ALBERT

Description: Nature Materials 14, 13 (2015). doi:10.1038/nmat4189 Author: Pep Pàmies

Description: Nature Materials 14, 16 (2015). doi:10.1038/nmat4185 Author: Philip Ball

Description: Nature Materials 14, 43 (2015). doi:10.1038/nmat4088 Authors: Thomas C. Fitzgibbons, Malcolm Guthrie, En-shi Xu, Vincent H. Crespi, Stephen K. Davidowski, George D. Cody, Nasim Alem & John V. Badding Low-dimensional carbon nanomaterials such as fullerenes, nanotubes, graphene and diamondoids have extraordinary physical and chemical properties. Compression-induced polymerization of aromatic molecules could provide a viable synthetic route to ordered carbon nanomaterials, but despite almost a century of study this approach has produced only amorphous products. Here we report recovery to ambient pressure of macroscopic quantities of a crystalline one- dimensional sp3carbon nanomaterial formed by high-pressure solid-state reaction of benzene. X-ray and neutron diffraction, Raman spectroscopy, solid-state NMR, transmission electron microscopy and first-principles calculations reveal close- packed bundles of subnanometre-diameter sp3-bonded carbon threads capped with hydrogen, crystalline in two dimensions and short-range ordered in the third. These nanothreads promise extraordinary properties such as strength and stiffness higher than that of sp2carbon nanotubes or conven tional high-strength polymers. They may be the first member of a new class of ordered sp3 nanomaterials synthesized by kinetic control of high-pressure solid-state reactions.

Description: Nature Materials 14, 61 (2015). doi:10.1038/nmat4109 Authors: Lang Feng, Bezia Laderman, Stefano Sacanna & Paul Chaikin In polymer–colloid mixtures, non-adsorbing polymers dispersed with much larger colloids provide a universal yet specific entropic attraction between the colloids. Such so-called depletion interaction arises from an osmotic-pressure imbalance caused by the polymers and is considered to be independent of temperature. Here we show that, for the most commonly used polymer–colloid depletion systems, the polymer undergoes a crossover from non-adsorbing to adsorbing and that, consequently, the effective colloidal interactions depend on temperature. We also find that a combination of the enthalpic (polymer bridging) and entropic (polymer exclusion) interactions, both attractive, leads to a re-entrant regime where the colloids are dispersed and form solids both on heating and on cooling. We provide a simple model to explain the observed transitions and to fill the theoretical gap at the polymer-adsorption crossover. Our findings open possibilities for colloidal self-assembly, the formation of colloidal crystals and glasses, and the behaviour of temperature-controlled viscoelastic materials.

Description: Nature Materials 14, 73 (2015). doi:10.1038/nmat4117 Authors: Daichi Matsunami, Asaya Fujita, Koshi Takenaka & Mika Kano

Description: Nature Materials 14, 79 (2015). doi:10.1038/nmat4119 Authors: Ruijuan Xu, Shi Liu, Ilya Grinberg, J. Karthik, Anoop R. Damodaran, Andrew M. Rappe & Lane W. Martin

Description: Nature Materials 14, 18 (2015). doi:10.1038/nmat4183 Author: Marc de Boissieu Computer simulations of one-component three-dimensional icosahedral quasicrystals will help to understand the mechanisms that may stabilize them in experiments.

Description: Nature Materials 14, 23 (2015). doi:10.1038/nmat4089 Authors: Ulrike G. K. Wegst, Hao Bai, Eduardo Saiz, Antoni P. Tomsia & Robert O. Ritchie

Description: Nature Materials 14, 87 (2015). doi:10.1038/nmat4114 Authors: Alexandre Teulle, Michel Bosman, Christian Girard, Kargal L. Gurunatha, Mei Li, Stephen Mann & Erik Dujardin

Description: Nature Materials 14, 19 (2015). doi:10.1038/nmat4180 Author: Eric M. Furst Janus ellipsoids self-assemble into self-limiting fibres that can be reversibly actuated by applying an electric field.

Description: Nature Materials 14, 13 (2015). doi:10.1038/nmat4188 Author: Luigi Martiradonna

Description: Nature Materials 14, 13 (2015). doi:10.1038/nmat4190 Author: Alison Stoddart

Description: Nature Materials 14, 37 (2015). doi:10.1038/nmat4116 Authors: Makoto Hashimoto, Elizabeth A. Nowadnick, Rui-Hua He, Inna M. Vishik, Brian Moritz, Yu He, Kiyohisa Tanaka, Robert G. Moore, Donghui Lu, Yoshiyuki Yoshida, Motoyuki Ishikado, Takao Sasagawa, Kazuhiro Fujita, Shigeyuki Ishida, Shinichi Uchida, Hiroshi Eisaki, Zahid Hussain, Thomas P. Devereaux & Zhi-Xun Shen In the high-temperature (Tc) cuprate superconductors, a growing body of evidence suggests that the pseudogap phase, existing below the pseudogap temperature T∗, is characterized by some broken electronic symmetries distinct from those associated with superconductivity. In particular, recent scattering experiments have suggested that charge ordering competes with superconductivity. However, no direct link of an interplay between the two phases has been identified from the important low-energy excitations. Here, we report an antagonistic singularity at Tc in the spectral weight of Bi2Sr2CaCu2O8+δ as compelling evidence for phase competition, which persists up to a high hole concentration p ~ 0.22. Comparison with theoretical calculations confirms that the singularity is a signature of competition between the order parameters for the pseudogap and superconductivity. The observation of the spectroscopic singularity at finite temperatures over a wide doping range provides new insights into the nature of the competitive interplay between the two orders and the complex phase diagram near the pseudogap critical point.

Description: Nature Materials 14, 48 (2015). doi:10.1038/nmat4113 Authors: Tania Rodenas, Ignacio Luz, Gonzalo Prieto, Beatriz Seoane, Hozanna Miro, Avelino Corma, Freek Kapteijn, Francesc X. Llabrés i Xamena & Jorge Gascon Composites incorporating two-dimensional nanostructures within polymeric matrices have potential as functional components for several technologies, including gas separation. Prospectively, employing metal–organic frameworks (MOFs) as versatile nanofillers would notably broaden the scope of functionalities. However, synthesizing MOFs in the form of freestanding nanosheets has proved challenging. We present a bottom-up synthesis strategy for dispersible copper 1,4-benzenedicarboxylate MOF lamellae of micrometre lateral dimensions and nanometre thickness. Incorporating MOF nanosheets into polymer matrices endows the resultant composites with outstanding CO2 separation performance from CO2/CH4 gas mixtures, together with an unusual and highly desired increase in the separation selectivity with pressure. As revealed by tomographic focused ion beam scanning electron microscopy, the unique separation behaviour stems from a superior occupation of the membrane cross-section by the MOF nanosheets as compared with isotropic crystals, which improves the efficiency of molecular discrimination and eliminates unselective permeation pathways. This approach opens the door to ultrathin MOF–polymer composites for various applications.

Description: Publication year: 2012 Source: Dendrochronologia Kathryn Allen, David M. Drew, Geoffrey M. Downes, Robert Evans, Patrick Baker, Michael Grose The great majority of dendroclimatological work in Australia has thus far relied on ring-width chronologies only. We report novel results from a pilot study that show the potential to develop density-based climatically sensitive chronologies from two long-lived conifers endemic to Tasmania: Pencil Pine and Celery Top Pine. Cross-dating of average ring density profiles within each of the two sites examined was comparable with the better replicated ring-width chronologies from the sites. Cross-dating potential for maximum density was also indicated. Correlations between density and climate for both species were stronger and more persistent across a window of several months than correlations between ring width and climate. These stronger correlations suggest that temperature reconstructions based on average density may be possible. The ability to develop high resolution temperature-sensitive chronologies would allow for spatial comparisons across regions such as Tasmania that are affected by multiple broad-scale climate systems. A particularly novel result was the finding that maximum density was significantly related to stream-flow at the end of the growing season. Further work is required to assess the potential to reconstruct temperature, and to reconstruct stream-flow for important Tasmanian catchments over the past 500–800 years.

Description: Publication year: 2012 Source: Dendrochronologia Hannu Hökkä, Hannu Salminen, Erkki Ahti The climate conditions of the current and previous growing seasons have been shown to influence growth of coniferous trees in mineral soils sites. These dependencies may be different in peatlands where growth is generally more dependent on variations in soil water conditions. In the Nordic and Baltic countries, millions of hectares of peatlands and wetlands have been drained in order to enhance forest production. These drainage networks do not guarantee stable soil water conditions for the whole stand rotation. It is thus likely that precipitation in particular may have a different influence on annual growth in peatland to that in mineral soil sites. We studied the effect of precipitation and temperature on the inter-annual diameter growth of Scots pine ( Pinus sylvestris L.) in Finland in drained peatland forests. The diameter growth data were limited to periods when growth response to drainage had levelled out. For comparison, growth data were also collected from adjacent mineral soil trees. The climate variables were monthly mean temperature and precipitation in a given location estimated from observations at the nearest weather stations by means of spatial smoothing. We used mixed linear models in describing the annual diameter growth of individual trees as a function of tree size and stand properties and expressed the residual variation as a function of climate parameters. The peatland and mineral soil growth variations showed different dependence on climate parameters. Peatland trees within 5 m of a ditch showed different climate responses compared to those located further away. Precipitation in July was negatively correlated with the diameter growth of peatland trees but there was no correlation with temperature. Growth of trees in mineral soils was positively correlated with March and April mean temperatures and May and June mean precipitation. The residual growth indices showed largely similar patterns in peatlands and mineral soil sites.

Description: Publication year: 2012 Source: Dendrochronologia Keyan Fang, Xiaohua Gou, Fahu Chen, Yingjun Li, Fen Zhang, Miklos Kazmer Individual tree-ring series may show changed growth trends and divergent climate–growth associations even within a site, highlighting the need to examine tree growth and its climate association before building a chronology. We provided a case study for the stratification and temporal variability of tree growth and its climate associations of individual cores for three mountain ranges in north central China. Tree growth is mainly limited by moisture conditions in previous July–September and current June–August. Repeated sampling and field investigations of Picea wilsonii at Xinglong Mountain over a growth year of 2004 suggested that the growing season is from about the end of April to the end of September. It appears that the moisture conditions in previous and current growing seasons are crucial for tree growth in this region. However, a decrease in drought limitation was observed for a few tree-ring series. We thereby built the pooled chronology and sub-site chronologies with only drought-sensitive tree rings similar climate–growth relationships from the three mountain slopes. Growth disturbances of tree-ring series are detected by checking the occurrence of successively low values of the biweight series, which are treated by fitting a flexible curve.

Description: Publication year: 2012 Source: Dendrochronologia Esther Jansma, Rowin J. van Lanen, Kit Sturgeon, Steve Mohlke, Peter W. Brewer Dendrochronological data formats in general offer limited space for recording associated metadata. Such information is often recorded separately from the actual time series, and often only on paper. TRiDaBASE has been developed to improve metadata administration. It is a relational Microsoft Access database that allows users to register digital metadata according to TRiDaS, to generate TRiDaS XML for uploading to TRiDaS-based analytical systems and repositories, and to ingest TRiDaS XML created elsewhere for local querying and analyses.

Description: Publication year: 2012 Source: Dendrochronologia Igor Drobyshev, P. Charles Goebel, Yves Bergeron, R. Gregory Corace The study of forests dominated by red pine ( Pinus resinosa Ait.), one of the few fire-resistant tree species of eastern North America, provides an opportunity to reconstruct long-term fire histories and examine the temporal dynamics of climate forcing upon forest fire regimes. We used a 300-year long spatially explicit dendrochronological reconstruction of the fire regime for Seney National Wildlife Refuge (SNWR, 38,531 ha), eastern Upper Michigan to: (1) identify fire size thresholds with strong vs. weak climate controls, (2) evaluate effect of landform type (outwash channel vs. sand ridges) in modifying climate–fire associations, and (3) check for the presence of temporal changes in the climate control of large fire events over the time period 1700–1983. We used a summer drought sensitive red pine chronology (ITRDB code can037 ) as a proxy of past fire-related climate variability. Results indicated that fires 〉60 ha in sand-ridge-dominated portions of SNWR and 〉100 ha in outwash channels were likely climatically driven events. Climate–fire associations varied over time with significant climate–fire linkages observed for the periods 1700–1800 (pre-EuroAmerican), 1800–1900 (EuroAmerican settlement) and 1900–1983 (modern era). Although an increase in fire activity at the turn of 20th century is commonly associated with human sources of ignitions, our results suggest that such an increase was also likely a climatically driven episode.

Description: Publication year: 2012 Source: Dendrochronologia Maxim Yermokhin This article presents for the first time Scots pine tree-ring chronology created from historical timber (XVII–XIX cc.) from central Belarus. The chronology includes 59 tree-ring series which were collected from the different wood structures in the Nesvizh castle. This samples show different stages of the castle renovations. The chronology presented in this paper embraces 222 years covering the period between 1608 and 1829.

Description: Publication year: 2012 Source: Dendrochronologia Pavel Pavlovich Silkin, Natalia Victorovna Ekimova This study addressed distribution of calcium and strontium in Siberian spruce ( Picea obovata Ledeb.) and Siberian fir ( Abies sibirica Ledeb.) tree-rings and its dependence on these woody species cell structure. Calcium concentration was found to decrease gradually from earlywood to latewood, whereas strontium showed an opposite trend. However, their trends at the scale of several rings are co-directed in the samples analyzed. A strong linear relationship was identified between the distribution of Sr/Ca concentration ratio and tree-ring density profile for both woody species. Radiographic density of Siberian spruce tree-ring cell walls and Ca and Sr concentrations in them were determined to have negative correlation with cell wall thickness. In earlywood of annual rings of a spruce the radiographic density of cell wall reaches 2.0 g/cm 3 and decreases to 1.2 g/cm 3 in latewood. The hypothesis put forward in this study to explain these strontium and calcium distributions in the tree-rings is that the concentrations of the element ions change with development of different cell wall layers. The high value of radiographic density of a cellular wall in earlywood and its relationship with cell wall thickness can be explained by the presence of ions of calcium in a cellular wall. Ions of calcium absorb X-ray radiation more strongly in comparison with light chemical elements. It can become the reason of observable relationship between radiographic density of cell wall and cell wall thickness.

Description: Publication year: 2012 Source: Dendrochronologia Xiaohua Gou, Fen Zhang, Yang Deng, Gregory J. Ettl, Meixue Yang, Linlin Gao, Keyan Fang Tree-line ecotones are strongly climatically limited and serve as potential monitors of climate change. We employed annual growth increment from tree-rings, and tree density and age structure data derived from two Juniperus przewalskii tree-line sites in the eastern part of the Qilian Mountains, northeastern Tibetan Plateau, to detect the responses of tree growth and population dynamics to climate change. High temperature favors tree growth and is associated with increased tree density at tree-line, and an advance in tree-line position. Significantly positive correlations were found between ring-width and mean monthly air temperatures in current and previous June, July and August. Tree recruitment began to increase rapidly at the two sites after the Little Ice Age, but then decreased starting in the 1970s. The number of trees established coincides with temperature changes. The warming trend after the Little Ice Age favors increases of tree density and an advance of tree-line. The majority of trees established during the period of 1931–1970, which coincides well with the rapid radial growth of the trees.

Description: Publication year: 2012 Source: Dendrochronologia, Volume 30, Issue 1 X. Arnan, B.C. López, J. Martínez-Vilalta, M. Estorach, R. Poyatos Trees can reach ages that in some cases amount to thousands of years. In the Mediterranean region, olive trees ( Olea europaea ) have traditionally been considered a particularly long-lived species. The main objective of this study was to assess the age of large olive trees considered to be millenarian and classified as monumental trees in northeastern Spain. We extracted cores of 14 individuals and obtained 8 sections of trees which had already been cut in the area where the largest olive trees in the northeastern Iberian Peninsula are found. The age of the sampled olive trees was assessed by counting the number of annual growth rings. Tree rings did not cross-date well, neither within nor between individuals, but boundaries between likely annual rings were clearly distinct. We found a linear relationship between DBH and tree age (in years) (Age = 2.11 × diameter(cm) + 88.93, R 2 = 0.80), which was used to estimate the age of unsampled olive trees. The maximum estimated age (627 ± 110 years) is among the greatest ages reported for olive trees around the world (700 years) and among the oldest trees in Mediterranean ecosystems.

Description: Publication year: 2012 Source: Dendrochronologia Marc Macias-Fauria, Aslak Grinsted, Samuli Helama, Jari Holopainen Proxy data forms natural time series used to lengthen instrumental climatic records, and may contain a significant portion of autocorrelation. Increased serial correlation limits the number of independent observations, not satisfying the assumptions of conventional statistical methods. We estimate the significance of calibration and verification statistics used in dendroclimatic reconstructions by combining Monte-Carlo iterations with frequency (Ebisuzaki) or time (Burg) domain time series modelling. Significance tests are presented for Coefficient of Determination ( R 2 ), Coefficient of Correlation ( r 2 ), Reduction of Error (RE) and Coefficient of Error (CE) for time series ranging from very low to very high autocorrelation. Increased autocorrelation implies higher occurrences of relatively high but spurious reconstruction statistics. Ebisuzaki time series modelling shows greater robustness and its use is recommended over Burg's method, which penalizes the restriction in the number of autocorrelation coefficients imposed by the Akaike Information Criterion. Positive RE and CE values, traditionally viewed as successful reconstruction statistics, are not necessarily significant and depend on the temporal structure of the time series used. This approach is further implemented successfully to compute confidence intervals based on the temporal structure of the residuals of the transfer function. A Matlab ® package and a Windows executable file for non-Matlab ® users are provided to perform the described analyses.

Description: Publication year: 2012 Source: Dendrochronologia, Volume 30, Issue 1 Kristof Haneca, Vincent Debonne A detailed dendrochronological survey was performed on the medieval roofs of the Church of Our Lady (CoOL) in Damme, Belgium. Seen its complex architectural history, special attention was paid to the identification of consecutive building phases, based on combined architectural historical research and tree-ring dating. In total 64 increment cores were taken throughout the roof structures of the CoOL. All roof timbers are made of European oak ( Quercus robur / petraea ), of which only few have surviving sapwood or bark. Tree-ring dating confirms the late 13th/early 14th century construction date of the roofs. For all chronologies that were composed, the highest correlation values are found with reference chronologies covering the catchment area of the river Meuse. From the dating results of the timbers of the CoOL it becomes clear that the same timber source was used for nearly a century. On several of the examined roof timbers, rafting joints were observed, demonstrating that the timbers were indeed tied together as a raft and floated down the river. By implementing sapwood estimates in a Bayesian chronological model (OxCal), tree-ring series with surviving sapwood from coeval roof structures were combined in order to narrow down the time range for the felling date. Based on the refined interpretation of the felling dates, several consecutive building phases can now be identified and dated, leading to a new interpretation of the architectural history of the CoOL. Intriguingly, a marked interruption in building activities is observed around 1300. Probably this is related to the instable political situation at that time, caused by the armed conflict that emerged between the Count of Flanders and the king of France. Since Damme served as the outport of the riotous city of Bruges, it was alternately seized by the French and Flemish, both consuming considerable amounts of timber and other building materials for military fortifications. Potentially this led to a shortage in building materials and provoked a stop in building activities. This paper demonstrates the power of Bayesian models to refine the interpretation of dendrochronological dates in architectural analyses of medieval historical buildings.

Description: Publication year: 2012 Source: Dendrochronologia, Volume 30, Issue 1 Kristina Sohar, Adomas Vitas, Alar Läänelaid Pedunculate oak ( Quercus robur L.) is one of the widely used and dendrochronologically investigated species in Europe. Still, it is a problematical dating object if its outermost section is missing partly or totally. Thus, we need sapwood estimation of living trees. As sapwood amount varies geographically, numbers of sapwood rings have been published for different regions in Europe but no such estimation has been done for the Baltic States yet. Therefore, this paper deals with the estimation of pedunculate oak sapwood growing in the eastern Baltic region, i.e. in Finland, Estonia, Latvia, and Lithuania. In total, 668 oak core samples of living trees from 43 stands were investigated. Ring widths were measured and the number of sapwood rings was determined according to two criteria: difference of colour and absence of tyloses in earlywood vessels. The samples were divided into two sets, according to the t H -values between site chronologies and the major geobotanical sub-provinces. Thus, the nine Finnish and western Estonian sites were attributed to the western region and the 34 eastern Estonian, Latvian and Lithuanian sites to the eastern region. As the result of a statistical analysis, we explain that the number of oak sapwood rings ranges from 4.09 to 20.85 and 6.45 to 18.02 within 95% confidence limits in the western and eastern regions, respectively. For the three Baltic countries and southern Finland in general, we recommend to consider a sapwood estimate of 6.18–18.71 rings. Regarding earlier studies, the general European trend of decreasing sapwood ring number towards the east was confirmed. A geographical pattern of eastward decrease of the median sapwood ring number was noticed in the Baltics as well. The chronology based upon 668 samples of living oak trees from all sites covered the period of 1631–2008.

Description: Publication year: 2012 Source: Dendrochronologia, Volume 30, Issue 1 Julia Bartens, Henri D. Grissino-Mayer, Susan D. Day, P. Eric Wiseman Live oak ( Quercus virginiana Mill.) is a long lived, broadleaf, evergreen species native to the lower Coastal Plain of the southern and southeastern United States and is frequently planted in the urban environment. However, live oak has received limited attention for its potential for dendrochronological analyses possibly because its growth-ring boundaries may be less defined due to the absence of a distinct dormancy period. The objective of this explorative study was to determine whether live oak rings in both urban and historic trees could be accurately identified and measured for dendrochronological applications. One hundred urban live oaks were assessed as well as four cross-sectional specimens from historic sites in the southeastern United States. Age of all cored live oak ranged from 7 to 29 (average = 16.8 rings), while cross-sections were taken from trees with an average age of 175 years. A chronology was created from cores that had the highest interseries correlations ( n = 27), resulting in an average interseries correlation of 0.654. The analysis of live oak cross sections revealed that the rings on live oak are very faint and barely discernible, delimited mainly by a faint row of earlywood vessels with no or barely visible terminal parenchyma. Rings on these sections were erratic (i.e., fading out along the circumference) and non-concentric (i.e., a particular ring could be both wide and narrow at certain points along the circumference) so that any attempt to measure the rings on opposing radii would have produced meaningless results. However, based on the results of this study, we conclude that the dendrochronological analysis of live oak is possible with careful sample preparation and analysis and that results would be reliable, even for urban trees. Results of this study suggest that urban tree-ring series with higher interseries correlations were more vigorous than those with lower values, suggesting that urban environmental stresses related to individual sites may decrease the usefulness of crossdating techniques for evaluating annual rings on younger, urban trees.

Description: Publication year: 2012 Source: Dendrochronologia, Volume 30, Issue 1 Rob Wilson, C. Richard Bates Following the successful utilisation of lake preserved sub-fossil woody material to extend living Scots pine chronologies in Scandinavia, ongoing research in the Scottish Highlands aims to build a similar multi-millennial long climatically sensitive pine chronology. This paper details explorative research testing the use of sonar methods to facilitate the search for sub-fossil material in lake environments. Although the method clearly identifies elongate anomalies that are consistent with submerged tree stems in water depths 〉1.5 m, it does not allow the identification of sub-fossil wood remnants in shallow water (〈1.0 m) or heavily vegetated bays. Therefore, for the successful survey of lakes, a combination of traditional and sonar methods must be applied. Ongoing research will now explore the utilisation of these methods to more remote locations where boat access is not possible.

Description: Publication year: 2011 Source: Dendrochronologia, Volume 29, Issue 4 Yongxiang Zhang, Xuemei Shao, Martin Wilmking Knowledge of the spatial pattern and temporal relationships between tree-growth and climatic factors are important not only for the projection of forest growth under varying climate but for dendroclimatology in general. Here, we systematically investigated tree-growth climate relationships of Picea crassifolia at upper treeline in the Qilian Mts., northwestern China. 297 trees from eleven sites, covering a large part of the natural range of this species, show increasing and partly divergent correlations with temperature in the most recent decades. The dominant signal at all sites was a strengthening of negative correlations of annual radial growth with summer temperature. In a subset of trees at six sites, a strengthening positive correlation with summer temperatures existed as well. Wetter and high altitude sites tended to show a higher percentage of trees that are positively correlated with warming temperatures, indicating that some individuals there may take advantage of warmer conditions. Divergent responses between the two sub-populations clustered by their response to climate factor were significantly stronger in the last 30 years compared to earlier time slices. In the same time frame, hydrothermal conditions of the investigation area changed to a drier and warmer combination. Drought conditions, most likely affecting the radial growth of most P. crassifolia , have been intensifying over time and expanding spatially from the middle Qilian Mts. to most of our study area during the last half century. While explanations such as methodological effects due to trend removal or human disturbance at the sampling sites might be able to explain the result at single sites, the spatial and temporal co-occurrence of large scale changes in climate and tree growth suggests a causal link between them.

Description: Publication year: 2011 Source: Dendrochronologia, Volume 29, Issue 3 Martin de Luis, Klemen Novak, José Raventós, Jožica Gričar, Peter Prislan, Katarina Čufar Research was carried out on the wood formation process and the intra-annual density fluctuations (IADFs) in Mediterranean Aleppo pine ( Pinus halepensis Mill.) trees from the coastal site of Guardamar, and inland Maigmo in south-eastern Spain. Samples taken at breast height of the trees were inspected to define the frequency of tree rings with latewood-like cells in earlywood (E-ring) and with earlywood-like cells in latewood (L-ring). L-rings were generally more frequent, especially on the warmer, dryer, coastal site of Guardamar. Dendrochronological techniques using tree-ring features vs. climate showed that L-rings were formed in Guardamar when August and/or September precipitation was higher than normal and in Maigmo when August precipitation was higher than normal. The formation of E-rings was promoted when winter and early spring were warmer than long term average. By studying intra-annual tree-ring formation at a cellular level, we found that at Maigmo in 2004 (MAI2004) all monitored trees presented a normal ring with normal earlywood and latewood and gradual transition between both. At Guardamar in 2005 (GUA2005) a typical L-ring was formed in the majority of monitored trees. In GUA2005 the wood formation started before February and the transition from early- to latewood occurred in late spring. In summer, the cambial cell production occurred at a very low rate, but an increased production of xylem cells took place in September when the amount of precipitation was twice as high as the long term average. During this period, a band of earlywood-like cells was formed, followed by the production of latewood-like cells that continued until the end of December. The normal ring in MAI2004 was formed because climatic factors triggering IADF did not occur (no precipitation in August 2004). After a modest cell production of cambium in September, only few latewood-like cells were produced. According to the strong agreement of results obtained from studying long-term dendrochronological series and intra-annual information on wood formation, such combined study indicates a high potential for use in explaining the environmental signals registered by a tree during different phases of wood formation.

Description: Publication year: 2011 Source: Dendrochronologia, Volume 29, Issue 1 Peter H. Nishimura, Colin P. Laroque Despite their suitability for dendroclimatological research, the boreal regions of central and western Labrador remain under-researched. In an attempt to evaluate the growth trends and climatic response of this region's trees, master chronologies have been developed for its four dominant conifer species. Balsam fir ( Abies balsamea (L.) Mill.), white spruce ( Picea glauca (Moench) Voss), black spruce ( Picea mariana (Mill.) Britton, Sterns, Poggenb.) and eastern larch ( Larix laricina (DuRoi) K. Koch) were sampled systematically within a 3 × 4 grid of twelve sites at the intersection of 62°W, 64°W and 66°W longitude, and latitudes 52°N, 53°N, 54°N and 55°N. The two most dominant species at each site were sampled, yielding a total of twenty-four master chronologies, all of which reflected a highly significant common signal at each site. The chronologies were subjected to a response function analysis to determine the nature of the growth–climate relationships in the region. Summer temperature proved to be the predominant limiting factor with regard to radial growth at most sites. The onset of the optimum temperature regime, however, varies across the network of sites, revealing evidence of a gradient of continentality in the data. Growth–temperature correlations indicated a significant relationship with July temperature at most eastern sites, while western sites tended to correlate with May, June and August temperatures. Central sites tended to correlate with June–July temperatures. We interpret these results as demonstrating the bioclimatic gradient of change between coastally proximal, maritime-influenced sites and inland, continentally influenced locales. This transition occurs approximately 330 km inland from the open Labrador Sea.

Description: Publication year: 2011 Source: Dendrochronologia, Volume 29, Issue 4 S. Szymczak, M.M. Joachimski, A. Bräuning, T. Hetzer, J. Kuhlemann Stable isotopes in tree rings have widely been used for palaeoclimate reconstructions since tree rings record climatic information at annual resolution. However, various wood components or different parts of an annual tree-ring may differ in their isotopic compositions. Thus, sample preparation and subsequent laboratory analysis are crucial for the isotopic signal retained in the final tree-ring isotope series used for climate reconstruction and must therefore be considered for the interpretation of isotope–climate relationships. This study focuses on wood of Corsican Pine trees ( Pinus nigra ssp. laricio ) as this tree species allows to reconstruct the long-term climate evolution in the western Mediterranean. In a pilot study, we concentrated on methodological issues of sample preparation techniques in order to evaluate isotope records measured on pooled whole tree-ring cellulose and whole tree-ring bulk wood samples. We analysed 80-year long carbon and oxygen chronologies of Corsican Pine trees growing near the upper tree line on Corsica. Carbon and oxygen isotope records of whole tree-ring bulk wood and whole tree-ring cellulose from a pooled sample of 5 trees were correlated with the climate parameters monthly precipitation, temperature and the self-calibrating Palmer Drought Severity Index (sc-PDSI). Results show that the offsets in carbon and oxygen isotopes of bulk wood and cellulose are not constant over time. Both isotopes correlate with climate parameters from late winter and summer. The carbon and oxygen isotope ratios of cellulose are more sensitive to climatic variables than those of bulk wood. The results of this study imply that extraction of cellulose is a pre-requisite for the reconstruction of high-resolution climate records from stable isotope series of P. nigra ssp. laricio .

Description: Publication year: 2011 Source: Dendrochronologia, Volume 29, Issue 3 Annie Deslauriers, Sergio Rossi, Audrey Turcotte, Hubert Morin, Cornélia Krause Continuous measurements of stem radius variation in trees are obtained with automatic dendrometers that provide time series composed of seasonal tree growth and circadian rhythms of water storage and depletion. Several variables can be extracted from the raw data, such as amplitude and duration of radius increase and contraction, which are useful for understanding intra-annual tree growth, tree physiology and for performing growth–climate relationships. These measurements constitute a large dataset whose manipulation needs numerous algorithms and automatic procedures to efficiently and rapidly extract the information. This paper presents a three-step procedure using two SAS routines to extract the time series describing radius variation and associate them with environmental parameters. The first routine organizes and corrects data and generates outputs in the form of files and plots to visualize the results and improve data correction (first step). The second step consists of a reclassification of the hours of contraction or expansion that have been misclassified by the automatic process. The second routine classifies the daily patterns of stem variation into the three phases of contraction, expansion and radius increment and associates the environmental parameters (third step). An example of the procedure is given, with an explanation of the outputs generated. The advantages and shortcomings of the procedure and its importance for the intra-annual analyses of tree growth are discussed.

Description: Available online 3 October 2012 Publication year: 2012 Source: Dendrochronologia In order to detect the response of trees to environmental pollution in Shenyang during the last century, tree rings of two 100+ year old Chinese pine ( Pinus tabulaeformis Carr.) were analyzed for nine trace element concentrations (K, Ca, Mg, Mn, Cu, Zn, Al, Pb and Cd) and compared to local environmental change. The concentrations of Cu, Zn and Al had significant ( p 〈 0.01) increasing trends after 1940s and correlated significantly ( p 〈 0.01), with increasing production of nonferrous metal from local industrial processing. Concentrations of nutrient element (K, Ca and Mg) showed significant ( p 〈 0.01) increasing trend from heartwood to sapwood with declines in the last three decades. Significant correlation between climatic factors and element concentration in tree rings were also found, in which the temperature (November to May) and relative humidity in April and May showed significant positive correlation with Ca, Zn and Cu ( p 〈 0.05) as well as Al ( p 〈 0.01) concentrations in tree rings. April rainfall showed significant positive correlation with K and Zn ( p 〈 0.05) as well as Al ( p 〈 0.01) concentration in tree rings. The results suggest that tree rings from Chinese pine in Shenyang are sensitive to environmental change and have the potential to be used as a biomonitor for the environmental pollution. The results also demonstrate the feasibility of applying dendrochemical techniques to areas with limited samples.

Description: Available online 3 September 2012 Publication year: 2012 Source: Dendrochronologia To understand the effect of climate on tree-ring features, such as width or density, tree-ring data have to be calibrated against instrumental records. The high degree of multicollinearity among monthly time series of climate data violates the assumption of independent predictor variables in ordinary least squares regression. Bootstrapped confidence intervals of parameter estimates via regression against the principle components of the predictor variables are a possible solution to that problem. Package bootRes for R implements a flexible interface for bootstrapped response and correlation function analysis and tackles some shortcomings of currently available software. Given the increasing popularity of the free R software for statistical analysis, bootRes should facilitate both using R as a computational environment among tree-ring scientists and implementing new approaches to dendroclimatic calibration.

Description: Available online 23 September 2012 Publication year: 2012 Source: Dendrochronologia The opening of the Silk Road vigorously promoted economic and cultural exchanges between Central Asia, Europe, northern India and China. The easternmost section of the ancient trade route was established during the Qin-Han period (221 BC to 220 AD). Previous research has shown that there were three routes: the first is known as the “Hexi Route”, the second is known as the “Juyan Route” or “Prairie Route”, and the third is known as the “Qinghai Route”. The Qinghai Route has long been viewed as merely an auxiliary line of the Hexi Route which was used when the main Hexi Route was blocked by warfare. Others believe that the Qinghai Route was used during the 5th to 6th century when it was controlled by Tuyuhun Kingdom. Yet, by the 7th to 8th century, after the Tibetan occupation of the region, it was no longer a main trade route. Dendrochronology, the study of tree-rings, is a precise dating method that can be accurate to the year. In this study, wood remains excavated from tombs along the ancient Qinghai Route were studied by the means of dendrochronology in order to determine the date and better understand when Qinghai Route was used. In the tombs a lot of commercial goods such as silk products, pottery, lacquer carpentry were found. The date of the tombs determined by dendrochronology when viewed together with other archaeological data, showed that from the early Tang Dynasty to the High Tang Dynasty (early 7th century to late 8th century), the Qinghai Route was one of the routes of communication between the West and China. This disproves the hypothesis that this route was only used during the 5th to 6th century.

Description: Available online 25 August 2012 Publication year: 2012 Source: Dendrochronologia In dendrochronological dating, we encounter the trouble that some samples cannot be dated due to the occurrence of anomalies in the tree-ring series. When dating subfossil wood for the extension of existing master chronologies, this may be an especially unwanted circumstance as subfossil wood is scarce and each sample is valuable. In Moravia (Czech Republic) outbreaks of the cockchafer ( Melolontha sp.) used to appear with a disastrous effect on agricultural crops, and, for a dendrochronologist, on samples of wood to be dated. Oak ring width reduction caused by cockchafer induced defoliation can superimpose climate induced growth variations and may complicate dating of historical or subfossil samples. For this study, 33 samples of sub-fossil trunks were assessed; 19 of which were attacked by cockchafer. For comparison, we analysed a total of nine living oak trees from the forest district Strážnice-Vracov, recently attacked by the cockchafer. Occurrence of the cockchafer was reported there in 1999, 2003 and 2007. We found clear growth patterns with cyclic narrow rings every 4 years. This allowed us to create an artificial curve expressing the recurring cycles of cockchafer outbreaks which assisted us in the detection of the same pattern in subfossil tree growth. The tree-ring series of the attacked living oak stand as well as the 19 individual tree-ring series from subfossil oak trunks could not be dated using standard chronologies and showed a high resemblance to the cockchafer life cycle. Additionally, we found out that the living oak stand was attacked in 1983, 1987, 1991 and 1995 as well. The results support the hypothesis that the periodical reduction observed in tree-rings at regular increments is caused by cockchafer infestation. This evidence is further supported by characteristic anatomical features in early wood. A mean tree-ring series was created from the individual tree-ring series of subfossil oaks even though radiocarbon dating showed completely different ages of samples. This means that the affected tree-ring series cannot be used for dendrochronological dating and dendroclimatological analyses. These series cannot be used without preceding mathematical and statistical modification.

Description: Inspiring interfaces Nature Materials 11, 827 (2012). doi:10.1038/nmat3440 The arts and social sciences communities could enhance the commercial prospects of new materials.

Description: Interior design Nature Materials 11, 829 (2012). doi:10.1038/nmat3445 Author: Alison Stoddart

Description: Restrained fingering Nature Materials 11, 829 (2012). doi:10.1038/nmat3446 Author: Pep Pàmies

Description: Superlenses sharpen up Nature Materials 11, 829 (2012). doi:10.1038/nmat3444 Author: Joerg Heber

Description: Nanoparticle immunotherapy: Combo combat Nature Materials 11, 831 (2012). doi:10.1038/nmat3434 Author: C. Jeffrey Brinker Nanoparticle-enabled, sustained delivery of soluble hydrophilic cytokines and hydrophobic inhibitors engages the innate and adaptive immune systems to fight cancer.

Description: Metal/molecule interfaces: Dispersion forces unveiled Nature Materials 11, 834 (2012). doi:10.1038/nmat3436 Author: Jan van Ruitenbeek The role of dispersion forces in molecule–metal bonding has often been underestimated or ignored. Two groups now report independent single-molecule experiments that illustrate and quantify the effect of such interactions on bonding strength.

Description: Oxide interfaces: Instrumental insights Nature Materials 11, 833 (2012). doi:10.1038/nmat3425 Authors: James M. Rondinelli & Steven J. May A powerful new set of tools combining artificial synthesis and in situ characterization of correlated oxides unites the processes of materials discovery and understanding, and reveals the origin of a dimensionality-induced metal–insulator transition.

Description: Organic semiconductors: No more breaks for electrons Nature Materials 11, 836 (2012). doi:10.1038/nmat3427 Author: Anna Köhler In semiconducting polymers, the mobility of negative charges is typically much smaller than that of positive charges. Identification of a universal electron-trap level that is associated with water complexation now clarifies this difference and provides guidelines for the design of improved organic semiconductors.

Description: Crystal nucleation: Nucleus in a droplet Nature Materials 11, 838 (2012). doi:10.1038/nmat3441 Author: Peter G. Vekilov Real-time transmission electron microscopy shows that the formation of crystal nuclei of organic molecules in solution occurs inside dense liquid nanoclusters.

Description: Mechanical properties: Overcoming old barriers Nature Materials 11, 837 (2012). doi:10.1038/nmat3423 Author: G. J. Ackland Dislocation motion is crucial to the deformation of materials. The discovery that at least at lower temperatures quantum effects play an important role in this process considerably improves quantitative predictions of mechanical properties.

Description: Photonics: Upconversion goes broadband Nature Materials 11, 842 (2012). doi:10.1038/nmat3426 Authors: Xiaoji Xie & Xiaogang Liu Upconversion nanoparticles that convert low-energy light into high-energy light hold promise for boosting solar-cell efficiency and enabling highly sensitive biological assays. But their spectral conversion under broadband excitation has been challenging, until now.

Description: Soft robotics: Bionic jellyfish Nature Materials 11, 841 (2012). doi:10.1038/nmat3438 Author: Viola Vogel A polymeric tissue-engineered structure capable of swimming in a similar manner to a jellyfish is created by mimicking the structural design, stroke kinematics and fluid dynamics of the organism.

Description: Rare-earth ion singled out Nature Materials 11, 829 (2012). doi:10.1038/nmat3447 Author: Andrea Taroni

Description: Quantum effect on thermally activated glide of dislocations Nature Materials 11, 845 (2012). doi:10.1038/nmat3401 Authors: Laurent Proville, David Rodney & Mihai-Cosmin Marinica Crystal plasticity involves the motion of dislocations under stress. So far, atomistic simulations of this process have predicted Peierls stresses, the stress needed to overcome the crystal resistance in the absence of thermal fluctuations, of more than twice the experimental values, a discrepancy best-known in body-centred cubic crystals. Here we show that a large contribution arises from the crystal zero-point vibrations, which ease dislocation motion below typically half the Debye temperature. Using Wigner’s quantum transition state theory in atomistic models of crystals, we found a large decrease of the kink-pair formation enthalpy due to the quantization of the crystal vibrational modes. Consequently, the flow stress predicted by Orowan’s law is strongly reduced when compared with its classical approximation and in much closer agreement with experiments. This work advocates that quantum mechanics should be accounted for in simulations of materials and not only at very low temperatures or in light-atom systems.

Description: Spin excitations in a single La2CuO4 layer Nature Materials 11, 850 (2012). doi:10.1038/nmat3409 Authors: M. P. M. Dean, R. S. Springell, C. Monney, K. J. Zhou, J. Pereiro, I. Božović, B. Dalla Piazza, H. M. Rønnow, E. Morenzoni, J. van den Brink, T. Schmitt & J. P. Hill Cuprates and other high-temperature superconductors consist of two-dimensional layers that are crucial to their properties. The dynamics of the quantum spins in these layers lie at the heart of the mystery of the cuprates. In bulk cuprates such as La2CuO4, the presence of a weak coupling between the two-dimensional layers stabilizes a three-dimensional magnetic order up to high temperatures. In a truly two-dimensional system however, thermal spin fluctuations melt long-range order at any finite temperature. Here, we measure the spin response of isolated layers of La2CuO4 that are only one-unit-cell-thick. We show that coherent magnetic excitations, magnons, known from the bulk order, persist even in a single layer of La2CuO4, with no evidence for more complex correlations such as resonating valence bond correlations. These magnons are, therefore, well described by spin-wave theory (SWT). On the other hand, we also observe a high-energy magnetic continuum in the isotropic magnetic response that is not well described by two-magnon SWT, or indeed any existing theories.

Description: Material witness: Bringing crystals to life Nature Materials 11, 840 (2012). doi:10.1038/nmat3437 Author: Philip Ball

Description: Quantum many-body interactions in digital oxide superlattices Nature Materials 11, 855 (2012). doi:10.1038/nmat3405 Authors: Eric J. Monkman, Carolina Adamo, Julia A. Mundy, Daniel E. Shai, John W. Harter, Dawei Shen, Bulat Burganov, David A. Muller, Darrell G. Schlom & Kyle M. Shen Controlling the electronic properties of interfaces has enormous scientific and technological implications and has been recently extended from semiconductors to complex oxides that host emergent ground states not present in the parent materials. These oxide interfaces present a fundamentally new opportunity where, instead of conventional bandgap engineering, the electronic and magnetic properties can be optimized by engineering quantum many-body interactions. We use an integrated oxide molecular-beam epitaxy and angle-resolved photoemission spectroscopy system to synthesize and investigate the electronic structure of superlattices of the Mott insulator LaMnO3 and the band insulator SrMnO3. By digitally varying the separation between interfaces in (LaMnO3)2n/(SrMnO3)n superlattices with atomic-layer precision, we demonstrate that quantum many-body interactions are enhanced, driving the electronic states from a ferromagnetic polaronic metal to a pseudogapped insulating ground state. This work demonstrates how many-body interactions can be engineered at correlated oxide interfaces, an important prerequisite to exploiting such effects in novel electronics.

Description: Van der Waals interactions at metal/organic interfaces at the single-molecule level Nature Materials 11, 872 (2012). doi:10.1038/nmat3403 Authors: Sriharsha V. Aradhya, Michael Frei, Mark S. Hybertsen & L. Venkataraman Van der Waals (vdW) interaction, and its subtle interplay with chemically specific interactions and surface roughness at metal/organic interfaces, is critical to the understanding of structure–function relations in diverse areas, including catalysis, molecular electronics and self-assembly. However, vdW interactions remain challenging to characterize directly at the fundamental, single-molecule level both in experiments and in first principles calculations with accurate treatment of the non-local, London dispersion interactions. In particular, for metal/organic interfaces, efforts so far have largely focused on model systems consisting of adsorbed molecules on flat metallic surfaces with minimal specific chemical interaction. Here we show, through measurements of single-molecule mechanics, that pyridine derivatives can bind to nanostructured Au electrodes through an additional binding mechanism beyond the chemically specific N–Au donor–acceptor bond. Using density functional theory simulations we show that vdW interactions between the pyridine ring and Au electrodes can play a key role in the junction mechanics. These measurements thus provide a quantitative characterization of vdW interactions at metal/organic interfaces at the single-molecule level.

Description: Heterogeneous nucleation of organic crystals mediated by single-molecule templates Nature Materials 11, 877 (2012). doi:10.1038/nmat3408 Authors: Koji Harano, Tatsuya Homma, Yoshiko Niimi, Masanori Koshino, Kazu Suenaga, Ludwik Leibler & Eiichi Nakamura Fundamental understanding of how crystals of organic molecules nucleate on a surface remains limited because of the difficulty of probing rare events at the molecular scale. Here we show that single-molecule templates on the surface of carbon nanohorns can nucleate the crystallization of two organic compounds from a supersaturated solution by mediating the formation of disordered and mobile molecular nanoclusters on the templates. Single-molecule real-time transmission electron microscopy indicates that each nanocluster consists of a maximum of approximately 15 molecules, that there are fewer nanoclusters than crystals in solution, and that in the absence of templates physisorption, but not crystal formation, occurs. Our findings suggest that template-induced heterogeneous nucleation mechanistically resembles two-step homogeneous nucleation.

Description: Unification of trap-limited electron transport in semiconducting polymers Nature Materials 11, 882 (2012). doi:10.1038/nmat3384 Authors: H. T. Nicolai, M. Kuik, G. A. H. Wetzelaer, B. de Boer, C. Campbell, C. Risko, J. L. Brédas & P. W. M. Blom

Description: Probing oxygen vacancy concentration and homogeneity in solid-oxide fuel-cell cathode materials on the subunit-cell level Nature Materials 11, 888 (2012). doi:10.1038/nmat3393 Authors: Young-Min Kim, Jun He, Michael D. Biegalski, Hailemariam Ambaye, Valeria Lauter, Hans M. Christen, Sokrates T. Pantelides, Stephen J. Pennycook, Sergei V. Kalinin & Albina Y. Borisevich

Description: Stepping up MoS2 integration Nature Materials 11, 829 (2012). doi:10.1038/nmat3448 Author: Christian Martin

Description: Publication year: 2012 Source: Dendrochronologia Shuzhi Wang, Xiuhai Zhao The opening of the Silk Road vigorously promoted economic and cultural exchanges between Central Asia, Europe, northern India and China. The easternmost section of the ancient trade route was established during the Qin-Han period (221 BC to 220 AD). Previous research has shown that there were three routes: the first is known as the “Hexi Route”, the second is known as the “Juyan Route” or “Prairie Route”, and the third is known as the “Qinghai Route”. The Qinghai Route has long been viewed as merely an auxiliary line of the Hexi Route which was used when the main Hexi Route was blocked by warfare. Others believe that the Qinghai Route was used during the 5th to 6th century when it was controlled by Tuyuhun Kingdom. Yet, by the 7th to 8th century, after the Tibetan occupation of the region, it was no longer a main trade route. Dendrochronology, the study of tree-rings, is a precise dating method that can be accurate to the year. In this study, wood remains excavated from tombs along the ancient Qinghai Route were studied by the means of dendrochronology in order to determine the date and better understand when Qinghai Route was used. In the tombs a lot of commercial goods such as silk products, pottery, lacquer carpentry were found. The date of the tombs determined by dendrochronology when viewed together with other archaeological data, showed that from the early Tang Dynasty to the High Tang Dynasty (early 7th century to late 8th century), the Qinghai Route was one of the routes of communication between the West and China. This disproves the hypothesis that this route was only used during the 5th to 6th century.

Description: Graphene field-effect transistors as room-temperature terahertz detectors Nature Materials 11, 865 (2012). doi:10.1038/nmat3417 Authors: L. Vicarelli, M. S. Vitiello, D. Coquillat, A. Lombardo, A. C. Ferrari, W. Knap, M. Polini, V. Pellegrini & A. Tredicucci The unique optoelectronic properties of graphene make it an ideal platform for a variety of photonic applications, including fast photodetectors, transparent electrodes in displays and photovoltaic modules, optical modulators, plasmonic devices, microcavities, and ultra-fast lasers. Owing to its high carrier mobility, gapless spectrum and frequency-independent absorption, graphene is a very promising material for the development of detectors and modulators operating in the terahertz region of the electromagnetic spectrum (wavelengths in the hundreds of micrometres), still severely lacking in terms of solid-state devices. Here we demonstrate terahertz detectors based on antenna-coupled graphene field-effect transistors. These exploit the nonlinear response to the oscillating radiation field at the gate electrode, with contributions of thermoelectric and photoconductive origin. We demonstrate room temperature operation at 0.3 THz, showing that our devices can already be used in realistic settings, enabling large-area, fast imaging of macroscopic samples.

Description: Combination delivery of TGF-β inhibitor and IL-2 by nanoscale liposomal polymeric gels enhances tumour immunotherapy Nature Materials 11, 895 (2012). doi:10.1038/nmat3355 Authors: Jason Park, Stephen H. Wrzesinski, Eric Stern, Michael Look, Jason Criscione, Ragy Ragheb, Steven M. Jay, Stacey L. Demento, Atu Agawu, Paula Licona Limon, Anthony F. Ferrandino, David Gonzalez, Ann Habermann, Richard A. Flavell & Tarek M. Fahmy

Description: A ferroelectric memristor Nature Materials 11, 860 (2012). doi:10.1038/nmat3415 Authors: André Chanthbouala, Vincent Garcia, Ryan O. Cherifi, Karim Bouzehouane, Stéphane Fusil, Xavier Moya, Stéphane Xavier, Hiroyuki Yamada, Cyrile Deranlot, Neil D. Mathur, Manuel Bibes, Agnès Barthélémy & Julie Grollier Memristors are continuously tunable resistors that emulate biological synapses. Conceptualized in the 1970s, they traditionally operate by voltage-induced displacements of matter, although the details of the mechanism remain under debate. Purely electronic memristors based on well-established physical phenomena with albeit modest resistance changes have also emerged. Here we demonstrate that voltage-controlled domain configurations in ferroelectric tunnel barriers yield memristive behaviour with resistance variations exceeding two orders of magnitude and a 10 ns operation speed. Using models of ferroelectric-domain nucleation and growth, we explain the quasi-continuous resistance variations and derive a simple analytical expression for the memristive effect. Our results suggest new opportunities for ferroelectrics as the hardware basis of future neuromorphic computational architectures.

Description: Publication year: 2012 Source: Dendrochronologia Pierre Mérian, Jean-Claude Pierrat, François Lebourgeois Regional chronology and climate–growth relationships assessment are known to be sensitive to sampling effort. To disentangle the respective benefits of increasing whether the number of plots or the number of trees per plot when investigating climate–growth relationships under temperate conditions, we propose to simulate samples from a set of 84 plots established in plantations of Corsican pine ( Pinus nigra Arnold ssp. laricio Poiret var. Corsicana ), within which 10 dominant trees were cored in 1992. The effect of sampling effort was investigated through 20 modalities of sampled plots (from 3 to 84) and 10 modalities of sampled trees per plot (from 1 to 10). Regional chronology was studied using the mean effective correlation and the expressed population signal, while climate–growth relationships were evaluated through correlation functions. The calculation of the correlation functions also allowed testing the effect of sampling effort on various climatic regressors presenting different climate–growth correlation strengths. The accuracy of the dendroecological investigations increased with increasing sample size: estimating climate sensitivity with a regional chronology built from a small sample led to a general under-estimation of the climate–growth correlations. Decreasing sample size also increased the risk of estimating (i) “false” non-significant correlations for the most influencing climatic regressors, and (ii) “false” significant correlations for the less influencing ones. Increasing the number of plots was found of a greater interest than increasing the number of trees per plot to improve the climate–growth relationships assessment. Finally, the analysis revealed that the improvement of the expressed population signal with increasing sampling effort did not linearly mirror the bettering in the climate–growth correlations assessment.

Description: Publication year: 2012 Source: Dendrochronologia Mingxing Cui, Xingyuan He, Nicole Davi, Zhenju Chen, Xianliang Zhang, Junjie Peng, Wei Chen In order to detect the response of trees to environmental pollution in Shenyang during the last century, tree rings of two 100+ year old Chinese pine ( Pinus tabulaeformis Carr.) were analyzed for nine trace element concentrations (K, Ca, Mg, Mn, Cu, Zn, Al, Pb and Cd) and compared to local environmental change. The concentrations of Cu, Zn and Al had significant ( p 〈 0.01) increasing trends after 1940s and correlated significantly ( p 〈 0.01), with increasing production of nonferrous metal from local industrial processing. Concentrations of nutrient element (K, Ca and Mg) showed significant ( p 〈 0.01) increasing trend from heartwood to sapwood with declines in the last three decades. Significant correlation between climatic factors and element concentration in tree rings were also found, in which the temperature (November to May) and relative humidity in April and May showed significant positive correlation with Ca, Zn and Cu ( p 〈 0.05) as well as Al ( p 〈 0.01) concentrations in tree rings. April rainfall showed significant positive correlation with K and Zn ( p 〈 0.05) as well as Al ( p 〈 0.01) concentration in tree rings. The results suggest that tree rings from Chinese pine in Shenyang are sensitive to environmental change and have the potential to be used as a biomonitor for the environmental pollution. The results also demonstrate the feasibility of applying dendrochemical techniques to areas with limited samples.

Description: Publication year: 2012 Source: Dendrochronologia M. Wilmking, M. Hallinger, R. Van Bogaert, T. Kyncl, F. Babst, W. Hahne, G.P. Juday, M. de Luis, K. Novak, C. Völlm Woody plants growing in seasonal climates normally form one growth ring each year. However, under severe stress conditions they may not complete annual wood production all the way down to the root collar resulting in continuously missing outer rings at lower stem sections (CMORs). Here we test whether CMORs occur at different distributional margins of woody plant species, where stress levels are expected to be high. We tested 13 species (202 individuals) of trees and shrubs growing at elevational and latitudinal shrub- and tree-lines, under conditions that are normally associated with a reduction of radial growth such as drought, cold or nutrient deficiency. Samples were collected from Alaska, north western Russia, Central Europe, Scandinavia and south eastern Spain. Annual radial growth was measured along several disks or cores of each individual applying the serial sectioning technique. Individuals of nine species showed CMORs. The proportion of individuals with CMORs within a sampled species and site ranged from 0% to 80%. The number of CMORs within an individual increased with decreasing sampling height on the stem. Significant correlations existed between the amount of CMORs and (i) cambial age, (ii) stem length, (iii) stem proportion/length below peat surface, and (iv) herbivore-caused defoliation intensity depending on the species and sampling location. Our results suggest that CMORs can be associated with a cambium that may be inactive, yet functional, for up to 18 years. We conclude that CMORs can occur in a wide variety of species, growth forms and biomes, suggesting a general strategy of woody plant growth. To avoid miss-dating in dendrochronological studies, we further recommend the use of the serial sectioning technique for woody plants growing in unfavorable environments, above all, when sample size is limited and when no established chronology for cross-dating is available.

Description: Publication year: 2012 Source: Dendrochronologia Martin Worbes, Nils Raschke The rising discussion on carbon balance of tropical forests often does not consider the sequestration potential of secondary dry forests, which are becoming an increasing importance due to land use change and reforestation. We have developed an easy applicable tool for the estimation of biomass increment of tropical secondary forest stands on the base of tree ring analysis. The existence of annual rings was shown by a combination of anatomical examination and radiocarbon estimations. With tree ring analysis, forest inventories and destructive sampling the above-ground biomass increment of secondary forest stands of age between 9 and 48 years in the dry forest region of Guanacaste, Costa Rica were estimated. The above-ground biomass increment of the tree layer varies between 2.4 and 3.2 Mg/ha yr in different stands. Lianas contribute with up to 23% additional production. Differences in productivity among the stands along a chronosequence were not significant. The measured carbon allocation potential of 1.7–2.1 Mg C/ha yr lies in the range of reported values from other tropical dry forests and old growth humid forests as well.

Description: Publication year: 2012 Source: Dendrochronologia D.M. Brown, M.G.L. Baillie In the course of building the 7000 year Belfast long oak chronology a series of depletion problems were encountered. These problems were overcome by 1984 when the completion of the Long Chronology was announced. The solution to the bridging of the various ‘gaps’ in the Irish chronology lay in the use of long sections of oak chronology from Britain. Now that a quarter of a century has elapsed and large numbers of additional oak samples, and site assemblages, have been accumulated it seems reasonable to review the ‘gaps’ in order to see if the Irish chronology could now be constructed without the use of British material. That is, are the depletion periods in the Irish chronology still evident, and if so, what might they imply about past conditions and human populations? The perhaps surprising conclusion is that the original depletions are still evident after 25 years of quasi-random sampling by archaeologists and palaeoecologists throughout Ireland.

Description: Nature Materials 11, 995 (2012). doi:10.1038/nmat3519 This year marks a quarter of a century since the birth of photonic crystals. Overcoming early difficulties, the field has made a range of technological developments possible as well as the emergence of new science at the interface between condensed-matter physics and photonics.

Description: Nature Materials 11, 1000 (2012). doi:10.1038/nmat3504 Twenty five years since the birth of the field of photonic crystals, Eli Yablonovitch talks to Nature Materials about his pioneering contributions to the field and his vision for nanophotonics.

Description: Nature Materials 11, 1002 (2012). doi:10.1038/nmat3511 Author: Pep Pàmies

Description: Nature Materials 11, 1004 (2012). doi:10.1038/nmat3494 Author: Kathryn J. Wahl Friction classically decreases with decreasing load. Nanoscale measurements on chemically modified graphite now show an opposite trend related to local deformation, which could serve as a probe for determining the exfoliation energy of layered materials.

Description: Nature Materials 11, 1006 (2012). doi:10.1038/nmat3501 Author: Jon Dobson A magnetic on/off switch for cell-death signalling in cancer cells is developed using antibodies conjugated to magnetic nanoparticles. The control of cell death in in vivo systems is demonstrated by a tell-tale morphological change within the zebrafish.

Description: Nature Materials 11, 1002 (2012). doi:10.1038/nmat3515 Author: Christian Martin

Description: Nature Materials 11, 996 (2012). doi:10.1038/nmat3493 Authors: Igor Aharonovich & Olga Shenderova

Description: Nature Materials 11, 1011 (2012). doi:10.1038/nmat3508 Author: Philip Ball

Description: Nature Materials 11, 1017 (2012). doi:10.1038/nmat3442 Authors: Kevin Vynck, Matteo Burresi, Francesco Riboli & Diederik S. Wiersma Elaborating reliable and versatile strategies for efficient light coupling between free space and thin films is of crucial importance for new technologies in energy efficiency. Nanostructured materials have opened unprecedented opportunities for light management, notably in thin-film solar cells. Efficient coherent light trapping has been accomplished through the careful design of plasmonic nanoparticles and gratings, resonant dielectric particles and photonic crystals. Alternative approaches have used randomly textured surfaces as strong light diffusers to benefit from their broadband and wide-angle properties. Here, we propose a new strategy for photon management in thin films that combines both advantages of an efficient trapping due to coherent optical effects and broadband/wide-angle properties due to disorder. Our approach consists of the excitation of electromagnetic modes formed by multiple light scattering and wave interference in two-dimensional random media. We show, by numerical calculations, that the spectral and angular responses of thin films containing disordered photonic patterns are intimately related to the in-plane light transport process and can be tuned through structural correlations. Our findings, which are applicable to all waves, are particularly suited for improving the absorption efficiency of thin-film solar cells and can provide a new approach for high-extraction-efficiency light-emitting diodes.

Description: Nature Materials 11, 1044 (2012). doi:10.1038/nmat3454 Authors: Phillip Christopher, Hongliang Xin, Andiappan Marimuthu & Suljo Linic

Description: Nature Materials 11, 1059 (2012). doi:10.1038/nmat3455 Authors: Elke Verheyen, Lennart Joos, Kristof Van Havenbergh, Eric Breynaert, Nataliia Kasian, Elena Gobechiya, Kristof Houthoofd, Charlotte Martineau, Manuel Hinterstein, Francis Taulelle, Veronique Van Speybroeck, Michel Waroquier, Sara Bals, Gustaaf Van Tendeloo, Christine E. A. Kirschhock & Johan A. Martens

Description: Nature Materials 11, 1081 (2012). doi:10.1038/nmat3461 Authors: Yasuhiro Ikezoe, Gosuke Washino, Takashi Uemura, Susumu Kitagawa & Hiroshi Matsui

Description: A decade in numbers Nature Materials 11, 743 (2012). doi:10.1038/nmat3424 On the tenth anniversary of the launch of Nature Materials, we look back at how authors, reviewers and editors have contributed to the journal by evaluating data such as decision types and times, and the geographical share of submitted and published manuscripts.

Description: Material witness: Shock relief Nature Materials 11, 747 (2012). doi:10.1038/nmat3411 Author: Philip Ball

Description: Mesoporous silica: Holey quasicrystals Nature Materials 11, 749 (2012). doi:10.1038/nmat3414 Author: Sarah H. Tolbert The self-assembly of surfactant micelles in the formation of templated mesoporous silicas can be tuned to produce mesoporous materials with quasicrystalline ordering, proving that quasicrystals are indeed a general form of ordered but non-periodic matter.

Description: Electronics: Electronic materials through time Nature Materials 11, 751 (2012). doi:10.1038/nmat3407 Authors: B. Keimer, J. Maier & J. Mannhart Complex materials that challenge existing electronic materials are the subject of intense research. In particular, correlated electron effects and ionic properties, and their interplay, promise new functionalities.

Description: Hybrid electrolytes Nature Materials 11, 745 (2012). doi:10.1038/nmat3419 Author: Vincent J. Dusastre

Description: Understanding endocytosis Nature Materials 11, 745 (2012). doi:10.1038/nmat3421 Author: Pep Pàmies

Description: Tissue engineering: Perfusable vascular networks Nature Materials 11, 746 (2012). doi:10.1038/nmat3412 Author: Gabor Forgacs A rapid vascular casting approach that uses carbohydrate glass as a sacrificial template allows tissues to be built that can be kept alive for longer in the laboratory until needed for transplantation.

Description: Dielectric nanoparticles: Polarizability reveals identity Nature Materials 11, 748 (2012). doi:10.1038/nmat3410 Authors: Enrique Sahagún & Juan José Sáenz Improvements in electrostatic force microscopy now make it possible to measure the dielectric constant of isolated low-polarizable nanoparticles and viruses, thus enabling the label-free identification of dielectric nanomaterials of similar morphology.

Description: Up and away Nature Materials 11, 745 (2012). doi:10.1038/nmat3422 Author: Christian Martin

Description: Publication year: 2012 Source: Dendrochronologia Nesibe Köse, Ünal Akkemik, Hasan Nüzhet Dalfes, Mehmet Sinan Özeren, Doğanay Tolunay Pinus nigra Arn. subsp. pallasiana (black pine) is one of the most widely grown tree in Turkey. It is the third most widely distributed tree species after Quercus L. and Pinus brutia Ten. Black pine grows in 20% of all forested areas in Turkey. In this dendroecological study, we identified the most important climate factors affecting radial growth of black pine in western Anatolia and classified its responses to climate. Twenty-eight site chronologies developed by different researchers were used in the analysis. Response functions were calculated for each chronology to identify the effect of climate on radial growth. Hierarchical cluster analysis was used to sort response functions and to classify the chronologies into groups based on climate responses. The individual responses of these chronologies to temperature and precipitation were classified in four main groups. Climatic and phytogeographic differences were the major factors influencing the formation of clusters. The results suggest that the major limiting factor is drought caused by low precipitation, especially in May, in almost all sites. The drought effect is much stronger in the transition region to the steppe, Central Anatolia and Mediterranean Regions than the Black Sea Region. Black pine trees respond positively to higher temperature at the beginning of growing season in almost all areas except in transition region to the steppe.

Description: Plasmonics making waves Nature Materials 11, 745 (2012). doi:10.1038/nmat3418 Author: Joerg Heber

Description: Block and deliver Nature Materials 11, 745 (2012). doi:10.1038/nmat3420 Author: Alison Stoddart

Description: Multiferroicity in an organic charge-transfer salt that is suggestive of electric-dipole-driven magnetism Nature Materials 11, 755 (2012). doi:10.1038/nmat3400 Authors: Peter Lunkenheimer, Jens Müller, Stephan Krohns, Florian Schrettle, Alois Loidl, Benedikt Hartmann, Robert Rommel, Mariano de Souza, Chisa Hotta, John A. Schlueter & Michael Lang Multiferroics, showing simultaneous ordering of electrical and magnetic degrees of freedom, are remarkable materials as seen from both the academic and technological points of view. A prominent mechanism of multiferroicity is the spin-driven ferroelectricity, often found in frustrated antiferromagnets with helical spin order. There, as for conventional ferroelectrics, the electrical dipoles arise from an off-centre displacement of ions. However, recently a different mechanism, namely purely electronic ferroelectricity, where charge order breaks inversion symmetry, has attracted considerable interest. Here we provide evidence for ferroelectricity, accompanied by antiferromagnetic spin order, in a two-dimensional organic charge-transfer salt, thus representing a new class of multiferroics. We propose a charge-order-driven mechanism leading to electronic ferroelectricity in this material. Quite unexpectedly for electronic ferroelectrics, dipolar and spin order arise nearly simultaneously. This can be ascribed to the loss of spin frustration induced by the ferroelectric ordering. Hence, here the spin order is driven by the ferroelectricity, in marked contrast to the spin-driven ferroelectricity in helical magnets.

Description: Cross-sectional imaging of individual layers and buried interfaces of graphene-based heterostructures and superlattices Nature Materials 11, 764 (2012). doi:10.1038/nmat3386 Authors: S. J. Haigh, A. Gholinia, R. Jalil, S. Romani, L. Britnell, D. C. Elias, K. S. Novoselov, L. A. Ponomarenko, A. K. Geim & R. Gorbachev By stacking various two-dimensional (2D) atomic crystals on top of each other, it is possible to create multilayer heterostructures and devices with designed electronic properties. However, various adsorbates become trapped between layers during their assembly, and this not only affects the resulting quality but also prevents the formation of a true artificial layered crystal upheld by van der Waals interaction, creating instead a laminate glued together by contamination. Transmission electron microscopy (TEM) has shown that graphene and boron nitride monolayers, the two best characterized 2D crystals, are densely covered with hydrocarbons (even after thermal annealing in high vacuum) and exhibit only small clean patches suitable for atomic resolution imaging. This observation seems detrimental for any realistic prospect of creating van der Waals materials and heterostructures with atomically sharp interfaces. Here we employ cross sectional TEM to take a side view of several graphene–boron nitride heterostructures. We find that the trapped hydrocarbons segregate into isolated pockets, leaving the interfaces atomically clean. Moreover, we observe a clear correlation between interface roughness and the electronic quality of encapsulated graphene. This work proves the concept of heterostructures assembled with atomic layer precision and provides their first TEM images.

Description: Rapid casting of patterned vascular networks for perfusable engineered three-dimensional tissues Nature Materials 11, 768 (2012). doi:10.1038/nmat3357 Authors: Jordan S. Miller, Kelly R. Stevens, Michael T. Yang, Brendon M. Baker, Duc-Huy T. Nguyen, Daniel M. Cohen, Esteban Toro, Alice A. Chen, Peter A. Galie, Xiang Yu, Ritika Chaturvedi, Sangeeta N. Bhatia & Christopher S. Chen In the absence of perfusable vascular networks, three-dimensional (3D) engineered tissues densely populated with cells quickly develop a necrotic core. Yet the lack of a general approach to rapidly construct such networks remains a major challenge for 3D tissue culture. Here, we printed rigid 3D filament networks of carbohydrate glass, and used them as a cytocompatible sacrificial template in engineered tissues containing living cells to generate cylindrical networks that could be lined with endothelial cells and perfused with blood under high-pressure pulsatile flow. Because this simple vascular casting approach allows independent control of network geometry, endothelialization and extravascular tissue, it is compatible with a wide variety of cell types, synthetic and natural extracellular matrices, and crosslinking strategies. We also demonstrated that the perfused vascular channels sustained the metabolic function of primary rat hepatocytes in engineered tissue constructs that otherwise exhibited suppressed function in their core.

Description: A Janus cobalt-based catalytic material for electro-splitting of water Nature Materials 11, 802 (2012). doi:10.1038/nmat3385 Authors: Saioa Cobo, Jonathan Heidkamp, Pierre-André Jacques, Jennifer Fize, Vincent Fourmond, Laure Guetaz, Bruno Jousselme, Valentina Ivanova, Holger Dau, Serge Palacin, Marc Fontecave & Vincent Artero