1,720,991 research outputs found
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Design and evaluation of a small-scale portable hybrid rocket engine test stand
No full textThis paper presents the design and evaluation of a small, portable hybrid rockettest stand that can accommodate up to a 3-in diameter engine casing. The primary goal
of this study is to determine the most effective way to build a hybrid rocket test stand for
fundamental research purposes. Various design ideas were considered, including the use of
roller bearings and a vertically oriented test stand. The final design of the stand is oriented
horizontally with the use of 3 flat aluminum plates mounted to linear bearings on T-slot
structural framing. The linear bearings allow the most forward aluminum plate to contact
and press against the load cell while maintaining minimal friction with the T-slot structural
framing. The oxidizer delivery system begins at a 10-lb NOS bottle at 775-psi, going through
an adjustable pressure regulator, through an on/off solenoid valve, and finally through an
orifice plate before being injected into the combustion chamber. The test stand uses a Futek
LLB400 button load cell with a 500-lb capacity, to measure the thrust produced by the
engine. A LabVIEW Virtual Instrument controls the solenoid valve, the ignition process,
and thrust measurement. Thrust and impulse evaluations of the hybrid rocket engine were
conducted on a 1.5-in diameter solid fuel grain over various mass flow rates controlled by the
pressure regulator at 200, 300, and 400-psi, the open area of the orifice plate at 0.24-in, and
nozzle throat diameters at 13/64-in, 16/64-in, 19/64-in and 25/64-in. All solid fuel grains
were composed of 3D printed Polylactic Acid and had a typical Bates grain geometry with
a core size of 0.65-in, length of 3.5-in, and 50% infill. The constructed test stand showed an
optimal range of nozzle sizes between the #16 and #19 nozzles. The stand also demonstrated
the ability to resolve differences in thrust and impulse at a 90% confidence level; showing the
design of the test stand is viable for future research purposes. Future studies should focus
on various fuel grain diameters, NOS injector designs, pre- and post-combustion chambers,
and different fuel grain geometries and compositions
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe 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
Characterization of degraded drag-reducing polymer solution and its impact on the structure of turbulence
No full textTurbulence is often described in terms of either a random process or interacting coherent structures, which is really a choice of which parts of the turbulence to ignore. Focusing on coherent structures reducing the complexity of the problem, which is required to make flow control a possibility. The primary focus of the current study is to analyze how coherent structures within a turbulent boundary layer are modified with the addition of drag-reducing polymer solution (polyethylene oxide, PEO). The performance is known to be concentration dependent, so to mitigate the impact of concentration gradients within the boundary layer the study was performed within a homogeneous polymer ocean. However, this requires the PEO to be exposed to a pump that is known to cause mechanical degradation via chain scission, which significantly impact the polymers behavior. Thus mechanical degradation of dilute PEO solutions was investigated with a turbulent pipe flow setup. Comparative analysis between degraded and non-degraded PEO samples at the same mean molecular weight showed that deviations in the polymer performance scaled with the normalized difference between the initial and final molecular weights. Furthermore, based on literature as well as the current results it was shown that the polymer performance deviations are most likely related to changes in the molecular weight distribution. It was also shown that these deviations could be minimized by increasing the residence time. Limiting the turbulent boundary layer operation conditions to the range where it was shown that the degradation had negligible impact on the PEO performance, allowed a detailed study of the impact of the polymers on the turbulent boundary layer coherent structures. It was observed that the anisotropy of the flow scales increases in proportion to drag reduction, which is consistent with the anisotropy of the fluctuating velocity scales observed in the literature
Study of Flow Patterns and Void Fraction in Vertical Downward Two Phase Flow
No full textAn experimental investigation on the flow patterns and void fraction in vertical downward two phase flow was carried out accompanied by exhaustive literature review. The flow patterns and the variation of the void fraction with the flow patterns were compared against the experimental data in the present study. Detailed flow visualization was helpful for insightful discussion on the appearance of the flow patterns. Drift flux model was examined and it was shown that the void fraction correlations developed for vertical upward flow can be applied to predict the void fraction in vertical downward flow. Finally this thesis concluded by a rigorous analysis of the void fraction correlations followed by the recommendation of the best flow pattern independent correlation. Flow visualization confirmed the existence of the five major flow patterns in the downward two phase flow. The characteristics of the bubbly and slug flow were elucidated on the basis of photographic evidences. The experimental measurement of the void fraction contributed in assembly of a comprehensive void fraction data set. Owing to the flexibility of the drift flux model it was found to be the most successful model to predict the void fraction in downward two phase flow. The performance analysis of the void fraction correlations was useful in identifying the top performing flow pattern independent void fraction correlations. This analysis gave a better understanding of the physical structure of the drift flux models and concluded with the recommendation of the requirements of an ideal downward two phase void fraction model.Mechanical & Aerospace Engineerin
Simulation of Supersonic Injection of Underexpanded Aerated Liquid Jet
No full textThe present computational study for underexpanded 2D and axisymmetric nozzle configuration is carried out for both gas-only and aerated liquid jet. The study is motivated by the application of fuel injection in air-breathing propulsion systems, e.g. scramjet engines, ramjet engines and afterburners. The simulation of gas-only jet carried out using Ansys-Fluent student version. The results show that air reaches sonic condition at the injector exit due to the Fanno flow effect in the injector passage. The aerated liquid jet flow from the injector is alternately expanded by Prandtl-Meyer expansion fan and compressed by oblique shock waves due to the difference between the back (chamber) pressure and the flow pressure. The process then repeats itself and shock (Mach) diamonds are formed downstream of the injector exit similar to those typical of exhaust plumes of propulsion system. The numerical results of gas-only jet for 2D and axisymmetric configuration are validated with theory of gas dynamics and experimental results. The numerical results of gas-only jet are in good agreement with theory and experiment. Similar to gas-only jet, simulation of aerated liquid jet is carried out for both 2D and axisymmetric nozzle configuration. The simulation of aerated liquid jet is conducted using VOF model and SST k-? turbulence model. The test conditions included: jet exit diameter of 1 mm and Gas to Liquid Ratio as 4%. The simulated result of 2D aerated liquid jet is compared with 2D gas-only jet using the contours of Mach number and static pressure. The flow field of axisymmetric aerated liquid jet differs from the 2D aerated liquid jet field; this can be explained based on the nozzle configuration. The present results also compare the cone angle expansion of aerated liquid jet. The cone angle expansion of aerated liquid jet is agreed with Prandtl-Meyer expansion analysis for 2D configuration and method of characteristics for axisymmetric configuration. The computed cone angle is always smaller than the theory, and this is probably due to inertia of the liquid jet. Present investigation shows that, the experimental results for aerated liquid jet expansion angle can be explained with the method of characteristics rather than the 2D Prandtl-Meyer expansion analysis.Mechanical & Aerospace Engineerin
Clap and Fling Interaction of Bristled Wings: Effects of Varying Reynolds Number and Bristle Spacing on Force Generation and Flow Structures
No full textThe smallest flying insects with body lengths under 1 mm, such as thrips and fairyflies, typically show the presence of long bristles on their wings. Thrips have been observed to use wing-wing interaction via 'clap and fling' for flapping flight at low Reynolds number (Re) on the order of 10, where a wing pair comes into close contact at the end of upstroke and fling apart at the beginning of downstroke. We examined the effects of varying the following parameters on force generation and flow structures formed during clap and fling: (1) Re ranging from 5 to 15 for a bristled wing pair (G/D=17) and a geometrically equivalent solid wing pair; and (2) ratio of spacing between bristles to bristle diameter (G/D) for Re=10. The G/D ratio in 70 thrips species were quantified from published forewing images. Scaled-up physical models of three bristled wing pairs of varying G/D (5, 11, 17) and a solid wing pair (G/D=0) were fabricated. A robotic model was used for this study, in which a wing pair was immersed in an aquarium tank filled with glycerin and driven by stepper motors to execute clap and fling kinematics. Dimensionless lift and drag coefficients were determined from strain gauge measurements. Phase-locked particle image velocimetry (PIV) measurements were used to examine flow through the bristles. Chordwise PIV was used to visualize the leading edge vortex (LEV) and trailing edge vortex (TEV) formed over the wings during clap and fling. With increasing G/D, larger reduction was observed in peak drag coefficients as compared to reduction in peak lift coefficients. Net circulation, defined as the difference in circulation (strength) of LEV and TEV, diminished with increasing G/D. Reduction in net circulation resulted in reducing lift generated by bristled wings as compared to solid wings. Leaky, recirculating flow through the bristles provided large drag reduction during fling of a bristled wing pair. If flight efficiency is defined as the ratio of lift to drag, largest peak lift to peak drag ratios were obtained in bristled wings as compared to the solid wings across the entire range of Re and G/D tested.Mechanical & Aerospace Engineerin
Measurement of Thermal Conductivity of Pipe Insulation Systems at below Ambient Temperature and in Wet Condensing Conditions with Moisture Ingress
Full text linkWhen pipes are used for chilled water, glycol brines, refrigerants, and other chilled fluids, energy must be spent to compensate for heat gains through the wall of the pipes. Higher fluid temperature at the point of use decreases the efficiency of the end-use heat exchangers and increases the parasitic energy consumption. Mechanical pipe insulation systems are often used to limit the heat gains and save energy in commercial buildings. Pipe insulation systems play an important role for the health of the occupied space. When a chilled pipe is uninsulated or inadequately insulated, condensation might occur and water will drip onto other building surfaces possibly causing mold growth. The critical issue with cold pipes is that the temperature difference between the pipe and its surrounding ambient air drives water vapor in to the insulation system and condensation commonly occurs when the water vapor comes in contact with the chilled pipe surface. This thesis experimentally studies this issue for pipe insulation systems operating at below ambient temperature. The moisture content and the associated thermal conductivity of several pipe insulation systems were measured at various wet condensing conditions with moisture ingress. Accelerated type tests in laboratory showed the propensity of moisture accumulation in several insulation systems due to the cylindrical configuration, split joints, and micro-imperfections in the jacketing system. The data in the present work showed that the thermal conductivity increased systematically when water vapor entered the pipe insulation system.Mechanical & Aerospace Engineerin
- …
