51 research outputs found
Estimation of fatigue strength of TiN coatings using cyclic micro-impact testing
This study delves into the behaviour of a thin TiN coating on a tool steel
substrate material under dynamic and cyclic impacts through a comprehensive
approach combining experimental testing and computational modelling. In dynamic
impact tests, a pendulumbased setup investigates material responses under
varying acceleration loads, revealing a distinctive "ringing effect" as the
indenter bounces off the specimen's surface, with all plastic deformation
concentrated during the initial impact. The study also quantifies dynamic
hardness values, highlighting load-dependent behaviour and assessing the
coating system's energy dissipation capabilities. In cyclic impact tests,
materials experience permanent plastic deformation with each cycle, ultimately
leading to coating failure. Chemical analysis identifies an interlayer between
the coating and substrate, while cross-sectional analysis reveals the extent of
coating damage due to cycling and load. A three-dimensional map is constructed,
connecting acceleration load, sensed depth, and cycles to coating failure, and
an empirical equation characterizes the relationship between depth and cycles
before failure. The computational model scrutinizes traction component
distribution during loading and unloading, with a focus on normal and shear
tractions. The findings suggest the potential significance of normal traction
in interface fatigue failure. Overall, offering implications for understanding
and mitigating fatigue-related failures across various applications
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Critical Race Theory, Columbia Law School and the Legacies of Slavery: The Black Male Initiative
This episode examines Columbia Law School’s history and legacy of slavery and the extent to which the remnants of that legacy reverberate throughout our campus today. With a specific lens on the experiences of Black men on campus and in the wider society, we draw parallels between the hyper surveillance and vilification experienced by Frederick Wells on the law school’s campus in 1924 and the experiences of Black male students on and off campus in recent years
Miniature intravascular photoacoustic endoscopy with coaxial excitation and detection
Recent research pointed out that the degree of inflammation in the adventitia could correlate with the severity of atherosclerotic plaques. Intravascular photoacoustic endoscopy can provide the information of arterial morphology and plaque composition, and even detecting the inflammation. However, most reported work used a non-coaxial configuration for the photoacoustic catheter design, which formed a limited light-sound overlap area for imaging so as to miss the adventitia information. Here we developed a novel 0.9 mm-diameter intravascular photoacoustic catheter with coaxial excitation and detection to resolve the aforementioned issue. A miniature hollow ultrasound transducer with a 0.18 mm-diameter orifice in the center was successfully fabricated. To show the significance and merits of our design, phantom and ex vivo imaging experiments were conducted on both coaxial and non-coaxial catheters for comparison. The results demonstrated that the coaxial catheter exhibited much better photoacoustic/ultrasound imaging performance from the intima to the adventitia
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The ecological limits of poverty alleviation in an African forest-agriculture landscape
Cocoa yields in Ghana remain low. This has variously been attributed to low rates of fertilizer application, pollinator limitation, and particularly dry growing conditions. In this paper we use an African forest-agriculture landscape dominated by cocoa (Theobroma cacao) to develop an ecological production function, allowing us to identify key ecological and management limits acting on cocoa yields simultaneously. These included more consistent application of fertilizers inter-annually, distributing rotting biomass throughout the farm and reducing the incidence of capsid attacks. By relaxing these limits, we estimate plausible increases in yields and, by extension, farm incomes. Our analysis reveals that resulting increases in cocoa yields requiring both ecological and intensive management interventions could be significant (113 ± 60%); however, benefits are disproportionately realized by the wealthiest households. We found that wealthier households benefited proportionally more from ecological intensification methods (e.g., leaving more rotting biomass in their farms) and the poorest households benefited proportionally more from capital-intensive intensification methods (e.g., pesticide and fertilizer applications). We treated poverty as multi-dimensional, and show that only certain dimensions of poverty (school attendance, assets, and food security) are significantly related to cocoa incomes, while several other dimensions (access to clean water, sanitation and electricity, and infant mortality) are not. We explore how increased household cocoa incomes could impact different dimensions of poverty. Our findings suggest, that if all households adopted the optimal level of each of these management options, and in so doing had similar poverty profiles to those households already managing optimally, we would see the community-averaged probability: a child of a household misses school decrease from 47 to 31%, a household would be able to acquire assets increase from 40 to 59% and a household would have access to an adequate amount of food increase from 62 to 79%
Analysis of Temperature-to-Polarization Leakage in BICEP3 and Keck CMB Data from 2016 to 2018
The Bicep/Keck Array experiment is a series of small-aperture refracting telescopes observing degree-scale Cosmic Microwave Background polarization from the South Pole in search of a primordial B-mode signature. As a pair differencing experiment, an important systematic that must be controlled is the differential beam response between the co-located, orthogonally polarized detectors. We use high-fidelity, in-situ measurements of the beam response to estimate the temperature-to-polarization (T → P) leakage in our latest data including observations from 2016 through 2018. This includes three years of Bicep3 observing at 95 GHz, and multifrequency data from Keck Array. Here we present band-averaged far-field beam maps, differential beam mismatch, and residual beam power (after filtering out the leading difference modes via deprojection) for these receivers. We show preliminary results of "beam map simulations," which use these beam maps to observe a simulated temperature (no Q/U) sky to estimate T → P leakage in our real data
CRT2 S1Ep4: Critical Race Theory, Columbia Law School and the Legacies of Slavery: The Black Male Initiative
This episode examines Columbia Law School’s history and legacy of slavery and the extent to which the remnants of that legacy reverberate throughout our campus today. With a specific lens on the experiences of Black men on campus and in the wider society, we draw parallels between the hyper surveillance and vilification experienced by Frederick Wells on the law school’s campus in 1924 and the experiences of Black male students on and off campus in recent years.
With the assistance of our esteemed panelists, Professor Katherine Franke, Professor Darren Hutchinson, and Professor Athena Mutua, we explore a number of critical race theories in an attempt to grapple with the unique experiences and perspectives of Black men and our responsibilities to the past.https://scholarship.law.columbia.edu/crt2/1005/thumbnail.jp
High-energy-density cathode achieved via the activation of a three-electron reaction in sodium manganese vanadium phosphate for sodium-ion batteries
Schwarz domain decomposition methods for the fluid-fluid system with friction-type interface conditions
An improved mathematical model for a pumped hydro storage system considering electrical, mechanical, and hydraulic losses
Development and validation of an UPLC-MS/MS method for the quantification of columbin in biological matrices: Applications to absorption, metabolism, and pharmacokinetic studies
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