1,721,110 research outputs found
Detection of Explosives Using a Micro-cantilever Array Nano-Calorimeter System
Get PDFOver the past few decades, the likeliness of an attack from explosives has increased dramatically. Hence, the need to find a reliable device with the ability to detect
explosives has increased even more. Sensing schemes based on micro-cantilever beams and their bending responses to specific explosives are considered to be an effective
technique for explosives detection. In this study the bending responses of an array of micro-cantilever beams integrated with micro-heaters are recorded when they are
exposed to various combustible materials. The results show that the micro-cantilever beams display a distinct response when exposed to different combustible materials. In
the experiments it was observed that typically the deflection of the micro-cantilever beam in response to the thermal bi-metallic actuation was greater when exposed to
acetone vapors than that for alcohol and air. Also, the deflection of the beam was greater for experiments using iso-propyl alcohol than that for air. These results are consistent with prior reports in the literature
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Design, simulation and analysis of a molecular nano-sensor operating at terahertz frequencies for energetic materials.
Get PDFNano-sensors, as an application of nanotechnology, are extremely important for environmental, medical and security applications. Terahertz science is an exciting new field that is set to impact the field of sensing to a large extent. I proposed to combine the fields of nanotechnology and terahertz science and develop a molecular nano-sensor that operates at terahertz frequencies. I focused our sensing on energetic materials, particularly nitromethane, and conducted an extensive analysis on its frequency spectrum. The study also focused on designing the nano-sensor and determining its terahertz operation characteristics. I subjected it to various conditions through the use of molecular dynamics simulations. Finally we analyzed the simulation results and provided a proof of the concept that we had a working molecular nano-sensor that operates at terahertz frequencies and senses energetic materials. The results from the frequency analysis of nitromethane showed that the frequency characteristics determined from our simulations were in close agreement with the ones determined experimentally. In addition to this we also successfully demonstrated the use of a Lennard Jones potential to model the CN bond scission of nitromethane. Finally, the results from the interactions between the nano-sensor and nitromethane showed that the presence of nitromethane causes sufficient change in the terahertz frequency characteristics of the nano-sensor providing a means to detect nitromethane
Synthesis of gold nano-particles in a microfluidic platform for water quality monitoring applications
Get PDFA microfluidic lab-on-a-chip (LOC) device for in-situ synthesis of gold nano-particles
was developed. The long term goal is to develop a portable hand-held diagnostic
platform for monitoring water quality (e.g., detecting metal ion pollutants).
The LOC consists of micro-chambers housing different reagents and samples that feed to
a common reaction chamber. The reaction products are delivered to several waste
chambers in a pre-defined sequence to enable reagents/ samples to flow into and out of
the reaction chamber. Passive flow actuation is obtained by capillary driven flow
(wicking) and dissolvable microstructures called ���salt pillars���. The LOC does not require
any external power source for actuation and the passive microvalves enable flow
actuation at predefined intervals. The LOC and the dissolvable microstructures are
fabricated using a combination of photolithography and soft lithography techniques.
Experiments were conducted to demonstrate the variation in the valve actuation time
with respect to valve position and geometric parameters. Subsequently, analytical models were developed using one dimensional linear diffusion theory. The analytical
models were in good agreement with the experimental data. The microvalves were
developed using various salts: polyethylene glycol, sodium chloride and sodium acetate.
Synthesized in-situ in our experiments, gold nano-particles exhibit specific colorimetric
and optical properties due to the surface plasmon resonance effect. These stabilized
mono-disperse gold nano-particles can be coated with bio-molecular recognition motifs
on their surfaces. A colorimetric peptide assay was thus developed using the intrinsic
property of noble metal nano-particles. The LOC device was further developed on a
paper microfluidics platform. This platform was tested successfully for synthesis of gold
nano-particles using a peptide assay and using passive salt-bridge microvalves.
This study proves the feasibility of a LOC device that utilizes peptide assay for
synthesis of gold nano-particles in-situ. It could be highly significant in a simple
portable water quality monitoring platform
Experiments and Analysis of Aqueous Electrode Processing for Energy Storage
Get PDFThere is an ever-growing demand for Lithium-Ion Batteries in a widespread series of applications, where battery life and reliability are of key importance. There exist novel materials that are helping increase battery reliability and life but there is a lack of environment friendly and cost-effective processing techniques that are used to produce such energy storage devices. Current processing techniques use N-methyl-2 pyrrolidone as a solvent for electrode slurry, which is expensive and has the potential to damage the environment, increasing the risk of cancer and reproductive toxicity. Therefore, there is a need to move towards a solvent that is environmentally friendly, cheap to produce and can serve as a potential replacement. In this work, the use of deionized water has been experimentally evaluated to create an electrode processing technique that could become an environmentally friendly and cost-effective technique to produce Lithium-Ion Batteries.
This study focuses on the concepts of Lithium-Ion Batteries and their current electrode processing techniques. The proposed Aqueous Processing technique for electrode manufacture is discussed in detail along with a discussion of challenges currently being faced in this area. A 1-D physics based drying model is also developed as part of this study that is based upon evaporation, diffusion and sedimentation.
My analysis has shown that the proposed Aqueous Processing can be implemented using low-cost preparation methods and deionized water. Drying temperature has an effect on the agglomeration of particles that could impact the electrochemical performance of the electrode. My analysis has also shown that an optimal amount of dispersant needs to be added to reduce the effect of agglomeration while maintaining good film adhesion. The results from the 1-D show that at a higher drying temperature a larger volume fraction is observed at the top surface of the electrode
Evaluation of the Thermal Performance for a Wire Mesh/Hollow Glass Microsphere Composite Structure as a Conduction Barrier
Get PDFAn experimental investigation exploring the use of wire mesh/hollow glass
microsphere combination for use as thermal insulation was conducted with the aim to
conclude whether or not it represents a superior insulation technology to those on the
market.
Three primary variables, including number of wire mesh layers, filler material,
and temperature dependence were studied using an apparatus that was part of
L.I.C.H.E.N (LabVIEW Integrated Conduction Heat Experiment Network), a setup
whose basic components allow three vertically stacked samples to be thermally and
mechanically controlled. Knowing the temperature profile in the upper and lower
samples allows for determination of thermal conductivity of the middle material through
the use of Fourier?s law. The numbers of layers investigated were two, four, six, and
eight, with each separated by a metallic liner. The filler materials included air, s15, s35
and s60HS 3MTM hollow glass microspheres. The experiments were conducted at four
temperatures of 300, 330, 366, and 400K with an interface pressure of 20 Psi. The experimental results indicated the ?number of layers? used was the primary
factor in determining the effective thermal conductivity value. The addition of hollow
glass microspheres as filler material resulted in statistically insignificant changes in
effective thermal conductivity. Increasing the number of wire mesh layers resulted in a
corresponding increase in effective thermal conductivity of the insulation. Changes in
temperature had little to no effect on thermal conductivity.
The effective thermal conductivity values for the proposed insulation structure
ranged from 0.22 to 0.65 W/m-K, the lowest of which came from the two layer case
having air as filler material. The uncertainties associated with the experimental results
fell between 10 to 20 percent in all but a few cases. In the best performing cases, when
compared with existing insulation technologies, thermal conductivity was approximately
3 to 10 times higher than these methods of insulation. Thus, the proposed insulation
scheme with hollow glass-sphere filler material does not represent superior technology,
and would be deemed uncompetitive with those readily available in the insulation
market
Nanolithographic control of carbon nanotube synthesis
Get PDFA method offering precise control over the synthesis conditions to obtain carbon
nanotube (CNT) samples of a single chirality (metallic or semi-conducting) is presented.
Using this nanolithographic method of catalyst deposition, the location of CNT growth is
also precisely defined.
This technique obviates three significant hurdles that are preventing the exploitation
of CNT in micro- and nano-devices. Microelectronic applications (e.g., interconnects,
CNT gates, etc.) require precisely defined locations and spatial density, as well as
precisely defined chirality for the synthesized CNT. Conventional CVD synthesis
techniques typically yield a mixture of CNT (semi-conducting and metallic types) that
grow at random locations on a substrate in high number density, which leads to extreme
difficulty in application integration.
Dip Pen Nanolithography (DPN) techniques were used to deposit the catalysts at
precisely defined locations on a substrate and to precisely control the catalyst
composition as well as the size of the patterned catalyst. After deposition of catalysts, a
low temperature Chemical Vapor Deposition (CVD) process at atmospheric pressure
was used to synthesize CNT. Various types of catalysts (Ni, Co, Fe, Pd, Pt, and Rh) were
deposited in the form of metal salt solutions or nano-particle solutions. Various characterization studies before and after CVD synthesis of CNT at the location of the
deposited catalysts showed that the CNT were of a single chirality (metallic or semiconducting)
as well as a single diameter (with a very narrow range of variability).
Additionally, X-ray photoelectron spectroscopy (XPS) was used to characterize the
deposited samples before and after the CVD, as was lateral force microscopy (LFM) for
determination of the successful deposition of the catalyst material immediately after
DPN as well as following the CVD synthesis of the samples. The diameter of the CNT
determines the chirality. The diameter of the CNT measured by TEM was found to be
consistent with the chirality measurements obtained from Raman Spectroscopy for the
different samples. Hence, the results showed that CNT samples of a single chirality can
be obtained by this technique. The results show that the chirality of the synthesized CNT
can be controlled by changing the synthesis conditions (e.g., size of the catalyst patterns,
composition of the catalysts, temperature of CVD, gas flow rates, etc.)
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