1,142 research outputs found
Understanding Electric Field-Enhanced Transport for the Measurement of Nanoparticles and Their Assembly on Surfaces
The goal of this dissertation is to understand the synthesis, characterization, and integration of nanoparticles and nanoparticle-based devices by electric field-enhanced transport of nanoparticles. Chapter 1 describes the factors used for determining particle trajectories and found that electric fields provide the directional electrostatic force to overcome other non-directional influences on particle trajectories. This idea is widely applied in the nanoparticle classification, characterization, and assembly onto substrate surfaces as investigated in the following chapters.
Chapter 2 presents a new assembly method to position metal nanoparticles delivered from the gas phase onto surfaces using the electrostatic force generated by biased p-n junction patterned substrates. Aligned deposition patterns of metal nanoparticles were observed, and the patterning selectivity quantified. A simple model accounting for the generated electric field, and the electrostatic, van der Waals, and image forces was used to explain the observed results. Chapter 2.2 describes a data set for particle size resolved deposition, from which a Brownian dynamics model for the process can be evaluated. Brownian motion and fluid convection of nanoparticles, as well as the interactions between the charged nanoparticles and the patterned substrate, including electrostatic force, image force and van der Waals force, are accounted for in the simulation. Using both experiment and simulation the effects of the particle size, electric field intensity, and the convective flow on coverage selectivity have been investigated. Coverage selectivity is most sensitive to electric field, which is controlled by the applied reverse bias voltage across the p-n junction. A non-dimensional analysis of the competition between the electrostatic and diffusion force is found to provide a means to collapse a wide range of process operating conditions and an effective indicator or process performance. Directed assembly of size-selected nanoparticles has been applied in the study of nanoparticle enhanced fluorescence (NEF) bio-sensing devices.
Chapter 3 presents results of a systematic examination of functionalized gold nanoparticles by electrospray-differential mobility analysis (ES-DMA). Formation of selfassembled monolayers (SAMs) of alkylthiol molecules and singly stranded DNA (ssDNA) on the Au-NP surface was detected from a change in particle mobility, which could be modeled to extract the surface packing density. A gas-phase temperature-programmed desorption (TPD) kinetic study of SAMs on the Au-NP found the data to be consistent with a second order Arrhenius based rate law, yielding an Arrhenius-factor of 1×1011 s-1 and an activation energy ~105 kJ/mol. This study suggests that the ES-DMA can be added to the tool set of characterization methods being employed and developed to study the structure and properties of coated nanoparticles.
Chapter 3.2 demonstrates this ES-DMA as a new method to investigate colloidal aggregation and the parameters that govern it. Nanoparticle suspensions were characterized by sampling a Au nanoparticle (Au-NP) colloidal solution via electrospray (ES), followed by differential ion-mobility analysis (DMA) to determine the mobility distribution, and thus the aggregate distribution. By sampling at various times, the degree of flocculation and the flocculation rate are determined and found to be inversely proportional to the ionic strength and proportional to the residence time. A stability ratio at different ionic strengths, the critical concentration, and surface potential or surface charge density of Au-NPs are obtained from these data. This method should be a generically useful tool to probe the early stages of colloidal aggregation.
Study of ES-DMA is extended to include the characterizations of a variety of materials. Biologically interested materials such as viruses and antibodies could also be characterized. These results show ES-DMA provides a general way to characterize the colloidal materials as well as aerosolized particles
Preparation of Metal Organic Framework (MOF) Derived Bimetallic Catalyst for Dry Reforming of Methane
In the past decade, efforts have been
focused on development of catalyst to show high activity for dry reforming of
methane (DRM). The development of catalyst has been crucial to be carried out
as this may significantly reduce the concentration of most common greenhouse
gases, namely methane (CH4) and carbon dioxide (CO2) in
the atmosphere. In present work, a series of varying molar ratio of Ni:Ce metal
organic framework (MOF) derived catalysts were grown on alumina in one step.
The synthesis steps were in accordance to reported solvothermal method for the
syntheses of NH2-MIL-88B with slight modification. This was followed
by reduction at 500°C in hydrogen environment for 1 h. The physical and
chemical properties of the catalysts were probed by powder XRD, BET surface
area analysis, EDX, ICP, CO2-TPD and H2-TPR. XRD showed
that diffraction patterns were in agreement with the diffraction pattern of MOF
synthesized in previous work, thus confirmed the successful formation of the MOF
structure. The variation in the molar ratio of Ni:Ce did not show significant
difference in the diffraction pattern of the MOF-derived catalysts. For reduction
phase, sharp diffraction peaks were detected at 2? = 44.5°, 51.85°, and 76.37°, which can be
indexed to (1 1 1), (2 0 0) and (2 2 0) planes of face-centered cubic (FCC)
metallic Ni, respectively. The addition of Ce promoted smaller particle size of
Ni, ranging from 4.6 nm to 6.88 nm. The presence of CeO2 was
observed at 2? = 28.6°, 33.0°, and 56.4°. Elemental distribution was compared
between EDX and ICP-OES. ICP-OES and EDX analyses indicated that weight percent
of bimetallic metal of Ni and Ce was consistent, in which the amount of
respective metal obeyed the ratio trend of the metal precursors added during
the MOF synthesis. This suggested the homogeneity of the catalyst, even though
EDX showed relatively higher weight percent than ICP-OES. The catalytic performance
of catalysts showed that 1Ni1Ce exhibited better conversion of CH4
and CO2, with 63.5% and 86.8% respectively at 800oC, and
the conversion tend to increase at a higher temperature. The results were
convincing for the design of a performing catalyst for DRM process
The Mechanism of Ubiquitination in the Cullin-RING E3 Ligase Machinery: Conformational Control of Substrate Orientation
In cullin-RING E3 ubiquitin ligases, substrate binding proteins, such as VHL-box, SOCS-box or the F-box proteins, recruit substrates for ubiquitination, accurately positioning and orienting the substrates for ubiquitin transfer. Yet, how the E3 machinery precisely positions the substrate is unknown. Here, we simulated nine substrate binding proteins: Skp2, Fbw7, β-TrCP1, Cdc4, Fbs1, TIR1, pVHL, SOCS2, and SOCS4, in the unbound form and bound to Skp1, ASK1 or Elongin C. All nine proteins have two domains: one binds to the substrate; the other to E3 ligase modules Skp1/ASK1/Elongin C. We discovered that in all cases the flexible inter-domain linker serves as a hinge, rotating the substrate binding domain, optimally and accurately positioning it for ubiquitin transfer. We observed a conserved proline in the linker of all nine proteins. In all cases, the prolines pucker substantially and the pucker is associated with the backbone rotation toward the E2/ubiquitin. We further observed that the linker flexibility could be regulated allosterically by binding events associated with either domain. We conclude that the flexible linker in the substrate binding proteins orients the substrate for the ubiquitin transfer. Our findings provide a mechanism for ubiquitination and polyubiquitination, illustrating that these processes are under conformational control
Azetidinium lead iodide for perovskite solar cells
Hybrid organic–inorganic perovskites have been established as good candidate materials for emerging photovoltaics, with device efficiencies of over 22% being reported. There are currently only two organic cations, methylammonium and formamidinium, which produce 3D perovskites with band gaps suitable for photovoltaic devices. Numerous computational studies have identified azetidinium as a potential third cation for synthesizing organic–inorganic perovskites, but to date no experimental reports of azetidinium containing perovskites have been published. Here we prepare azetidinium lead iodide for the first time. Azetidinium lead iodide is a stable, bright orange material which does not appear to form a 3D or a 2D perovskite. It was successfully used as the absorber layer in solar cells. We also show that it is possible to make mixed cation devices by adding the azetidinium cation to methylammonium lead iodide. Computational studies show that the substitution of up to 5% azetidinium into the methylammonium lead iodide is energetically favourable and that phase separation does not occur at these concentrations. Mixed azetidinium–methylammonium cells show improved performance and reduced hysteresis compared to methylammonium lead iodide cells
Calibrating Extinction-Free Star Formation Rate Diagnostics with 33GHz Free-Free Emission in NGC6946
Abridged: Using free-free emission measured in the Ka-band (26-40GHz) for 10
star-forming regions in the nearby galaxy NGC6946, including its starbursting
nucleus, we compare a number of SFR diagnostics that are typically considered
to be unaffected by interstellar extinction: i.e., non-thermal radio (i.e.,
1.4GHz), total infrared (IR; 8-1000um), and warm dust (i.e., 24um) emission,
along with the hybrid (obscured + unobscured) indicators of H\alpha+24um and
UV+IR. The 33GHz free-free emission is assumed to provide the most accurate
measure of the current SFR. Among the extranuclear star-forming regions, the
24um, H\alpha+24um and UV+IR SFR calibrations are in good agreement with the
33GHz free-free SFRs. However, each of the SFR calibrations relying on some
form of dust emission overestimate the nuclear SFR by a factor of ~2. This is
more likely the result of excess dust heating through an accumulation of
non-ionizing stars associated with an extended episode of star formation in the
nucleus rather than increased competition for ionizing photons by dust. SFR
calibrations using the non-thermal radio continuum yield values which only
agree with the free-free SFRs for the nucleus, and underestimate the SFRs from
the extranuclear star-forming regions by a factor of ~2. This result likely
arises from the CR electrons decaying within the starburst region with
negligible escape compared to the young extranuclear star-forming regions.
Finally, we find that the SFRs estimated using the total 33GHz emission agree
well with the free-free SFRs due to the large thermal fractions present at
these frequencies even when local diffuse backgrounds are not removed. Thus,
rest-frame 33GHz observations may act as a reliable method to measure the SFRs
of galaxies at increasingly high redshift without the need of ancillary radio
data to account for the non-thermal emission.Comment: 18 pages, 7 Figures, Accepted for publication in Ap
The Role of Age in Predicting the Outcome of Caustic Ingestion in Adults: A Retrospective Analysis
<p>Abstract</p> <p>Background</p> <p>Although the outcomes of caustic ingestion differ between children and adults, it is unclear whether such outcomes differ among adults as a function of their age. This retrospective study was performed to ascertain whether the clinical outcomes of caustic ingestion differ significantly between elderly and non-elderly adults.</p> <p>Methods</p> <p>Medical records of patients hospitalized for caustic ingestion between June 1999 and July 2009 were reviewed retrospectively. Three hundred eighty nine patients between the ages of 17 and 107 years were divided into two groups: non-elderly (< 65 years) and elderly (≥ 65 years). Mucosal damage was graded using esophagogastroduodenoscopy (EGD). Parameters examined in this study included gender, intent of ingestion, substance ingested, systemic and gastrointestinal complications, psychological and systemic comorbidities, severity of mucosal injury, and time to expiration.</p> <p>Results</p> <p>The incidence of psychological comorbidities was higher for the non-elderly group. By contrast, the incidence of systemic comorbidities, the grade of severity of mucosal damage, and the incidence of systemic complications were higher for the elderly group. The percentages of ICU admissions and deaths in the ICU were higher and the cumulative survival rate was lower for the elderly group. Elderly subjects, those with systemic complications had the greatest mortality risk due to caustic ingestion.</p> <p>Conclusions</p> <p>Caustic ingestion by subjects ≥65 years of age is associated with poorer clinical outcomes as compared to subjects < 65 years of age; elderly subjects with systemic complications have the poorest clinical outcomes. The severity of gastrointestinal tract injury appears to have no impact on the survival of elderly subjects.</p
Adsorption and Conformation of Serum Albumin Protein on Gold Nanoparticles Investigated Using Dimensional Measurements and in Situ Spectroscopic Methods
An outcome analysis of self-expandable metallic stents in central airway obstruction: a cohort study
<p>Abstract</p> <p>Background</p> <p>Self-expandable metallic stents (SEMSs) have provided satisfactory management of central airway obstruction. However, the long-term benefits and complications of this management modality in patients with benign and malignant obstructing lesions after SEMS placement are unclear. We performed this cohort study to analyze the outcomes of Ultraflex SEMSs in patients with tracheobronchial diseases.</p> <p>Methods</p> <p>Of 149 patients, 72 with benign and 77 with malignant tracheobronchial disease received 211 SEMSs (benign, 116; malignant, 95) and were retrospectively reviewed in a tertiary hospital.</p> <p>Results</p> <p>The baseline characteristics of patients who received SEMS implantation for benign conditions and those who underwent implantation for malignant conditions were significantly different. These characteristics included age (mean, 63.9 vs. 58; <it>p </it>< 0.01), gender (male, 62% vs. 90%; <it>p </it>< 0.0001), smoking (47% vs. 85%; <it>p </it>< 0.0001), forced expiratory volume in 1 second (mean, 0.9 vs. 1.47 L/s; <it>p </it>< 0.0001), follow-up days after SEMS implantation (median; 429 vs. 57; <it>p </it>< 0.0001), and use of covered SEMS (36.2% vs. 94.7%; <it>p </it>< 0.0001). Symptoms improved more after SEMS implantation in patients with benign conditions than in those with malignant conditions (76.7% vs. 51.6%; <it>p </it>< 0.0001). The overall complication rate after SEMS implantation in patients with benign conditions was higher than that in patients with malignancy (42.2% vs. 21.1%; <it>p </it>= 0.001). Successful management of SEMS migration, granulation tissue formation, and SEMS fracture occurred in 100%, 81.25%, and 85% of patients, respectively.</p> <p>Conclusions</p> <p>Patients who received SEMS implantation owing to benign conditions had worse lung function and were older than those who received SEMS for malignancies. There was higher complication rate in patients with benign conditions after a longer follow-up period owing to the nature of the underlying diseases.</p
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