Large-format 3D printing enabled by dual-curing urethane elastomers

Direct-ink-writing (DIW) is an Additive Manufacturing (AM) technique that provides a versatile approach to fabricating arbitrarily shaped objects by exploiting the shear-thinning properties of polymeric-based inks. One major drawback of DIW is that shear-thinning inks are limited to a maximum height before the combined weight of additionally deposited layers exceeds the yield stress of the underlying layers and causes the material to flow. Previous methods to combat this drawback have included intermittent or continuous exposure of the process to ultra-violet (UV) radiation to cure the material in place. However, these approaches require specific parameters that limit the UV-curable inks to specific applications and do not address the challenges associated with printing high-aspect-ratio objects. Here, we report a stepwise UV and heat curing process that facilitates DIW of a range of inks with varying rheological properties and that is no longer dimensionally limited by a yield stress. This stepwise curing process is enabled by small amounts of acrylates that cure to the back of the functionalized urethane prepolymers to promote rapid gelation in the object during extrusion, and a post thermal-curing step of the major urethane components once printing is complete. This method of fabrication effectively eliminates dimensional constraints of objects during fabrication, as well as expands the rheological range of printable inks. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. LLNL-ABS-795840

PAH/PAH(CF3)n Donor/Acceptor Charge-Transfer Complexes in Solution and in Solid-State Co-Crystals

A solution, solid-state, and computational study is reported of polycyclic aromatic hydrocarbon PAH/PAH(CF3)n donor/acceptor (D/A) charge-transfer complexes that involve six PAH(CF3)n acceptors with known gas-phase electron affinities that range from 2.11(2) to 2.805(15) eV and four PAH donors, including seven CT co-crystal X-ray structures that exhibit hexagonal arrays of mixed π-stacks with 1/1, 1/2, or 2/1 D/A stoichiometries (PAH=anthracene, azulene, coronene, perylene, pyrene, triphenylene; n=5, 6). These are the first D/A CT complexes with PAH(CF3)n acceptors to be studied in detail. The nine D/A combinations were chosen to allow several structural and electronic comparisons to be made, providing new insights about controlling D/A interactions and the structures of CT co-crystals. The comparisons include, among others, CT complexes of the same PAH(CF3)n acceptor with four PAH donors and CT complexes of the same donor with four PAH(CF3)n acceptors. All nine CT complexes exhibit charge-transfer bands in solution with λmax between 467 and 600 nm. A plot of E(λmax) versus [IE(donor)−EA(acceptor)] for the nine CT complexes studied is linear with a slope of 0.72±0.03 eV eV−1. This plot is the first of its kind for CT complexes with structurally related donors and acceptors for which precise experimental gas-phase IEs and EAs are known. It demonstrates that conclusions based on the common assumption that the slope of a CT E(λmax) versus [IE−EA] plot is unity may be incorrect in at least some cases and should be reconsidered. © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinhei

A faux hawk fullerene with PCBM-like properties

Reaction of C60, C6F5CF2I, and SnH(n-Bu)3 produced, among other unidentified fullerene derivatives, the two new compounds 1,9-C60(CF2C6F5)H (1) and 1,9-C60(cyclo-CF2(2-C6F4)) (2). The highest isolated yield of 1 was 35% based on C60. Depending on the reaction conditions, the relative amounts of 1 and 2 generated in situ were as high as 85% and 71%, respectively, based on HPLC peak integration and summing over all fullerene species present other than unreacted C60. Compound 1 is thermally stable in 1,2-dichlorobenzene (oDCB) at 160 °C but was rapidly converted to 2 upon addition of Sn2(n-Bu)6 at this temperature. In contrast, complete conversion of 1 to 2 occurred within minutes, or hours, at 25 °C in 90/10 (v/v) PhCN/C6D6 by addition of stoichiometric, or sub-stoichiometric, amounts of proton sponge (PS) or cobaltocene (CoCp2). DFT calculations indicate that when 1 is deprotonated, the anion C60(CF2C6F5)− can undergo facile intramolecular SNAr annulation to form 2 with concomitant loss of F−. To our knowledge this is the first observation of a fullerene-cage carbanion acting as an SNAr nucleophile towards an aromatic C–F bond. The gas-phase electron affinity (EA) of 2 was determined to be 2.805(10) eV by low-temperature PES, higher by 0.12(1) eV than the EA of C60 and higher by 0.18(1) eV than the EA of phenyl-C61-butyric acid methyl ester (PCBM). In contrast, the relative E1/2(0/−) values of 2 and C60, −0.01(1) and 0.00(1) V, respectively, are virtually the same (on this scale, and under the same conditions, the E1/2(0/−) of PCBM is −0.09 V). Time-resolved microwave conductivity charge-carrier yield × mobility values for organic photovoltaic active-layer-type blends of 2 and poly-3-hexylthiophene (P3HT) were comparable to those for equimolar blends of PCBM and P3HT. The structure of solvent-free crystals of 2 was determined by single-crystal X-ray diffraction. The number of nearest-neighbor fullerene–fullerene interactions with centroid⋯centroid (⊙⋯⊙) distances of ≤10.34 Å is significantly greater, and the average ⊙⋯⊙ distance is shorter, for 2 (10 nearest neighbors; ave. ⊙⋯⊙ distance = 10.09 Å) than for solvent-free crystals of PCBM (7 nearest neighbors; ave. ⊙⋯⊙ distance = 10.17 Å). Finally, the thermal stability of 2 was found to be far greater than that of PCBM

A survey on the challenges, limitations, and opportunities of online testing of infants and young children during the COVID-19 pandemic: using our experiences to improve future practices

In developmental psychology, the widespread adoption of new methods for testing children does not typically occur over a matter of months. Yet, the COVID-19 pandemic and its associated social distancing requirements created a sudden need among many research groups to use a new method with which they had little or no experience: online testing. Here, we report results from a survey of 159 researchers detailing their early experiences with online testing. The survey approach allowed us to create a general picture of the challenges, limitations, and opportunities of online research, and it identified aspects of the methods that have the potential to impact interpretations of findings. We use the survey results to present considerations to improve online research practices

Literature survey on epidemiology and pathology of gangliocytic paraganglioma

<p>Abstract</p> <p>Background</p> <p>Although gangliocytic paraganglioma (GP) has generally been regarded as a neuroendocrine tumor, its origin remains unclear. We therefore aimed to investigate the details of this disease by carefully analyzing and extracting common features of the disease as presented in selected publications.</p> <p>Methods</p> <p>We searched for English and Japanese cases of GP using the PubMed and IgakuChuoZasshi databases on August 2010. We then extracted and sampled raw data from the selected publications and performed appropriate statistical analyses. Additionally, we evaluated the expression of hormone receptors based on our previously reported case.</p> <p>Results</p> <p>192 patients with GP were retrieved from the databases. Patient ages ranged from 15 y to 84 y (mean: 52.3 y). The gender ratio was 114:76 (male to female, 2 not reported). Maximum diameter of the tumors ranged from 5.5 mm to 100 mm (mean: 25.0 mm). The duodenum (90.1%, 173/192) was found to be the most common site of the disease. In 173 patients with duodenal GP, gastrointestinal bleeding (45.1%, 78/173) was found to be the most common symptom of the disease, followed by abdominal pain (42.8%, 74/173), and anemia (14.5%, 25/173). Rate of lymph node metastasis was 6.9% (12/173). Our statistical analysis indicated that significant differences were found for gender between GP within the submucosal layer and exceeding the submucosal layer. Furthermore, our immunohistochemical evaluation showed that both epithelioid and pancreatic islet cells showed positive reactivity for progesterone receptors.</p> <p>Conclusions</p> <p>Our literature survey revealed that there were many more cases of GP exceeding the submucosal layer than were expected. Meanwhile, our statistical analyses and immunohistochemical evaluation supported the following two hypotheses. First, vertical growth of GP might be affected by progesterone exposure. Second, the origin of GP might be pancreatic islet cells. However, it is strongly suspected that our data have been affected by publication bias and to confirm these hypotheses, further investigation is required.</p

Estrogen- and Progesterone (P4)-Mediated Epigenetic Modifications of Endometrial Stromal Cells (EnSCs) and/or Mesenchymal Stem/Stromal Cells (MSCs) in the Etiopathogenesis of Endometriosis

Endometriosis is a common chronic inflammatory condition in which endometrial tissue appears outside the uterine cavity. Because ectopic endometriosis cells express both estrogen and progesterone (P4) receptors, they grow and undergo cyclic proliferation and breakdown similar to the endometrium. This debilitating gynecological disease affects up to 15% of reproductive aged women. Despite many years of research, the etiopathogenesis of endometrial lesions remains unclear. Retrograde transport of the viable menstrual endometrial cells with retained ability for attachment within the pelvic cavity, proliferation, differentiation and subsequent invasion into the surrounding tissue constitutes the rationale for widely accepted implantation theory. Accordingly, the most abundant cells in the endometrium are endometrial stromal cells (EnSCs). These cells constitute a particular population with clonogenic activity that resembles properties of mesenchymal stem/stromal cells (MSCs). Thus, a significant role of stem cell-based dysfunction in formation of the initial endometrial lesions is suspected. There is increasing evidence that the role of epigenetic mechanisms and processes in endometriosis have been underestimated. The importance of excess estrogen exposure and P4 resistance in epigenetic homeostasis failure in the endometrial/endometriotic tissue are crucial. Epigenetic alterations regarding transcription factors of estrogen and P4 signaling pathways in MSCs are robust in endometriotic tissue. Thus, perspectives for the future may include MSCs and EnSCs as the targets of epigenetic therapies in the prevention and treatment of endometriosis. Here, we reviewed the current known changes in the epigenetic background of EnSCs and MSCs due to estrogen/P4 imbalances in the context of etiopathogenesis of endometriosis

Fluorinated materials synthesis and characterization for energy storage and energy conversion applications

2015 Summer.The synthesis and characterization of multiple fluorinated, p-block, cage, and organic compounds will be presented. The research effort is split up in to main topics, (i) fluorinated superweak anions based on B12 cages, and (ii) perfluoroalkylation of polycyclic aromatic hydrocarbon (PAH) and fullerene compounds. In the first three chapters, superweak anion research is presented; a new purification method for the synthetic intermediate K2B12F12, synthesis and thermal and physical characterization of highly purified (H3O)2B12F12·nH2O, Li2B12F12 and Na2B12F12 (synthesized from K2B12F12), and an HF-free, improved synthesis method and characterization of KB12F11NH3. Furthermore, the unanticipated, rapid fluorination of KB12H11NH3 in the presence of HF, contrary to, previously observed, slowed fluorination of K2B12H12 in the presence of HF, will also be described. Single crystal X-ray structures of three new isomers of C60(CF3)10 are discussed, and one putative isomer of C60(CF3)10 is confirmed along with comparisons of their crystal packing properties compared to 1,9-C60(cyclo-CF2(2-C6F4)), and industry-standard fullerene acceptor phenyl-C61-butyric acid methyl ester (PCBM). Discussion of how the structural and electrochemical data of the new C60(CF3)10 isomers and 1,9-C60(cyclo-CF2(2-C6F4)) agree with currently accepted literature will also be discussed. A new metal reactor design for the radical reactions of CF3I and polycyclic aromatic hydrocarbons (PAH) and fullerenes, and initial results will be discussed and compared to previous reaction methods. Single crystal X-ray structures of four separate compounds believed to be "trapped intermediates" formed from the radical substitution reaction isolated from radical reactions with CF3I using different PAHs and different reactions conditions will be discussed as well as the implications these trapped intermediates have on the proposed mechanism of CF3• radical substitution reactions. Crystal packing and nearest molecule analysis of five PAH(CF3)n will be compared to a single crystal X-ray structure of triphenylene with a C4F4 substitution. Insights into the structural effects of CF3 substitutions compared to the flat C4F4 substitutions, and, how those effects would translate into electronic communication in the solid state will be discussed. Finally, wet milling of metallurgical grade silicon in an attritor mill, under anaerobic and aerobic conditions with and without surface passivating additives to study the affects oxygen and additives can have on milled particle properties such as, crystallinity by powder X-ray diffraction, surface bonds by X-ray photoelectronspectroscopy, dynamic light scattering particle size, N2 gas uptake BET surface area and reactivity towards oxygen will be discussed. Under anaerobic conditions silicon was found to form Si–C bonds in the presence of dry- air-free heptane. Additionally, the extensive effect oxygen has on the comminution of silicon and the surprising result that, even in aerobic conditions, formation of Si–C bonds is observed. All of the research described in this dissertation has applications in one or multiple energy storage or energy conversion devices. The superweak anion salts as electrolyte salts in battery or fuel cell, C60(CF3)10 and 1,9-C60(cyclo-CF2(2-C6F4)), as electron acceptor materials in organic photovoltaic devices, and multiple PAH(CF3)n compounds as OLED active layer materials

Jahn–Teller Effect in the B₁₂F₁₂ Radical Anion and Energetic Preference of an Octahedral B₆(BF₂)₆ Cluster Structure over an Icosahedral Structure for the Elusive Neutral B₁₂F₁₂

The B₁₂F₁₂^– radical anion was generated by oxidation of [CoCp₂⁺]₂B₁₂F₁₂^2– with AsF₅ in SO₂. In the crystal structure of [CoCp₂⁺]­B₁₂F₁₂^–, the anion displays a lowered symmetry (<i>D</i>_2<i>h</i>) instead of an <i>I_h</i>-symmetric dianion as a result of Jahn–Teller distortion. Moreover, shortening of the B–F bonds and subtle changes of the B–B bonds are observed. DFT calculations show that, for the unknown neutral B₁₂F₁₂, unprecedented structural isomers [e.g., octahedral B₆(BF₂)₆] are energetically favored instead of an icosahedral structure. The structures and energetics are compared with those of the analogous chlorine compounds