Magnetic field sensors using 13-spin cat states

Measurement devices could benefit from entangled correlations to yield a measurement sensitivity approaching the physical Heisenberg limit. Building upon previous magnetometric work using pseudo-entangled spin states in solution-state NMR, we present two conceptual advancements to better prepare and interpret the pseudo-entanglement resource as well as the use of a 13-spin cat state to measure the local magnetic field with a sensitivity beyond the standard quantum limit.Comment: 6 pages, 5 figures; v2: corrected figure 3, expanded conclusion, simplified explanation of equation 2; v3: accepted versio

Naturally p-hydroxybenzoylated lignins in palms

The industrial production of palm oil concurrently generates a substantial amount of empty fruit bunch (EFB) fibers that could be used as a feedstock in a lignocellulose-based biorefinery. Lignin byproducts generated by this process may offer opportunities for the isolation of value-added products, such as p-hydroxybenzoate (pBz), to help offset operating costs. Analysis of the EFB lignin by nuclear magnetic resonance (NMR) spectroscopy clearly revealed the presence of bound acetate and pBz, with saponification revealing that 1.1 wt% of the EFB was pBz; with a lignin content of 22.7 %, 4.8 % of the lignin is pBz that can be obtained as a pure component for use as a chemical feedstock. Analysis of EFB lignin by NMR and derivatization followed by reductive cleavage (DFRC) showed that pBz selectively acylates the γ-hydroxyl group of S units. This selectivity suggests that pBz, analogously with acetate in kenaf, p-coumarate in grasses, and ferulate in a transgenic poplar augmented with a feruloyl-CoA monolignol transferase (FMT), is incorporated into the growing lignin chain via its γ-p-hydroxybenzoylated monolignol conjugate. Involvement of such conjugates in palm lignification is proven by the observation of novel p-hydroxybenzoylated non-resinol β–β-coupled units in the lignins. Together, the data implicate the existence of p-hydroxybenzoyl-CoA:monolignol transferases that are involved in lignification in the various willows (Salix spp.), poplars and aspen (Populus spp., family Salicaceae), and palms (family Arecaceae) that have p-hydroxybenzoylated lignins. Even without enhancing the levels by breeding or genetic engineering, current palm oil EFB ‘wastes’ should be able to generate a sizeable stream of p-hydroxybenzoic acid that offers opportunities for the development of value-added products derived from the oil palm industry

Ultrafast entangling gates between nuclear spins using photo-excited triplet states

The representation of information within the spins of electrons and nuclei has been powerful in the ongoing development of quantum computers. Although nuclear spins are advantageous as quantum bits (qubits) due to their long coherence lifetimes (exceeding seconds), they exhibit very slow spin interactions and have weak polarisation. A coupled electron spin can be used to polarise the nuclear spin and create fast single-qubit gates, however, the permanent presence of electron spins is a source of nuclear decoherence. Here we show how a transient electron spin, arising from the optically excited triplet state of C60, can be used to hyperpolarise, manipulate and measure two nearby nuclear spins. Implementing a scheme which uses the spinor nature of the electron, we performed an entangling gate in hundreds of nanoseconds: five orders of magnitude faster than the liquid-state J coupling. This approach can be widely applied to systems comprising an electron spin coupled to multiple nuclear spins, such as NV centres, while the successful use of a transient electron spin motivates the design of new molecules able to exploit photo-excited triplet states.Comment: 5 pages, 3 figure

Evaluation of individual and ensemble probabilistic forecasts of COVID-19 mortality in the United States

Short-term probabilistic forecasts of the trajectory of the COVID-19 pandemic in the United States have served as a visible and important communication channel between the scientific modeling community and both the general public and decision-makers. Forecasting models provide specific, quantitative, and evaluable predictions that inform short-term decisions such as healthcare staffing needs, school closures, and allocation of medical supplies. Starting in April 2020, the US COVID-19 Forecast Hub (https://covid19forecasthub.org/) collected, disseminated, and synthesized tens of millions of specific predictions from more than 90 different academic, industry, and independent research groups. A multimodel ensemble forecast that combined predictions from dozens of groups every week provided the most consistently accurate probabilistic forecasts of incident deaths due to COVID-19 at the state and national level from April 2020 through October 2021. The performance of 27 individual models that submitted complete forecasts of COVID-19 deaths consistently throughout this year showed high variability in forecast skill across time, geospatial units, and forecast horizons. Two-thirds of the models evaluated showed better accuracy than a naïve baseline model. Forecast accuracy degraded as models made predictions further into the future, with probabilistic error at a 20-wk horizon three to five times larger than when predicting at a 1-wk horizon. This project underscores the role that collaboration and active coordination between governmental public-health agencies, academic modeling teams, and industry partners can play in developing modern modeling capabilities to support local, state, and federal response to outbreaks

The United States COVID-19 Forecast Hub dataset

Academic researchers, government agencies, industry groups, and individuals have produced forecasts at an unprecedented scale during the COVID-19 pandemic. To leverage these forecasts, the United States Centers for Disease Control and Prevention (CDC) partnered with an academic research lab at the University of Massachusetts Amherst to create the US COVID-19 Forecast Hub. Launched in April 2020, the Forecast Hub is a dataset with point and probabilistic forecasts of incident cases, incident hospitalizations, incident deaths, and cumulative deaths due to COVID-19 at county, state, and national, levels in the United States. Included forecasts represent a variety of modeling approaches, data sources, and assumptions regarding the spread of COVID-19. The goal of this dataset is to establish a standardized and comparable set of short-term forecasts from modeling teams. These data can be used to develop ensemble models, communicate forecasts to the public, create visualizations, compare models, and inform policies regarding COVID-19 mitigation. These open-source data are available via download from GitHub, through an online API, and through R packages

Using 2D NMR spectroscopy to assess effects of UV radiation on cell wall chemistry during litter decomposition

Litter chemistry is one of the most studied controls on decomposition in terrestrial ecosystems. Solar radiation has been shown to increase litter decomposition rates in arid ecosystems through the process of photodegradation. However, it remains unclear how photodegradation affects litter chemistry, especially the abundance and composition of lignin, which is thought to play a key role in photodegradation. Using two-dimensional nuclear magnetic resonance (2D NMR) spectroscopic methods, we quantified the molecular-level changes in litter chemistry associated with photodegradation. Litter of Bromus diandrus was exposed in the field to two levels of radiation [with and without ultraviolet (UV) wavelengths] and two durations of exposure (2.5 months during summer, and 1 year). Through fiber analysis by sequential digestion, we found that the litter hemicellulose fraction decreased significantly from 31.6 to 24.9 % after 1 year of decomposition. In litter exposed for 1 year, the hemicellulose fraction was significantly lower in litter with UV exposure compared to litter without UV exposure (23.8 vs. 25.9 %). These results indicate that UV photodegradation has a small but significant effect on litter chemistry compared to other decomposition processes. Even though fiber analysis showed no loss of total lignin, 2D NMR analysis demonstrated that UV exposure reduced the major lignin structural units containing β-aryl ether inter-unit linkages by 9 % and decreased the relative abundance of lignin p-hydroxyphenyl units by 20 %. The 2D NMR analysis also revealed that lignin guaiacyl units were preferentially lost after 1 year of decomposition relative to the reference material, but no effects of UV exposure on guaiacyl units were observed. These results suggest that photodegradation causes partial degradation, not necessarily complete breakdown, of lignin structures. Our data also demonstrate that applications of 2D NMR methods are valuable for acquiring detailed information on lignin and polysaccharide chemistry during both biotic and abiotic decomposition processes

Photolysis of an asymmetrically substituted diazene in solution and in the crystalline state

In this work we study the product distribution in the steady state photolysis of a diazene, (1-biphenyl-4-yl-1-methyl-ethyl)-tert-butyl diazene, and a ketone, 2,4-bis(biphenyl-4-yl)-2,4-dimethyl-pentan-3-one, in the solid state and in solution. The two compounds yield 1-biphenyl-4-yl-1-methyl-ethyl (BME) radicals upon photolysis. The ketone yields two units of this radical, whereas the diazene yields one BME and one tert-butyl radical. Product analysis of the two compounds in solution makes it possible to differentiate their origin from their corresponding geminate cages, and from the different encounter pairs in the case of the asymmetrically substituted diazene photolysis. In this way we obtain a complete reaction scenery for the diazene, a compound with interesting features as a radical photoinitiator and as a cage effect probe in fluid media. The reaction in cages containing two BME radicals shows a decrease by a factor of 4 in the ratio of combination to disproportionation products upon going from the solid to the liquid phase. On the contrary, the reaction in cages containing a BME and a tert-butyl radical shows a 30-fold increase in combination to disproportionation ratio in liquid compared to the crystal. We analyze the reasons for these differences considering the differences in the reactivity of the radicals and in cage rigidity.Fil: Hoijemberg, Pablo Ariel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; ArgentinaFil: Karlen, Steven D.. University of California at Los Angeles; Estados UnidosFil: Sanramé, Carlos Norberto. University of California at Los Angeles; Estados UnidosFil: Aramendia, Pedro Francisco. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; ArgentinaFil: García Garibay, Miguel Angel. University of California at Los Angeles; Estados Unido