120 research outputs found
Suprasellar Epidermoid Cyst Originating from the Infundibulum: Case Report and Literature Review.
Epidermoid cysts account for a small fraction of intracranial brain tumors, most commonly found in the cerebellopontine angle and parasellar cisterns. Here we present a rare case of an epidermoid cyst located in the suprasellar region, specifically originating from the infundibulum. Only one additional case with an epidermoid cyst originating within the pituitary stalk has been previously reported in the literature. The patient in this case presented with headaches, diplopia and blurred vision without any endocrinopathy. The patient\u27s pre-operative evaluation was significant for pseudotumor cerebri, hyponatremia, obesity, and a history of smoking; post-operative course was significant for neurogenic diabetes insipidus
Machine learning-assisted design of material properties
Designing functional materials requires a deep search through multidimensional spaces for system parameters that yield desirable material properties. For cases where conventional parameter sweeps or trial-and-error sampling are impractical, inverse methods that frame design as a constrained optimization problem present an attractive alternative. However, even efficient algorithms require time- and resource-intensive characterization of material properties many times during optimization, imposing a design bottleneck. Approaches that incorporate machine learning can help address this limitation and accelerate the discovery of materials with targeted properties. In this article, we review how to leverage machine learning to reduce dimensionality in order to effectively explore design space, accelerate property evaluation, and generate unconventional material structures with optimal properties. We also discuss promising future directions, including integration of machine learning into multiple stages of a design algorithm and interpretation of machine learning models to understand how design parameters relate to material properties.This work was primarily supported by the National Science Foundation through the Center
for Dynamics and Control of Materials: an NSF MRSEC under Cooperative Agreement No.
DMR-1720595. The authors acknowledge an Arnold O. Beckman Postdoctoral Fellowship
(ZMS) and the Welch Foundation (Grant Nos. F-1599 and F-1696) for support.Center for Dynamics and Control of Material
Wertheim’s thermodynamic perturbation theory with double- bond association and its application to colloid–linker mixtures
We extend Wertheim’s thermodynamic perturbation theory to derive the association free energy of a multicomponent mixture for which
double bonds can form between any two pairs of the molecules’ arbitrary number of bonding sites. This generalization reduces in limiting
cases to prior theories that restrict double bonding to at most one pair of sites per molecule. We apply the new theory to an associating mixture
of colloidal particles (“colloids”) and flexible chain molecules (“linkers”). The linkers have two functional end groups, each of which may bond
to one of several sites on the colloids. Due to their flexibility, a significant fraction of linkers can “loop” with both ends bonding to sites on the
same colloid instead of bridging sites on different colloids. We use the theory to show that the fraction of linkers in loops depends sensitively
on the linker end-to-end distance relative to the colloid bonding-site distance, which suggests strategies for mitigating the loop formation that
may otherwise hinder linker-mediated colloidal assembly.This research was primarily supported by the
National Science Foundation through the Center for Dynamics and
Control of Materials: an NSF MRSEC under Cooperative Agree-
ment No. DMR-1720595, with additional support from an Arnold
O. Beckman Postdoctoral Fellowship (Z.M.S.) and the Welch Foun-
dation (Grant Nos. F-1696 and F-1848).Center for Dynamics and Control of Material
Effects of linker flexibility on phase behavior and structure of linked colloidal gels
Colloidal nanocrystal gels can be assembled using a difunctional "linker"
molecule to mediate bonding between nanocrystals. The conditions for gelation
and the structure of the gel are controlled macroscopically by the linker
concentration and microscopically by the linker's molecular characteristics.
Here, we demonstrate using a toy model for a colloid-linker mixture that linker
flexibility plays a key role in determining both phase behavior and structure
of the mixture. We fix the linker length and systematically vary its bending
stiffness to span the flexible, semiflexible, and rigid regimes. At fixed
linker concentration, flexible-linker and rigid-linker mixtures phase separate
at low colloid volume fractions in agreement with predictions of first-order
thermodynamic perturbation theory, but the semiflexible-linker mixtures do not.
We correlate and attribute this qualitatively different behavior to undesirable
"loop" linking motifs that are predicted to be more prevalent for linkers with
end-to-end distances commensurate with the locations of chemical bonding sites
on the colloids. Linker flexibility also influences the spacing between linked
colloids, suggesting strategies to design gels with desired phase behavior,
structure, and by extension, structure-dependent properties.Comment: 11 pages, 8 figures, supplementary materia
Universal Gelation of Metal Oxide Nanocrystals via Depletion Attractions
Nanocrystal gelation provides a powerful framework to translate nanoscale
properties into bulk materials and to engineer emergent properties through the
assembled microstructure. However, many established gelation strategies rely on
chemical reactions and specific interactions, e.g., stabilizing ligands or ions
on the surface of the nanocrystals, and are therefore not easily transferrable.
Here, we report a general gelation strategy via non-specific and purely
entropic depletion attractions applied to three types of metal oxide
nanocrystals. The gelation thresholds of two compositionally distinct spherical
nanocrystals agree quantitatively, demonstrating the adaptability of the
approach for different chemistries. Consistent with theoretical phase behavior
predictions, nanocrystal cubes form gels at a lower polymer concentration than
nanocrystal spheres, allowing shape to serve as a handle to control gelation.
These results suggest that the fundamental underpinnings of depletion-driven
assembly, traditionally associated with larger colloidal particles, are also
applicable at the nanoscale
Colorimetric quantification of linking in thermoreversible nanocrystal gel assemblies
Nanocrystal gels can be responsive, tunable materials, but designing their structure and properties is challenging.
By using reversibly bonded molecular linkers, gelation can be realized under conditions predicted by thermody-
namics. However, simulations have offered the only microscopic insights, with no experimental means to monitor
linking leading to gelation. We introduce a metal coordination linkage with a distinct optical signature allowing
us to quantify linking in situ and establish structural and thermodynamic bases for assembly. Because of coupling
between linked indium tin oxide nanocrystals, their infrared absorption shifts abruptly at a chemically tunable
gelation temperature. We quantify bonding spectroscopically and use molecular simulation to understand
temperature-dependent bonding motifs, revealing that gel formation is governed by reaching a critical number of
effective links that extend the nanocrystal network. Microscopic insights from our colorimetric linking chemistry
enable switchable gels based on thermodynamic principles, opening the door to rational design of programmable
nanocrystal networks.We would like to thank the University of Texas at Austin Mass Spectrometry and NMR Facility
for the use of the Bruker AVANCE III 500: NIH grant number 1 S10 OD021508-01 and the Texas
Materials Institute for the use of the SAXSLAB Ganesha, acquired using an NSF MRI grant
CBET-1624659. We thank the Texas Advanced Computing Center (TACC) at the University
of Texas at Austin for HPC resources. Funding: This research was primarily supported by the
National Science Foundation through the Center for Dynamics and Control of Materials: an
NSF Materials Research Science and Engineering Center (NSF MRSEC) under Cooperative
Agreement DMR-1720595. E.V.A. acknowledges support from the Welch Regents Chair
(F-0046). D.J.M. and T.M.T. also acknowledge support by the Welch Foundation (F-1696
and F-1848). This work was also supported by an NSF Graduate Research Fellowships
(DGE-1610403) to S.A.V. and Arnold O. Beckman Postdoctoral Fellowship to Z.M.S.Center for Dynamics and Control of Material
Uncovering risky behaviors of expatriate teenagers in the United Arab Emirates: A survey of tobacco use, nutrition and physical activity habits
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Modular mixing in plasmonic metal oxide nanocrystal gels with thermoreversible links
Gelation offers a powerful strategy to assemble plasmonic nanocrystal networks incorporating both the distinctive optical properties of con-
stituent building blocks and customizable collective properties. Beyond what a single-component assembly can offer, the characteristics of
nanocrystal networks can be tuned in a broader range when two or more components are intimately combined. Here, we demonstrate
mixed nanocrystal gel networks using thermoresponsive metal–terpyridine links that enable rapid gel assembly and disassembly with ther-
mal cycling. Plasmonic indium oxide nanocrystals with different sizes, doping concentrations, and shapes are reliably intermixed in linked
gel assemblies, exhibiting collective infrared absorption that reflects the contributions of each component while also deviating systematically
from a linear combination of the spectra for single-component gels. We extend a many-bodied, mutual polarization method to simulate the
optical response of mixed nanocrystal gels, reproducing the experimental trends with no free parameters and revealing that spectral devia-
tions originate from cross-coupling between nanocrystals with distinct plasmonic properties. Our thermoreversible linking strategy directs
the assembly of mixed nanocrystal gels with continuously tunable far- and near-field optical properties that are distinct from those of the
building blocks or mixed close-packed structures.This research was primarily supported by the National Science
Foundation through the Center for Dynamics and Control of Mate-
rials: an NSF MRSEC under Cooperative Agreement No. DMR-
1720595, with additional support from an Arnold O. Beckman
Postdoctoral Fellowship (Z.M.S.) and the Welch Foundation (Grant
Nos. F-1696 and F-1848). E.V.A. acknowledges support from the
Welch Regents Chair (No. F-0046). We acknowledge the Texas
Advanced Computing Center (TACC) at the University of Texas at
Austin for providing HPC resources.Center for Dynamics and Control of Material
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