5632 research outputs found
Sort by
Optical imaging and spectroscopy for the study of the human brain: status report
No full textThis report is the second part of a comprehensive two-part series aimed at reviewing an extensive and diverse toolkit of novel methods to explore brain health and function. While the first report focused on neurophotonic tools mostly applicable to animal studies, here, we highlight optical spectroscopy and imaging methods relevant to noninvasive human brain studies. We outline current state-of-the-art technologies and software advances, explore the most recent impact of these technologies on neuroscience and clinical applications, identify the areas where innovation is needed, and provide an outlook for the future directions
Morning SARS-CoV-2 Testing Yields Better Detection of Infection Due to Higher Viral Loads in Saliva and Nasal Swabs upon Waking
No full textOptimizing specimen collection methods to achieve the most reliable SARS-CoV-2 detection for a given diagnostic sensitivity would improve testing and minimize COVID-19 outbreaks. From September 2020 to April 2021, we performed a household-transmission study in which participants self-collected specimens every morning and evening throughout acute SARS-CoV-2 infection. Seventy mildly symptomatic participants collected saliva, and of those, 29 also collected nasal swab specimens. Viral load was quantified in 1,194 saliva and 661 nasal swab specimens using a high-analytical-sensitivity reverse transcription-quantitative PCR (RT-qPCR) assay. Viral loads in both saliva and nasal swab specimens were significantly higher in morning-collected specimens than in evening-collected specimens after symptom onset. This aspect of the biology of SARS-CoV-2 infection has implications for diagnostic testing. We infer that morning collection would have resulted in significantly improved detection and that this advantage would be most pronounced for tests with low to moderate analytical sensitivity. Collecting specimens for COVID-19 testing in the morning offers a simple and low-cost improvement to clinical diagnostic sensitivity of low- to moderate-analytical-sensitivity tests.
Importance: Our findings suggest that collecting saliva and nasal swab specimens in the morning immediately after waking yields higher SARS-CoV-2 viral loads than collection later in the day. The higher viral loads from morning specimen collection are predicted to significantly improve detection of SARS-CoV-2 in symptomatic individuals, particularly when using moderate- to low-analytical-sensitivity COVID-19 diagnostic tests, such as rapid antigen tests
The 2019 Outburst of the 2005 Classical Nova V1047 Cen: A Record Breaking Dwarf Nova Outburst or a New Phenomenon?
No full textWe present a detailed study of the 2019 outburst of the cataclysmic variable V1047 Cen, which hosted a classical nova eruption in 2005. The peculiar outburst occurred 14 yr after the classical nova event and lasted for more than 400 days, reaching an amplitude of around 6 magnitudes in the optical. Early spectral follow-up revealed what could be a dwarf nova (accretion disk instability) outburst. However, the outburst duration, high-velocity (>2000 km s⁻¹) features in the optical line profiles, luminous optical emission, and presence of prominent long-lasting radio emission together suggest a phenomenon more exotic and energetic than a dwarf nova outburst. The outburst amplitude, radiated energy, and spectral evolution are also not consistent with a classical nova eruption. There are similarities between V1047 Cen’s 2019 outburst and those of classical symbiotic stars, but pre-2005 images of the field of V1047 Cen indicate that the system likely hosts a dwarf companion, implying a typical cataclysmic variable system. Based on our multiwavelength observations, we suggest that the outburst may have started with a brightening of the disk due to enhanced mass transfer or disk instability, possibly leading to enhanced nuclear shell burning on the white dwarf, which was already experiencing some level of quasi-steady shell burning. This eventually led to the generation of a wind and/or bipolar, collimated outflows. The 2019 outburst of V1047 Cen appears to be unique, and nothing similar has been observed in a typical cataclysmic variable system before, hinting at a potentially new astrophysical phenomenon
The EXO-200 detector, part II: auxiliary systems
No full textThe EXO-200 experiment searched for neutrinoless double-beta decay of 136Xe with a single-phase liquid xenon detector. It used an active mass of 110 kg of 80.6%-enriched liquid xenon in an ultra-low background time projection chamber with ionization and scintillation detection and readout. This paper describes the design and performance of the various support systems necessary for detector operation, including cryogenics, xenon handling, and controls. Novel features of the system were driven by the need to protect the thin-walled detector chamber containing the liquid xenon, to achieve high chemical purity of the Xe, and to maintain thermal uniformity across the detector
Does Tyrosine Protect S. coelicolor Laccase from Oxidative Degradation or Act as an Extended Catalytic Site?
No full textWe have investigated the roles of tyrosine (Tyr) and tryptophan (Trp) residues in the four-electron reduction of oxygen catalyzed by Streptomyces coelicolor laccase (SLAC). During normal enzymatic turnover in laccases, reducing equivalents are delivered to a type 1 Cu center (Cu_(T1)) and then are transferred over 13 Å to a trinuclear Cu site (TNC: (Cu_(T3))₂Cu_(T2)) where O₂ reduction occurs. The TNC in SLAC is surrounded by a large cluster of Tyr and Trp residues that can provide reducing equivalents when the normal flow of electrons is disrupted. Prior studies by Canters and co-workers [J.Am.Chem.Soc.2009, 131 (33), 11680-11682] have shown that when O₂ reacts with a reduced SLAC variant lacking the Cu_(T1) center, a Tyr108• radical near the TNC forms rapidly. We have found that the Tyr108• radical is reduced 10 times faster than Cu_(T1)²⁺ by excess ascorbate, possibly because of radical transfer along Tyr/Trp chains
Optical superluminal motion measurement in the neutron-star merger GW170817
No full textThe afterglow of the binary neutron-star merger GW1708171 gave evidence for a structured relativistic jet and a link between such mergers and short gamma-ray bursts. Superluminal motion, found using radio very long baseline interferometry (VLBI), together with the afterglow light curve provided constraints on the viewing angle (14–28 degrees), the opening angle of the jet core (less than 5 degrees) and a modest limit on the initial Lorentz factor of the jet core (more than 4). Here we report on another superluminal motion measurement, at seven times the speed of light, leveraging Hubble Space Telescope precision astrometry and previous radio VLBI data for GW170817. We thereby obtain a measurement of the Lorentz factor of the wing of the structured jet, as well as substantially improved constraints on the viewing angle (19–25 degrees) and the initial Lorentz factor of the jet core (more than 40)
Data compression for quantum machine learning
No full textThe advent of noisy-intermediate scale quantum computers has introduced the exciting possibility of achieving quantum speedups in machine learning tasks. These devices, however, are composed of a small number of qubits and can faithfully run only short circuits. This puts many proposed approaches for quantum machine learning beyond currently available devices. We address the problem of compressing classical data into efficient representations on quantum devices. Our proposed methods allow both the required number of qubits and depth of the quantum circuit to be tuned. We achieve this by using a correspondence between matrix-product states and quantum circuits and further propose a hardware-efficient quantum circuit approach, which we benchmark on the Fashion-MNIST dataset. Finally, we demonstrate that a quantum circuit-based classifier can achieve competitive accuracy with current tensor learning methods using only 11 qubits
Private or Public Equity? The Evolving Entrepreneurial Finance Landscape
No full textThe US entrepreneurial finance market has changed dramatically over the last two decades. Entrepreneurs who raise their first round of venture capital retain 30% more equity in their firm and are more likely to control their board of directors. Late-stage start-ups are raising larger amounts of capital in the private markets from a growing pool of traditional and new investors. These private market changes have coincided with a sharp decline in the number of firms going public—and when firms do go public, they are older and have raised more private capital. To understand these facts, we provide a systematic description of the differences between private and public firms. Next, we review several regulatory, technological, and competitive changes affecting both start-ups and investors that help explain how the trade-offs between going public and staying private have changed. We conclude by listing several open research questions
Adaptation of Range-Doppler Algorithm for Efficient Beamforming of Monostatic and Multistatic Ultrasound Signals
No full textAlgorithmic changes that increase beamforming speed have become increasingly relevant to processing synthetic aperture (SA) ultrasound data. In particular, beamforming SA data in a spatio-temporal frequency domain using the F-k (Stolt) migration have been shown to reduce the beamforming time by up to two orders of magnitude compared with the conventional delay-and-sum (DAS) beamforming, and it has been used in applications where large amounts of raw data make real-time frame rates difficult to attain, such as multistatic SA imaging and plane-wave Doppler imaging with large ensemble lengths. However, beamforming signals in a spatio-temporal Fourier space can require loading large blocks of data at once, making it memory-intensive and less suited for parallel (i.e., multithreaded) processing. As an alternative, we propose beamforming in a range-Doppler (RD) frequency domain using the range-Doppler algorithm (RDA) that has originally been developed for SA radar (SAR) imaging. Through simulation and phantom experiments, we show that RDA achieves similar lateral resolution and contrast compared with DAS and F-k migration. At the same time, higher axial sidelobes in RDA images can be reduced via (temporal) frequency binning. Like the F-k migration, RDA significantly reduces the overall number of computations relative to DAS, and it achieves ten times lower processing time on a single CPU. Because RDA uses only a spatial Fourier transform (FT), it requires two times less memory than the F-k migration to process the simulated multistatic data and can be executed on as many as a thousand parallel threads (compared with eight parallel threads for the F-k migration), making it more suitable for implementation on modern graphics processing units (GPUs). While RDA is not as parallelizable as DAS, it is expected to hold a significant speed advantage on devices with moderate parallel processing capabilities (up to several thousand cores), such as point-of-care and low-cost ultrasound devices
Computational analysis of experiments on shock detachment in hypersonic flow of nitrogen and carbon dioxide over a wedge
No full textOne of the most dramatic effects of vibrational and chemical non-equilibrium in hypersonic flows occurs in the bow-shock detachment process in flow over a wedge. This was shown theoretically and in reflected shock tunnel experiments by Hornung & Smith (J. Fluid Mech., vol. 93, 1979, pp. 225–239). In the present work, the effect is first demonstrated by computation of two-dimensional non-equilibrium flows. The effect of the finite transverse extent of the wedge is then studied by three-dimensional computations of non-relaxing flows. An analytical formula is obtained that gives the shock detachment distance of a finite wedge for ideal-gas and equilibrium flows. In the experiment, the finite transverse extent of the wedge competes with the non-equilibrium effects, as each introduces a new length scale. The carbon dioxide and nitrogen flows of the experiment are therefore computed in three dimensions and with two-temperature chemistry accounting for vibrational and chemical non-equilibrium. In the case of nitrogen flow, the agreement between experiment and computation is not good, the experimental detachment distance being larger. A number of possible reasons are quantitatively examined. A conclusive resolution of the discrepancy is considered to require a repeat of the experiment with more accurately characterized conditions. In the case of the carbon dioxide experiments, the computed results agree remarkably well with experiment. This is partially due to the fact that the condition is very close to equilibrium, where the sensitivity of the detachment process to relaxation effects is small. The analytical expression for the dimensionless detachment distance agrees very well with all the three-dimensional computations of non-relaxing flows