62588 research outputs found
Sort by
Comparing net-proton distribution μr based values in Au+Au collisions at √sNN =14.6 GeV using mid-η and forward(backward)-η determined centrality
No full textThe strong nuclear force, as modeled by Quantum Chromodynamics (QCD), has been extensively studied in recent years in order to learn its thermodynamic properties. Modern collider experiments have been able to access the thermodynamic regime where QCD matter transitions from ordinary (hadronic) matter to a Quark-Gluon Plasma (QGP), which is characterised by colour parton degrees of freedom. This change in phase suggests a phase diagram; as such, many experiments have been aimed at finding the Critical Point (CP) in this phase diagram at the terminus of the 1st order phase transition line between hadronic matter and QGP. Among the observables theorised to be sensitive to the QCD CP are thenet-proton distribution moment (?r) based cumulant ratios, C3/C2 and C4/C2 (S? and ??2, respectively), which are believed to vary monotonically with centre-of-momentum collision energy (?sNN ) in the absence of critical phenomena, but which are also correlated to the correlation/interaction length (?) and thus may show non-monotonic correlation with ?sNN near the CP as ? diverges at the CP.The sensitivity of S? and ??2 to volume fluctuations implies they are sensitive to centrality fluctuations (CF); thus the method of centrality selection and determination is highly important to ?r based analyses. In current analyses of the Beam Energy Scan (BES) program at the Solenoidal Tracker at RHIC (STAR), both ?r analysis and centrality determination are carried out using the Time Projection Chamber (TPC); a mid-rapidity detector with a pseudorapidity (?) acceptance range of?? 1. Using the same ? range to determine both net-proton ?r based values and centrality introduces the potential for autocorrelation errors (ACE). The acceptance range of the STAR Event Plane Detector (EPD) is 2.1 ?? 5.1, thus using the EPD to determine centrality while using the TPC for particle identification would avoid the potential for ACE.This thesis analyses net-proton distribution ?2/? and S? values at ?sNN = 14.6 GeV using both mid and forward(backward) ? determined centrality. Mid-? centrality (XRM 3) is determined with the STAR TPC, which is also a main detector used in particle identification by which net-proton distribution (?Np) arrays are generated, and forward(backward)-? centrality (XEP D) is determined with the STAR EPD. In simulation, it is found that ?Np ?2/? values differ between distribution cuts made using XRM 3 and XEP D, but that both are in range of ?2/? values found usingcentrality determined via the impact parameter (b) in the most central bin (0-5%). In experiment, the ?2/? and S? values determined using XRM 3 and XEP D based centrality selection differ as the simulation values, with the ?2/? values being within error of the simulation values. For both ?2/? and S?, values found using XEP D as the centrality determination observable are higher across the centrality range than those found using XRM 3 as a centrality selector. This finding is congruent with XRM 3 centrality selection based analyses of ?Np ?r based observables suffering from ACE at ?sNN = 14.6 GeV in the STAR experiment.This work will aid in vetting the results of any ?Np ?r based analyses in the STAR Collaboration, particularly net-proton kurtosis (??2) studies. The techniques evaluated herein can be readily applied to other BES collision energies, making this a valuable addition to current analyses across the STAR BES range without adding much in the way of additional work for researchers searching for the QCD CP
Adapting Topic Modeling for Computational Analysis of Framing Processes
No full textThis thesis investigates a new approach for leveraging hierarchical topic modeling techniques to analyze and compare dominant frames found during major current events. We focus on the COVID-19 pandemic as it was an international crisis at an unprecedented magnitude, and one of the first of its kind to have full media coverage and social media discussion. We present the latent theta role model, a computational approach to framing analysis that develops latent variables in the form of distribution over words and distributions over grammatical relations to help understand the link between words and grammatical relations. With this newfound understanding of topics and theta roles, this technique can provide clearer insights about framing over Latent Dirichlet Allocation (LDA) topic modeling results. As a result, frames can be developed or solidified from previous qualitative framing analysis
Significance of Short‐Wavelength Magnetic Anomaly Low Along the East Pacific Rise Axis, 9°50′N
No full textMagnetic anomaly variations near mid‐ocean ridge spreading centers are sensitive to a variety of crustal accretionary processes as well as geomagnetic field variations when the crust forms. We collected near‐bottom vector magnetic anomaly data during a series of 21 autonomous underwater vehicle Sentry dives near 9°50′N on the East Pacific Rise (EPR) covering ∼26 km along‐axis. These data document the 2–3 km wide axial anomaly high that is commonly observed at fast‐spreading ridges but also reveal the presence of a superimposed ∼800 m full wavelength anomaly low. The anomaly low is continuous for ≥13 km along axis and may extend over the entire survey region. A more detailed survey of hydrothermal vents near 9°50.3′N reveals ∼100 m diameter magnetic lows, which are misaligned relative to active vents and therefore cannot explain the continuous axial low. The axial magnetization low persists in magnetic inversions with variable extrusive source thickness, indicating that to the extent to which layer 2A constitutes the sole magnetic source, variations in its thickness alone cannot account for the axial low. Lava accumulation models illustrate that high geomagnetic intensity over the past ∼2.5 kyr, and decreasing intensity over the past ∼900 years, are both consistent with the broad axial anomaly high and the superimposed shorter wavelength low. The continuity of this axial low, and similar features elsewhere on the EPR suggests, that either crustal accretionary processes responsible for this anomaly are common among fast‐spread ridges, or that the observed magnetization low may partially reflect global geomagnetic intensity fluctuations. , Plain Language Summary Near‐bottom magnetic anomaly data provide valuable information on crustal accretion processes at mid‐ocean ridges. Using autonomous underwater vehicle data, we analyze near‐bottom magnetic anomalies at the EPR 9°50′N to study crustal accretion at mid‐ocean ridges. We find a continuous axial anomaly low superimposed on the typical broad axial magnetic high, located along the spreading axis covering an along‐axis distance of more than 10 km. This axial anomaly low has been observed at other fast‐spreading mid‐ocean ridges, but the cause of the anomaly low is not well understood. Using magnetic inversion results and numerical models, we consider three possible causes for the axial anomaly low: variations in the thickness of the pillow lavas that are typically modeled as being the primary contributor to the magnetic signal, variations in Earth\u27s geomagnetic field intensity, and hydrothermal vents chemically altering the magnetic minerals in the seafloor basalts. While the global occurrence of the axial anomaly low at other ridges makes it likely that geomagnetic field variations contribute to the low, it is likely that the observed axial magnetic low is caused by a combination of these three factors. , Key Points Near‐bottom magnetic data reveal a short‐wavelength low superimposed on the broader axial high along the fast‐spreading East Pacific Rise near 9°50′N Magnetic anomaly data provide insight into crustal accretionary processes and temporal variations in geomagnetic field intensity Vector magnetic anomaly data allows for the analysis of magnetic anomalies independent of uncertainties associated with reduction to the pol
Enhanced luminescence efficiency in Eu-doped GaN superlattice structures revealed by terahertz emission spectroscopy
No full textAbstractEu-doped Gallium nitride (GaN) is a promising candidate for GaN-based red light-emitting diodes, which are needed for future micro-display technologies. Introducing a superlattice structure comprised of alternating undoped and Eu-doped GaN layers has been observed to lead to an order-of-magnitude increase in output power; however, the underlying mechanism remains unknown. Here, we explore the optical and electrical properties of these superlattice structures utilizing terahertz emission spectroscopy. We find that ~0.1% Eu doping reduces the bandgap of GaN by ~40‚ÄâmeV and increases the index of refraction by ~20%, which would result in potential barriers and carrier confinement within a superlattice structure. To confirm the presence of these potential barriers, we explored the temperature dependence of the terahertz emission, which was used to estimate the barrier potentials. The result revealed that even a dilutely doped superlattice structure induces significant confinement for carriers, enhancing carrier recombination within the Eu-doped regions. Such an enhancement would improve the external quantum efficiency in the Eu-doped devices. We argue that the benefits of the superlattice structure are not limited to Eu-doped GaN, which provides a roadmap for enhanced optoelectronic functionalities in all rare-earth-doped semiconductor systems.</jats:p
Rapid prototyping of high-resolution large format microfluidic device through maskless image guided in-situ photopolymerization
No full textAbstractMicrofluidic devices have found extensive applications in mechanical, biomedical, chemical, and materials research. However, the high initial cost, low resolution, inferior feature fidelity, poor repeatability, rough surface finish, and long turn-around time of traditional prototyping methods limit their wider adoption. In this study, a strategic approach to a deterministic fabrication process based on in-situ image analysis and intermittent flow control called image-guided in-situ maskless lithography (IGIs-ML), has been proposed to overcome these challenges. By using dynamic image analysis and integrated flow control, IGIs-ML provides superior repeatability and fidelity of densely packed features across a large area and multiple devices. This general and robust approach enables the fabrication of a wide variety of microfluidic devices and resolves critical proximity effect and size limitations in rapid prototyping. The affordability and reliability of IGIs-ML make it a powerful tool for exploring the design space beyond the capabilities of traditional rapid prototyping.</jats:p
The brain regulatory program predates central nervous system evolution
No full textAbstractUnderstanding how brains evolved is critical to determine the origin(s) of centralized nervous systems. Brains are patterned along their anteroposterior axis by stripes of gene expression that appear to be conserved, suggesting brains are homologous. However, the striped expression is also part of the deeply conserved anteroposterior axial program. An emerging hypothesis is that similarities in brain patterning are convergent, arising through the repeated co-option of axial programs. To resolve whether shared brain neuronal programs likely reflect convergence or homology, we investigated the evolution of axial programs in neurogenesis. We show that the bilaterian anteroposterior program patterns the nerve net of the cnidarian Nematostella along the oral-aboral axis arguing that anteroposterior programs regionalized developing nervous systems in the cnidarian–bilaterian common ancestor prior to the emergence of brains. This finding rejects shared patterning as sufficient evidence to support brain homology and provides functional support for the plausibility that axial programs could be co-opted if nervous systems centralized in multiple lineages.</jats:p
Artificial intelligence in communication impacts language and social relationships
No full textAbstractArtificial intelligence (AI) is already widely used in daily communication, but despite concerns about AI’s negative effects on society the social consequences of using it to communicate remain largely unexplored. We investigate the social consequences of one of the most pervasive AI applications, algorithmic response suggestions (“smart replies”), which are used to send billions of messages each day. Two randomized experiments provide evidence that these types of algorithmic recommender systems change how people interact with and perceive one another in both pro-social and anti-social ways. We find that using algorithmic responses changes language and social relationships. More specifically, it increases communication speed, use of positive emotional language, and conversation partners evaluate each other as closer and more cooperative. However, consistent with common assumptions about the adverse effects of AI, people are evaluated more negatively if they are suspected to be using algorithmic responses. Thus, even though AI can increase the speed of communication and improve interpersonal perceptions, the prevailing anti-social connotations of AI undermine these potential benefits if used overtly.</jats:p
Predicting wildfire ignition induced by dynamic conductor swaying under strong winds
No full textAbstractDuring high wind events with dry weather conditions, electric power systems can be the cause of catastrophic wildfires. In particular, conductor-vegetation contact has been recognized as the major ignition cause of utility-related wildfires. There is a urgent need for accurate wildfire risk analysis in support of operational decision making, such as vegetation management or preventive power shutoffs. This work studies the ignition mechanism caused by transmission conductor swaying out to nearby vegetation and resulting in flashover. Specifically, the studied limit state is defined as the conductor encroaching into prescribed minimum vegetation clearance. The stochastic characteristics of the dynamic displacement response of a multi-span transmission line are derived through efficient spectral analysis in the frequency domain. The encroachment probability at a specified location is estimated by solving a classical first-excursion problem. These problems are often addressed using static-equivalent models. However, the results show that the contribution of random wind buffeting to the conductor dynamic displacement is appreciable under turbulent strong winds. Neglecting this random and dynamic component can lead to an erroneous estimation of the risk of ignition. The forecast duration of the strong wind event is an important parameter to determine the risk of ignition. In addition, the encroachment probability is found highly sensitive to vegetation clearance and wind intensity, which highlights the need of high resolution data for these quantities. The proposed methodology offers a potential avenue for accurate and efficient ignition probability prediction, which is an important step in wildfire risk analysis.</jats:p