Studies on carbon and DNA preservation in allophanic soils and paleosols on Holocene tephras in New Zealand

The recovery of ancient DNA (aDNA) and palaeoenvironmental DNA (PalEnDNA) from soils and sediments has enabled detailed paleontological and ecological records to be obtained. Because of the superior ability of allophanic soils and Andisols to adsorb considerable soil organic matter (SOM), and to slow the rate of carbon turnover in such soils, I hypothesised that environmental DNA can be preserved in allophanic soils and Andisols together with SOM, and that such DNA may be able to help reveal past environments. I characterised the preserved SOM in stratigraphic successions of buried paleosols on Holocene tephras of known age in northern New Zealand and attempted to extract and analyse the DNA to search for possible PalEnDNA. Using synchrotron radiation-based carbon near-edge X-ray absorption fine structure (C NEXAFS) spectroscopy, I found the compositions and proportions of carbon functional groups of SOM in allophanic paleosols on precisely-dated Holocene tephras (c. 12,000 to 1718 calendar [cal] years BP) at four sites in northern New Zealand were similar and dominated by carboxylic functional groups, with subordinate amounts of quinonic, aromatic, and aliphatic groups. Differences in clay and allophane contents, stratigraphic position, age, parenttephra composition (andesitic versus rhyolitic), and mode of soil origin (retardant versus developmental upbuilding pedogenesis) seemed not to affect the structure of SOM over time. The similarity of the SOM in allophanic paleosols of different ages implied its preservation in allophanic soils over a long time, and the presence of quinonic carbon, normally very susceptible to degradation and transformation, shows that the allophanic soils have protected it very effectively. The quinonic carbon in buried horizons is thus indicative of the preservation of biological materials originating from bacteria and plants. The SOM originated through upbuilding pedogenesis: as soil genesis began in a newly-deposited tephra at the soil surface, allophane formed and it sequestered SOM from the modern (surface) organic cycle dominated by inputs from broadleaf-podocarp forest. Ongoing tephra deposition then caused the land surface to rise so that once-surface horizons were buried more deeply and hence became increasingly divorced from the modern organic cycle over time. The SOM adsorbed when the soil horizon was at the land surface was preserved in the buried soils because a fractal pore network of allophane aggregates and nanopores encapsulated and shielded the ‘old’ or relict SOM (including quinonic carbon) derived from past environments of the Holocene. To provide fundamental knowledge about the interaction of allophane, DNA, and SOM in soils, I examined the adsorption capacity and adsorption mechanisms of salmon-sperm DNA on pure synthetic allophane and humic acidrich synthetic allophane. The pure synthetic allophane was able to adsorb up to 34 μg/mg of salmon-sperm DNA, but the humic acid-rich synthetic allophane adsorbed only 3.5 μg/mg of salmon-sperm DNA. Salmon-sperm DNA was adsorbed chemically through its phosphate group to the aluminol groups of synthetic allophane, and adsorbed chemically through humic acid covering the synthetic allophane spherules, and thus became bound indirectly to synthetic allophane. The chemical adsorption of salmon-sperm DNA on synthetic allophane led to the aggregation of allophane spherules to form nanoaggregates and microaggregates, and ~80% of total adsorbed DNA on allophane was held physically within the interstices (pores) between allophane spherules and nanoaggregates. The encapsulated DNA within the stable allophane-DNA aggregates may not be accessible to enzymes nor microbes, hence enabling DNA protection and preservation in allophanic soils. By implication, organic carbon is therefore likely to be sequestered and protected in allophanic soils (Andisols) in the same way as demonstrated here for DNA − that is, predominantly by encapsulation within a tortuous network of nanopores and submicropores amidst stable nanoaggregates and microaggregates, rather than by chemisorption alone. A novel two-step method was developed to isolate DNA from allophane, based in part on experiments devised to extract salmon-sperm DNA from synthetic allophane. The two-step method for DNA extraction from allophanic soils is based on (1) chelating DNA and blocking adsorptive sites on allophane using EDTA and phosphate, respectively, and (2) dissolving allophane using acidified ammonium oxalate. The DNA yield from three allophanic paleosols on Holocene tephras was up to 44.5 μg/g soil (oven-dry basis). The extracted DNA was then successfully purified via gel electrophoresis followed by a gel purification kit, and the amplifiable and sequenced DNA extracted from a paleosol (which had been at the land surface for around 4000 years between c. 9423 and c. 5526 calendar years BP) on Rotoma tephra contained New Zealand endemic and exotic plants that differed from the European grasses growing currently on the land surface. The difference in vegetation indicates that the DNA extraction method I (with others) have developed is able to access environmental DNA originating from previous vegetation cover. The DNA extraction method could be used to facilitate the search for possible PalEnDNA in allophanic paleosols for reconstructing the past terrestrial environments as well as to investigate the biodiversity in allophanic soils and the origins of SOM. Allophanic soils are demonstrably able to protect environmental DNA from degradation for a long period of time, and such DNA is able to reveal past environments. However, the duration over which that environmental DNA can be preserved in allophanic soils needs to be resolved, and additional investigations of gene diversity in allophanic paleosols of different ages using high-throughput sequencing (HTS) are required to determine the taxonomic profiles recovered in paleosols and to rule out contamination of modern DNA

Evaluating the character and preservation of DNA within allophane clusters in buried soils on Holocene tephras, northern New Zealand

Clay minerals possess sorptive capacities for organic and inorganic matter, including DNA (Lorenz and Wackernagel, 1994), and hence reduce the utilization and degradation of organic matter or DNA by microorganisms. Buried allophane-rich soils on tephras (volcanic-ash beds) on the North Island, dated using tephrochronology, provide a valuable paleobiological ‘laboratory’ for studying the preservation of ancient DNA (aDNA) (Haile et al., 2007). Allophane comprises Al-rich nanocrystalline spherules ~3.5-5 nm in diameter (Fig. 1) with extremely large surface areas (up to 1000 m2 g-1). Moreover, allophanic soils are strongly associated with organic matter (Parfitt, 2009), and so we hypothesize that allophane also plays an important role for DNA protection within such soils

Customized Virtual Assistant Invocation Based on Device Orientation and Mode

Hotword-less virtual assistant interaction, referred to as look-to-talk, can be triggered when the user is within a certain distance from a device that provides the virtual assistant and looks at the device. With user permission, machine learning (ML) models analyze real-time video, audio, and text to determine if a given user utterance is intended as an instruction to the virtual assistant or an utterance directed to someone else in the room. This disclosure describes look-to-talk functionality that is applicable to not only stationary devices, but also mobile devices such as smartphones or tablets. The techniques detect changes in device orientation or mode to trigger look-to-talk functionality. In recognition of the fact that sensor data captured by a stationary device can be different that that captured by a mobile device, look-to-talk parameters and ML models are adapted to the device orientation and mode

Ventricular divergence correlates with epicardial wavebreaks and predicts ventricular arrhythmia in isolated rabbit hearts during therapeutic hypothermia

INTRODUCTION: High beat-to-beat morphological variation (divergence) on the ventricular electrogram during programmed ventricular stimulation (PVS) is associated with increased risk of ventricular fibrillation (VF), with unclear mechanisms. We hypothesized that ventricular divergence is associated with epicardial wavebreaks during PVS, and that it predicts VF occurrence. METHOD AND RESULTS: Langendorff-perfused rabbit hearts (n = 10) underwent 30-min therapeutic hypothermia (TH, 30°C), followed by a 20-min treatment with rotigaptide (300 nM), a gap junction modifier. VF inducibility was tested using burst ventricular pacing at the shortest pacing cycle length achieving 1:1 ventricular capture. Pseudo-ECG (p-ECG) and epicardial activation maps were simultaneously recorded for divergence and wavebreaks analysis, respectively. A total of 112 optical and p-ECG recordings (62 at TH, 50 at TH treated with rotigaptide) were analyzed. Adding rotigaptide reduced ventricular divergence, from 0.13±0.10 at TH to 0.09±0.07 (p = 0.018). Similarly, rotigaptide reduced the number of epicardial wavebreaks, from 0.59±0.73 at TH to 0.30±0.49 (p = 0.036). VF inducibility decreased, from 48±31% at TH to 22±32% after rotigaptide infusion (p = 0.032). Linear regression models showed that ventricular divergence correlated with epicardial wavebreaks during TH (p<0.001). CONCLUSION: Ventricular divergence correlated with, and might be predictive of epicardial wavebreaks during PVS at TH. Rotigaptide decreased both the ventricular divergence and epicardial wavebreaks, and reduced the probability of pacing-induced VF during TH

Siren's Song in the AI Ocean: A Survey on Hallucination in Large Language Models

While large language models (LLMs) have demonstrated remarkable capabilities across a range of downstream tasks, a significant concern revolves around their propensity to exhibit hallucinations: LLMs occasionally generate content that diverges from the user input, contradicts previously generated context, or misaligns with established world knowledge. This phenomenon poses a substantial challenge to the reliability of LLMs in real-world scenarios. In this paper, we survey recent efforts on the detection, explanation, and mitigation of hallucination, with an emphasis on the unique challenges posed by LLMs. We present taxonomies of the LLM hallucination phenomena and evaluation benchmarks, analyze existing approaches aiming at mitigating LLM hallucination, and discuss potential directions for future research.Comment: work in progress; 32 page

Electronic states of disordered grain boundaries in graphene prepared by chemical vapor deposition

Perturbations of the two dimensional carbon lattice of graphene, such as grain boundaries, have significant influence on the charge transport and mechanical properties of this material. Scanning tunneling microscopy measurements presented here show that localized states near the Dirac point dominate the local density of states of grain boundaries in graphene grown by chemical vapor deposition. Such low energy states are not reproduced by theoretical models which treat the grain boundaries as periodic dislocation-cores composed of pentagonal-heptagonal carbon rings. Using ab initio calculations, we have extended this model to include disorder, by introducing vacancies into a grain boundary consisting of periodic dislocation-cores. Within the framework of this model we were able to reproduce the measured density of states features. We present evidence that grain boundaries in graphene grown on copper incorporate a significant amount of disorder in the form of two-coordinated carbon atoms. © 2013 Elsevier Ltd. All rights reserved

Characterizing porous microaggregates and soil organic matter sequestered in allophanic paleosols on Holocene tephras using synchrotron-based X-ray microscopy and spectroscopy

Allophanic tephra-derived soils can sequester sizable quantities of soil organic matter (SOM). However, no studies have visualized the fine internal porous structure of allophanic soil microaggregates, nor studied the carbon structure preserved in such soils or paleosols. We used synchrotron radiation-based transmission X-ray microscopy (TXM) to perform 3D-tomography of the internal porous structure of dominantly allophanic soil microaggregates, and carbon near-edge X-ray absorption fine-structure (C NEXAFS) spectroscopy to characterize SOM in ≤ 12,000-year-old tephra-derived allophane-rich (with minor ferrihydrite) paleosols. The TXM tomography showed a vast network of internal, tortuous nano-pores within an allophanic microaggregate comprising nanoaggregates. SOM in the allophanic paleosols at four sites was dominated by carboxylic/carbonyl functional groups with subordinate quinonic, aromatic, and aliphatic groups. All samples exhibited similar compositions despite differences between the sites. That the SOM does not comprise specific types of functional groups through time implies that the functional groups are relict. The SOM originated at the land/soil surface: ongoing tephra deposition (intermittently or abruptly) then caused the land-surface to rise so that the once-surface horizons were buried more deeply and hence became increasingly isolated from inputs by the surficial/modern organic cycle. The presence of quinonic carbon, from biological processes but vulnerable to oxygen and light, indicates the exceptional protection of SOM and bio-signals in allophanic paleosols, attributable both to the porous allophane (with ferrihydrite) aggregates that occlude the relict SOM from degradation, and to rapid burial by successive tephra-fallout, as well as strong Al-organic chemical bonding. TXM and C NEXAFS spectroscopy help to unravel the fine structure of soils and SOM and are of great potential for soil science studies

DNA adsorption by nanocrystalline allophane spherules and nanoaggregates, and implications for carbon sequestration in Andisols

This study provides fundamental knowledge about the interaction of allophane, deoxyribonucleic acid (DNA), and organic matter in soils, and how allophane sequesters DNA. The adsorption capacities of salmon-sperm DNA on pure synthetic allophane (characterised morphologically and chemically) and on humic-acid-rich synthetic allophane were determined, and the resultant DNA–allophane complexes were characterised using synchrotron-radiation-derived P X-ray absorption near-edge fine structure (XANES) spectroscopy and infrared (IR) spectroscopy. The synthetic allophane adsorbed up to 34 μg mg⁻¹ of salmon-sperm DNA. However, the presence of humic acid significantly lowered the DNA uptake on the synthetic allophane to 3.5 μg mg⁻¹ by occupying the active sites on allophane so that DNA was repulsed. Both allophane and humic acid adsorbed DNA chemically through its phosphate groups. IR spectra for the allophane–DNA complex showed a chemical change of the Si–O–Al stretching of allophane after DNA adsorption, possibly because of the alteration of the steric distance of the allophane outer wall, or because of the precipitation of aluminium phosphate on allophane after DNA adsorption on it, or both. The aluminol groups of synthetic allophane almost completely reacted with additions of small amounts of DNA (~ 2–6 μg mg⁻¹ ), but the chemical adsorption of DNA on allophane simultaneously led to the formation of very porous allophane aggregates up to ~ 500 μm in diameter. The formation of the allophane nano- and microaggregates enabled up to 28 μg mg⁻¹ of DNA to be adsorbed (~ 80% of total) within spaces (pores) between allophane spherules and allophane nanoaggregates (as “physical adsorption”), giving a total of 34 μg mg⁻¹ of DNA adsorbed by the allophane. The stability of the allophane–DNA nano- and microaggregates likely prevents encapsulated DNA from exposure to oxidants, and DNA within small pores between allophane spherules and nanoaggregates may not be accessible to enzymes or microbes, hence enabling DNA protection and preservation in such materials. By implication, substantial organic carbon is therefore likely to be sequestered and protected in allophanic soils (Andisols) in the same way as demonstrated here for DNA, that is, predominantly by encapsulation within a tortuous network of nanopores and submicropores amidst stable nanoaggregates and microaggregates, rather than by chemisorption alone

A new method to extract and purify DNA from allophanic soils and paleosols, and potential for paleoenvironmental reconstruction and other applications

Andisols, developed from late-Quaternary tephra (volcanic ash) deposits and dominated by the nanocrystalline aluminosilicate, allophane, contain large stores of organic matter and are potential reservoirs for DNA. However, DNA recovery from Andisols and other allophane-bearing soils has been difficult and inefficient because of strong chemical bonding between DNA and both allophane and organic matter, and also because much DNA can be encased and physically protected in nanopores in allophane nano/microaggregates. We have therefore developed a new two-step DNA isolation method for allophanic soils and buried paleosols, including those low in clay, which circumvents these problems. The method centres on (1) releasing mainly microbial DNA, and extracellular (unbound) DNA, using an alkaline phosphate buffer (“Rai’s lysis buffer”) that blocks re-adsorption sites on the allophanic materials, and (2) the novel application of acidified ammonium oxalate (Tamm’s reagent) to dissolve the allophane and to release DNA which had been chemically-bound and also which had been protected within nanopores. Ammonium oxalate has not previously been applied to soil DNA extraction. DNA yields up to 44.5 µg g-1 soil (oven-dry basis) were obtained from three field-moist natural allophanic soil samples from northern New Zealand using this two-step method. Following extraction, we evaluated different DNA purification methods. Gel electrophoresis of the extracted DNA followed by gel purification of the DNA from the agarose gel, despite some DNA loss, was the only purification method that removed sufficient humic material for successful DNA amplification using the polymerase chain reaction (PCR) of multiple gene regions. Sequencing of PCR products obtained from a buried allophanic paleosol at 2.2-m depth on a sandy Holocene tephra yielded endemic and exotic plants that differed from the European grasses growing currently on the soil’s surface. This difference suggests that the DNA extraction method is able to access (paleo)environmental DNA derived from previous vegetation cover. Our DNA extraction and purification method hence may be applied to Andisols and allophane-bearing paleosols, potentially offering a means to isolate paleoenvironmental DNA and thus facilitate reconstruction of past environments in volcanic landscapes, datable using tephrochronology, and also aid biodiversity understanding of andic soils and paleosols

Charge Transport in Polycrystalline Graphene: Challenges and Opportunities

Graphene has attracted significant interest both for exploring fundamental science and for a wide range of technological applications. Chemical vapor deposition (CVD) is currently the only working approach to grow graphene at wafer scale, which is required for industrial applications. Unfortunately, CVD graphene is intrinsically polycrystalline, with pristine graphene grains stitched together by disordered grain boundaries, which can be either a blessing or a curse. On the one hand, grain boundaries are expected to degrade the electrical and mechanical properties of polycrystalline graphene, rendering the material undesirable for many applications. On the other hand, they exhibit an increased chemical reactivity, suggesting their potential application to sensing or as templates for synthesis of one-dimensional materials. Therefore, it is important to gain a deeper understanding of the structure and properties of graphene grain boundaries. Here, we review experimental progress on identification and electrical and chemical characterization of graphene grain boundaries. We use numerical simulations and transport measurements to demonstrate that electrical properties and chemical modification of graphene grain boundaries are strongly correlated. This not only provides guidelines for the improvement of graphene devices, but also opens a new research area of engineering graphene grain boundaries for highly sensitive electrobiochemical devices