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Improving Oxygen Reduction Performance of Surface-Layer-Controlled Pt–Ni Nano-Octahedra via Gaseous Etching
No full textThis study demonstrates an atomic composition manipulation on Pt–Ni nano-octahedra to enhance their electrocatalytic performance. By selectively extracting Ni atoms from the {111} facets of the Pt–Ni nano-octahedra using gaseous carbon monoxide at an elevated temperature, a Pt-rich shell is formed, resulting in an ∼2 atomic layer Pt-skin. The surface-engineered octahedral nanocatalyst exhibits a significant enhancement in both mass activity (∼1.8-fold) and specific activity (∼2.2-fold) toward the oxygen reduction reaction compared with its unmodified counterpart. After 20,000 potential cycles of durability tests, the surface-etched Pt–Ni nano-octahedral sample shows a mass activity of 1.50 A/mg_(Pt), exceeding the initial mass activity of the unetched counterpart (1.40 A/mg_(Pt)) and outperforming the benchmark Pt/C (0.18 A/mg_(Pt)) by a factor of 8. DFT calculations predict this improvement with the Pt surface layers and support these experimental observations. This surface-engineering protocol provides a promising strategy for developing novel electrocatalysts with improved catalytic features
Exact relationships between the GW approximation and equation-of-motion coupled-cluster theories through the quasi-boson formalism
No full textWe describe the relationship between the GW approximation and various equation-of-motion (EOM) coupled-cluster (CC) theories. We demonstrate the exact equivalence of the G₀W₀ approximation and the propagator theory for an electron–boson problem in a particular excitation basis. From there, we establish equivalence within the quasi-boson picture to the IP+EA-EOM unitary CC propagator. We analyze the incomplete description of screening provided by the standard similarity-transformed IP+EA-EOM-CC and the recently introduced G₀W₀ Tamm–Dancoff approximation. We further consider the approximate decoupling of IP and EA sectors in EOM-CC treatments and devise the analogous particle–hole decoupling approach for the G₀W₀ approximation. Finally, we numerically demonstrate the exact relationships and magnitude of the approximations in the calculations of a set of molecular ionization potentials and electron affinities
A simple force balance model of subduction initiation
No full textThe initiation and development of subduction zones are associated with substantial stress changes both within plates and at plate boundaries. We formulate a simple analytical model based on the force balance equation of a subduction zone, and validate it with numerical calculations of highly non-linear, coupled thermomechanical system. With two kinds of boundary conditions with either fixed velocity or fixed force in the far-field, we quantitatively analyse the role of each component in the force balance equation, including slab pull, interplate friction, plate bending and basal traction, on the kinematics and stress state of a subducting plate. Based on the numerical and analytical models, we discuss the evolution of plate curvature, the role of plastic yielding and elasticity, and how different factors affect the timing of subduction initiation. We demonstrate with the presence of plastic yielding for a plate of thickness, H, that the bending force is proportional to H², instead of H³ as previously thought. Although elasticity increases the force required to start nucleating subduction it does not substantially change the total work required to initiate a subduction zone when the yielding stress is small. The analytical model provides an excellent fit to the total work and time to initiate subduction and the force and velocity as a function of convergence and time. Plate convergence and weakening rate during nucleation are the dominant factors influencing the force balance of the plate, and 200 km of plate convergence is typically required to bring a nascent subduction zone into a self-sustaining state. The closed-form solution now provides a framework to better interpret even more complex, time-dependent systems in three dimensions
Making a head: Neural crest and ectodermal placodes in cranial sensory development
No full textDuring development of the vertebrate sensory system, many important components like the sense organs and cranial sensory ganglia arise within the head and neck. Two progenitor populations, the neural crest, and cranial ectodermal placodes, contribute to these developing vertebrate peripheral sensory structures. The interactions and contributions of these cell populations to the development of the lens, olfactory, otic, pituitary gland, and cranial ganglia are vital for appropriate peripheral nervous system development. Here, we review the origins of both neural crest and placode cells at the neural plate border of the early vertebrate embryo and investigate the molecular and environmental signals that influence specification of different sensory regions. Finally, we discuss the underlying molecular pathways contributing to the complex vertebrate sensory system from an evolutionary perspective, from basal vertebrates to amniotes
Investigating Deep Brain Stimulation of the Habenula: A Review of Clinical Studies
No full textObjectives. The aim of this study was to examine the current scientific literature on deep brain stimulation (DBS) targeting the habenula for the treatment of neuropsychiatric disorders including schizophrenia, major depressive disorder, and obsessive-compulsive disorder (OCD).
Materials and Methods. Two authors performed independent data base searches using the PubMed, Cochrane, PsycINFO, and Web of Science search engines. The data bases were searched for the query (“deep brain stimulation” and “habenula”). The inclusion criteria involved screening for human clinical trials written in English and published from 2007 to 2020. From the eligible studies, data were collected on the mean age, sex, number of patients included, and disorder treated. Patient outcomes of each study were summarized.
Results. The search yielded six studies, which included 11 patients in the final analysis. Treated conditions included refractory depression, bipolar disorder, OCD, schizophrenia, and major depressive disorder. Patients with bipolar disorder unmedicated for at least two months had smaller habenula volumes than healthy controls. High-frequency stimulation of the lateral habenula attenuated the rise of serotonin in the dorsal raphe nucleus for treating depression. Bilateral habenula DBS and patient OCD symptoms were reduced and maintained at one-year follow up. Low- and high-frequency stimulation DBS can simulate input paths to the lateral habenula to treat addiction, including cocaine addiction. More data are needed to draw conclusions as to the impact of DBS for schizophrenia and obesity.
Conclusions. The habenula is a novel target that could aid in reducing neuropsychiatric symptoms and should be considered in circuit-specific investigation of neuromodulation for psychiatric disorders. More information needs to be gathered and assessed before this treatment is fully approved for treatment of neuropsychiatric conditions
A Dichotomy for Polish Modules
No full textLet R be a ring equipped with a proper norm. We show that under suitable conditions on R, there is a natural basis under continuous linear injection for the set of Polish R-modules which are not countably generated. When R is a division ring, this basis can be taken to be a singleton
Optimal structures for failure resistance under impact
No full textThe complex physics and numerous failure modes of structural impact creates challenges when designing for impact resistance. While simple geometries of layered material are conventional, advances in 3D printing and additive manufacturing techniques have now made tailored geometries or integrated multi-material structures achievable. Here, we apply gradient-based topology optimization to the design of such structures. We start by constructing a variational model of an elastic–plastic material enriched with gradient phase-field damage, and present a novel method to efficiently compute its transient dynamic time evolution. We consider a finite element discretization with explicit updates for the displacements. The damage field is solved through an augmented Lagrangian formulation, splitting the operator coupling between the nonlinearity and non-locality. Sensitivities over this trajectory are computed through the adjoint method, and we develop a numerical method to solve the resulting adjoint dynamical system. We demonstrate this formulation by studying the optimal design of 2D solid–void structures undergoing blast loading. Then, we explore the trade-offs between strength and toughness in the design of a spall-resistant structure composed of two materials of differing properties undergoing dynamic impact
Uncertainty Analysis of Dynamic Rupture Measurements Obtained Through Ultrahigh-Speed Digital Image Correlation
No full textBackground: The full-field behavior of dynamic shear cracks, with their highly transient features, has recently been quantified by employing Digital Image Correlation (DIC) coupled with ultrahigh-speed photography (at 1-2 million frames/sec). The use of ultrahigh-speed DIC has enabled the observation of complex structures associated with the evolution of the dynamic shear fractures under controlled laboratory conditions, providing a detailed description of their distinctive full-field kinematic features. This has allowed to identify, for instance, the spatiotemporal characteristics of sub-Rayleigh and intersonic shear ruptures, and to measure the evolution of dynamic friction during rupture propagation of frictional shear ruptures.
Objective: Capturing such highly transient phenomena represents a challenging metrological process influenced by both ultra-fast imaging procedures and DIC analysis parameters. However, the effect of these parameters on the quantification of the rupture features has not been assessed yet. Here, a simulated experiment framework is presented and employed to evaluate the uncertainties associated with ultrahigh-speed DIC measurements.
Methods: Finite element simulations replicate laboratory experiments of dynamic ruptures spontaneously propagating along frictional interfaces. Experimental images of the specimen acquired with an ultrahigh-speed camera are numerically deformed by the displacement fields obtained from the numerical simulations and are analyzed using the same DIC analysis procedure as in the laboratory experiments.
Results: The displacement, particle velocity, and strain fields obtained from the DIC analysis are compared with the ground-truth fields of the numerical simulations, correlating the measurement resolution with the physical length scale of the propagating Mode II rupture. In addition, the full-field data are employed to estimate the capability of the ultrahigh-speed DIC setup to infer the dynamic friction evolution.
Conclusions: This methodology allows us to quantify the accuracy of the ultrahigh-speed DIC measurements in resolving the complex spatiotemporal structures of dynamic shear ruptures, focusing on the impact of the key correlation parameters
Oldsite, K₂Fe²⁺[(UO₂)(SO₄)₂]₂(H₂O)₈, a new uranyl sulfate mineral from Utah, USA: its description and implications for the formation and occurrences of uranyl sulfate minerals
No full textOldsite (IMA2021-075), ideally K₂Fe²⁺[(UO₂)(SO₄)₂]₂(H₂O)₈, is a new uranyl sulfate mineral found on specimens from the North Mesa Mine group, Temple Mountain, San Rafael district, Emery County, Utah, USA. It is a secondary mineral occurring with alum-(K), halotrichite, metavoltine, quartz, römerite, stanleyite, sulphur, szomolnokite and mathesiusite. It forms rectangular blades flattened on {010} and elongated on [001], reaching ~0.3 mm in length. Crystals are yellow in colour, transparent with a vitreous lustre; the streak is very pale yellow. The mineral is non-fluorescent. Cleavage is excellent on {100} and perfect on {010}; the Mohs hardness is ~2. Crystals are brittle with irregular, splintery fracture. The density measured by flotation in a mixture of methylene iodide and toluene is 3.31 g⋅cm⁻³; the calculated density is 3.298 g⋅cm⁻³ for the empirical formula and 3.330 g⋅cm⁻³ for the ideal formula. Oldsite is biaxial (+), with α = 1.552(2), β = 1.556(2) and γ = 1.588(2) (measured in white light). The 2V measured directly on a spindle stage is 37(1)°; the calculated 2V is 39.6°. Dispersion is r 3σ(I). Oldsite is an Fe²⁺ analogue of svornostite; its crystal structure is based upon infinite chains of uranyl-sulfate polyhedra, which comprises pentagonal UO₇ bipyramids sharing four of their equatorial vertices with sulfate tetrahedra such that each tetrahedron is linked to two uranyl bipyramids to form an infinite chain (the free, non-linking equatorial vertex of the uranyl bipyramid is an H₂O group). The broader discussion on the origin and composition of uranyl sulfate minerals is made. The new mineral name honours American mineralogist, Dr. Travis A. Olds for his contribution to uranium mineralogy
On the poles of two-time-scale systems
No full textIn this note, the authors will study how the poles of a linear time-invariant singularly perturbed system are varied versus singular parameter ε, where the poles of the slow and fast subsystems are assumed to be placed in the prescribed regions. An explicit bound is derived such that the poles of the original full order system remain in these regions. Finally, two examples are illustrated to show the applications of the proposed results