The present study investigates the shock wave propagation and diffraction characteristics in a micro-shock tube with sudden expansion and compares with the well-established classical shock wave ...diffraction in macro-length scale sudden expansions using computational techniques. The Knudsen number for the present micro-shock tube falls in the slip regime and therefore the fluid flow is simulated using the continuum-based Navier–Stokes equation with Maxwell’s slip jump boundary condition. It is found that the shock wave attenuates rapidly in micro-shock tube compared to the shock wave propagation in macro-shock tube. The shock wave diffraction in micro-steps shows similar characteristics compared to macro-steps, such as reflection of the diffracted shock wave from the outer wall and the subsequent transition from regular reflection to Mach reflection, the vortex formation at the step corner, Mach reflection shock structure in the shock-processed gas exiting from the shock tube. However, the secondary shock wave formed due to the interaction of the reflected shock wave with the corner vortex is not seen for the micro-step case compared to the macro-step case. This can be attributed to the reduction in shock strength produced by the thick boundary layer in micro-shock tubes. Different step sizes have been compared for the micro-shock tube with sudden expansion ranging from the step size 1.5 to 3. Also, a detailed comparison has been done between micro- and macro-shock tube with sudden expansion. It is also found that the use of slip velocity increases the shock wave propagation speed compared to the no-slip boundary condition.
Additive manufacturing is a versatile technology that is touted to be the future of manufacturing sector. Additive manufacturing has enormous potential to transform the industry and finds its ...application in aerospace, automotive, construction and biomedical sector. Houses have been 3D printed in recent times by employing a concrete mix, and with such progress, one can say that this technology is well on its way to create the next Industrial Revolution. Stereolithography (SLA) can be used for producing parts with complex geometries that require high levels of detailing and precision.Stenting is commonly done in surgical procedures such as Angioplasty to enable and restore the flow of blood to the heart. Metal stents are widely used in such surgical procedures and these stents have some drawbacks such as limitations in customization and profiling. The metal stents are limited in their ability to be tailored to the blood vessel profile of the patient. This has led to an increase in demand for polymer stents, which provide a degree of flexibility and customization with respect to the patient’s profile.This thesis study focuses on the design and development of a Projection based SLA system that can produce complex structures for several applications. This printing setup was designed and developed to print polymer stents with high levels of precision and fine featuring. The central idea of SLA is to print layers by means of illuminating resin with a light source. A layer is fabricated at a time and other layers are consecutively built upon the previous one to constitute the part. A light source of wavelength 385 nm has been employed for the study, along with a set of assemblage of components. The functionality of developed printer system was tested by printing stents after zeroing in on parameters such as layer thickness, UV light intensity and exposure time.Some of the commonly available testing setups for evaluating mechanical performance generally support metal parts, in most cases, with a limited few supporting polymer structures. To overcome this challenge, along with the DLP SLA printer, a mechanical testing setup was also developed to validate printed parts for their mechanical performance. The developed DLP SLA system can print highly precise structures and can be used for applications in several fields.
Spin coated poly(N-vinylcarbazole) (PVK) sandwiched between thermally evaporated aluminum (Al) electrodes on a glass substrate showed unipolar Write Once Read Many times (WORM) characteristics. The ...pristine devices were in the low resistance ON state exhibiting ohmic behavior and at a voltage near -2 V, they switched abruptly to the high resistance OFF state showing space charge limited current (SCLC). We suggest that the rupturing of metallic filaments due to Joule heating may explain the effect. The WORM devices exhibited an ON/OFF ratio of 10(8), a retention of 1000 s and an endurance of ∼10(6) cycles in both ON and OFF states.
Spin coated poly(
N
-vinylcarbazole) (PVK) sandwiched between thermally evaporated aluminum (Al) electrodes on a glass substrate showed unipolar Write Once Read Many times (WORM) characteristics. The ...pristine devices were in the low resistance ON state exhibiting ohmic behavior and at a voltage near −2 V, they switched abruptly to the high resistance OFF state showing space charge limited current (SCLC). We suggest that the rupturing of metallic filaments due to Joule heating may explain the effect. The WORM devices exhibited an ON/OFF ratio of 10
8
, a retention of 1000 s and an endurance of ∼10
6
cycles in both ON and OFF states.
Al/PVK/Al unipolar WORM devices with
R
ON
/
R
OFF
ratios of 10
8
.
Given the increasing popularity of real-time video communication over enterprise wireless networks, ensuring good quality of experience is becoming critical. A common problem in such networks is that ...the clients typically adopt the strategy of associating to the access point with the highest signal strength, which can lead to load imbalance, unfair throughput allocation, and low overall video quality. In this paper, we propose to improve load balancing across video clients by selectively triggering directed roams of chosen clients, while explicitly accounting for the cost of roaming. We formulate the problem of identifying the directed roams to perform as an optimization problem where the objective function reflects both the overall utility of all video clients and the cost due to roaming. We subsequently apply relaxations to the original NP-Hard problem, and propose a three-stage algorithm that efficiently computes an approximate solution. Simulations show that by selectively roaming just 5% of the clients, we increase throughput relative to an initial strongest signal based association by at least 10% for over half of the clients and by at least 20% for over a quarter of the clients. We also increase aggregate throughput, improve fairness and thereby increase the overall video quality.
Nanocomposite technology opens up a new era in the study of polymeric materials. Carbon nanotubes, due to their extremely high mechanical strength finds use as a filler material in many polymer ...matrices and can be viewed as one of the most promising area driven towards commercial applications. Nevertheless nanoclay is also equally good as filler in increasing the mechanical, barrier as well as thermal characteristics of chlorobutyl rubber (CIIR) matrix. The synergistic effect produced by nanoclay and carbon nanotube in enhancing the properties of chlorobutyl rubber enhances its efficacy towards the fabrication of industrially relevant materials. The nanocomposites were prepared using cloisite 30 B and carbon nanotubes separately and a hybrid nanocomposite was prepared by incorporating these two fillers to evaluate the synergistic effect of the fillers. The mechanical, dielectric, solvent diffusion and barrier properties of the nanocomposites were analyzed. The results show an enhancement in the aforementioned properties and reveal that both the carbon nanotubes and nanoclay contribute synergistically towards the enhancement in properties. Moreover the enhanced solvent resistance as well as gas barrier properties suggests the feasibility of the utilization of the material in the production of chemical protective clothing. Evaluation of thermal decontamination of the proposed CPC material reveals its potential for its effective reuse.
Chlorobutyl rubber comprises a significant type of butyl rubber with attractive properties. Inspection of the various aspects of the dielectric properties of chlorobutyl rubber nanocomposites ...containing organically modified layered silicates (nano clay) in a particular range of frequency was carried out at different filler loadings. Owing to the interaction of the organically modified silicate layers with the chlorobutyl rubber matrix, a conductive pathway is created which enables the improvement in the dielectric properties of the nanocomposites. A comparative study of the dielectric properties of composites containing various types of organically modified layered silicates was done. Modeling of the dielectric properties were done and the relevance of experimental results were evaluated with the existing models.
We propose an interpretable model to score the bias present in web documents, based only on their textual content. Our model incorporates assumptions reminiscent of the Bradley-Terry axioms and is ...trained on pairs of revisions of the same Wikipedia article, where one version is more biased than the other. While prior approaches based on absolute bias classification have struggled to obtain a high accuracy for the task, we are able to develop a useful model for scoring bias by learning to perform pairwise comparisons of bias accurately. We show that we can interpret the parameters of the trained model to discover the words most indicative of bias. We also apply our model in three different settings - studying the temporal evolution of bias in Wikipedia articles, comparing news sources based on bias, and scoring bias in law amendments. In each case, we demonstrate that the outputs of the model can be explained and validated, even for the two domains that are outside the training-data domain. We also use the model to compare the general level of bias between domains, where we see that legal texts are the least biased and news media are the most biased, with Wikipedia articles in between. Given its high performance, simplicity, interpretability, and wide applicability, we hope the model will be useful for a large community, including Wikipedia and news editors, political and social scientists, and the general public.
