Design of a Novel Integrated Ultrasonic Tool Holder for Friction Stir Welding

Ultrasonic vibration used in friction stir welding (FSW) has shown advantages in reducing welding defects and improving welding quality. How to design an ultrasonic tool holder is a challenge because the holder is rotating in a confined space. In this study, we design a 20 kHz integrated ultrasonic tool holder in FSW. This novel configuration can be applied in general machining equipment. The elastic modulus is measured by non-destructive acoustic testing to attain the precise frequency. Three FSW transducers with alloy steel are designed by the modal analysis and the transducer prototypes are fabricated. The effect of pre-tightening force on transducer frequency is investigated, where the prestress of the piezoelectric stack instead of the torque is tested to achieve an optimal working frequency. The vibration of the transducers is measured by a Doppler Vibrometer System. It proved that the resonant frequencies are well consistent between simulation model and the experiment by the elastic modulus testing and the pre-tightening optimization. Moreover, the experiment demonstrates that the vibration amplitude is significantly different, even in a slight difference of steel material properties are adopted. The dynamic performance of the designed transducers is acceptable by the vibration measurement.

“The World Had Forgotten about Us”: Heterotopian Resistance in Richard Flanagan’s Wanting and Lloyd Jones’s Mister Pip

This article explores how the different forms of heterotopias present in Richard Flanagan’s Wanting (2008) and Lloyd Jones’s Mister Pip (2006) articulate problematic identity politics and cultural memory. In Wanting, the collocation of Mathinna’s story with that of the lost Franklin expedition offers a form of reclaiming. This article argues that Flanagan’s novel moves from heterotopias of deviation to a crisis heterotopia, displacing and debunking the compensation function of the colonial heterotopia to highlight the crushing of Aboriginal identity. This shifting heterotopia is doubled by Mathinna’s heterotopic carceral body, that is, body as confined space, which qualifies the act of reclaiming. In Mister Pip, heterotopias concern cultural memory as the island of Bougainville, secluded from the rest of the world, turns into the repository of the villagers’ culture juxtaposed with the reading of Charles Dickens’s Great Expectations (1860–1861). This article argues that Jones’s creation of a palimpsestic heterotopia allows him to resist Eurocentric views as well as to actualize postcolonial concepts. Jones’s novel calls for a dynamic appropriation of literature. Matilda’s ‘Pacific version’ of Pip’s story reflects the cracks in the Victorian and contemporary exploitations of the island. Readers’ immersions in these heterotopias do not provide an escape from but a thoughtful commitment to the past.

The second Vassiliev measure of uniform random walks and polygons in confined space

Biopolymers, like chromatin, are often confined in small volumes. Confinement has a great effect on polymer conformations, including polymer entanglement. Polymer chains and other filamentous structures can be represented by polygonal curves in 3-space. In this manuscript, we examine the topological complexity of polygonal chains in 3-space and in confinement as a function of their length. We model polygonal chains by equilateral random walks in 3-space and by uniform random walks in confinement. For the topological characterization, we use the second Vassiliev measure. This is an integer topological invariant for polygons and a continuous functions over the real numbers, as a function of the chain coordinates for open polygonal chains. For uniform random walks in confined space, we prove that the average value of the Vassiliev measure in the space of configurations increases as $O(n^2)$ with the length of the walks or polygons. We verify this result numerically and our numerical results also show that the mean value of the second Vassiliev measure of equilateral random walks in 3-space increases as $O(n)$. These results reveal the rate at which knotting of open curves and not simply entanglement are affected by confinement.

A review of COVID-19 transmission dynamics and clinical outcomes on cruise ships worldwide, January to October 2020

Background Cruise ships provide an ideal setting for transmission of SARS-CoV-2, given the socially dense exposure environment. Aim To provide a comprehensive review of COVID-19 outbreaks on cruise ships. Methods PubMed was searched for COVID-19 cases associated with cruise ships between January and October 2020. A list of cruise ships with COVID-19 was cross-referenced with the United States Centers for Disease Control and Prevention’s list of cruise ships associated with a COVID-19 case within 14 days of disembarkation. News articles were also searched for epidemiological information. Narratives of COVID-19 outbreaks on ships with over 100 cases are presented. Results Seventy-nine ships and 104 unique voyages were associated with COVID-19 cases before 1 October 2020. Nineteen ships had more than one voyage with a case of COVID-19. The median number of cases per ship was three (interquartile range (IQR): 1–17.8), with two notable outliers: the Diamond Princess and the Ruby Princess, which had 712 and 907 cases, respectively. The median attack rate for COVID-19 was 0.2% (IQR: 0.03–1.5), although this distribution was right-skewed with a mean attack rate of 3.7%; 25.9% (27/104) of voyages had at least one COVID-19-associated death. Outbreaks involving only crew occurred later than outbreaks involving guests and crew. Conclusions In the absence of mitigation measures, COVID-19 can spread easily on cruise ships in a susceptible population because of the confined space and high-density contact networks. This environment can create superspreader events and facilitate international spread.

Demystifying Constructive Strategies on Designing Functionalized Lamellar Nb2CTx Nanosheet Membrane Architectures under Confined Space

Lamellar membranes of Nb2CTx nanosheets have received significant research interests as cost-effective and efficient materials for desalination, water purification, energy conversion and storage, and ion separation. However, the constructive strategies...

A novel theory of life and its implications on viruses and robots

A novel theory of life is proposed and its implications on the viruses and the future robots are discussed. The universal laws of physics are inferred phenomena that originate from the observed regularity in the physical realm. An apparent distinct feature of living beings compared to the nonliving ones is the presence of a higher level of regularity, which is indicative of a supplemental set of governing laws within the sphere of life. In this article a living or animate being is defined concisely as a natural entity whose internal changes and external behavior cannot be predicted by the universal laws and forces of physics alone at all times. Everything else is nonliving or inanimate. Likewise, life is defined as a supplemental set of laws and influences that act over a confined space which constitutes the domain of life, superimposed on the universal laws and forces of physics. Also, life is shown to be a field phenomenon like a quantum field, except that life pervades a bounded region rather than the entire spacetime. It is argued that life is an agency with causal power rather than an ordinary emergent property, and that a virus qualifies as a living being. The proposed field theory of life predicts that the future robots are unlikely to acquire life, and that the notion of highly intelligent future robots posing an existential threat to humanity is, in all likelihood, an illusion.