Assembly and mechanical characterization of suspended boron nitride nanotubes

This study details the dielectrophoretic assembly and mechanical characterization of boron nitride nanotubes on silicon chips with gold electrodes. The chips were fabricated from 4in round silicon wafers with a 100nm-thick low stress silicon nitride insulating layer on the top and bottom. The electrodes were patterned using photo- and electron-beam lithography and dry etching, and the wafers were cut into 4 x 6mm chips. The boron nitride nanotubes studied were obtained from NIA and were synthesized via a unique pressurized vapor/condensor method, which produced long, small-diameter BNNTs without the use of a catalyst. These nanotubes were studied due to their desirable mechanical and electrical properties, which allow for unique applications in various areas of science, engineering, and technology. Applications span from magnetic manipulation to the formation of biocomposites, from nano-transistors to humidity and pH sensors, and from MRI contrast agents to drug delivery. The nanotubes and nanotube bundles characterized were suspended over gaps of 300 to 500nm. This study was unique in that assembly was performed using dielectrophoresis, allowing for batch fabrication of chips and devices. Also, stiffness measurements were performed using AFM, eliminating the reliance of other methods upon electron microscopes, and allowing for imaging and measurements to occur simultaneously and at high resolution. It was found that DEP parameters of V = 2.0Vpp, f = 1kHz, and t = 2min provided the best results for mechanical testing. The nanotubes tested had suspended lengths of 300nm, the width of the electrode gap, and diameters of 15–65nm. Chips were imaged with both scanning electron microscopy and atomic force microscopy. Force-displacement measurements with atomic force microscopy were used to find stiffness values in the range of 1–16N/m. These stiffness values, when plugged into a simple double-clamped beam model, indicated Young’s moduli of approximately 1–1600GPa. Within this wide range, it was shown that a decrease in diameter strongly correlated exponentially to an increase in Young’s modulus. Work in this study was divided between assembly and characterization. Therefore, a lot of time was spent working to optimize dielectrophoresis parameters, followed by SEM and AFM imaging. Parameters that were adjusted included DEP voltage and time, pre-DEP sonication times, as well as adding a centrifuging procedure to attempt to better separate nanotube bundles in solution. Another method discussed but not pursued was the use of surfactants to agitate the solution, thus separating the nanotubes. The reason this material in particular was so difficult to separate was twofold. First, the small size of the nanotubes—individual BNNTs have diameters on the order of ∼5 nanometers—generates very strong nanoscale van der Waals forces holding the nanotubes together. Larger nanotubes—with diameters on the order of 50 to 100nm or more—suffer less from this problem. Also, the dipoles created by the boron-nitrogen bonds cause attraction between adjacent nanotubes. The results shown in this thesis include DEP parameters, SEM and AFM images, and force- displacement curves leading to nanotube stiffness and Young’s modulus values. The force-displacement tests via AFM are also detailed and explained

Alcohol metabolizing genes and alcohol phenotypes in an Israeli household sample

BACKGROUND: Alcohol dehydrogenase 1B and 1C (ADH1B and ADH1C) variants have been robustly associated with alcohol phenotypes in East Asian populations, but less so in non-Asian populations where prevalence of the most protective ADH1B allele is low (generally <5%). Further, the joint effects of ADH1B and ADH1C on alcohol phenotypes have been unclear. Therefore, we tested the independent and joint effects of ADH1B and ADH1C on alcohol phenotypes in an Israeli sample, with higher prevalence of the most protective ADH1B allele than other non-Asian populations. METHODS: A structured interview assessed lifetime drinking and alcohol use disorders (AUDs) in adult Israeli household residents. Four single nucleotide polymorphisms (SNPs) were genotyped: ADH1B (rs1229984, rs1229982, and rs1159918) and ADH1C (rs698). Regression analysis examined the association between alcohol phenotypes and each SNP (absence vs. presence of the protective allele) as well as rs698/rs1229984 diplotypes (also indicating absence or presence of protective alleles) in lifetime drinkers (n = 1,129). RESULTS: Lack of the ADH1B rs1229984 protective allele was significantly associated with consumption- and AUD-related phenotypes (OR = 1.77 for AUD; OR = 1.83 for risk drinking), while lack of the ADH1C rs698 protective allele was significantly associated with AUD-related phenotypes (OR = 2.32 for AUD). Diplotype analysis indicated that jointly ADH1B and ADH1C significantly influenced AUD-related phenotypes. For example, among those without protective alleles for ADH1B or ADH1C, OR for AUD was 1.87 as compared to those without the protective allele for ADH1B only and was 3.16 as compared to those with protective alleles for both ADH1B and ADH1C. CONCLUSIONS: This study adds support for the relationship of ADH1B and ADH1C and alcohol phenotypes in non-Asians. Further, these findings help clarify the mixed results from previous studies by showing that ADH1B and ADH1C jointly effect AUDs, but not consumption. Studies of the association between alcohol phenotypes and either ADH1B or ADH1C alone may employ an oversimplified model, masking relevant information

District Health Managers' Perceptions of Supervision in Malawi and Tanzania.

Mid-level cadres are being used to address human resource shortages in many African contexts, but insufficient and ineffective human resource management is compromising their performance. Supervision plays a key role in performance and motivation, but is frequently characterised by periodic inspection and control, rather than support and feedback to improve performance. This paper explores the perceptions of district health management teams in Tanzania and Malawi on their role as supervisors and on the challenges to effective supervision at the district level. This qualitative study took place as part of a broader project, "Health Systems Strengthening for Equity: The Power and Potential of Mid-Level Providers". Semi-structured interviews were conducted with 20 district health management team personnel in Malawi and 37 council health team members in Tanzania. The interviews covered a range of human resource management issues, including supervision and performance assessment, staff job descriptions and roles, motivation and working conditions. Participants displayed varying attitudes to the nature and purpose of the supervision process. Much of the discourse in Malawi centred on inspection and control, while interviewees in Tanzania were more likely to articulate a paradigm characterised by support and improvement. In both countries, facility level performance metrics dominated. The lack of competency-based indicators or clear standards to assess individual health worker performance were considered problematic. Shortages of staff, at both district and facility level, were described as a major impediment to carrying out regular supervisory visits. Other challenges included conflicting and multiple responsibilities of district health team staff and financial constraints. Supervision is a central component of effective human resource management. Policy level attention is crucial to ensure a systematic, structured process that is based on common understandings of the role and purpose of supervision. This is particularly important in a context where the majority of staff are mid-level cadres for whom regulation and guidelines may not be as formalised or well-developed as for traditional cadres, such as registered nurses and medical doctors. Supervision needs to be adequately resourced and supported in order to improve performance and retention at the district level

The Early Ultraviolet Light-Curves of Type II Supernovae and the Radii of Their Progenitor Stars

We present a sample of 34 normal SNe II detected with the Zwicky Transient Facility, with multi-band UV light-curves starting at $t \leq 4$ days after explosion, as well as X-ray detections and upper limits. We characterize the early UV-optical colors and provide prescriptions for empirical host-extinction corrections. We show that the $t > 2\,$days UV-optical colors and the blackbody evolution of the sample are consistent with the predictions of spherical phase shock-cooling (SC), independently of the presence of `flash ionization" features. We present a framework for fitting SC models which can reproduce the parameters of a set of multi-group simulations without a significant bias up to 20% in radius and velocity. Observations of about half of the SNe II in the sample are well-fit by models with breakout radii $<10^{14}\,$cm. The other half are typically more luminous, with observations from day 1 onward that are better fit by a model with a large $>10^{14}\,$cm breakout radius. However, these fits predict an early rise during the first day that is too slow. We suggest these large-breakout events are explosions of stars with an inflated envelope or a confined CSM with a steep density profile, at which breakout occurs. Using the X-ray data, we derive constraints on the extended ($\sim10^{15}$ cm) CSM density independent of spectral modeling, and find most SNe II progenitors lose $<10^{-4} M_{\odot}\, \rm yr^{-1}$ a few years before explosion. This provides independent evidence the CSM around many SNe II progenitors is confined. We show that the overall observed breakout radius distribution is skewed to higher radii due to a luminosity bias. We argue that the $66^{+11}_{-22}\%$ of red supergiants (RSG) explode as SNe II with breakout radii consistent with the observed distribution of field RSG, with a tail extending to large radii, likely due to the presence of CSM.Comment: Submitted to ApJ. Comments are welcome at [email protected] or [email protected]

NMDA and Dopamine Converge on the NMDA-Receptor to Induce ERK Activation and Synaptic Depression in Mature Hippocampus

The formation of enduring internal representation of sensory information demands, in many cases, convergence in time and space of two different stimuli. The first conveys the sensory input, mediated via fast neurotransmission. The second conveys the meaning of the input, hypothesized to be mediated via slow neurotransmission. We tested the biochemical conditions and feasibility for fast (NMDA) and slow (dopamine) neurotransmission to converge on the Mitogen Activated Protein Kinase signaling pathways, crucial in several forms of synaptic plasticity, and recorded its effects upon synaptic transmission. We detected differing kinetics of ERK2 activation and synaptic strength changes in the CA1 for low and high doses of neurotransmitters in hippocampal slices. Moreover, when weak fast and slow inputs are given together, they converge on ERK2, but not on p38 or JNK, and induce strong short-term synaptic depression. Surprisingly, pharmacological analysis revealed that a probable site of such convergence is the NMDA receptor itself, suggesting it serves as a detector and integrator of fast and slow neurotransmission in the mature mammalian brain, as revealed by ERK2 activation and synaptic function

Multiple novel prostate cancer susceptibility signals identified by fine-mapping of known risk loci among Europeans

Genome-wide association studies (GWAS) have identified numerous common prostate cancer (PrCa) susceptibility loci. We have fine-mapped 64 GWAS regions known at the conclusion of the iCOGS study using large-scale genotyping and imputation in 25 723 PrCa cases and 26 274 controls of European ancestry. We detected evidence for multiple independent signals at 16 regions, 12 of which contained additional newly identified significant associations. A single signal comprising a spectrum of correlated variation was observed at 39 regions; 35 of which are now described by a novel more significantly associated lead SNP, while the originally reported variant remained as the lead SNP only in 4 regions. We also confirmed two association signals in Europeans that had been previously reported only in East-Asian GWAS. Based on statistical evidence and linkage disequilibrium (LD) structure, we have curated and narrowed down the list of the most likely candidate causal variants for each region. Functional annotation using data from ENCODE filtered for PrCa cell lines and eQTL analysis demonstrated significant enrichment for overlap with bio-features within this set. By incorporating the novel risk variants identified here alongside the refined data for existing association signals, we estimate that these loci now explain ∼38.9% of the familial relative risk of PrCa, an 8.9% improvement over the previously reported GWAS tag SNPs. This suggests that a significant fraction of the heritability of PrCa may have been hidden during the discovery phase of GWAS, in particular due to the presence of multiple independent signals within the same regio

Effects of geometry and phase on material damage response under high-speed impact

Peridynamics, presented by Silling in 2000 [1], is a reformulation of the elastic theory from differential equations to integral equations, which are more equipped to handle discontinuities, such as crack initiation and propagation. Because of this, peridynamics is an effective tool to address many of the problems relevant to the aerospace and defense industries. For example, airborne sand particles and raindrops cause local damage to aircraft in flight. This damage manifests itself as radial and subsurface lateral cracking, as well as increased surface roughness. All of these damage morphologies may result in undesired degradation of mechanical and optical properties. This dissertation aims to address the question of how peridynamics (PD) can be used as a tool to help understand impact problems and resultant damage. Three main types of problems will be discussed: (1) modeling of quasi-static nano- and micro-indentation in PD; (2) solid impact experiments and simulations involving glass micro-spheres impacting coated and uncoated advanced ceramics, and sand particles impacting optical glasses; and (3) the implementation of a new, fully three-dimensional hyperelastic material model in state-based PD to simulate nylon bead impact and capture the damage patterns relevant to raindrop impact. In the first portion, a new method for modeling indentation in PD is presented using the principle of viscous damping and automatic convergence checking. In these simulations, depth-controlled indentation is performed by splitting up the total indentation depth into multiple stages, and applying damping at each stage to ensure the system reaches equilibrium before allowing for failure. PD results show good agreement to experimental data, in terms of crack lengths and force-displacement curves. In a chapter about solid particle impact, two studies are presented. In the first, glass spheres with diameters ranging from 200 to 700 um impact multi-spectral zinc sulfide (MS-ZnS) with various coating systems. It was found that samples containing the REP coating had better resistance to damage than those without. This resistance was evident in all three damage metrics used: impact pit diameter, radial crack length, and lateral crack size. Simulations were carried out in bond-based PD, with good agreement to experiments regarding damage metrics and rebound velocity. The second solid particle impact study involved sand particles impacting four different types of optical glasses: BK7, alumino-boro-silicate, fused silica, and Pyrex. First, data from experiments was analyzed, and a multi-variable power law regression was performed to show that sand particle shape plays a significant role in resultant damage. This was confirmed via bond-based PD simulations, with damage quantities agreeing well with experimental values. Finally, the problem of how to model raindrop impact using nylon beads was examined. Due to the large amounts of elastic strain experienced by the nylon beads during impact experiments, it was determined that a hyperelastic material model could be a good fit. Based on elastic theory and classical continuum mechanics, a new, fully three-dimensional Neo-Hookean material model was implemented in nonordinary state-based peridynamics. This model was verified against results and finite element analysis, with very good agreement. Preliminary simulations including damage show good results, consistent with experiments

Goods Worthy of a Free People: Sugar, Commerce, and Consumer Rights in the French Revolution

At the end of the eighteenth century, the French island colony of Saint Domingue was the largest producer of sugar in the world. Powered by a brutal system of plantation slavery, the colony pumped wealth into France, boosted trade, and fueled consumption across France and Europe by providing a cheap and abundant supply of sugar and coffee. French urban dwellers from up and down the social scale became habitual consumers of these colonial commodities, and integrated them into their social, domestic, and working lives. In the summer of 1791, however, a massive uprising of enslaved laborers rocked the sugar-producing island colony. The rebellion—which marked the beginning of the Haitian Revolution—sent the plantation system crashing down and the French sugar market into disarray. This dissertation uses sugar to investigate the economic, political, and social impact of the Haitian Revolution on revolutionary France. It traces the consequences of the massive slave uprising on the island colony to the metropole, where the price of sugar skyrocketed and consequently prompted a series of consumer riots in the capital. Analyzing these riots in addition to debates around sugar consumption and economic policy, this dissertation shows how the sugar crisis fueled contestation and competing claims between consumers, merchants, and authorities. Through sugar, revolutionaries debated larger questions about the purpose of the Revolution, the rights of citizens, and their vision for society in a post-Old-Regime political order. Historians typically analyze the Haitian Revolution in the context of political and philosophical thought around slavery, race, colonialism, and citizenship. This dissertation broadens our understanding of the Haitian Revolution’s important but little-examined economic impact on France and the French Revolution, and a second layer of social, political, and cultural-intellectual ramifications. This dissertation also contributes to the history of consumption in the French Revolution. Scholars tend to approach consumption in this period as a symbolic practice rooted in material culture and directed from the top down. In contrast, this dissertation uses sugar to explore how consumers politicized the act of consumption itself and channeled their notion of citizenship through their identities as consumers

Goods Worthy of a Free People: Sugar, Commerce, and Consumer Rights in the French Revolution

At the end of the eighteenth century, the French island colony of Saint Domingue was the largest producer of sugar in the world. Powered by a brutal system of plantation slavery, the colony pumped wealth into France, boosted trade, and fueled consumption across France and Europe by providing a cheap and abundant supply of sugar and coffee. French urban dwellers from up and down the social scale became habitual consumers of these colonial commodities, and integrated them into their social, domestic, and working lives. In the summer of 1791, however, a massive uprising of enslaved laborers rocked the sugar-producing island colony. The rebellion—which marked the beginning of the Haitian Revolution—sent the plantation system crashing down and the French sugar market into disarray. This dissertation uses sugar to investigate the economic, political, and social impact of the Haitian Revolution on revolutionary France. It traces the consequences of the massive slave uprising on the island colony to the metropole, where the price of sugar skyrocketed and consequently prompted a series of consumer riots in the capital. Analyzing these riots in addition to debates around sugar consumption and economic policy, this dissertation shows how the sugar crisis fueled contestation and competing claims between consumers, merchants, and authorities. Through sugar, revolutionaries debated larger questions about the purpose of the Revolution, the rights of citizens, and their vision for society in a post-Old-Regime political order. Historians typically analyze the Haitian Revolution in the context of political and philosophical thought around slavery, race, colonialism, and citizenship. This dissertation broadens our understanding of the Haitian Revolution’s important but little-examined economic impact on France and the French Revolution, and a second layer of social, political, and cultural-intellectual ramifications. This dissertation also contributes to the history of consumption in the French Revolution. Scholars tend to approach consumption in this period as a symbolic practice rooted in material culture and directed from the top down. In contrast, this dissertation uses sugar to explore how consumers politicized the act of consumption itself and channeled their notion of citizenship through their identities as consumers