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What is the intention to move and when does it occur?
No full textIn 1983 Benjamin Libet and colleagues published a paper apparently challenging the view that the conscious intention to move precedes the brain’s preparation for movement. The experiment initiated debates about the nature of intention, the neurophysiology of movement, and philosophical and legal understanding of free will and moral responsibility. Here we review the concept of “conscious intention” and attempts to measure its timing. Scalp electroencephalographic activity prior to movement, the Bereitschaftspotential, clearly begins prior to the reported onset of conscious intent. However, the interpretation of this finding remains controversial. Numerous studies show that the Libet method for determining intent, W time, is not accurate and may be misleading. We conclude that intention has many different aspects, and although we now understand much more about how the brain makes movements, identifying the time of conscious intention is still elusive
Preparing quantum states by measurement-feedback control with Bayesian optimization
No full textThe preparation of quantum states is crucial for enabling quantum computations and simulations. In this work, we present a general framework for preparing ground states of many-body systems by combining the measurement-feedback control process (MFCP) with machine learning techniques. Specifically, we employ Bayesian optimization (BO) to enhance the efficiency of determining the measurement and feedback operators within the MFCP. As an illustration, we study the ground state preparation of the one-dimensional Bose–Hubbard model. Through BO, we are able to identify optimal parameters that can effectively drive the system towards low-energy states with a high probability across various quantum trajectories. Our results open up new directions for further exploration and development of advanced control strategies for quantum computations and simulations
Valid questions: the development and evaluation of a new library learning analytics survey
No full textPurpose. This article describes the development processes, sampling and analysis practices and the assessment of reliability and validity of a new survey that sought to evaluate undergraduate students' perceptions and expectations related to privacy and library participation in learning analytics studies. This article provides other researchers with information required to independently evaluate the survey's efficacy, as well as guidance for designing other surveys.
Design/methodology/approach. Following question development, pre-survey validity assessments were made using subject matter expert panel review and cognitive interviews. Post-hoc analysis of survey construct reliability was evaluated using the Omega coefficient, while exploratory factor analysis was utilized to assess construct validity. Survey design limitations and potential bias effects are also examined.
Findings. The survey exhibited a high level of reliability among research constructs, while the exploratory factor analysis results suggested that survey constructs contained multiple conceptual elements that should be measured separately for more nuanced analysis.
Practical implications. This article provides a model for other researchers wishing to re-use the survey described or develop similar surveys.
Social implications. As learning analytics interest continues to expand, engaging with the subjects, in this case students, of analysis is critical. Researchers need to ensure that captured measurements are appropriately valid in order to accurately represent the findings.
Originality/value. This survey is one of very few addressing library learning analytics that has undergone extensive validity analysis of the conceptual constructs
Displacement-noise-free interferometeric gravitational-wave detector using unidirectional neutrons with four speeds
No full textFor further gravitational wave (GW) detections, it is significant to invent a technique to reduce all kinds of mirror displacement noise dominant at low frequencies for ground-based detectors. The neutron displacement-noise-free interferometer (DFI) is one of the tools to reduce all the mirror displacement noise at lower frequencies. In this paper, we describe a further simplified configuration of a neutron DFI in terms of neutron incidence direction. In the new configuration, neutrons enter the interferometer with unidirectional incidence at four speeds as opposed to two bidirectional incidences of opposite directions at two speeds as reported previously. This simplification of the neutron DFI is significant for proof-of-principle experiments
Conformation Transition of a Homopolymer Chain in Binary Mixed Solvents
No full textOn the basis of a minimal lattice model, we apply the Wang–Landau Monte Carlo (MC) algorithm and a Flory-type mean-field theory to investigate the conformation of a homopolymer chain in a mixture of binary solvents A and B. This MC method enables us to accurately locate the conformation transitions and to determine their nature over a large parameter space. We find that in a good solvent A, adding a small amount of better solvent B causes a continuous collapse transition when the difference in the solvent quality is large. Increasing the fraction of solvent B results in a smooth reswelling of the chain. We explain these findings by the delicate interplay among the mixing entropy of binary solvents, the chain conformational entropy, and the competition in the interactions between the monomer and the two solvents
Behavior of Hydrogarnet‐Type Defects in Hydrous Stishovite at Various Temperatures and Pressures
No full textDense polymorphs of silica have been demonstrated experimentally to incorporate from 1.5 wt% to as much as 11.6 wt% H₂O as OH groups, with implications for the hydrogen budgets of Earth and other planets. This OH is thought to enter the SiO₂ structure via a charge-balanced substitution in which silicon vacancies (V_(Si)) are compensated by protonating four of the surrounding six oxygen atoms, often referred to as a hydrogarnet-type defect. There are many possible configurations for this defect structure in dense silica, but the nature of these configurations and whether they can be distinguished experimentally is unknown. We present here density functional theory calculations that systematically assess the possible configurations of a hydrogarnet-type defect in stishovite (rutile-type SiO₂), with direct comparisons to experimental vibrational spectroscopy data. We predict that stishovite synthesized at 450 K and 10 GPa quenched to room temperature is dominated by a single defect type with tetrahedral geometry. This leads to OH stretching modes (2,500–3,000 cm⁻¹) and SiOH bending modes (∼1,400–1,450 cm⁻¹) largely consistent with experimentally observed modes. One remaining issue is that our calculations produce results compatible with experimental data on H to D exchange, but do not explain why a considerable fraction of the 1,420 cm⁻¹ mode shifts by only 40 cm⁻¹ in deuterated samples. At elevated pressures and temperatures, we find that a second square planar defect configuration also becomes favorable, leading to modes that should allow differentiation from the tetrahedral configuration
Formation of rocky super-earths from a narrow ring of planetesimals
No full textThe formation of super-Earths, the most abundant planets in the Galaxy, remains elusive. These planets have masses that typically exceed that of the Earth by a factor of a few, appear to be predominantly rocky, although often surrounded by H/He atmospheres, and frequently occur in multiples. Moreover, planets that encircle the same star tend to have similar masses and radii, whereas those belonging to different systems exhibit remarkable overall diversity. Here we advance a theoretical picture for rocky planet formation that satisfies the aforementioned constraints: building upon recent work, which has demonstrated that planetesimals can form rapidly at discrete locations in the disk, we propose that super-Earths originate inside rings of silicate-rich planetesimals at approximately ~1 au. Within the context of this picture, we show that planets grow primarily through pairwise collisions among rocky planetesimals until they achieve terminal masses that are regulated by isolation and orbital migration. We quantify our model with numerical simulations and demonstrate that our synthetic planetary systems bear a close resemblance to compact, multi-resonant progenitors of the observed population of short-period extrasolar planets
PHANGS–JWST First Results: Stellar-feedback-driven Excitation and Dissociation of Molecular Gas in the Starburst Ring of NGC 1365?
No full textWe compare embedded young massive star clusters (YMCs) to (sub-)millimeter line observations tracing the excitation and dissociation of molecular gas in the starburst ring of NGC 1365. This galaxy hosts one of the strongest nuclear starbursts and richest populations of YMCs within 20 Mpc. Here we combine near-/mid-IR PHANGS–JWST imaging with new Atacama Large Millimeter/submillimeter Array multi-J CO (1–0, 2–1 and 4–3) and [C i] (1–0) mapping, which we use to trace CO excitation via R₄₂ = I_(CO(4−3))/I_(CO(2−1)_ and R₂₁ = I_(CO(2−1))/I_(CO(1−0)) and dissociation via R_(CICO) = I_([CI](1−0))/I_(CO(2−1)) at 330 pc resolution. We find that the gas flowing into the starburst ring from northeast to southwest appears strongly affected by stellar feedback, showing decreased excitation (lower R₄₂) and increased signatures of dissociation (higher R_(CICO)) in the downstream regions. There, radiative-transfer modeling suggests that the molecular gas density decreases and temperature and [CI/CO] abundance ratio increase. We compare R₄₂ and R_(CICO) with local conditions across the regions and find that both correlate with near-IR 2 μm emission tracing the YMCs and with both polycyclic aromatic hydrocarbon (11.3 μm) and dust continuum (21 μm) emission. In general, R_(CICO) exhibits ∼0.1 dex tighter correlations than R₄₂, suggesting C i to be a more sensitive tracer of changing physical conditions in the NGC 1365 starburst than CO (4–3). Our results are consistent with a scenario where gas flows into the two arm regions along the bar, becomes condensed/shocked, forms YMCs, and then these YMCs heat and dissociate the gas
Nonlinearities in Black Hole Ringdowns
No full textThe gravitational wave strain emitted by a perturbed black hole (BH) ringing down is typically modeled analytically using first-order BH perturbation theory. In this Letter we show that second-order effects are necessary for modeling ringdowns from BH merger simulations. Focusing on the strain's (ℓ,m)=(4,4) angular harmonic, we show the presence of a quadratic effect across a range of binary BH mass ratios that agrees with theoretical expectations. We find that the quadratic (4,4) mode amplitude exhibits quadratic scaling with the fundamental (2,2) mode -- its parent mode. The nonlinear mode's amplitude is comparable to or even larger than that of the linear (4,4) modes. Therefore correctly modeling ringdown -- improving mismatches by an order of magnitude -- requires the inclusion of nonlinear effects
Preparing random states and benchmarking with many-body quantum chaos
No full textProducing quantum states at random has become increasingly important in modern quantum science, with applications being both theoretical and practical. In particular, ensembles of such randomly distributed, but pure, quantum states underlie our understanding of complexity in quantum circuits1 and black holes, and have been used for benchmarking quantum devices in tests of quantum advantage. However, creating random ensembles has necessitated a high degree of spatio-temporal control placing such studies out of reach for a wide class of quantum systems. Here we solve this problem by predicting and experimentally observing the emergence of random state ensembles naturally under time-independent Hamiltonian dynamics, which we use to implement an efficient, widely applicable benchmarking protocol. The observed random ensembles emerge from projective measurements and are intimately linked to universal correlations built up between subsystems of a larger quantum system, offering new insights into quantum thermalization. Predicated on this discovery, we develop a fidelity estimation scheme, which we demonstrate for a Rydberg quantum simulator with up to 25 atoms using fewer than 10⁴ experimental samples. This method has broad applicability, as we demonstrate for Hamiltonian parameter estimation, target-state generation benchmarking, and comparison of analogue and digital quantum devices. Our work has implications for understanding randomness in quantum dynamics and enables applications of this concept in a much wider context