Helicity-Preserving Metasurfaces for Magneto-Optical Enhancement in Ferromagnetic [Pt/Co] N Films
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Materials Science↗
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Colossal Terahertz Emission with Ultrafast Tunability Based on Van der Waals Ferroelectric NbOI 2
Abstract Terahertz (THz) technology is critical for quantum material physics, biomedical imaging, ultrafast electronics, and next‐generation wireless communications. However, standing in the way of widespread applications is the scarcity of efficient ultrafast THz sources with on‐demand fast modulation and easy on‐chip integration capability. Here the discovery of colossal THz emission is reported from a van der Waals (vdW) ferroelectric semiconductor NbOI 2 . Using THz emission spectroscopy, a THz generation efficiency an order of magnitude higher than that of ZnTe, a standard nonlinear crystal for ultrafast THz generation is observed. The underlying generation mechanisms associated are further uncovered with its large ferroelectric polarization by studying the THz emission dependence on excitation wavelength, incident polarization, and fluence. Moreover, the ultrafast coherent amplification and annihilation of the THz emission and associated coherent phonon oscillations by employing a double‐pump scheme are demonstrated. These findings combined with first‐principles calculations, inform a new understanding of the THz light–matter interaction in emergent vdW ferroelectrics and pave the way to develop high‐performance THz devices on them for quantum materials sensing and ultrafast electronics.
Subedi, Sujan [Department of Materials Science and↗
Retarded Charge-Carrier Recombination in Photoelectrochemical Cells from Plasmon-Induced Resonance Energy Transfer
N-type metal oxides such as hematite (α-Fe 2 O 3 ) and bismuth vanadate (BiVO 4 ) are promising candidate materials for efficient photoelectrochemical water splitting; however, their short minority carrier diffusion length and restricted carrier lifetime result in undesired rapid charge recombination. In this paper, a 2D arranged globular Au nanosphere (NS) monolayer array with a highly ordered hexagonal hole pattern (hereafter, Au array) is introduced onto the surface of photoanodes comprised of metal oxide films via a facile drying and transfer-printing process. Through plasmon-induced resonance energy transfer, the Au array provides a strong electromagnetic field in the near-surface area of the metal oxide film. The near-field coupling interaction and amplification of the electromagnetic field suppress the charge recombination with long-lived photogenerated holes and simultaneously enhance the light harvesting and charge transfer efficiencies. Consequently, an over 3.3-fold higher photocurrent density at 1.23 V versus reversible hydrogen electrode (RHE) is achieved for the Au array/α-Fe 2 O 3 . Furthermore, the high versatility of this transfer printing of Au arrays is demonstrated by introducing it on the molybdenum-doped BiVO 4 film, resulting in 1.5-fold higher photocurrent density at 1.23 V versus RHE. The tailored metal film design can provide a potential strategy for the versatile application in various light-mediated energy conversion and optoelectronic devices.
2D pattern array↗
Scalable Hyperpolarized MRI Enabled by Ace‐SABRE of [1‐ 13 C]Pyruvate
Abstract Hyperpolarized (HP) MRI using [1– 13 C]pyruvate is emerging as a promising molecular imaging approach. Among hyperpolarization methods, Signal Amplification By Reversible Exchange (SABRE) is attractive because SABRE polarizes the substrates directly in room‐temperature solutions avoiding complex hardware. Most SABRE experiments have historically been performed in methanol, a relatively toxic and difficult‐to‐remove solvent. Here we demonstrate the use of a 80/20 acetone/water (A/W) solvent system (Ace‐SABRE) to provide hyperpolarized [1– 13 C]pyruvate with up to 17% polarization, then implement a solvent processing protocol to achieve injectable solutions retaining 74% of the initial polarization, and lastly we demonstrate HP in vivo spectroscopy and imaging using the Ace‐SABRE platform to showcase metabolic tracking in a hepatocellular carcinoma (HCC) tumor as well as HP‐MRI, both in direct comparison to dissolution dynamic nuclear polarization (d‐DNP) experiments. The Ace‐SABRE technique promises faster adoption of SABRE hyperpolarization in biological experiments, overall lowering the barriers to entry for HP‐NMR and HP‐MRI.
Chemistry↗
Rapid RASER MRI
Conventional Magnetic Resonance Imaging (MRI) relies on high-power Radio-Frequency (RF) pulses to excite nuclear spins and in turn generate NMR signals. These pulses require large high-power RF-amplifiers and cause heat deposition in the tissue, which must be minimized for safety, presenting a growing problem when moving toward ever-higher field MRI. An alternative to RF-pulse excitation is self-excitation of nuclear spins using Radiofrequency Amplification by Stimulated Emission of Radiation (RASER), where the nuclear spins undergo spontaneous transition, without RF excitation, from an over-populated state to a ground state. Here, the feasibility of recording rapid proton RASER MRI images of pyrazine at low concentration (120 mM) with large matrix (128x128 pixels) in as little as 78 ms is demonstrated at 500 MHz (11.7 T). We also recorded a time-series of images using a single bolus hyperpolarized pyrazine highlighting the feasibility of dynamic tracking. Here, the demonstrated approach allows recording MRI scans without transmit-receive electronics of the MRI scanner, which is highly desirable for portable MRI as well as the emerging field of hyperpolarized MRI using, e.g., HP protons, 129 Xe gas or HP 13 C labeled biomolecules as molecular tracers and imaging agents.
MRI↗
Carbon‐13 Hyperpolarization of α‐Ketocarboxylates with Parahydrogen in Reversible Exchange
Abstract Signal Amplification by Reversible Exchange (SABRE) is a relatively simple and fast hyperpolarization technique that has been used to hyperpolarize the α‐ketocarboxylate pyruvate, a central metabolite and the leading hyperpolarized MRI contrast agent. In this work, we show that SABRE can readily be extended to hyperpolarize 13 C nuclei at natural abundance on many other α‐ketocarboxylates. Hyperpolarization is observed and optimized on pyruvate (P 13C =17 %) and 2‐oxobutyrate (P 13C =25 %) with alkyl chains in the R‐group, oxaloacetate (P 13C =11 %) and alpha‐ketoglutarate (P 13C =13 %) with carboxylate moieties in the R group, and phenylpyruvate (P 13C =2 %) and phenylglyoxylate (P 13C =2 %) with phenyl rings in the R‐group. New catalytically active SABRE binding motifs of the substrates to the hyperpolarization transfer catalyst – particularly for oxaloacetate – are observed. We experimentally explore the connection between temperature and exchange rates for all of these SABRE systems and develop a theoretical kinetic model, which is used to fit the hyperpolarization build‐up and decay during SABRE activity.
McBride, Stephen J. [Department of Chemistry North↗
An Improved Design and Versatile New Lamination Fabrication Method for Twin Electrode Thin Layer Cells Utilizing Track‐etch Membranes
Abstract Reported here are laminated membrane electrodes, an improved design and more advantageous method of fabrication for previously reported thin layer cell electrode systems developed on track‐etch membranes. The laminated membrane approach potentially further improves flow resistance by dramatically reducing the surface area to volume ratio, but also produces a cohesive device that can be more readily applied to a broad range of applications. In addition, this new fabrication method was implemented in a scalable, commercial process and resulting product demonstrations indicate that volume manufacturing is feasible. Characterization of laminated membrane electrodes reveal redox cycling amplification factors as high as 30 with linear responses to variable concentrations of redox couple. These performance characteristics are shown to be comparable to similar generator‐collector systems fabricated through much more laborious laboratory methods. This combination of added versatility, cost‐reduced fabrication and exceptional performance clearly reveals unrealized potential of track‐etch membrane approaches and boosts their candidacy as powerful new options for generator‐collector electrode systems.
Hauke, Adam↗
Global hourly land surface air temperature datasets: inter‐comparison and climate change
ABSTRACT The land surface air temperature ( LSAT ) is one of the fundamental parameters to represent heat transfer and to modulate the moisture cycle between land and atmosphere. Here, we quantify the spatiotemporal characteristics of four newly developed hourly temperature products by merging reanalysis with in situ data Climatic Research Unit ( CRU ). Overall, LSATs from different hourly products are consistent with each other, and their differences are generally smaller in magnitude than biases between hourly products and monthly averaged daily maximum and minimum temperature data from CRU . While the true monthly mean (using hourly values) and the monthly mean (of daily maximum and minimum temperatures) and their seasonality [as represented by the (July–January) differences] differ, their trends agree with each other very well. The polar amplification ratio of average temperature trend north of 65°N to that over global land (excluding Greenland and Antarctica) is also similar among different products, with the annual ratio of around 1.7. The ratio in summer (June–August) is always smaller than the annual value for different periods among all products. Based on the probability distribution functions from the monthly anomalies of different variables, the coldest tenth percentile of temperature in each decade overall increases with time, while the warmest tenth percentile does not vary much from 1950–1979, followed by a rapid increase from 1980–2009. These results and additional sensitivity tests suggest that the 4‐h LSAT products can be widely used for climate analysis, model evaluation, and offline land surface modelling from 1948–2009.
Wang, Aihui↗
BCARS Simulated Phantom Dataset for Evaluation of Processing Pipelines
Broadband coherent anti-Stokes Raman scattering (BCARS) microscopy is a powerful label-free biological imaging technique, but the raw signal requires careful processing. The vibrationally resonant (Raman) fingerprint signal is usually small compared with instrumental noise sources and the nonresonant background (NRB) inherent in the BCARS signal. Fortunately, the NRB exhibits a systematic phase relationship with the coherent Raman response, acting as a heterodyne amplifier for the weak fingerprint signal. Due to this heterodyne effect, the Raman response can be recovered quantitatively and invariantly across different instruments, provided the NRB shape is known. Even with heterodyne amplification, the amplitudes of fingerprint signal components are often comparable to system noise. Singular value decomposition (SVD), which utilizes spatial information, is often employed for additional noise filtering. Consequently, finding optimal processing parameters to properly distinguish the NRB and Raman responses and suppress noise in the complex BCARS signal requires a reference system that realistically represents the spectral and spatial properties of BCARS signals obtained from biological samples. We present a digital tissue phantom that meets these criteria as a tool for testing candidate signal processing pipelines. The digital phantom is generated with simulated hyperspectral Raman images having system-specific noise and background characteristics. Here, we analyze phantom datasets with differing background and signal-to-noise conditions to evaluate their impact on the performance of multiple signal processing pipelines. Specifically, we investigate the application of a Butterworth filter-based routine to directly estimate the NRB from the BCARS signal. Additionally, we evaluate a Lorentzian wavelet transform as an alternative to the Hilbert transform for extracting the Raman spectrum from the BCARS signal. While we demonstrate this phantom for BCARS, it can be used for any spectroscopic Raman imaging approach.
Dixon, Jessica Z. [Georgia Institute of Technology↗
Distribution of mercury-cycling genes in the Arctic and equatorial Pacific Oceans and their relationship to mercury speciation
Humans are exposed to potentially harmful amounts of the neurotoxin monomethylmercury (MMHg) through consumption of marine fish and mammals. However, the pathways of MMHg production and bioaccumulation in the ocean remain elusive. In anaerobic environments, inorganic mercury (Hg) can be methylated to MMHg through an enzymatic pathway involving the hgcAB gene cluster. Recently, hgcA-like genes have been discovered in oxygenated marine water, suggesting the hgcAB methylation pathway, or a close analog, may also be relevant in the ocean. Using polymerase chain reaction amplification and shotgun metagenomics, we searched for but did not find the hgcAB gene cluster in Arctic Ocean seawater. However, we detected Hg-cycling genes from the mer operon (including organomercury lyase, merB), and hgcA-like paralogs (i.e., cdhD) in Arctic Ocean metagenomes. Finally, our analysis of Hg biogeochemistry and marine microbial genomics suggests that various microorganisms and metabolisms, and not just the hgcAB pathway, are important for Hg methylation in the ocean.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Isotopic analysis of sub-nanogram neodymium loads using new ATONA™ amplifiers
The long-term gains of the ATONA™ amplifiers are shown to have less than 1 ppm variability. Repeat measurements of the JNdi-1 reference material demonstrate the ability of the ATONA™ amplification technology to make measurements of 143 Nd/ 144 Nd ratios with 23 ppm external reproducibility on 100-pg loads. The effect of increasing integration time on analytical reproducibility is also displayed as increasing integration time from 10 to 30s reduced the external measurement uncertainty from 37 to 23 ppm. These measurements represent an improvement of more than a factor of 3 in external measurement reproducibility relative to previously published 143 Nd/ 144 Nd measurements of 100-pg loads. Furthermore, this new technology will allow for the measurement of smaller samples for precise isotope ratios and open new avenues of research in the geological and nuclear forensic communities.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Long- and short-read sequencing methods discover distinct circular RNA pools in Lotus japonicus
Circular RNAs (circRNAs) are covalently closed single-stranded RNAs, generated through a back-splicing process that links a downstream 5′ site to an upstream 3′ end. The only distinction in the sequence between circRNA and their linear cognate RNA is the back splice junction. Their low abundance and sequence similarity with their linear origin RNA have made the discovery and identification of circRNA challenging. We have identified almost 6000 novel circRNAs from Lotus japonicus leaf tissue using different enrichment, amplification, and sequencing methods as well as alternative bioinformatics pipelines. The different methodologies identified different pools of circRNA with little overlap. We validated circRNA identified by the different methods using reverse transcription polymerase chain reaction and characterized sequence variations using nanopore sequencing. We compared validated circRNA identified in L. japonicus to other plant species and showed conservation of high-confidence circRNA-expressing genes. This is the first identification of L. japonicus circRNA and provides a resource for further characterization of their function in gene regulation. CircRNAs identified in this study originated from genes involved in all biological functions of eukaryotic cells. The comparison of methodologies and technologies to sequence, identify, analyze, and validate circRNA from plant tissues will enable further research to characterize the function and biogenesis of circRNA in L. japonicus.
59 BASIC BIOLOGICAL SCIENCES↗
Delaying the inevitable: tidal disruption in microstate geometries
Microstate geometries in string theory replace the black-hole horizon with a smooth geometric “cap” at the horizon scale. In geometries constructed using superstratum technology, this cap has the somewhat surprising property that induces very large tidal deformations on infalling observers that are far away from it. We find that this large-distance amplification of the tidal effects is also present in horizonless microstate geometries constructed as bubbling solutions, but can be tamed by suitably arranging the bubbles to reduce the strength of some of the gravitational multipole moments. However, despite this taming, these tidal effects still become large at a significant distance from the microstructure. This result suggests that an observer will not fall unharmed into the structure replacing the black hole horizon.
79 ASTRONOMY AND ASTROPHYSICS↗
Early scrambling and capped BTZ geometries
Geodesic probes in certain horizonless microstate geometries experience extreme tidal forces long before reaching the region where these geometries differ significantl from the extremal BTZ black hole. The purpose of this paper is to show that this behavior is a universal feature of all geometries that have a long BTZ throat that terminates in a cap, regardless of the details of this cap. Hence, incoming probes will scramble into the microstate structure before they encounter the region where the charges of the solution are sourced, and the reason for this premature scrambling is the amplification of tiny geometrical deviations by the relativistic speeds of the probes. To illustrate the phenomenon, we construct a new family of smooth horizonless superstratum microstate geometries, dual to D1-D5 CFT states whose momentum charge is carried by excitations on CFT strands of length k. We also show that, in the large-k limit, these new superstrata resemble a blackened supertube solution everywhere except in the near-supertube region. Thus they resolve the singularity caused by the naive back-reaction of modes with non-linear instabilities near evanescent ergosurfaces.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Low-diffusion Xe-He gas mixtures for rare-event detection: electroluminescence yield
High pressure xenon Time Projection Chambers (TPC) based on secondary scintillation (electroluminescence) signal amplification are being proposed for rare event detection such as directional dark matter, double electron capture and double beta decay detection. The discrimination of the rare event through the topological signature of primary ionisation trails is a major asset for this type of TPC when compared to single liquid or double-phase TPCs, limited mainly by the high electron diffusion in pure xenon. Helium admixtures with xenon can be an attractive solution to reduce the electron diffusion significantly, improving the discrimination efficiency of these optical TPCs. We have measured the electroluminescence (EL) yield of Xe-He mixtures, in the range of 0 to 30% He and demonstrated the small impact on the EL yield of the addition of helium to pure xenon. For a typical reduced electric field of 2.5 kV/cm/bar in the scintillation region, the EL yield is lowered by ~ 2%, 3%, 6% and 10% for 10%, 15%, 20% and 30% of helium concentration, respectively. This decrease is less than what has been obtained from the most recent simulation framework in the literature. The impact of the addition of helium on EL statistical fluctuations is negligible, within the experimental uncertainties. The present results are an important benchmark for the simulation tools to be applied to future optical TPCs based on Xe-He mixtures.
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
A modern approach to superradiance
In this paper, we provide a simple and modern discussion of rotational super-radiance based on quantum field theory. We work with an effective theory valid at scales much larger than the size of the spinning object responsible for superradiance. Within this framework, the probability of absorption by an object at rest completely determines the superradiant amplification rate when that same object is spinning. We first discuss in detail superradiant scattering of spin 0 particles with orbital angular momentum ℓ = 1, and then extend our analysis to higher values of orbital angular momentum and spin. Along the way, we provide a simple derivation of vacuum friction — a ''quantum torque'' acting on spinning objects in empty space. Our results apply not only to black holes but to arbitrary spinning objects. We also discuss superradiant instability due to formation of bound states and, as an illustration, we calculate the instability rate Γ for bound states with massive spin 1 particles. For a black hole with mass M and angular velocity Ω, we find Γ ~ (GMμ) 7 Ω when the particle’s Compton wavelength 1/μ is much greater than the size GM of the spinning object. This rate is parametrically much larger than the instability rate for spin 0 particles, which scales like (GM μ) 9 Ω. This enhanced instability rate can be used to constrain the existence of ultralight particles beyond the Standard Model.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗