Topological Constraint Theory Analysis of Rigidity Transition in Highly Coordinate Amorphous Hydrogenated Boron Carbide

Topological constraint theory (TCT) has revealed itself to be a powerful tool in interpreting the behaviors of amorphous solids. The theory predicts a transition between a “rigid” overconstrained network and a “floppy” underconstrained network as a function of connectivity or average coordination number, 〈r〉. The predicted results have been shown experimentally for various glassy materials, the majority of these being based on 4-fold-coordinate networks such as chalcogenide and oxide glasses. Here, we demonstrate the broader applicability of topological constraint theory to uniquely coordinated amorphous hydrogenated boron carbide (a-BC:H), based on 6-fold-coordinate boron atoms arranged into partially hydrogenated interconnected 12-vertex icosahedra. We have produced a substantial set of plasma-enhanced chemical vapor deposited a-BC:H films with a large range of densities and network coordination, and demonstrate a clear threshold in Young\u27s modulus as a function of 〈r〉, ascribed to a rigidity transition. We investigate constraint counting strategies in this material and show that by treating icosahedra as “superatoms,” a rigidity transition is observed within the range of the theoretically predicted 〈r〉c value of 2.4 for covalent solids with bond-stretching and bond-bending forces. This experimental data set for a-BC:H is unique in that it represents a uniform change in connectivity with 〈r〉 and demonstrates a distinct rigidity transition with data points both above and below the transition threshold. Finally, we discuss how TCT can be applied to explain and optimize mechanical and dielectric properties in a-BC:H and related materials in the context of microelectronics applications

Carbon‐Enriched Amorphous Hydrogenated Boron Carbide Films for Very‐Low‐k Interlayer Dielectrics

A longstanding challenge in ultralarge‐scale integration has been the continued improvement in low‐dielectric‐constant (low‐k) interlayer dielectric materials and other specialized layers in back‐end‐of‐the‐line interconnect fabrication. Modeled after the success of carbon‐containing organosilicate materials, carbon‐enriched amorphous hydrogenated boron carbide (a‐BxC:Hy) films are grown by plasma‐enhanced chemical vapor deposition from ortho‐carborane and methane. These films contain more extraicosahedral sp3 hydrocarbon groups than nonenriched a‐BxC:Hy films, as revealed by FTIR and NMR spectroscopy, and also exhibit lower dielectric constants than their nonenriched counterparts, notably due to low densities combined with a low distortion and orientation contribution to the total polarizability. Films with dielectric constant as low as 2.5 are reported with excellent electrical stability (leakage current of 10−9 A cm−2 at 2 MV cm−1 and breakdown voltage of >6 MV cm−1), good thermal conductivity of 0.31 ± 0.03 W m−1 K−1, and high projected Young’s modulus of 12 ± 3 GPa. These properties rival those of leading SiOC:H materials, and position a‐BxC:Hy as an important complement to traditional Si‐based materials to meet the complex needs of next‐generation interconnect fabrication.Carbon‐enriched amorphous hydrogenated boron carbide films are demonstrated with dielectric constant (k) as low as 2.5—attributed to low densities combined with network‐rigidifying CH2 bridging groups—as well as excellent electrical, thermal, and mechanical properties, rivaling those of state‐of‐the‐art silicon‐based low‐k dielectric materials.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/141869/1/aelm201700116_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/141869/2/aelm201700116.pd

The Public Repository of Xenografts enables discovery and randomized phase II-like trials in mice

More than 90% of drugs with preclinical activity fail in human trials, largely due to insufficient efficacy. We hypothesized that adequately powered trials of patient-derived xenografts (PDX) in mice could efficiently define therapeutic activity across heterogeneous tumors. To address this hypothesis, we established a large, publicly available repository of well-characterized leukemia and lymphoma PDXs that undergo orthotopic engraftment, called the Public Repository of Xenografts (PRoXe). PRoXe includes all de-identified information relevant to the primary specimens and the PDXs derived from them. Using this repository, we demonstrate that large studies of acute leukemia PDXs that mimic human randomized clinical trials can characterize drug efficacy and generate transcriptional, functional, and proteomic biomarkers in both treatment-naive and relapsed/refractory disease

D27-pLpxL, an Avirulent Strain of Yersinia pestis, Primes T Cells That Protect against Pneumonic Plague▿

Vaccinating with live, conditionally attenuated, pigmentation (Pgm)-deficient Yersinia pestis primes T cells that protect mice against pneumonic plague. However, Pgm-deficient strains are not considered safe for human use because they retain substantial virulence in animal models. Y. pestis strains engineered to express Escherichia coli LpxL are avirulent owing to constitutive production of lipopolysaccharide with increased Toll-like receptor 4-activating ability. We generated an LpxL-expressing Pgm-deficient strain (D27-pLpxL) and demonstrate here that this avirulent strain retains the capacity to prime protective T cells. Compared with unvaccinated controls, mice immunized intranasally with live D27-pLpxL exhibit a decreased bacterial burden and increased survival when challenged intranasally with virulent Y. pestis. T cells provide a substantial degree of this protection, as vaccine efficacy is maintained in B-cell-deficient μMT mice unless those animals are depleted of CD4 and CD8 T cells at the time of challenge. Upon challenge with Y. pestis, pulmonary T-cell numbers decline in naive mice, whereas immunized mice show increased numbers of CD44high CD43high effector T cells and T cells primed to produce tumor necrosis factor alpha and gamma interferon; neutralizing these cytokines at the time of challenge abrogates protection. Immunization does not prevent dissemination of Y. pestis from the lung but limits bacterial growth and pathology in visceral tissue, apparently by facilitating formation of granuloma-like structures. This study describes a new model for studying T-cell-mediated protection against pneumonic plague and demonstrates the capacity for live, highly attenuated, Y. pestis vaccine strains to prime protective memory T-cell responses safely

Modulating Short Wavelength Fluorescence with Long Wavelength Light

Two molecules in which the intensity of shorter-wavelength fluorescence from a strong fluorophore is modulated by longer-wavelength irradiation of an attached merocyanine-spirooxazine reverse photochromic moiety have been synthesized and studied. This unusual fluorescence behavior is the result of quenching of fluorophore fluorescence by the thermally stable, open, zwitterionic form of the spirooxazine, whereas the photogenerated closed, spirocyclic form has no effect on the fluorophore excited state. The population ratio of the closed and open forms of the spirooxazine is controlled by the intensity of the longer-wavelength modulated light. Both square wave and sine wave modulation were investigated. Because the merocyanine-spirooxazine is an unusual reverse photochrome with a thermally stable long-wavelength absorbing form and a short-wavelength absorbing photogenerated isomer with a very short lifetime, this phenomenon does not require irradiation of the molecules with potentially damaging ultraviolet light, and rapid modulation of fluorescence is possible. Molecules demonstrating these properties may be useful in fluorescent probes, as their use can discriminate between probe fluorescence and various types of adventitious autofluorescence from other molecules in the system being studied

A Web Application about Herd Immunity Using Personalized Avatars: Development Study

Background: Herd immunity or community immunity refers to the reduced risk of infection among susceptible individuals in a population through the presence and proximity of immune individuals. Recent studies suggest that improving the understanding of community immunity may increase intentions to get vaccinated. Objective: This study aims to design a web application about community immunity and optimize it based on users\u2019 cognitive and emotional responses. Methods: Our multidisciplinary team developed a web application about community immunity to communicate epidemiological evidence in a personalized way. In our application, people build their own community by creating an avatar representing themselves and 8 other avatars representing people around them, for example, their family or coworkers. The application integrates these avatars in a 2-min visualization showing how different parameters (eg, vaccine coverage, and contact within communities) influence community immunity. We predefined communication goals, created prototype visualizations, and tested four iterative versions of our visualization in a university-based human-computer interaction laboratory and community-based settings (a cafeteria, two shopping malls, and a public library). Data included psychophysiological measures (eye tracking, galvanic skin response, facial emotion recognition, and electroencephalogram) to assess participants\u2019 cognitive and affective responses to the visualization and verbal feedback to assess their interpretations of the visualization\u2019s content and messaging. Results: Among 110 participants across all four cycles, 68 (61.8%) were women and 38 (34.5%) were men (4/110, 3.6%; not reported), with a mean age of 38 (SD 17) years. More than half (65/110, 59.0%) of participants reported having a university-level education. Iterative changes across the cycles included adding the ability for users to create their own avatars, specific signals about who was represented by the different avatars, using color and movement to indicate protection or lack of protection from infectious disease, and changes to terminology to ensure clarity for people with varying educational backgrounds. Overall, we observed 3 generalizable findings. First, visualization does indeed appear to be a promising medium for conveying what community immunity is and how it works. Second, by involving multiple users in an iterative design process, it is possible to create a short and simple visualization that clearly conveys a complex topic. Finally, evaluating users\u2019 emotional responses during the design process, in addition to their cognitive responses, offers insights that help inform the final design of an intervention. Conclusions: Visualization with personalized avatars may help people understand their individual roles in population health. Our app showed promise as a method of communicating the relationship between individual behavior and community health. The next steps will include assessing the effects of the application on risk perception, knowledge, and vaccination intentions in a randomized controlled trial. This study offers a potential road map for designing health communication materials for complex topics such as community immunity