5632 research outputs found
Sort by
Heterometallic uranium/molybdenum nitride synthesis via partial N-atom transfer
No full textThe reaction of a Mo(ii) terminal nitride with U(iii) generates the first example of a transition metal capped uranium nitride. The nitride is triply bonded to U(v) and singly bonded to Mo(0) with a U–Mo interaction and reacts with CO to yield cyanate
Integrated nonlinear photonics: new opportunities in the nanometer and femtosecond scales
No full textEvident from more than 50 years of table-top nonlinear optics, utilizing strong quadratic nonlinearities in integrated photonics can significantly expand the potentials of photonics for applications ranging from sensing to computing. In the past few years, nanophotonic lithium niobate (LN) has emerged as one of the most promising integrated photonic platforms with strong quadratic nonlinearity. In this talk we present some of our recent experimental results on realization and utilizing of dispersion-engineered and quasi-phase-matched devices in nanophotonic LN for intense optical parametric amplification, ultrafast ultra-low-energy all-optical switching, and ultra-low-energy broadband sources in the mid-infrared. We also present some recent experimental and numerical results on how resonators with only strong quadratic nonlinearities exhibit phase transitions in the spectral domain, and pulse compression. We show a path for realization of such nonlinear resonators at the wavelength-scale and discuss how networks of such resonators can lead to topological and non-Hermitian dynamics in the classical and quantum regimes
Foundry-fabricated grating coupler demultiplexer inverse-designed via fast integral methods
No full textSilicon photonics is an emerging technology which, enabling nanoscale manipulation of light on chips, impacts areas as diverse as communications, computing, and sensing. Wavelength division multiplexing is commonly used to maximize throughput over a single optical channel by modulating multiple data streams on different wavelengths concurrently. Traditionally, wavelength (de)multiplexers are implemented as monolithic devices, separate from the grating coupler, used to couple light into the chip. This paper describes the design and measurement of a grating coupler demultiplexer—a single device which combines both light coupling and demultiplexing capabilities. The device was designed by means of a custom inverse design algorithm which leverages boundary integral Maxwell solvers of extremely rapid convergence as the mesh is refined. To the best of our knowledge, the fabricated device enjoys the lowest insertion loss reported for grating demultiplexers, small size, high splitting ratio, and low coupling-efficiency imbalance between ports, while meeting the fabricability constraints of a standard UV lithography process
DNA–Carbon Nanotube Binding Mode Determines the Efficiency of Carbon Nanotube-Mediated DNA Delivery to Intact Plants
No full textEfficient delivery of DNA, RNA, and genome engineering machinery to plant cells will enable efforts to genetically modify plants for global food security, sustainable energy production, synthetic biology applications, and climate change resilience. For the delivery of functional genetic units into plant cells, nanoparticles, particularly carbon nanotubes (CNTs), have attracted considerable interest. Although some success has been achieved using CNT-based approaches, the efficiency and practicality of the method for genome editing applications remain elusive. This is partly due to insufficient knowledge about the mechanisms of CNT-mediated delivery and expression of CNT-condensed DNA in plants. Here, we characterize the transcription and transformation efficiency of DNA deposited on CNTs coated with positively charged polymers by applying multiple experimental settings and reporter systems controlling the delivery and expression of DNA in plants. We found that the formation of partially condensed DNA on the CNT surface is a prerequisite for transfection and expression. In addition, we show that DNA irreversibly binds to the CNT and does not detach completely from the CNT surface. These results, together with an in vitro transcription assay, suggest that only the partially condensed part of the DNA is accessible to the cellular transcription machinery. Thus, the overall transcription and translation efficiency remains low, in particular for the large DNA units that are required for genome editing applications. Understanding the underlying mechanisms and limitations of CNT-mediated delivery of DNA through the plant cell wall is of considerable importance in guiding efforts to design nanomaterials for efficient transformation, agricultural trait engineering, and synthetic biology applications
Quantum entanglement in the Sachdev-Ye-Kitaev Model and its generalizations
No full textEntanglement is one of the most important concepts in quantum physics. We review recent progress in understanding the quantum entanglement in many-body systems using large-N solvable models: the Sachdev—Ye—Kitaev (SYK) model and its generalizations. We present the study of entanglement entropy in the original SYK model using three different approaches: the exact diagonalization, the eigenstate thermalization hypothesis, and the path-integral representation. For coupled SYK models, the entanglement entropy shows linear growth and saturation at the thermal value. The saturation is related to replica wormholes in gravity. Finally, we consider the steady-state entanglement entropy of quantum many-body systems under repeated measurements. The traditional symmetry breaking in the enlarged replica space leads to the measurement-induced entanglement phase transition
Slantwise Convection in the Irminger Sea
No full textThe subpolar North Atlantic is a site of significant carbon dioxide, oxygen, and heat exchange with the atmosphere. This exchange, which regulates transient climate change and prevents large-scale hypoxia throughout the North Atlantic, is thought to be mediated by vertical mixing in the ocean's surface mixed layer. Here we present observational evidence that waters deeper than the conventionally defined mixed layer are affected directly by atmospheric forcing in this region. When northerly winds blow along the Irminger Sea's western boundary current, the Ekman response pushes denser water over lighter water, potentially triggering slantwise convection. We estimate that this down-front wind forcing is four times stronger than air–sea heat flux buoyancy forcing and can mix waters to several times the conventionally defined mixed layer depth. Slantwise convection is not included in most large-scale ocean models, which likely limits their ability to accurately represent subpolar water mass transformations and deep ocean ventilation
Realistic HI scale heights of Milky Way-mass galaxies in the FIREbox cosmological volume
No full textAccurately reproducing the thin cold gas discs observed in nearby spiral galaxies has been a long standing issue in cosmological simulations. Here, we present measurements of the radially resolved HI scale height in 22 non-interacting Milky Way-mass galaxies from the FIREbox cosmological volume. We measure the HI scale heights using five different approaches commonly used in the literature: fitting the vertical volume density distribution with a Gaussian, the distance between maximum and half-maximum of the vertical volume density distribution, a semi-empirical description using the velocity dispersion and the galactic gravitational potential, the analytic assumption of hydrostatic equilibrium, and the distance from the midplane which encloses ≳60 per cent of the HI mass. We find median HI scale heights, measured using the vertical volume distribution, that range from ~100 pc in the galactic centres to ~800 pc in the outskirts and are in excellent agreement with recent observational results. We speculate that the presence of a realistic multiphase interstellar medium, including cold gas, and realistic stellar feedback are the drivers behind the realistic HI scale heights
A Semi-automatic Indexing Pipeline for Medical Document Retrieval in Resource-constrained Settings
No full textMedical document indexing can benefit from both automation and human feedback. This research develops a semi-automatic indexing pipeline (SIP) for medical document retrieval in resource-constrained settings. The SIP includes an affordable and efficient automated process for preparing and indexing continuing medical education documents and a human feedback loop to validate recommended terms. It leverages pre-trained Named-entity Recognition models to identify appropriate terms from the MeSH vocabulary and higher-level subject terms from UMLS. The SIP achieved a precision of 59%, a recall of 64%, and an F1 score of 61% based on the expert evaluation of 124 distinct medical documents. The combination of automation with a human expert feedback loop demonstrates a model strategy for an affordable and practical approach to document indexing in resource-limited yet critical services. The SIP may be extended to other environments and information sources to improve the efficiency and accuracy of information retrieval
The irreducible mass and the horizon area of LIGO’s black holes
No full textThe mass of a Kerr black hole (BH) can be separated into irreducible and rotational components—the former is a lower limit to the energy that cannot be possibly extracted from the event horizon and is related to its area. Here we compute the irreducible masses of the stellar-mass BHs observed by gravitational-wave interferometers LIGO and Virgo. Using single-event data, we present a re-parameterization of the posterior distribution that explicitly highlights the irreducible and rotational contributions to the total energy. We exploit the area law to rank the black-hole mergers observed to date according to their irreversibility, thus providing a guide to selecting events for targeted tests of general relativity. Using population fits, we compute the rate by which the total area of black-hole horizons increases due to the observable mergers
Introduction to the special issue in honor of the contributions of Lynn Margulis (1938-2011) Lynn Margulis: a 20th-Century scientist and a visionary of biology
No full textLynn Margulis' vision for her field was far ahead of its time, as has been the case for so many 'prophets' in science. For example, the theory of heliocentrism, first formulated by Copernicus in 1543, was not widely accepted. The proof of this concept occurred some 60 + years later with Galileo’s development and application of the telescope, a breakthrough that brought him condemnation and house arrest by the Church. Similarly, in 1905, the Russian botanist Konstantin Mereschkowski posited the theory of the formation of the eukaryotic cell by endosymbiosis. However, it was not until 60 + years later, using the newly available technology of the electron microscope, that Lynn Margulis provided the first proof of this concept. The idea was so revolutionary in science that reviewers rejected her manuscript for publication in more than a dozen scientific journals before it was published in 1967 by the Journal of Theoretical Biology