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Nanoindentation and fluorescence spectroscopy provide spatially resolved mechanical and chemical characterization for degradation of poly (ethylene-co-vinyl acetate) (EVA) encapsulants aged under accelerated weathering and in field deployed photovoltaic (PV) modules. For the accelerated weathering tests, two different EVA formulations in the glass/EVA/glass-laminated coupons were exposed to ultraviolet (UV) light for 180 days at three different temperatures (40, 60, and 80 °C) and UV intensities (0.4, 2.2, and 2.9 W/m2/nm at 340 nm). The fluorescence spectra and moduli were uniform through the cross section of both EVA formulations at the lowest temperature and UV intensity; however, under the highest temperature and UV intensity, the UV irradiated sides showed lower moduli and higher fluorescence compared to the opposite sides. For EVA obtained from PV modules deployed 27 years in Sacramento, CA, USA, changes in fluorescence intensity across the thickness were relatively greater than changes in modulus. On the other hand, for EVA obtained from the same type of module stored in the shed for 27 years, no fluorescence was observed, and a uniform modulus was seen through the EVA layer, but with substantially higher values than those obtained from the field-deployed modules. The different extent of changes between laboratory and field exposures suggests the importance of considering effects of temperature and UV intensity for designing a reliable accelerated testing. This study uniquely demonstrates the capability of microscale characterization using nanoindentation and fluorescence microscopy to monitor mechanical and chemical degradation of EVA encapsulants in PV modules.

Fermionic atoms in optical lattices have served as a useful model system in which to study and emulate the physics of strongly correlated matter. Driven by the advances of high-resolution microscopy, the current research focus is on two-dimensional systems1-3, in which several quantum phases-such as antiferromagnetic Mott insulators for repulsive interactions4-7 and charge-density waves for attractive interactions8-have been observed. However, the lattice structure of real materials, such as bilayer graphene, is composed of coupled layers and is therefore not strictly two-dimensional, which must be taken into account in simulations. Here we realize a bilayer Fermi-Hubbard model using ultracold atoms in an optical lattice, and demonstrate that the interlayer coupling controls a crossover between a planar antiferromagnetically ordered Mott insulator and a band insulator of spin-singlets along the bonds between the layers. We probe the competition of the magnetic ordering by measuring spin-spin correlations both within and between the two-dimensional layers. Our work will enable the exploration of further properties of coupled-layer Hubbard models, such as theoretically predicted superconducting pairing mechanisms9,10.

Background The knowledge gap regarding post-logging carbon recovery by increased growth is becoming more crucial to understand the significant contribution of forest to climate change mitigation. We assessed the ability of tropical forests in Indonesia to recover carbon following conventional logging. We evaluated carbon re-growth of 10,415 trees in permanent sample plots (PSPs) in East Kalimantan. Four different post-harvesting silvicultural treatments including liberation, refining, thinning, and control were applied in the PSPs. We estimated the carbon recovery period using three different scenarios of total carbon losses due to logging. In the first scenario, we used an existing factor of logging damage and increased it for assuming the range of carbon losses due to different logging practices. Results Under the existing conventional logging practice, the concession annually emits 51.18 tC∙ha− 1, of which 16.8% are extracted from the forest as raw timber, 38% are logging losses, and 45.2% are emissions due to infrastructure development for logging operation. Increasing the logging damage factor two and three times led to an increase in carbon emission to 70.76 and 90.34 tC∙ha− 1, respectively. The recovery time of the aboveground carbon is 26 years in Scenario 1, 36 years in Scenario 2, and 46 years in Scenario 3. We found no significant effect of the silvicultural treatment type on carbon recovery, but significant effect of the sites was observed. Conclusions We found that the time taken to restore the carbon to the level found in undisturbed forests is considerably longer than the current intervention cycles. The time needed to recover biomass and carbon-stock noticeably depends on the intensity of logging interventions, demonstrating the benefits of using improved harvesting e.g., reduced impact logging to reduce emissions. The study found that site variability has a significant effect on the carbon recovery time. Different silvicultural treatments, on the other hand, have no effect on the recovery time. The study suggests that it is not appropriate to establish an intervention cycle based on arbitrary choice; the time between interventions must be based on logging losses and site specific growth potential to ensure sustainable management of forests.

We study experimentally and theoretically the response of a two-component Fermi condensate in the strongly-interacting regime to a quench of the interaction strength. The quench is realized using a radio-frequency $\pi$-pulse to a third internal level with a different interaction strength. We find that the quench excites the monopole mode of the trap in the hydrodynamic regime and that an initial change of the condensate properties takes place on a time scale comparable or even larger than the quasi-particle relaxation time.

Sustainable forest management activities, such as future crop tree (FCT) release treatments, became part of the REDD+ strategy to avoid carbon emissions from forests. FCT release treatments are intended to achieve increased growth of FCTs by removing competitor trees. This initially leads to a reduction of the forest carbon pool and represents a carbon debt. We estimated that the time it takes for FCTs to offset the carbon debt through increased growth on experimental sites of 10 km&sup2, in Belize, Guyana, Suriname, and Trinidad and Tobago. We further investigated whether the costs of treatment can be compensated by the generated financial carbon benefits. An average of 2.3 FCT per hectare were released through the removal of an average of 3.3 competitors per hectare. This corresponds to an average above ground biomass (AGB) deficit of 2.3 Mg FCT-1. Assuming a 30% increase in growth, the FCT would need on average 130 years to offset the carbon loss. For carbon prices from US$ 5 to 100 Mg CO2e-1 an additional increment between 0.6 and 22.7 Mg tree-1 would be required to cover the treatment costs of US$ 4.2 to 8.4 FCT-1. Assuming a carbon price of US$ 10 Mg CO2e-1, the additional increment required would be between 5.8 and 11.4 Mg tree-1, thus exceeding the biological growth potential of most individual trees. The release of FCTs does not ensure an increase in forest carbon stocks, and refinancing of treatment costs is problematic.

Reducing Emissions from Deforestation and Degradation (REDD+) has been identified as a potentially cost-effective climate change mitigation strategy. The success of REDD+ in preventing deforestation and degradation in dry forests will depend partly on whether financial incentives for forest conservation can cover smallholders' opportunity costs of forgone uses of the forest. We therefore compared the opportunity costs of the main forest use activities (slash-and-burn agriculture or charcoal production) with potential benefits from the sale of carbon credits under REDD+ from a smallholder perspective for a case study in southwestern Madagascar. Calculations are based on an assessment of carbon stocks in the dry spiny forests as well as benefit and cost data from interviews with smallholders. To assess the risks and uncertainties associated with opportunity costs and the REDD+ benefits, we used a Monte Carlo modeling approach. We compare net present values for opportunity costs and potential community profits from REDD+ at discount rates of 5% and 20% over a project period of 25 years. Our results show that REDD+ community profits can outweigh the profits from charcoal production and the profits from slash-and-burn agriculture in 54–57% of the cases, despite opportunity costs being highly variable for both land uses. Charcoal production in particular has low opportunity costs as smallholders only engage in this activity when no other sources of income are available. The case study shows that potential REDD+ payments can provide sufficient financial incentives to preserve dry forests with low carbon stocks but relatively low opportunity costs of preservation.

Higgs and Goldstone modes are possible collective modes of an order parameter upon spontaneously breaking a continuous symmetry. Whereas the low-energy Goldstone (phase) mode is always stable, additional symmetries are required to prevent the Higgs (amplitude) mode from rapidly decaying into low-energy excitations. In high-energy physics, where the Higgs boson has been found after a decades-long search, the stability is ensured by Lorentz invariance. In the realm of condensed--matter physics, particle--hole symmetry can play this role and a Higgs mode has been observed in weakly-interacting superconductors. However, whether the Higgs mode is also stable for strongly-correlated superconductors in which particle--hole symmetry is not precisely fulfilled or whether this mode becomes overdamped has been subject of numerous discussions. Experimental evidence is still lacking, in particular owing to the difficulty to excite the Higgs mode directly. Here, we observe the Higgs mode in a strongly-interacting superfluid Fermi gas. By inducing a periodic modulation of the amplitude of the superconducting order parameter $\Delta$, we observe an excitation resonance at frequency $2\Delta/h$. For strong coupling, the peak width broadens and eventually the mode disappears when the Cooper pairs turn into tightly bound dimers signalling the eventual instability of the Higgs mode.

Cold atom experiments commonly use broad magnetic Feshbach resonances to manipulate the interaction between atoms. In order to induce quantum dynamics by a change in the interaction strength, rapid (∼μs) magnetic field changes over several tens of Gauss are required. Here, we present a compact design of a coil and its control circuit for a change in the magnetic field up to 36 G in 3 µs. The setup comprises two concentric solenoids with minimal space requirements, which can be readily added to existing apparatuses. This design makes the observation of non-equilibrium physics with broad Feshbach resonances accessible.

Fragmented forests and heterogeneous landscapes are likely to have less natural vegetation and smaller core areas, a low degree of landscape connectivity, high prevalence of anthropogenic edges, and high landscape heterogeneity, which may alter—at varying degrees—behavior of wildlife species such as attacks on humans. We evaluated whether or not forest fragmentation (e.g. shape, size and distribution of forest patches measured as landscape shape index, effective mesh size, and landscape heterogeneity), habitats (proportion of bush and grassland, distance to water sources), and human disturbances (human population density) have a significant relationship with frequencies of human deaths and injuries by Bengal tiger ( Panthera tigris tigris ), common leopard ( Panthera pardus ), one-horned rhinoceros ( Rhinoceros unicornis ) and Asiatic elephant ( Elephas maximus ). Data on human injury and death were obtained from a national survey over five years (2010–2014). The relationship between wildlife attacks and landscape attributes were investigated using a zero-inflated Poisson regression model. Attacks by tigers were significantly and positively associated with forest fragmentation (effective mesh size which is high in a landscape consisting of disconnected small patches). Attacks by common leopards were strongly positively related with landscape heterogeneity, and negatively related to the proportion of bush and grassland. Attacks by one-horned rhinoceros were positively significantly related to the distance to water sources, and proportion of bush and grassland in the landscape. Attacks by elephants were strongly and positively associated with the forest fragmentation (landscape shape index, which increases as patches in the landscapes becomes disaggregated). These results suggest that forest fragmentation is inevitably a critical driver of human–wildlife conflicts, although the extent of effects varies depending on species specific habitat requirements.

The remnant populations of Gharials, Gavialis gangeticus, are now confined to the large, deep rivers of northern India and Nepal. In lowland Nepal, the populations are restricted to a few stretches of the Narayani–Rapti and Karnali–Babai river systems. Periodic censuses of the wild populations have been made over the past 12 yr. Here, we present population trends of Gharials in the Narayani, Rapti, and Babai rivers based on these surveys. The results indicate that the combined numbers of adults and subadults have been gradually increasing since 2005, but the numbers of adults are low and female biased, with very few males recorded from all study sites. In 1978, Nepal established a captive breeding center in Chitwan National Park, from which captive-bred animals have been periodically released 4–7 yr after hatching, at which time the animals are about 1.5 m total length. The detection of hatchlings and subadult classes that are smaller than these released animals in the rivers indicates that ther...

The mechanism of fermionic pairing is the key to understanding various phenomena such as high-temperature superconductivity and the pseudogap phase in cuprate materials. We study the pair correlations in the attractive Hubbard model using ultracold fermions in a two-dimensional optical lattice. By combining the fluctuation-dissipation theorem and the compressibility equation of state, we extract the interacting pair correlation functions and deduce a characteristic length scale of pairs as a function of interaction and density filling. At sufficiently low filling and weak on-site interaction, we observe that the pair correlations extend over a few lattice sites even at temperatures above the superfluid transition temperature.

We study the particle-hole symmetry in the Hubbard model using ultracold fermionic atoms in an optical lattice. We demonstrate the mapping between charge and spin degrees of freedom and, in particular, show the occurrence of a state with "incompressible" magnetization for attractive interactions. Our results present a novel approach to quantum simulation by giving access to strongly correlated phases of matter through an experimental mapping to easier detectable observables.

We have constructed an apparatus containing a linear ion trap and a high-finesse optical cavity in the ultraviolet spectral range. In our construction, we have avoided all organic materials inside the ultrahigh vacuum chamber. We show that, unlike previously reported, the optical cavity does not degrade in performance over a time scale of 9 months.

Several forest related EU policy instruments have set forest relevant quantitative or qualitative targets. We identify the forest relevant targets in current EU policy instruments, and examine whether the pan-European Criteria and Indicators for Sustainable Forest Management (Forest Europe, 2015a) are sufficient to satisfy the information needs of EU policy makers when monitoring progress towards these targets. We apply a computer-based quantitative analysis of forest related EU policy instruments, using key words. In the policy instruments we analysed, forest relevant targets are completely integrated with targets for other sectors in a wider context. Relatively few of the identified forest relevant targets are quantitative; qualitative targets are predominant. In our analysis we show that the pan-European Criteria and Indicators for Sustainable Forest Management, as they stand, would require adjustments to several of the indicators to provide information on progress towards the identified forest relevant quantitative and qualitative targets. Our results can contribute to reporting on progress towards forest-relevant targets in EU forest related policies, notably by identifying what parameters could be measured and might facilitate forest related target setting in revisions and development of policy instruments, particularly the revision of the EU Forest Strategy.

The determination of the geographical origin of wood can be highly relevant for several reasons: On the one hand, it can help to prevent illegal logging and timber trade, on the other hand, it is of special interest for archaeological artefacts made of wood, as well as for a variety of biological questions. For this reason, different extraction methods were first tested for the analysis of polar and non-polar metabolites using liquid chromatography coupled electrospray ionization quadrupole time-of-flight mass spectrometry (UHPLC-ESI-QTOF-MS). A two-phase extraction with chloroform, methanol and water proved to be particularly successful. Subsequently, cedrela (Cedrela odorata) samples from South America were measured to distinguish geographic origin. Using multivariate data analysis, numerous origin-dependent differences could be extracted. The identification of the marker substances indicated that several metabolic pathways were affected by the geographical influences, some of them probably indicating pest infections.

Silvicultural treatments are a common tool for increasing commercial timber production. Their impact on the growth or mortality of the remaining stand is well researched. This study focuses on the economic aspects of silvicultural treatments in neotropical forests. We have selected liberation treatments and consider them to be investments that are expected to pay for themselves through the additional growth of released trees and corresponding timber prices following a 30-year rotation period. The study is based on empirical data collected on experimental sites of 10 km2 in Belize, Guyana, Suriname, Trinidad and Tobago. To determine the timber price or additional growth required to cover the treatment costs, we used a reverse approach based on net present values. The treatment costs range between US$4.5 and US$8.9 per released tree. The additional growth required per released tree to cover the expenses for silvicultural treatments depends on treatment costs and achievable timber prices and varies from 0.02 to 3.5 m3. Conversely, if a potential increase in growth is assumed, timber prices must be between 34 and 578 US$ m-3 to at least cover the cost of treatments. We found a high sensitivity of profitability related to the additional growth, the timber prices to be achieved, and the discount rate chosen, which significantly increases the financial risk of silvicultural treatments as an investment tool. The decision whether to use silvicultural treatments or not is often solely guided by the expected improvement in tree growth. We, however, show that growth alone is insufficient as a decision criterion. While treatment costs are known when the decision to implement the measures is made, future timber prices and harvesting costs as well as the additional growth actually achieved are subject to uncertainties. These uncertainties have a decisive influence on the economic risk assessment, which is reflected in the choice of the internal interest rate. Our study demonstrates that investments in silvicultural treatments involve a considerable financial risk and that the decision to carry out silvicultural treatments should always be the subject of a thorough investment calculation.

We investigate the nonequilibrium behavior of dilute, attractively interacting Fermi gases subjected to finite-duration ramps of their internal interaction strength. We identify three dynamical regimes as a function of ramp duration using a time-dependent version of the Bardeen-Cooper-Schrieffer theory of superconductivity to model these systems. For short ramp durations, these systems become nonsuperconducting; however, fermions with opposite momenta remain paired albeit with reduced amplitudes, and the associated pair amplitude distribution is nonthermal. In this first regime, the disappearance of superconductivity is due to the loss of phase coherence between pairs. By contrast, for intermediate ramp durations, superconductivity survives but the magnitude of the order parameter is reduced and presents long-lived oscillations. Finally, for long ramp durations, phase coherence is almost fully retained during the finite-duration interaction quench, and the steady state is characterized by a thermal-like pair amplitude distribution. Using this approach, one can therefore dynamically tune the coherence between pairs to control the magnitude of the superconducting order parameter and even engineer a nonequilibrium state made of preformed pairs.

In forest management, the sustainability of a multitude of economic, ecological and socio-economic impacts and services is assessed. The role of forests in the global carbon (C) cycle is almost exclusively assessed through an ecosystem approach that relates emissions from timber harvesting and removals through biomass growth and C sequestration. While harvested wood leads to a reduction in the C-stock in forest C-pools, the use of wood for energy and production of wood-based materials results in significant emission reductions by substituting in place of greenhouse gas (GHG) intensive fuels and energy-intensive non-wood materials respectively. We present a new indicator approach for the assessment of sustainable forest management that includes the entire emissions and removals associated with the harvested wood along the wood product value chain and thus represents represents C-sustainability with respect to emissions and removals. The indicator is implemented in two variants. If information available on wood use and the carbon offsets associated with it is sufficient, the indicator can be derived by presenting emissions from wood harvesting and removals from wood use in the form of a carbon balance (C-balance indicator). If the balance is even or if removals predominate, forest management fulfills the requirement of C-sustainability. If the information is insufficient, the emissions from the wood harvest and possible wood processing losses are summed up, and the necessary displacement factor (DF) is calculated, which is necessary to compensate the corresponding emissions by carbon offsets of the wood use (DF-indicator). A comparison of the necessary displacement factor with common carbon offsets of typical wood uses allows an assessment of C-sustainability. The effectiveness of the C-indicator for assessing sustainable forest management is illustrated by two case studies. We found that in order to achieve carbon neutrality, substitution factors between 1.9 (lignite) and 2.5 (gas) are necessary, depending on the fossil fuel substituted. If no energetic substitution is assumed, the DF increases to a value of 3.3. In situations with high harvest losses, the necessary DFs well exceed values that can be achieved even under very positive assumptions; C-sustainability is therefore not met. Both approaches allow an assessment of C-sustainability beyond forest boundaries by giving appropriate weight to the importance of wood use in the carbon cycle. In addition to the implication of the indicator to evaluate SFM, we claim that this indicator is responsive to the emerging global forest related international processes and their reporting requirements such as Reducing Emissions from Deforestation and forest Degradation in Developing Countries (REDD+) as well as nationally appropriate mitigation actions (NDCs, Low Emission Development Strategy).

Despite the widespread use and strong promotion of the sustainable forest management approach, there are still uncertainties about the actual contribution of current forest management practices to sustainability. We studied the problem of sustainable timber production in four tropical countries (Belize, Guyana, Suriname, and Trinidad and Tobago). Data assessed on experimental plots covering 10 km2 were used to compare management practices of four forest tenure types that commonly exist in the study countries: large scale concessions (LSC), private forests (PR), periodic block system forests (PBS), and community managed forests (CM). As an indicator of sustainable timber production, we calculated the recovery times expected under the initial condition of the stands and compared them with currently practiced cutting cycles. Three growth scenarios were simulated using diameter growth rates (1.6/2.7/4.5 mm year&minus, 1) from empirical data from studies in the region. Initial volumes were determined for all commercial trees as well as for commercial trees with a DBH-threshold &ge, 45 cm. Highest initial volumes were found in LSC and PBS managed forests. Lowest volumes were found in CM and PR forests. Assuming the lowest growth rate for all commercial trees, none of the stands studied reached the initial pre-harvest volumes within the currently practiced cutting cycles. Assuming the highest growth rate for all trees, LSC, PBS, and PR forests reach the initial pre-harvest volume. Looking at the subset of commercial trees with a DBH &ge, 45 cm, all stands will reach the initial volume within 30 years only if the highest growth rate is assumed. We show that general harvest codes do not guarantee sustainable forest management in the tropics. Local stand conditions must always be one of the guiding principles of sustainable timber utilization. Applying the rigid rules, which do not take into account the current conditions of the stands, entails long-term risk of forest degradation.

The REDD+ initiative applies a market-based approach to reducing greenhouse gas emissions from deforestation and forest degradation. The difference between the carbon stock of forests under historical deforestation and forest degradation rates and the actual C-stock achieved by forest conservation measures will be compensated financially. The difference in C-stocks is provided by a system of measurement, reporting and verification (MRV). We investigated trade-offs between costs and revenue of a REDD+ MRV system by applying a simulation study focusing on varying forest degradation intensities in natural forests. We showed the decisive influence of cost on the efficiency of REDD+. Resulting payments could be too low or even negative, especially in high forest low deforestation countries. Under current carbon process countries implementing REDD + activities need additional financial support for the development and implementation of MRV systems. We recommend that the optimization of the MRV design must meet accuracy and cost requirements. The optimization criterion for MRV systems should not be the highest possible accuracy, but the highest possible carbon credits. This contradicts the requirements for the greatest possible accuracy, as stipulated in the International Panel on Climate Change’s (IPCC) and Forest Carbon Partnership Facility’s (FCPF) recommendations for action.

The knowledge of the material properties is a key-aspect to the engineering of reliable products. Such a material property, the permeability towards water and oxygen, is not only of importance for packaging but also for the microelectronic and solar industry. For standard applications with low requirements permeation rates of single permeates can be measured with commercially available instruments. In this publication simultaneous measurements of several permeates are analyzed showing the interdependence of permeation rates of three major permeates (water vapor, oxygen and nitrogen gas) depending on their concentration. Based on these results the measurements of the permeability for single permeates can only be seen as an approximation by ignoring competitive effects of different permeates as found for most application environments.

We coherently manipulate spin correlations in a two-component atomic Fermi gas loaded into an optical lattice using spatially and time-resolved Ramsey spectroscopy combined with high-resolution \textit{in situ} imaging. This novel technique allows us not only to imprint spin patterns but also to probe the static magnetic structure factor at arbitrary wave vector, in particular the staggered structure factor. From a measurement along the diagonal of the $1^\mathrm{st}$ Brillouin zone of the optical lattice, we determine the magnetic correlation length and the individual spatial spin correlators. At half filling, the staggered magnetic structure factor serves as a sensitive thermometer for the spin temperature, which we employ to study the thermalization of spin and density degrees of freedom during a slow quench of the lattice depth.

We measure entropy and short-range correlations of ultracold fermionic atoms in an optical lattice for a range of interaction strengths, temperatures, and fillings. In particular, we extract the mutual information between a single lattice site and the rest of the system from a comparison between the reduced density matrix of a single lattice site and the thermodynamic entropy. Moreover, we determine the single-particle density matrix between nearest neighbors from thermodynamic observables and show that even in a strongly interacting Mott insulator fermions are significantly delocalized over short distances in the lattice.

A simple experimental setup for temperature dependent mass spectrometric measurements has been constructed. It consists of a heated sample chamber and a mass spectrometer and allows for measurements under inert gas and ambient air. Based on initial measurements on two extruded polystyrene (XPS) samples a methodology for the data analysis has been developed. With this methodology the outgassing temperature of volatile compounds, which were used as blowing agents, has been identified. Furthermore, the composition of the blowing agents has been analyzed by temperature dependent mass spectra. The results indicate the use of ambient air in one material and a mixture of the banned blowing agents R142b and R22, both hydrochlorofluorocarbons (HCFC), in the other material. The here described methodology provides an easy to use approach to identify such compounds, for example as part of environmental or quality control.

The world’s forests play a pivotal role in the mitigation of global climate change. By photosynthesis they remove CO2 from the atmosphere and store carbon in their biomass. While old trees are generally acknowledged for a long carbon residence time, there is no consensus on their contribution to carbon accumulation due to a lack of long-term individual tree data. Tree ring analyses, which use anatomical differences in the annual formation of wood for dating growth zones, are a retrospective approach that provides growth patterns of individual trees over their entire lifetime. We developed time series of diameter growth and related annual carbon accumulation for 61 trees of the species Cedrela odorata L. (Meliacea), Hymenaea courbaril L. (Fabacea) and Goupia glabra Aubl. (Goupiacea). The trees grew in unmanaged tropical wet-forests of Suriname and reached ages from 84 to 255 years. Most of the trees show positive trends of diameter growth and carbon accumulation over time. For some trees we observed fluctuating growth—periods of lower growth alternate with periods of increased growth. In the last quarter of their lifetime trees accumulate on average between 39 percent (C. odorata) and 50 percent (G. glabra) of their final carbon stock. This suggests that old-growth trees in tropical forests do not only contribute to carbon stocks by long carbon resistance times, but maintain high rates of carbon accumulation at later stages of their life time.

We study a dispersion-compensated high-finesse optical Fabry-Perot microcavity under high-intensity cw pumping. The Kerr non-linearity in the optical coatings causes a spontaneous four-wave mixing process, which leads to the emission of time-correlated photon pairs. The photon frequencies are shifted by $\pm 1$ free spectral range relative to the pump frequency. This setup allows for constructing a photon-pair source with precisely adjustable frequency difference between the emitted photons, which may have applications in quantum communication., Comment: accepted for publication in PRA

Near zero temperature, quantum magnetism can non-trivially arise from short-range interactions, but the occurrence of magnetic order depends crucially on the interplay of interactions, lattice geometry, dimensionality and doping. Even though the consequences of this interplay are not yet fully understood, quantum magnetism is believed to be connected to a range of complex phenomena in the solid state, for example, in the context of high-$T_c$ superconductivity and spin liquids in frustrated lattices. Ultracold atomic Fermi gases in optical lattices constitute an experimental system with unrivalled tunability and detection capabilities to explore quantum magnetism by analog quantum simulation. In this work, we study the emergence of antiferromagnetic correlations between ultracold fermionic atoms in two dimensions with decreasing temperature. We determine the magnetic susceptibility of the Hubbard model from simultaneous measurements of the in-situ density of both spin components. At half-filling and strong interactions our data approach the Heisenberg model of localized spins with antiferromagnetic correlations. Moreover, we observe the disappearance of magnetic correlations when the system is doped away from half-filling. Our observation of the dependence of quantum magnetism on doping paves the way for future studies on the emergence of pseudogap and pairing phenomena away from half-filling., 7 pages, 4 figures

We study the behavior of a single laser-driven trapped ion inside a microscopic optical Fabry-Perot cavity. In particular, we demonstrate a fiber Fabry-Perot cavity operating on the principal ${S}_{1/2}\ensuremath{\rightarrow}{P}_{1/2}$ electric dipole transition of an ${\mathrm{Yb}}^{+}$ ion at 369 nm with an ion-cavity coupling strength of $g=2\ensuremath{\pi}\ifmmode\times\else\texttimes\fi{}67(1)$ MHz. We employ the cavity to study the generation of single photons and observe cavity-induced backaction in the Purcell-enhanced emission of photons. Tuning of the amplitude and phase between the driving field and the cavity field built up from photons scattered into the cavity mode by the ion allows us to enhance or suppress the total rate of photon emission from the ion-cavity system.

The effects of elevated CO2 and interaction effects between elevated CO2 and nutrient supplies on growth and the C/N ratio of European beech (Fagus sylvatica L.) saplings were studied. One-year-old beech saplings were grown in a greenhouse at ambient (385 ppm) and elevated CO2 (770 ppm/950 ppm), with or without fertilization for two growing seasons. In this study, emphasis is placed on the combined fertilization including phosphorus, potassium and nitrogen with two level of elevated CO2. The fertilized plants grown under elevated CO2 had the highest net leaf photosynthesis rate (Ac). The saplings grown under elevated CO2 had a significantly lower stomatal conductance (gs) than saplings grown under ambient air. No interaction effect was found between elevated CO2 and fertilization on Ac. A interaction effect between CO2 and fertilization, as well as between date and fertilization and between date and CO2 was detected on gs. Leaf chlorophyll content index (CCI) and leaf nitrogen content were strongly positively correlated to each other and both of them decreased under elevated CO2. At the end of both growing seasons, stem dry weight was greater under elevated CO2 and root dry weight was not affected by different treatments. No interaction effect was detected between elevated CO2 and nutrient supplies on the dry weight of different plant tissues (stems and roots). However, elevated CO2 caused a significant decrease in the nitrogen content of plant tissues. Nitrogen reduction in the leaves under elevated CO2 was about 10% and distinctly higher than in the stem and root. The interaction effect of elevated CO2 and fertilization on C/N ratio in plants tissues was significant. The results led to the conclusion that photosynthesis and the C/N ratio increased while stomatal conductance and leaf nitrogen content decreased under elevated CO2 and nutrient-limited conditions. In general, under nutrient-limited conditions, the plant responses to elevated CO2 were decreased.

We experimentally demonstrate coupling of an atomically thin, free-standing graphene membrane to an optical cavity. By changing the position of the membrane along the standing-wave field of the cavity, we tailor the dissipative coupling between the membrane and the cavity, and we show that the dissipative coupling can outweigh the dispersive coupling. Such a system, for which controlled dissipation prevails dispersion, will prove useful for novel laser-cooling schemes in optomechanics. In addition, we have determined the continuous-wave optical damage threshold of free-standing monolayer graphene of \( 1.8(4)\kern3.33333pt \mathrm{MW}/{\mathrm{cm}}^2 \) at 780 nm.

Understanding the phases of strongly correlated quantum matter is challenging because they arise from the subtle interplay between kinetic energy, interactions, and dimensionality. In this quest it has turned out that even conceptually simple models of strongly correlated fermions, which often only approximately represent the physics of the solid state, are very hard to solve. Since the conjecture by P. W. Anderson that the two-dimensional Hubbard model describes the main features of high-T$_c$ superconductivity in the cuprates, there has been a major, yet inconclusive, research effort on determining its fundamental thermodynamic properties. Here we present an experimental determination of the equation of state of the repulsive two-dimensional Hubbard model over a broad range of interactions, $0\leq U/t \lesssim 20$, and temperatures, down to $k_BT/t=0.63(2)$, using high-resolution imaging of ultracold atoms in optical lattices. The equation of state fully characterizes the thermodynamics of the Hubbard model, and our results constitute benchmarks for state-of-the-art theoretical approaches., Comment: 8 pages, 4 figures

Background The focus of REDD+ is sensu stricto on maintaining forest carbon stocks. We extend the scope of sustainable management of forest from forests to timber utilization, and study carbon offsets resulting from the utilization of harvested timber for bio energy or harvested wood products (HWPs). The emission budget of harvesting operations depends on the loss of standing biomass by timber extracted from the forest site and logging losses on the one side, and on the other on the wood end use and the utilization of processing residues. We develop two scenarios to quantify the magnitude of CO2 emissions by (1) energetic utilization, and (2) energetic and material utilization of harvested timber and compare the substitution effects for different fossil energy sources. Results The direct energetic use of harvested timber does not compensate for the losses of forest carbon stock. Logging residuals and displacement factors reflecting different wood use constitute by far the most important factor in potential emission reductions. Substitution effects resulting from energetic use of mill residuals and from HWPs have only a subordinated contribution to the total emissions as well as the type of fossil fuel utilized to quantify substitution effects. Material substitution effects associated with harvested wood products show a high potential to increase the climate change benefits. Conclusions The observation and perception of REDD+ should not be restricted to sustainable management and reduced impact logging practices in the forest domain but should be extended to the utilization of extracted timber. Substitution effects from material and energetic utilization of harvested timber result in considerable emission reductions, which can compensate for the loss of forest carbon, and eventually contribute to the overall climate change mitigation benefits from forestry sector.

The crossover between a metal and a Mott insulator leads to a localization of fermions from delocalized Bloch states to localized states. We experimentally study this crossover using fermionic atoms in an optical lattice by measuring thermodynamic and local (on-site) density correlations. In the metallic phase at incommensurable filling we observe the violation of the local fluctuation-dissipation theorem indicating that the thermodynamics of the system cannot be characterized by local observables alone. In contrast, in the Mott insulator we observe the convergence of local and thermodynamic fluctuations indicating the absence of long-range density-density correlations.

Injury and death from wildlife attacks often result in people feeling violent resentment and hostility against the wildlife involved and, therefore, may undermine public support for conservation. Although Nepal, with rich biodiversity, is doing well in its conservation efforts, human-wildlife conflicts have been a major challenge in recent years. The lack of detailed information on the spatial and temporal patterns of human-wildlife conflicts at the national level impedes the development of effective conflict mitigation plans. We examined patterns of human injury and death caused by large mammals using data from attack events and their spatiotemporal dimensions collected from a national survey of data available in Nepal over five years (2010–2014). Data were analyzed using logistic regression and chi-square or Fisher's exact tests. The results show that Asiatic elephants and common leopards are most commonly involved in attacks on people in terms of attack frequency and fatalities. Although one-horned rhinoceros and bears had a higher frequency of attacks than Bengal tigers, tigers caused more fatalities than each of these two species. Attacks by elephants peaked in winter and most frequently occurred outside protected areas in human settlements. Leopard attacks occurred almost entirely outside protected areas, and a significantly greater number of attacks occurred in human settlements. Attacks by one-horned rhinoceros and tigers were higher in the winter, mainly in forests inside protected areas; similarly, attacks by bears occurred mostly within protected areas. We found that human settlements are increasingly becoming conflict hotspots, with burgeoning incidents involving elephants and leopards. We conclude that species-specific conservation strategies are urgently needed, particularly for leopards and elephants. The implications of our findings for minimizing conflicts and conserving these imperiled species are discussed.

Reliable information on tree growth is a prerequisite for sustainable forest management (SFM). However, in tropical forests its implementation is often hampered by insufficient knowledge of the growth dynamics of trees. Although tree ring analysis of tropical trees has a long history, its application for SFM has only recently been considered. In the current study, we illustrate both the potentials and limitations of a retrospective growth assessment by tree ring analysis under the prevailing tropical conditions in a Surinamese rain forest. For this purpose, 38 commercial tree species were screened and grouped into three categories according to the visibility of their tree ring boundaries: (I) tree rings absent or indistinct, (II) distinct but partially vague tree rings which enable approximate age estimation, (III) very distinct tree rings. In 22 out of 38 commercial tree species distinct to very distinct tree ring boundaries could be identified. The anatomy of tree ring boundaries was described following Worbes and Fichtler (2010). Four species with distinct growth rings, Cedrela odorata, Hymenaea courbaril, Pithecellobium corymbosum and Goupia glabra, were studied in greater detail. Time-series analysis was used to characterise their radial growth. From the tree ring width, the annual diameter increment and cumulative diameter growth were calculated to find long-term growth patterns. Pithecellobium corymbosum and partially Hymenaea courbaril followed a typical S-shaped growth curve. By contrast, Goupia glabra and Cedrela odorata did not exhibit an age-related decrease of growth, but showed a constant linear growth over their entire life span. If based on more sample trees, such data can provide target-oriented information for improving SFM in tropical forests.

This Letter comprises an experimental and theoretical investigation of the time evolution of a Fermi gas following fast and slow quenches of a one-dimensional optical double-well superlattice potential. We investigate both the local tunneling in the connected double wells and the global dynamics towards a steady state, i.e., a time-independent state. The local observables in the steady state resemble those of a thermal equilibrium state, whereas the global properties indicate a strong nonequilibrium situation.

Experiments with ultracold atomic gases can provide insight into more general phenomena, such as spin transport. A study of spin diffusion in a two-dimensional Fermi gas measured the lowest spin diffusion constant so far, approaching its quantum-limited value. Harnessing spins as information carriers has emerged as an elegant extension to the transport of electrical charges1. The coherence of such spin transport in spintronic circuits is determined by the lifetime of spin excitations and by spin diffusion. Fermionic quantum gases allow the study of spin transport from first principles because interactions can be precisely tailored and the dynamics is on directly observable timescales2,3,4,5,6,7,8,9,10,11,12. In particular, at unitarity, spin transport is dictated by diffusion and the spin diffusivity is expected to reach a universal, quantum-limited value on the order of the reduced Planck constant ħ divided by the mass m. Here, we study a two-dimensional Fermi gas after a quench into a metastable, transversely polarized state. Using the spin-echo technique13, for strong interactions, we measure the lowest transverse spin diffusion constant14,15 so far 6.3 (8) × 10-3 ħ/m. For weak interactions, we observe a collective transverse spin-wave mode that exhibits mode softening when approaching the strongly interacting regime.

The evaluation of the future dynamics of deforestation is essential to creating the basis for the effective implementation of REDD+ (Reducing Emissions from Deforestation and forest Degradation) initiatives. Such evaluation is often a challenging task, especially for countries that have to cope with a critical lack of data and capacities, higher uncertainties, and competing interests. We present a new modeling approach that makes use of available and easily accessible data sources to predict the spatial location of future deforestation. This approach is based on the Random Forest algorithm, which is a machine learning technique that enables evidence-based, data-driven decisions and is therefore often used in decision-making processes. Our objective is to provide a straightforward modeling approach that, without requiring cost-intensive assessments, can be applied in the early stages of REDD+, for a stepwise implementation approach of REDD+ projects in regions with limited availability of data, capital, technical infrastructure, or human capacities. The presented model focuses on building business-as-usual scenarios to identify and rank potentially suitable areas for REDD+ interventions. For validation purposes we applied the model to data from Nicaragua.

We report on the immersion of a spin qubit encoded in a single trapped ion into a spin-polarized neutral atom environment, which possesses both continuous (motional) and discrete (spin) degrees of freedom. The environment offers the possibility of a precise microscopic description, which allows us to understand dynamics and decoherence from first principles. We observe the spin dynamics of the qubit and measure the decoherence times (T-1 and T-2), which are determined by the spin-exchange interaction as well as by an unexpectedly strong spin-nonconserving coupling mechanism. DOI: 10.1103/PhysRevLett.110.160402

We derive analytical expressions for the frequency and damping of the lowest collective modes of a two-dimensional Fermi gas using kinetic theory. For strong coupling, we furthermore show that pairing correlations overcompensate the effects of Pauli blocking on the collision rate for a large range of temperatures, resulting in a rate which is larger than that of a classical gas. Our results agree well with experimental data, and they recover the observed cross-over from collisionless to hydrodynamic behaviour with increasing coupling for the quadruple mode. Finally, we show that a trap anisotropy within the experimental bounds results in a damping of the breathing mode which is comparable to what is observed, even for a scale invariant system., Comment: 8 pages, 3 figures (published version)

The control of chemical reactions is a recurring theme in physics and chemistry. Traditionally, chemical reactions have been investigated by tuning thermodynamic parameters, such as temperature or pressure. More recently, physical methods such as laser or magnetic field control have emerged to provide completely new experimental possibilities, in particular in the realm of cold collisions. The control of reaction pathways is also a critical component to implement molecular quantum information processing. For these undertakings, single particles provide a clean and well-controlled experimental system. Here, we report on the experimental tuning of the exchange reaction rates of a single trapped ion with ultracold neutral atoms by exerting control over both their quantum states. We observe the influence of the hyperfine interaction on chemical reaction rates and branching ratios, and monitor the kinematics of the reaction products. These investigations advance chemistry with single trapped particles towards achieving quantum-limited control of chemical reactions and indicate limits for buffer gas cooling of single ion clocks.

We realize and study an attractively interacting two-dimensional Fermi liquid. Using momentum-resolved photoemission spectroscopy, we measure the self-energy, determine the contact parameter of the short-range interaction potential, and find their dependence on the interaction strength. We successfully compare the measurements to a theoretical analysis, properly taking into account the finite temperature, harmonic trap, and the averaging over several two-dimensional gases with different peak densities.

In this chapter, we give an introduction to some of the fascinating many-body phenomena occurring in interacting low-dimensional ultracold atomic Bose gases. Low-dimensional quantum systems display significantly different physics from their three-dimensional counterparts, in particular because the increased thermal and quantum fluctuations tend to suppress the true long-range order associated with Bose–Einstein condensation. Specifically, we discuss the cases of 2D Bose gases at nonzero temperature and 1D gases at zero temperature. In both the cases, interactions between particles lead to exotic many-body phases, such as the Berezinskii–Kosterlitz–Thouless superfluid in 2D and the Tonks–Girardeau gas in 1D.

We present the realization of a combined trapped-ion and optical cavity system, in which a single ${\mathrm{Yb}}^{+}$ ion is confined by a micron-scale ion trap inside a $230\text{ }\text{ }\ensuremath{\mu}\mathrm{m}$-long optical fiber cavity. We characterize the spatial ion-cavity coupling and measure the ion-cavity coupling strength using a cavity-stimulated $\ensuremath{\Lambda}$ transition. Owing to the small mode volume of the fiber resonator, the coherent coupling strength between the ion and a single photon exceeds the natural decay rate of the dipole moment. This system can be integrated into ion-photon quantum networks and is a step towards cavity quantum electrodynamics based quantum information processing with trapped ions.

The line shape of radio frequency spectra of tightly bound Feshbach molecules in strong transverse confinement can be described by a simple analytic formula that includes final state interactions. By direct comparison to experimental data, we clarify the role of effective range corrections to two-body bound-state energies in lower dimensions., Comment: 8 pages, published version

We investigate the collective excitations of a harmonically trapped two-dimensional Fermi gas from the collisionless (zero sound) to the hydrodynamic (first sound) regime. The breathing mode, which is sensitive to the equation of state, is observed at a frequency two times the dipole mode frequency for a large range of interaction strengths and temperatures, and the amplitude of the breathing mode is undamped. This provides evidence for a dynamical SO(2,1) scaling symmetry of the two-dimensional Fermi gas. Moreover, we investigate the quadrupole mode to measure the shear viscosity of the two-dimensional gas and study its temperature dependence.

The immersion of a single ion confined by a radiofrequency trap in an ultracold atomic gas extends the concept of buffer gas cooling to a new temperature regime. The steady state energy distribution of the ion is determined by its kinetics in the radiofrequency field rather than the temperature of the buffer gas. Moreover, the finite size of the ultracold gas facilitates the observation of back-action of the ion onto the buffer gas. We numerically investigate the system's properties depending on atom-ion mass ratio, trap geometry, differential cross-section, and non-uniform neutral atom density distribution. Experimental results are well reproduced by our model considering only elastic collisions. We identify excess micromotion to set the typical scale for the ion energy statistics and explore the applicability of the mobility collision cross-section to the ultracold regime., Comment: 10 pages, 6 figures

We perform laser spectroscopy of Yb${}^{+}$ ions on the 4${f}^{14}6s{\phantom{\rule{0.16em}{0ex}}}^{2}\phantom{\rule{-0.16em}{0ex}}{S}_{1/2}$-$4{f}^{13}5d6s$ ${}^{3}\phantom{\rule{-0.16em}{0ex}}D{[3/2]}_{1/2}$ transition at 297 nm. The frequency measurements for ${}^{170}$Yb${}^{+}$, ${}^{172}$Yb${}^{+}$, ${}^{174}$Yb${}^{+}$, and ${}^{176}$Yb${}^{+}$ reveal the specific mass shift as well as the field shifts. In addition, we demonstrate laser cooling of Yb${}^{+}$ ions using this transition and show that light at 297 nm can be used as the second step in the photoionization of neutral Yb atoms.

We study cold heteronuclear atom ion collisions by immersing a trapped single ion into an ultracold atomic cloud. Using ultracold atoms as reaction targets, our measurement is sensitive to elastic collisions with extremely small energy transfer. The observed energy-dependent elastic atom-ion scattering rate deviates significantly from the prediction of Langevin but is in full agreement with the quantum mechanical cross section. Additionally, we characterize inelastic collisions leading to chemical reactions at the single particle level and measure the energy-dependent reaction rate constants. The reaction products are identified by in-trap mass spectrometry, revealing the branching ratio between radiative and non-radiative charge exchange processes.

Improved control of the motional and internal quantum states of ultracold neutral atoms and ions has opened intriguing possibilities for quantum simulation and quantum computation. Many-body effects have been explored with hundreds of thousands of quantum-degenerate neutral atoms, and coherent light-matter interfaces have been built. Systems of single or a few trapped ions have been used to demonstrate universal quantum computing algorithms and to search for variations of fundamental constants in precision atomic clocks. Until now, atomic quantum gases and single trapped ions have been treated separately in experiments. Here we investigate whether they can be advantageously combined into one hybrid system, by exploring the immersion of a single trapped ion into a Bose-Einstein condensate of neutral atoms. We demonstrate independent control over the two components of the hybrid system, study the fundamental interaction processes and observe sympathetic cooling of the single ion by the condensate. Our experiment calls for further research into the possibility of using this technique for the continuous cooling of quantum computers. We also anticipate that it will lead to explorations of entanglement in hybrid quantum systems and to fundamental studies of the decoherence of a single, locally controlled impurity particle coupled to a quantum environment.