@article{12611, abstract = {We investigate the energy balance and ablation regimes of glaciers in high-elevation, dry environments using glaciometeorological data collected on six glaciers in the semiarid Andes of North-Central Chile (29–34°S, 3127–5324 m). We use a point-scale physically based energy balance (EB) model and an enhanced Temperature-Index (ETI) model that calculates melt rates only as a function of air temperature and net shortwave radiation. At all sites, the largest energy inputs are net shortwave and incoming longwave radiation, which are controlled by surface albedo and elevation, respectively. Turbulent fluxes cancel each other out at the lower sites, but as elevation increases, cold, dry and wind-exposed conditions increase the magnitude of negative latent heat fluxes, associated with large surface sublimation rates. In midsummer (January), ablation rates vary from 67.9 mm w.e. d−1 at the lowest site (∼100% corresponding to melt), to 2.3 mm w.e. d−1 at the highest site (>85% corresponding to surface sublimation). At low-elevation, low-albedo, melt-dominated sites, the ETI model correctly reproduces melt using a large range of possible parameters, but both the performance and parameter transferability decrease with elevation for two main reasons: (i) the air temperature threshold approach for melt onset does not capture the diurnal variability of melt in cold and strong irradiated environments and (ii) energy losses decrease the correlation between melt and net shortwave radiation. We summarize our results by means of an elevation profile of ablation components that can be used as reference in future studies of glacier ablation in the semiarid Andes.}, author = {Ayala, A. and Pellicciotti, Francesca and MacDonell, S. and McPhee, J. and Burlando, P.}, issn = {0043-1397}, journal = {Water Resources Research}, keywords = {Water Science and Technology}, number = {7}, pages = {5601--5625}, publisher = {American Geophysical Union}, title = {{Patterns of glacier ablation across North-Central Chile: Identifying the limits of empirical melt models under sublimation-favorable conditions}}, doi = {10.1002/2016wr020126}, volume = {53}, year = {2017}, } @article{12612, abstract = {Supraglacial ponds play a key role in absorbing atmospheric energy and directing it to the ice of debris-covered glaciers, but the spatial and temporal distribution of these features is not well documented. We analyse 172 Landsat TM/ETM+ scenes for the period 1999–2013 to identify thawed supraglacial ponds for the debris-covered tongues of five glaciers in the Langtang Valley of Nepal. We apply an advanced atmospheric correction routine (Landcor/6S) and use band ratio and image morphological techniques to identify ponds and validate our results with 2.5 m Cartosat-1 observations. We then characterize the spatial, seasonal and interannual patterns of ponds. We find high variability in pond incidence between glaciers (May–October means of 0.08–1.69% of debris area), with ponds most frequent in zones of low surface gradient and velocity. The ponds show pronounced seasonality, appearing in the pre-monsoon as snow melts, peaking at the monsoon onset at 2% of debris-covered area, then declining in the post-monsoon as ponds drain or freeze. Ponds are highly recurrent and persistent, with 40.5% of pond locations occurring for multiple years. Rather than a trend in pond cover over the study period, we find high interannual variability for each glacier after controlling for seasonality.}, author = {MILES, EVAN S. and WILLIS, IAN C. and ARNOLD, NEIL S. and STEINER, JAKOB and Pellicciotti, Francesca}, issn = {1727-5652}, journal = {Journal of Glaciology}, keywords = {Earth-Surface Processes}, number = {237}, pages = {88--105}, publisher = {Cambridge University Press}, title = {{Spatial, seasonal and interannual variability of supraglacial ponds in the Langtang Valley of Nepal, 1999–2013}}, doi = {10.1017/jog.2016.120}, volume = {63}, year = {2017}, } @inproceedings{12905, author = {Schlögl, Alois and Kiss, Janos}, booktitle = {AHPC17 – Austrian HPC Meeting 2017}, location = {Grundlsee, Austria}, pages = {28}, publisher = {FSP Scientific Computing}, title = {{Scientific Computing at IST Austria}}, year = {2017}, } @article{1294, abstract = {We study controller synthesis problems for finite-state Markov decision processes, where the objective is to optimize the expected mean-payoff performance and stability (also known as variability in the literature). We argue that the basic notion of expressing the stability using the statistical variance of the mean payoff is sometimes insufficient, and propose an alternative definition. We show that a strategy ensuring both the expected mean payoff and the variance below given bounds requires randomization and memory, under both the above definitions. We then show that the problem of finding such a strategy can be expressed as a set of constraints.}, author = {Brázdil, Tomáš and Chatterjee, Krishnendu and Forejt, Vojtěch and Kučera, Antonín}, journal = {Journal of Computer and System Sciences}, pages = {144 -- 170}, publisher = {Elsevier}, title = {{Trading performance for stability in Markov decision processes}}, doi = {10.1016/j.jcss.2016.09.009}, volume = {84}, year = {2017}, } @inproceedings{13160, abstract = {Transforming deterministic ω -automata into deterministic parity automata is traditionally done using variants of appearance records. We present a more efficient variant of this approach, tailored to Rabin automata, and several optimizations applicable to all appearance records. We compare the methods experimentally and find out that our method produces smaller automata than previous approaches. Moreover, the experiments demonstrate the potential of our method for LTL synthesis, using LTL-to-Rabin translators. It leads to significantly smaller parity automata when compared to state-of-the-art approaches on complex formulae.}, author = {Kretinsky, Jan and Meggendorfer, Tobias and Waldmann, Clara and Weininger, Maximilian}, booktitle = {Tools and Algorithms for the Construction and Analysis of Systems}, isbn = {9783662545768}, issn = {1611-3349}, location = {Uppsala, Sweden}, pages = {443--460}, publisher = {Springer}, title = {{Index appearance record for transforming Rabin automata into parity automata}}, doi = {10.1007/978-3-662-54577-5_26}, volume = {10205}, year = {2017}, } @article{21098, abstract = {The growth of crystals of aromatic compounds from water much depends on the nature of the water solubilizing functions that they carry. Rationalizing crystallization from water, and structure elucidation, of aromatic molecular and supramolecular systems is of general value across various fields of chemistry. Taking helical aromatic foldamers as a test case, we have validated several short polar side chains as efficient substituents to provide both solubility in, and crystal growth ability from, water. New 8-amino-2-quinolinecarboxylic acids bearing charged or neutral aminomethyl, carboxymethyl, sulfonic acid, or bis(hydroxymethyl)-methoxy side chains in position 4 or 5, were prepared on a multi gram scale. Fmoc protection of the main chain amine and suitable protections of the side chains ensured compatibility with solid phase synthesis. One tetrameric and five octameric oligoamides displaying these side chains were synthesized and shown to be soluble in water. In all cases but one, crystals were obtained using the hanging drop method, thus validating the initial design principle to combine polarity and rigidity. The only case that resisted crystallization appeared to be due to exceedingly high water solubility endowed by eight sulfonic acid functions. The neutral side chain did provide crystal growth ability from water but contributed poorly to solubility.}, author = {Hu, Xiaobo and Dawson, Simon J. and Mandal, Pradeep K and de Hatten, Xavier and Baptiste, Benoit and Huc, Ivan}, issn = {2041-6539}, journal = {Chemical Science}, number = {5}, pages = {3741--3749}, publisher = {Royal Society of Chemistry}, title = {{Optimizing side chains for crystal growth from water: a case study of aromatic amide foldamers}}, doi = {10.1039/c7sc00430c}, volume = {8}, year = {2017}, } @article{21156, abstract = {The crystal structure of the tetradecanucleotide d(CCCCGGTACCGGGG)2 has previously been reported as an A-type double helix at a resolution of 2.5 Å in space group P41. Here, the structure of this sequence was determined at a significantly higher resolution of 1.65 Å in space group P41212. The differences in crystal packing between the former and latter are described. The crystallographic asymmetric unit consists of one tetradecanucleotide duplex that spans more than one full turn of the A-helix. This structure allowed the unambiguous identification of solvent interactions.}, author = {Karthik, Selvam and Thirugnanasambandam, Arunachalam and Mandal, Pradeep K and Gautham, Namasivayam}, issn = {2053-230X}, journal = {Acta Crystallographica Section F Structural Biology Communications}, number = {5}, pages = {259--265}, publisher = {International Union of Crystallography}, title = {{Crystal structure of d(CCGGGGTACCCCGG)2 at 1.4 Å resolution}}, doi = {10.1107/s2053230x17004770}, volume = {73}, year = {2017}, } @article{21157, abstract = {We present here a comparison of three different X-ray crystal structures of DNA tetradecamer sequence d(CCCGGGTACCCGGG)2 all at about 1.7 Å resolution. The sequence was designed as an attempt to form a DNA four-way junction with A-type helical arms. However, in the presence of zinc, magnesium, and in the absence of any metal ion, it does not take up the junction structure, but forms an A-type double helix. This allowed us to study possible conformational changes in the double helix due to the presence of metal ions. Upon addition of the zinc ion, there is a change in the space group from P41212 to P41. The overall conformation of the duplex remains the same. There are small changes in the interaction of the metal ions with the DNA. In the zinc-bound structure, there are two zinc ions that show direct interaction with the N7 atoms of terminal G13 bases at either end of the molecule. There are small changes in the interhelical contacts. The consequence of these differences is to break some of the symmetry and change the space group.}, author = {Karthik, S. and Thirugnanasambandam, A. and Mandal, Pradeep K and Gautham, N.}, issn = {1532-2335}, journal = {Nucleosides, Nucleotides and Nucleic Acids}, number = {5}, pages = {343--354}, publisher = {Informa UK Limited}, title = {{Comparison of X-ray crystal structures of a tetradecamer sequence d(CCCGGGTACCCGGG)2 at 1.7 Å resolution}}, doi = {10.1080/15257770.2017.1287378}, volume = {36}, year = {2017}, } @article{21558, abstract = {The Smith-Purcell effect, observed when an electron beam passes in the vicinity of a periodic structure, is a promising platform for the generation of electromagnetic radiation in previously unreachable spectral ranges. However, most of the studies of this radiation were performed on simple periodic gratings, whose radiation spectrum exhibits a single peak and its higher harmonics predicted by a well-established dispersion relation. Here, we propose a method to shape the spatial and spectral far-field distribution of the radiation using complex periodic and aperiodic gratings. We show, theoretically and experimentally, that engineering multiple peak spectra with controlled widths located at desired wavelengths is achievable using Smith-Purcell radiation. Our method opens the way to free-electron-driven sources with tailored angular and spectral responses, and gives rise to focusing functionality for spectral ranges where lenses are unavailable or inefficient.}, author = {Remez, Roei and Shapira, Niv and Roques-Carmes, Charles and Tirole, Romain and Yang, Yi and Lereah, Yossi and Soljačić, Marin and Kaminer, Ido and Arie, Ady}, issn = {2469-9934}, journal = {Physical Review A}, number = {6}, publisher = {American Physical Society}, title = {{Spectral and spatial shaping of Smith-Purcell radiation}}, doi = {10.1103/physreva.96.061801}, volume = {96}, year = {2017}, } @article{21569, abstract = {We present recent advances in metasurface-based photonics, which enables the realization of high performance planar lenses (metalenses) in the visible spectrum. They are enabled by a technique based on atomic layer deposition of titanium dioxide allowing for the fabrication of nanostructures with high fidelity. First, we demonstrate highly efficient metalenses with numerical aperture NA = 0.8 using the Pancharatnam-Berry phase approach. These metalenses can focus light into a diffraction-limited spot. They have efficiencies as high as 86% and provide high imaging resolution. Furthermore, by judicious design of the phase-shifting elements, we achieve a multispectral chiral metalens realized with a single metasurface layer. This chiral metalens can resolve both the chiral and spectral information of an object without the requirement of any additional optical components. Finally, we discuss the experimental realization of polarization-insensitive metalenses with NAs as high as 0.85. They are able to focus incident light to a spot as small as ~0.64λ with efficiencies up to 60%. Due to its straightforward and CMOS-compatible fabrication, this platform is promising for a wide range of applications ranging from camera modules, displays, laser-based imaging, microscopy, and spectroscopy to laser fabrication and lithography.}, author = {Khorasaninejad, Mohammadreza and Chen, Wei Ting and Zhu, Alexander Y. and Oh, Jaewon and Devlin, Robert C. and Roques-Carmes, Charles and Mishra, Ishan and Capasso, Federico}, issn = {1558-4542}, journal = {IEEE Journal of Selected Topics in Quantum Electronics}, number = {3}, pages = {43--58}, publisher = {Institute of Electrical and Electronics Engineers}, title = {{Visible wavelength planar metalenses based on titanium dioxide}}, doi = {10.1109/jstqe.2016.2616447}, volume = {23}, year = {2017}, } @inproceedings{21573, abstract = {We present a new platform that realizes high performance metasurfaces in the visible spectrum. This platform is based on atomic layer deposition of titanium dioxide and allows molding incident light wavefront to desired shapes including holographic images, optical vortices, and Bessel beams. The focus of this work will be on the design and demonstration of planar metalenses. We report on our recent experimental realization of high numerical aperture metalenses with efficiency as high as 86%. These metalenses can focus light into a diffraction-limited spot and can be employed for imaging purposes to provide sub-wavelength imaging resolution. In addition, by the judicious design of metalens building blocks, one can achieve a multispectral chiral metalens (MCML) within a single metasurface layer. The MCML can simultaneously resolve chiral and spectral information of an object without the requirement of additional optical components such as polarizers, wave-plates, or even gratings. Using this MCML, we map the chiroptical properties of a macroscopic chiral biological specimen across the visible range. Finally, since many applications require polarization insensitive planar lenses, we discuss the experimental realization of such metalenses with numerical apertures as high as NA=0.85. These metalenses can focus incident light to a spot as small as ~0.6lambda with efficiencies up to 70%. The straightforward and CMOS-compatible fabrication process of this platform is promising for a wide range of optics-based applications in multidisciplinary science and technology. }, author = {Khorasaninejad, Mohammadreza and Chen, Wei Ting and Zhu, Alexander Y. and Oh, Jaewon and Devlin, Robert C. and Roques-Carmes, Charles and Mishra, Ishan and Capasso, Federico}, booktitle = {High Contrast Metastructures VI}, location = {San Francisco, CA, United States}, title = {{Planar optics at visible wavelengths based on titanium dioxide }}, doi = {10.1117/12.2255916}, volume = {10113}, year = {2017}, } @inproceedings{21588, abstract = {We present experimental results demonstrating multiple order Smith-Purcell radiation in high aspect ratio Silicon Nanowires structures using low-energy electrons (2.5-10keV). These produce emission spanning the visible, paving the way to a fully tunable ultraviolet source.}, author = {Massuda, Aviram and Roques-Carmes, Charles and Solanki, Amit and Yang, Yi and Kooi, Steven E. and Habbal, Fawwaz and Kaminer, Ido and Soljačić, Marin}, booktitle = {Conference on Lasers and Electro-Optics}, location = {San Jose, CA, United States}, publisher = {Optica Publishing Group}, title = {{High-order Smith-Purcell radiation in silicon nanowires}}, doi = {10.1364/cleo_at.2017.jth5b.8}, year = {2017}, } @inproceedings{21615, abstract = {Focused electron beams can induce electromagnetic radiation from periodic surfaces. We have used low-energy electrons (1.5-6kV) to induce visible light emission from nanoscale gratings (50nm and 60nm). Our results coincide well with numerical simulations.}, author = {Massuda, Aviram and Roques-Carmes, Charles and Yang, Yujia and Kooi, Steven E. and Yang, Yi and Murdia, Chitraang and Berggren, Karl K. and Kaminer, Ido and Soljačić, Marin}, booktitle = {Conference on Lasers and Electro-Optics}, location = {San Jose, CA, United States}, publisher = {Optica Publishing Group}, title = {{Smith-Purcell radiation from low-energy electrons}}, doi = {10.1364/cleo_qels.2017.fm3h.6}, year = {2017}, } @article{1336, abstract = {Evolutionary algorithms (EAs) form a popular optimisation paradigm inspired by natural evolution. In recent years the field of evolutionary computation has developed a rigorous analytical theory to analyse the runtimes of EAs on many illustrative problems. Here we apply this theory to a simple model of natural evolution. In the Strong Selection Weak Mutation (SSWM) evolutionary regime the time between occurrences of new mutations is much longer than the time it takes for a mutated genotype to take over the population. In this situation, the population only contains copies of one genotype and evolution can be modelled as a stochastic process evolving one genotype by means of mutation and selection between the resident and the mutated genotype. The probability of accepting the mutated genotype then depends on the change in fitness. We study this process, SSWM, from an algorithmic perspective, quantifying its expected optimisation time for various parameters and investigating differences to a similar evolutionary algorithm, the well-known (1+1) EA. We show that SSWM can have a moderate advantage over the (1+1) EA at crossing fitness valleys and study an example where SSWM outperforms the (1+1) EA by taking advantage of information on the fitness gradient.}, author = {Paixao, Tiago and Pérez Heredia, Jorge and Sudholt, Dirk and Trubenova, Barbora}, issn = {0178-4617}, journal = {Algorithmica}, number = {2}, pages = {681 -- 713}, publisher = {Springer}, title = {{Towards a runtime comparison of natural and artificial evolution}}, doi = {10.1007/s00453-016-0212-1}, volume = {78}, year = {2017}, } @article{1337, abstract = {We consider the local eigenvalue distribution of large self-adjoint N×N random matrices H=H∗ with centered independent entries. In contrast to previous works the matrix of variances sij=\mathbbmE|hij|2 is not assumed to be stochastic. Hence the density of states is not the Wigner semicircle law. Its possible shapes are described in the companion paper (Ajanki et al. in Quadratic Vector Equations on the Complex Upper Half Plane. arXiv:1506.05095). We show that as N grows, the resolvent, G(z)=(H−z)−1, converges to a diagonal matrix, diag(m(z)), where m(z)=(m1(z),…,mN(z)) solves the vector equation −1/mi(z)=z+∑jsijmj(z) that has been analyzed in Ajanki et al. (Quadratic Vector Equations on the Complex Upper Half Plane. arXiv:1506.05095). We prove a local law down to the smallest spectral resolution scale, and bulk universality for both real symmetric and complex hermitian symmetry classes.}, author = {Ajanki, Oskari H and Erdös, László and Krüger, Torben H}, issn = {0178-8051}, journal = {Probability Theory and Related Fields}, number = {3-4}, pages = {667 -- 727}, publisher = {Springer}, title = {{Universality for general Wigner-type matrices}}, doi = {10.1007/s00440-016-0740-2}, volume = {169}, year = {2017}, } @article{1338, abstract = {We present a computer-aided programming approach to concurrency. The approach allows programmers to program assuming a friendly, non-preemptive scheduler, and our synthesis procedure inserts synchronization to ensure that the final program works even with a preemptive scheduler. The correctness specification is implicit, inferred from the non-preemptive behavior. Let us consider sequences of calls that the program makes to an external interface. The specification requires that any such sequence produced under a preemptive scheduler should be included in the set of sequences produced under a non-preemptive scheduler. We guarantee that our synthesis does not introduce deadlocks and that the synchronization inserted is optimal w.r.t. a given objective function. The solution is based on a finitary abstraction, an algorithm for bounded language inclusion modulo an independence relation, and generation of a set of global constraints over synchronization placements. Each model of the global constraints set corresponds to a correctness-ensuring synchronization placement. The placement that is optimal w.r.t. the given objective function is chosen as the synchronization solution. We apply the approach to device-driver programming, where the driver threads call the software interface of the device and the API provided by the operating system. Our experiments demonstrate that our synthesis method is precise and efficient. The implicit specification helped us find one concurrency bug previously missed when model-checking using an explicit, user-provided specification. We implemented objective functions for coarse-grained and fine-grained locking and observed that different synchronization placements are produced for our experiments, favoring a minimal number of synchronization operations or maximum concurrency, respectively.}, author = {Cerny, Pavol and Clarke, Edmund and Henzinger, Thomas A and Radhakrishna, Arjun and Ryzhyk, Leonid and Samanta, Roopsha and Tarrach, Thorsten}, journal = {Formal Methods in System Design}, number = {2-3}, pages = {97 -- 139}, publisher = {Springer}, title = {{From non-preemptive to preemptive scheduling using synchronization synthesis}}, doi = {10.1007/s10703-016-0256-5}, volume = {50}, year = {2017}, } @article{13380, abstract = {Although dissipative self-assembly is ubiquitous in nature, where it gives rise to structures and functions critical to life, examples of artificial systems featuring this mode of self-assembly are rare. Here, we identify the presence of ephemeral assemblies during seeded growth of gold nanoparticles. In this process, hydrazine reduces Au(III) ions, which attach to the existing nanoparticles “seeds”. The attachment is accompanied by a local increase in the concentration of a surfactant, which therefore forms a bilayer on nanoparticle surfaces, inducing their assembly. The resulting aggregates gradually disassemble as the surfactant concentration throughout the solution equilibrates. The lifetimes of the out-of-equilibrium aggregates depend on and can be controlled by the size of the constituent nanoparticles. We demonstrate the utility of our out-of-equilibrium aggregates to form transient reflective coatings on polar surfaces.}, author = {Sawczyk, Michał and Klajn, Rafal}, issn = {1520-5126}, journal = {Journal of the American Chemical Society}, keywords = {Colloid and Surface Chemistry, Biochemistry, General Chemistry, Catalysis}, number = {49}, pages = {17973--17978}, publisher = {American Chemical Society}, title = {{Out-of-equilibrium aggregates and coatings during seeded growth of metallic nanoparticles}}, doi = {10.1021/jacs.7b09111}, volume = {139}, year = {2017}, } @article{13381, abstract = {Self-assembly of inorganic nanoparticles has been used to prepare hundreds of different colloidal crystals, but almost invariably with the restriction that the particles must be densely packed. Here, we show that non–close-packed nanoparticle arrays can be fabricated through the selective removal of one of two components comprising binary nanoparticle superlattices. First, a variety of binary nanoparticle superlattices were prepared at the liquid-air interface, including several arrangements that were previously unknown. Molecular dynamics simulations revealed the particular role of the liquid in templating the formation of superlattices not achievable through self-assembly in bulk solution. Second, upon stabilization, all of these binary superlattices could be transformed into distinct “nanoallotropes”—nanoporous materials having the same chemical composition but differing in their nanoscale architectures.}, author = {Udayabhaskararao, Thumu and Altantzis, Thomas and Houben, Lothar and Coronado-Puchau, Marc and Langer, Judith and Popovitz-Biro, Ronit and Liz-Marzán, Luis M. and Vuković, Lela and Král, Petr and Bals, Sara and Klajn, Rafal}, issn = {1095-9203}, journal = {Science}, keywords = {Multidisciplinary}, number = {6362}, pages = {514--518}, publisher = {American Association for the Advancement of Science}, title = {{Tunable porous nanoallotropes prepared by post-assembly etching of binary nanoparticle superlattices}}, doi = {10.1126/science.aan6046}, volume = {358}, year = {2017}, } @article{13382, author = {van Esch, Jan H. and Klajn, Rafal and Otto, Sijbren}, issn = {1460-4744}, journal = {Chemical Society Reviews}, keywords = {General Chemistry}, number = {18}, pages = {5474--5475}, publisher = {Royal Society of Chemistry}, title = {{Chemical systems out of equilibrium}}, doi = {10.1039/c7cs90088k}, volume = {46}, year = {2017}, } @article{13383, abstract = {Two novel donor–acceptor Stenhouse adducts (DASAs) featuring the catechol moiety were synthesized and characterized. Both compounds bind strongly to the surfaces of magnetite nanoparticles. An adrenaline-derived DASA renders the particles insoluble in all common solvents, likely because of poor solvation of the zwitterionic isomer generated on the nanoparticle surfaces. Well-soluble nanoparticles were successfully obtained using dopamine-derived DASA equipped with a long alkyl chain. Upon its attachment to nanoparticles, this DASA undergoes an irreversible decoloration reaction owing to the formation of the zwitterionic form. The reaction follows first-order kinetics and proceeds more rapidly on large nanoparticles. Interestingly, decoloration can be suppressed in the presence of free DASA molecules in solution or at high nanoparticle concentrations.}, author = {Ahrens, Johannes and Bian, Tong and Vexler, Tom and Klajn, Rafal}, issn = {2367-0932}, journal = {ChemPhotoChem}, keywords = {Organic Chemistry, Physical and Theoretical Chemistry, Analytical Chemistry}, number = {5}, pages = {230--236}, publisher = {Wiley}, title = {{Irreversible bleaching of donor-acceptor stenhouse adducts on the surfaces of magnetite nanoparticles}}, doi = {10.1002/cptc.201700009}, volume = {1}, year = {2017}, }