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Maraging steels are known for their exceptional strength but suffer from limited work hardening and ductility. Here, we report an intermittent printing approach to tailor the microstructure and mechanical properties of maraging 250 steel via engineering of the thermal history during plasma arc additive manufacturing (PAAM). Through introducing a dwell time between adjacent layers, the maraging 250 steel is cooled below the martensite start temperature, triggering a thermally driven, insitu martensitic transformation during the printing process. Reheating or thermal cycling during subsequent layer deposition impedes complete martensitic transformation, enabling coexistence of martensite and retained austenite phases with elemental segregation. The enrichment of Ni in the austenite phase promotes stabilization of the retained austenite upon cooling down to room temperature. The retained austenite is yet metastable during deformation, leading to stressinduced martensitic transformation under loading. Specifically, a 3 min interlayer dwell time produces a maraging 250 steel with approximately 8% retained austenite, resulting in improved work hardening via martensitic transformation induced plasticity (TRIP) during deformation. Meanwhile, the higher cooling rate induced by the dwell time results in substantially refined grain structures with an increased dislocation density, leading to a simultaneously improved yield strength. Notably, the yield strength increases from 836 MPa (0 min dwell) to 990 MPa (3 min dwell), and the uniform elongation increases from 3.2% (0 min dwell) to 6.5% (3 min dwell). This intermittent deposition strategy demonstrates the potential to tune the microstructure and mechanical properties of maraging steels through engineering the thermal history during additive manufacturing.more » « lessFree, publiclyaccessible full text available March 1, 2026

Metric embeddings traditionally study how to map n items to a target metric space such that distance lengths are not heavily distorted. However, what if we are only interested in preserving the relative order of the distances, rather than their exact lengths? In this paper, we explore the fundamental question: given triplet comparisons of the form “item i is closer to item j than to item k,” can we find lowdimensional Euclidean representations for the n items that respect those distance comparisons? Such orderpreserving embeddings naturally arise in important applications—such as recommendations, ranking, crowdsourcing, psychometrics, and nearestneighbor search—and have been studied since the 1950s under the name of ordinal or nonmetric embeddings. Our main results include: NearlyTight Bounds on Triplet Dimension: We introduce the concept of triplet dimension of a dataset and show, surprisingly, that in order for an ordinal embedding to be tripletpreserving, its dimension needs to grow as n^2 in the worst case. This is nearly optimal, as n−1 dimensions always suffice. Tradeoffs for Dimension vs (Ordinal) Relaxation: We relax the requirement that every triplet must be exactly preserved and present almost tight lower bounds for the maximum ratio between distances whose relative order was inverted by the embedding. This ratio is known as (ordinal) relaxation in the literature and serves as a counterpart to (metric) distortion. New Bounds on Terminal and TopkNNs Embeddings: Moving beyond triplets, we study two wellmotivated scenarios where we care about preserving specific sets of distances (not necessarily triplets). The first scenario is Terminal Ordinal Embeddings where we aim to preserve relative distance orders to k given items (the “terminals”), and for that, we present matching upper and lower bounds. The second scenario is topkNNs Ordinal Embeddings, where for each item we aim to preserve the relative order of its k nearest neighbors, for which we present lower bounds. To the best of our knowledge, these are some of the first tradeoffs on tripletpreserving ordinal embeddings and the first study of Terminal and TopkNNs Ordinal Embeddings.more » « lessFree, publiclyaccessible full text available July 12, 2025

Free, publiclyaccessible full text available June 10, 2025

In this paper, we consider two fundamental cut approximation problems on large graphs. We prove new lower bounds for both problems that are optimal up to logarithmic factors. The first problem is approximating cuts in balanced directed graphs, where the goal is to build a data structure to provide a $(1 \pm \epsilon)$estimation of the cut values of a graph on $n$ vertices. For this problem, there are tight bounds for undirected graphs, but for directed graphs, such a data structure requires $\Omega(n^2)$ bits even for constant $\epsilon$. To cope with this, recent works consider $\beta$balanced graphs, meaning that for every directed cut, the total weight of edges in one direction is at most $\beta$ times the total weight in the other direction. We consider the foreach model, where the goal is to approximate a fixed cut with high probability, and the forall model, where the data structure must simultaneously preserve all cuts. We improve the previous $\Omega(n \sqrt{\beta/\epsilon})$ lower bound in the foreach model to $\tilde\Omega(n \sqrt{\beta}/\epsilon)$ and we improve the previous $\Omega(n \beta/\epsilon)$ lower bound in the forall model to $\Omega(n \beta/\epsilon^2)$. This resolves the main open questions of (Cen et al., ICALP, 2021). The second problem is approximating the global minimum cut in the local query model where we can only access the graph through degree, edge, and adjacency queries. We prove an $\Omega(\min\{m, \frac{m}{\epsilon^2 k}\})$ lower bound for this problem, which improves the previous $\Omega(\frac{m}{k})$ lower bound, where $m$ is the number of edges of the graph, $k$ is the minimum cut size, and we seek a $(1+\epsilon)$approximation. In addition, we observe that existing upper bounds with minor modifications match our lower bound up to logarithmic factors.more » « less

The libration spectrum of liquid H2O is resolved into an octupolar twisting libration band at 485 cm−1 and dipolar rocking–wagging libration bands at 707 and 743 cm−1 using polarization analysis of the hyperRaman scattering (HRS) spectrum. Dipole interactions and orientation correlation over distances less than 2 nm account for the 36 cm−1 splitting of the longitudinal and transverse polarized bands of the dipolar rocking–wagging libration mode, while the intensity difference observed for the bands is the result of libration correlation over distances larger than 200 nm. The coupled rock and wag libration in water is similar to libration modes in ice. The libration relaxation time determined from the width of the spectrum is 36–54 fs. Polarization analysis of the HRS spectrum also shows long range correlation for molecular orientation and hindered translation, bending and stretching vibrations in water.more » « lessFree, publiclyaccessible full text available March 21, 2025

Palaniappan, Kannappan ; Seetharaman, Gunasekaran (Ed.)Free, publiclyaccessible full text available June 10, 2025

We expand upon the synthetic utility of anionic rhenium complex Na[(BDI)ReCp] (1, BDI = N,N’bis(2,6diisopropylphenyl)3,5dimethylβdiketiminate) to generate several rhenium–phosphorus complexes. Complex 1 reacts in a metathetical manner with chlorophosphines Ph2PCl, MeNHPCl, and OHPCl to generate XLtype phosphido complexes 2, 3, and 4, respectively (MeNHPCl = 2chloro1,3dimethyl1,3,2diazaphospholidine; OHPCl = 2chloro1,3,2dioxaphospholane). Crystallographic and computational investigations of phosphido triad 2, 3, and 4 reveal that increasing the electronegativity of the phosphorus substituent (C < N < O) results in a shortening and strengthening of the rhenium–phosphorus bond. Complex 1 reacts with iminophosphane Mes*NPCl (Mes* = 2,4,6tritertbutylphenyl) to generate linear iminophosphanyl complex 5. In the presence of a suitable halide abstraction reagent, 1 reacts with the dichlorophosphine iPr2NPCl2 to afford cationic phosphinidene complex 6+. Complex 6+ may be reduced by one electron to form 6•, a rare example of a stable, paramagnetic phosphinidene complex. Spectroscopic and structural investigations, as well as computational analyses, are employed to elucidate the influence of the phosphorus substituent on the nature of the rhenium–phosphorus bond in 2 through 6. Furthermore, we examine several common analogies employed to understand metal phosphido, phosphinidene, and iminophosphanyl complexes.more » « lessFree, publiclyaccessible full text available June 17, 2025

Free, publiclyaccessible full text available January 30, 2025