimental results.
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| 18. |
- Nasedkin, Alexandr, et al.
(författare)
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Deconvoluting Protein (Un)folding Structural Ensembles Using X-Ray Scattering, Nuclear Magnetic Resonance Spectroscopy and Molecular Dynamics Simulation
- 2015
-
Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 10:5
-
Tidskriftsartikel (refereegranskat)abstract
- The folding and unfolding of protein domains is an apparently cooperative process, but transient intermediates have been detected in some cases. Such (un) folding intermediates are challenging to investigate structurally as they are typically not long-lived and their role in the (un) folding reaction has often been questioned. One of the most well studied (un) folding pathways is that of Drosophila melanogaster Engrailed homeodomain (EnHD): this 61-residue protein forms a three helix bundle in the native state and folds via a helical intermediate. Here we used molecular dynamics simulations to derive sample conformations of EnHD in the native, intermediate, and unfolded states and selected the relevant structural clusters by comparing to small/wide angle X-ray scattering data at four different temperatures. The results are corroborated using residual dipolar couplings determined by NMR spectroscopy. Our results agree well with the previously proposed (un) folding pathway. However, they also suggest that the fully unfolded state is present at a low fraction throughout the investigated temperature interval, and that the (un) folding intermediate is highly populated at the thermal midpoint in line with the view that this intermediate can be regarded to be the denatured state under physiological conditions. Further, the combination of ensemble structural techniques with MD allows for determination of structures and populations of multiple interconverting structures in solution.
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| 19. |
- Schumann, S., et al.
(författare)
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Determination of the Thermal Load Distribution in Internal Traverse Grinding using a Geometric-Kinematic Simulation
- 2015
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Ingår i: 15th CIRP Conference on Modelling of Machining Operations (15TH CMMO). - : Elsevier BV. - 2212-8271. ; 31, s. 322-327
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Konferensbidrag (refereegranskat)abstract
- During grinding processes, numerous grains interact with the workpiece material producing mechanical and thermal loads on the surface. In the field of thermal simulation of grinding processes, a widely used approach is to substitute numerous cutting edges by a single moving distributed heat source of a specific geometrical shape referring to the theory of Carslaw and Jaeger. This heat source is then moved across the modelled workpiece according to the specific kinematics of the grinding process. The geometrical shape of the substituted heat source can usually be determined using different approaches, e.g., predefined distribution functions or, more precisely, based on measurements of the shear stress within the contact zone. Referring to the state of the art, it is not possible to measure the shear stress within the contact zone during internal traverse grinding with roughing and finishing zone because of its very complex engagement conditions and the non-rectangular shape of its contact zone. In this work, a novel approach to determining a heat source distribution based on a geometric-kinematic simulation for internal traverse grinding is presented. This simulation identifies the ideal geometrical interaction of workpiece and grinding wheel. For this purpose, the specific material removal rate for each grain is calculated and accumulated with respect to the contact zone resulting in a three-dimensional thermal load distribution. This heat source can be used in finite element simulations to determine the thermal load on the workpiece. (C) 2015 The Authors. Published by Elsevier B.V.
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| 20. |
- Takala, Heikki, et al.
(författare)
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Light-induced structural changes in a monomeric bacteriophytochrome
- 2016
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Ingår i: Structural Dynamics. - : AIP Publishing. - 2329-7778. ; 3:5
-
Tidskriftsartikel (refereegranskat)abstract
- Phytochromes sense red light in plants and various microorganism. Light absorption causes structural changes within the protein, which alter its biochemical activity. Bacterial phytochromes are dimeric proteins, but the functional relevance of this arrangement remains unclear. Here, we use time-resolved X-ray scattering to reveal the solution structural change of a monomeric variant of the photosensory core module of the phytochrome from Deinococcus radiodurans. The data reveal two motions, a bend and a twist of the PHY domain with respect to the chromophore-binding domains. Infrared spectroscopy shows the refolding of the PHY tongue. We conclude that a monomer of the phytochrome photosensory core is sufficient to perform the light-induced structural changes. This implies that allosteric cooperation with the other monomer is not needed for structural activation. The dimeric arrangement may instead be intrinsic to the biochemical output domains of bacterial phytochromes. © Author(s) 2016.
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