Publications by Year: 2020

2020
Trepka K, Hauert R, Cancellieri C, Tao Y. A Robust Metal Oxide Thin Film with Saturation Magnetization Exceeding 2 Telsa [Internet]. SSRN 2020; Publisher's VersionAbstract
High saturation magnetization, hysteresis-less long linear response range, and resistance to devicefabrication conditions are figures of merit for magnetic materials in science and technology.Despite advances in materials research, many high-saturating micro- and nanomagnetic materialsare hysteresis-prone, have short linear ranges, and are sensitive to oxidation, resulting in deviceinefficiencies in high-frequency electronics and unpredictable responses in magnetic sensing applications.Holmium oxide is a promising material because of its high magnetic susceptibility,but synthetic options are limited, with low-temperature magnetism incompletely characterized.Here, we present physical vapor deposition synthesis and material characterization of polycrystallineholmium oxide thin films. The product has saturation magnetization exceeding 2 Tesla,linear range (μ0H) also exceeding 2 Tesla, zero magnetic remanence and coercivity, and resistanceto harsh processing conditions including oxygen plasma and concentrated hydrofluoricacid etching, making these thin films ideal for fabricating next-generation nanoscale magneticdevices in advanced scientific and engineering applications.
Trepka K, Tao Y. Magnetic characterization of rare-earth oxide nanoparticles [Internet]. Applied Physics Letters 2020;117(12) Publisher's VersionAbstract
High saturation magnetization and hysteresis-less magnetic responses are desirable for nanoparticles in scientific and technological applications. Rare-earth oxides are potentially promising materials because of their paramagnetism and high magnetic susceptibility in the bulk, but the magnetic properties of their nanoparticles remain incompletely characterized. Here, we present full M–H loops for commercial RE2O3 nanoparticles (RE = Er, Gd, Dy, Ho) with radii from 10–25 nm at room temperature and 4 K. The magnetic responses are consistent with two distinct populations of atoms, one displaying the ideal Re3+ magnetic moment and the other displaying a sub-ideal magnetic moment. If all sub-ideal ions are taken to be on the surface, the data are consistent with ≈2−10" id="MathJax-Element-1-Frame" role="presentation" style="border-bottom-color:currentColor;border-bottom-style:none;border-bottom-width:0px;border-image-outset:0;border-image-repeat:stretch;border-image-slice:100%;border-image-source:none;border-image-width:1;border-left-color:currentColor;border-left-style:none;border-left-width:0px;border-right-color:currentColor;border-right-style:none;border-right-width:0px;border-top-color:currentColor;border-top-style:none;border-top-width:0px;direction:ltr;display:inline;float:none;100%;none;font-style:normal;font-weight:normal;letter-spacing:normal;line-height:normal;margin-bottom:0px;margin-left:0px;margin-right:0px;margin-top:0px;max-height:none;max-width:none;min-height:0px;min-width:0px;overflow-wrap:normal;padding-bottom:0px;padding-left:0px;padding-right:2px;padding-top:0px;position:relative;text-align:left;text-indent:0px;text-transform:none;white-space:nowrap;word-spacing:normal;" tabindex="0">210≈2−10 nm surface layers of reduced magnetization. The magnetization of the rare-earth oxide nanoparticles at low temperatures (1.3–1.9 T) exceeds that of the best iron-based nanoparticles, making rare-earth oxides candidates for use in next-generation cryogenic magnetic devices that demand a combination of hysteresis-less response and high magnetization.
This work was supported by a Rowland Fellowship to Y.T. K.T. acknowledges support from the Rowland Institute and the Harvard Office of Undergraduate Research and Fellowships. The authors would like to thank Shaw Huang for assistance with SQUID and all group members for helpful discussions. SEM sample characterization studies were carried out at the Center for Nanoscale Systems (CNS) at Harvard University.
Kurtz DA, Rossman GR, Hunter BM. The Nature of the Mn(III) Color Centers in Elbaite Tourmalines [Internet]. Inorganic Chemistry 2020;59(14):9618-9626. Publisher's VersionAbstract
The characteristic red color of many natural tourmalines is due to the presence of Mn(III) cations substituting for aluminum and lithium. These sites originate as Mn(II) and are oxidized by natural γ-irradiation over geologic time as they sit in the Earth’s crust. Presented here is a thorough analysis of the spin-allowed and spin-forbidden transitions which give rise to the color of these gemstones. Ligand field analysis, supplemented by time-dependent density functional theory, was used to correct the historical assignments of the symmetry-allowed transitions in the polarized UV–visible absorption spectrum. Heat-induced reduction of the oxidized manganese sites provided a probe of the relationship between the spin-allowed and spin-forbidden bands. Notably, the intensity of the spin-forbidden transition was highly dependent on the neighboring ions in the Y-site. Simulations and modeling showed that increased intensity was observed only when two Mn(III) ions occupied adjacent substitutions in the Y-site via a proposed exchange-coupling mechanism.
Gude S, Pinçe E, Taute KM, Seinen A-B, Shimizu TS, Tans SJ. Bacterial coexistence driven by motility and spatial competition [Internet]. Nature 2020;(578):588-592. Publisher's VersionAbstract
Elucidating elementary mechanisms that underlie bacterial diversity is central to ecology1,2 and microbiome research3. Bacteria are known to coexist by metabolic specialization4, cooperation5 and cyclic warfare6,7,8. Many species are also motile9, which is studied in terms of mechanism10,11, benefit12,13, strategy14,15, evolution16,17 and ecology18,19. Indeed, bacteria often compete for nutrient patches that become available periodically or by random disturbances2,20,21. However, the role of bacterial motility in coexistence remains unexplored experimentally. Here we show that—for mixed bacterial populations that colonize nutrient patches—either population outcompetes the other when low in relative abundance. This inversion of the competitive hierarchy is caused by active segregation and spatial exclusion within the patch: a small fast-moving population can outcompete a large fast-growing population by impeding its migration into the patch, while a small fast-growing population can outcompete a large fast-moving population by expelling it from the initial contact area. The resulting spatial segregation is lost for weak growth–migration trade-offs and a lack of virgin space, but is robust to population ratio, density and chemotactic ability, and is observed in both laboratory and wild strains. These findings show that motility differences and their trade-offs with growth are sufficient to promote diversity, and suggest previously undescribed roles for motility in niche formation and collective expulsion–containment strategies beyond individual search and survival.
Wang G-H, Berdy BM, Velasquez O, Jovanovic N, Alkhalifa S, Minibiole KPC, Brucker R. Changes in Microbiome Confer Multigenerational Host Resistance after Sub-toxic Pesticides Exposure [Internet]. Cell Host & Microbe 2020;(27):213-224. Publisher's VersionAbstract

The gut is a first point of contact with ingested xeno- biotics, where chemicals are metabolized directly by the host or microbiota. Atrazine is a widely used pesticide, but the role of the microbiome metabolism of this xenobiotic and the impact on host responses is unclear. We exposed successive generations of the wasp Nasonia vitripennis to subtoxic levels of atrazine and observed changes in the structure and function of the gut microbiome that conveyed atra- zine resistance. This microbiome-mediated resis- tance was maternally inherited and increased over successive generations, while also heightening the rate of host genome selection. The rare gut bacteria Serratia marcescens and Pseudomonas protegens contributed to atrazine metabolism. Both of these bacteria contain genes that are linked to atrazine degradation and were sufficient to confer resistance in experimental wasp populations. Thus, pesticide exposure causes functional, inherited changes in the microbiome that should be considered when as- sessing xenobiotic exposure and as potential coun- termeasures to toxicity. 

Mathis MW, Mathis A. Deep learning tools for the measurement of animal behavior in neuroscience [Internet]. Current Opinion in Neurobiology 2020;60:1-11. Publisher's VersionAbstract
Recent advances in computer vision have made accurate, fast and robust measurement of animal behavior a reality. In the past years powerful tools specifically designed to aid the measurement of behavior have come to fruition. Here we discuss how capturing the postures of animals — pose estimation - has been rapidly advancing with new deep learning methods. While challenges still remain, we envision that the fast-paced development of new deep learning tools will rapidly change the landscape of realizable real-world neuroscience.
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