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An accelerated repair method for steel girders with severe end corrosion damage
No full textA novel repair method for corroded steel girder ends using ultra-high performance concrete (UHPC) has gained the attention of several departments of transportation. The method involves welding shear studs to the intact part of the web plate and encasing the end region in UHPC. This paper presents the findings of an experimental study on a full-scale girder aimed to assess the feasibility of rapid implementation of the repair. Reducing the construction complexities and time is critical in cases where access to the bridge is constrained or closing the bridge to traffic is not possible. To expedite and simplify repair construction, welded shear studs originally used to transfer loads to the UHPC cast were replaced with steel dowel rods. In place of conventional wooden formwork, a reusable flexible light-gauge sheet of steel was wrapped around the end. Installation of the shear connectors, installation of the form, and casting of the UHPC was completed by two workers within an eight-hour shift. The repaired girder was load tested after the UHPC gained a compressive strength of 96.5 MPa to demonstrate the adequacy of the repair for restoring the capacity of the intact girder end shortly after implementation. It is anticipated that this empirical data encourages the use of this repair technique to address the widespread problem of end corrosion in steel superstructures
Influence of Thermal Effects on the Breakup of Thin Films of Nanometric Thickness
No full textWe apply a previously developed asymptotic model [J. Fluid Mech. 915, A133 (2021)] to study instabilities of free surface films of nanometric thickness on thermally conductive substrates in two and three spatial dimensions. While the specific focus is on metal films exposed to laser heating, the model itself applies to any setup involving films on the nanoscale whose material parameters are temperature-dependent. For the particular case of metal films heated from above, an important aspect is that the considered heating is volumetric, since the absorption length of the applied laser pulse is comparable to the film thickness. In such a setup, absorption of thermal energy and film evolution are closely correlated and must be considered self-consistently. The asymptotic model allows for a significant simplification, which is crucial from both modeling and computational points of view, since it allows for asymptotically correct averaging of the temperature over the film thickness. We find that the properties of the thermally conductive substrate—in particular, its thickness and rate of heat loss—play a critical role in controlling the film temperature and dynamics. The film evolution is simulated using efficient GPU-based simulations which, when combined with the developed asymptotic model, allow for fully nonlinear time-dependent simulations in large three-dimensional computational domains. In addition to uncovering the role of the substrate and its properties in determining the film evolution, one important finding is that, at least for the considered range of material parameters, strong in-plane thermal diffusion in the film results in negligible spatial variations of temperature, and the film evolution is predominantly influenced by temporal variation of film viscosity and surface tension (dictated by average film temperature), as well as thermal conductivity of the substrate
Detailed Velocity and Heat Transfer Measurements in an Advanced Gas Turbine Vane Insert Using Magnetic Resonance Velocimetry and Infrared Thermometry
Get PDFThis work reports the results of paired experiments for a complex internal cooling flow within a gas turbine vane using magnetic resonance velocimetry (MRV) and steady-state infrared (IR) thermometry. A scaled model of the leading edge insert for a gas turbine vane with multi-pass impingement was designed, built using stereolithography fabrication methods, and tested using MRV techniques to collect a three-dimensional, three-component velocity field data set for a fully turbulent test case. Stagnation and recirculation zones were identified and assessed in terms of impact on potential cooling performance. A paired experiment employed an IR camera to measure the temperature profile data of a thin, heated stainless steel impingement surface modeling the inside turbine blade wall cooled by the impingement from the vane cooling insert, providing complementary data sets. The temperature data allow for the calculation of wall heat transfer (HT) characteristics, including the Nusselt number distribution for cooling performance analysis to inform design and validate computational models. Quantitative and qualitative comparisons of the paired results show that the flow velocity and cooling performance are highly coupled. Module-to-module variation in the surface Nusselt number distributions is evident, attributable to the complex interaction between transverse and impinging flows within the apparatus. Finally, a comparison with internal HT correlations is conducted using the data from Florschuetz et al. [1981, “Streamwiseflow and Heat Transfer Distributions for Jet Array Impingement With Crossflow,” ASME 1981 International Gas Turbine Conference and Products Show, American Society of Mechanical Engineers. doi:10.1115/1.3244463]. Measurement uncertainty was assessed and estimated to be approximately ±7% for velocity and ranging from ±3% to ±10% for Nusselt number
The Swedish Fighter Pilot Crisis
Get PDFHalf of Sweden’s fighter pilots are ready to quit, or go on an extended leave this fall, just as the country is poised to join NATO. The two are not linked, butone clearly has consequences for the other. Many Swedish air force pilots are demanding better compensation andthreatening mass migration to the private sector. The dispute has beendeveloping ever since the end of the Cold War, when Sweden took a verysignificant peace dividend. The country’s defense spending dropped fromaround 3% of GDP in 1990 to just 0.9% in 2015
Corrosion Mitigation for Mechanically-Fastened Fiber-Reinforced-Polymer Composites
Get PDFMechanically-Fastened Fiber Reinforced Polymer Composites (MF-FRPs) are currently being used to extend the useful service life of deteriorated bridges. However, the A325 Steel fastener assemblies used to attach the MF-FRP system to the bridges are experiencing noticeable corrosion. Through electrochemical polarization measurements and Tafel analysis, the expected lifetime of the A325 fastener assembly was determined and compared to other similar materials, Military Specification Grade 5 Steel (MTD-STD) and PH 17-4 Stainless Steel (PH 17-4). ASTM B117 salt fog testing was performed on each material fastener assembly to simulate the corrosion that should be experienced by each material. The electrochemical analysis and the ASTM B117 salt fog test confirmed the MIL-STD assembly corroded at a much slower rate compared to either A325 or PH 17-4. It was determined that the useful life of the fastener assembly could be extended from 6.5 year using A325 to 372 years using MIL-STD. Implementation of this engineering materials solution will extend the useful life of the MF-FRP fastener assembly however, a cost benefit analysis determined that continuing to use A325 is still the best option given the desired useful life of the MF-FRP retrofit system is 3 to 5 years
Malware Family Classification via Residual Prefetch Artifacts
No full textAutomated malware classification assigns unknown malware to known families. Most research in malware classification assumes that the defender has access to the malware for analysis. Unfortunately, malware can delete itself after execution. As a result, analysts are only left with digital residue, such as network logs or remnant artifacts of malware in memory or on the file system. In this paper, a novel malware classification method based on the Windows prefetch mechanism is presented and evaluated, enabling analysts to classify malware without a corresponding executable. The approach extracts features from Windows prefetch files, a file system artifact that contains historical process information such as loaded libraries and process dependencies. Results show that classification using these features with two different algorithms garnered F-Scores between 0.80 and 0.82, offering analysts a viable option for forensic analysis
The Future of Cyber-Enabled Influence Operations: Emergent Technologies, Disinformation, and the Destruction of Democracy
Get PDFNation-states have been embracing online influence campaigns through disinformation at breakneck speeds. Countries such as China and Russia have completely revamped their military doctrine to information-first platforms [1, 2] (Mattis, Peter. (2018). China’s Three Warfares in Perspective. War on the Rocks. Special Series: Ministry of Truth. https://warontherocks.com/2018/01/chinas-three-warfares-perspective/, Cunningham, C. (2020). A Russian Federation Information Warfare Primer. Then Henry M. Jackson School of International Studies. Washington University. https://jsis.washington.edu/news/a-russian-federation-information-war fare-primer/.) to compete with the United States and the West. The Chinese principle of “Three Warfares” and Russian Hybrid Warfare have been used and tested across the spectrum of operations ranging from competition to active conflict. With the COVID19 pandemic limiting most means of face-to-face interpersonal communi-cation, many other nations have transitioned to online tools to influence audiences both domestically and abroad [3] (Strick, B. (2020). COVID-19 Disinformation: Attempted Influence in Disguise. Australian Strategic Policy Institute. International Cyber Policy Center. https://www.aspi.org.au/report/covid-19-disinformation.) to create favorable environments for their geopolitical goals and national objectives. This chapter focuses on the landscape that allows nations like China and Russia to attack democratic institutions and discourse within the United States, the strategies and tactics employed in these campaigns, and the emergent technologies that will enable these nations to gain an advantage with key populations within their spheres of influence or to create a disadvantage to their competitors within their spheres of influence. Advancements in machine learning through generative adversarial networks [4] (Creswell, A; White, T; Dumoulin, V; Arulkumaran, K; Sengupta, B; Bharath, A. (2017) Generative Adversarial Networks: An Overview. IEE-SPM. April 2017. https://arxiv.org/pdf/1710.07035.pdf.) that create deepfakes [5] (Whit-taker, L; Letheren, K; Mulcahy, R. (2021). The Rise of Deepfakes: A Conceptual J. Littell envelope symbolenvelope symbolenvelope symbol Army Cyber Institute at the West Point, United States Military Academy, West Point, NY 10996, USA e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Switzerland AG 2022 A.Farhadietal. (eds.), The Great Power Competition Volume 3, https://doi.org/10.1007/978-3-031-04586-8_10 197 198 J. Littell Framework and Research Agenda for Marketing. https://journals.sagepub.com/doi/ abs/10.1177/1839334921999479.) and attention-based transformers [6](https:// arxiv.org/abs/1810.04805.) (Devlin et al., 2018) that create realistic speech patterns and interaction will continue to plague online discussion and information spread, attempting to cause further partisan divisions and decline of U.S. stature on the world stage and democracy as a whole.https://digitalcommons.usmalibrary.org/aci_books/1020/thumbnail.jp
An Investigation of Search Algorithms for Aerial Reconnaissance of an Area Target
No full textAs drone technology becomes increasingly accessible in commercial and defense sectors, it is important to establish efficient ways of employing the technology to leverage its inherent advantages. In the context of a chemical, biological, radiological, and nuclear (CBRN) attack, an unmanned aerial system (UAS) can provide an understanding of the area affected by contaminants in a faster and safer way than a manned reconnaissance mission. Commonly used deterministic paths provide comprehensive coverage but they can require a substantial amount of time to reach each sector within a search space. The recently proposed Lissajous search pattern provides easily tunable parameters that can be adjusted according to the search space and anticipated size of the target. This paper provides an evaluation of Lissajous patterns against canonical search patterns and investigates ways of maximizing their efficiency for various target sizes
Design and Test of an Autonomous Drone SWARM for Chemical Agent Detection
No full textThis technical report presents the details behind designing and testing a swarm of Unmanned Aerial Systems (UAS) that are capable of detecting and mapping a chemical plume. The sensor used onboard the UAS is a government-owned detector, although the technical approach used in this work is generalizable to other detectors of contaminants or chemical agents. The swarm of drones operates autonomously, with minimal user input but with operator oversight. Autonomous behaviors were built to search for and map a chemical plume over a given area. For UAS in search mode, a Lissajous pattern was chosen as the primary motion trajectory, owing to its surveying efficiency of minimizing time for distance traveled. If any of the agents within the swarm interact with a chemical plume (physical or simulated), the autonomy will cause the swarm behavior to adapt from the searching to mapping. In the mapping phase, each drone in the swarm performs circles around the chemical plume to map the perimeter of the plume. These circles are an important feature of the behavior because they allow the detectors to de-saturate from the chemicals. Finally, the team also developed and incorporated a visualization tool for real-time monitoring of chemical presence, to provide a Common Operating Picture for the user. Utilizing simulations, emulators, and real hardware, the team completed test flights of the swarm behavior to prove its functionality
How Nationalist China Attempted to Modernize its Military Food System During and After World War II
Get PDFIn 1949, the United States Government published the China White Paper as justification for withholding military aid to the Chinese Nationalist Government (KMT) during the Chinese Civil War, which many blamed as the cause of the KMT’s loss to the Chinese Communist Party (CCP).[1] In the China White Paper, the claim was made that “in no small measure, the predicament in which the National Government finds itself today is due to its failure to provide China with enough to eat.”[2] Six years prior to the American government making this conclusion in 1943, the KMT sent one of its leading public health official’s, Tsai Chiao, to visit America and describe some of China’s nutritional challenges to American scholarly audiences at the request of the Norman Wait Harris Memorial Foundation of the University of Chicago.[3] Chiao was Western educated at the University of California, Indiana University and the University of Chicago and was a physiologist at the National Central University in Nanjing.[4] He told his American audience that as a result of several Chinese nutritional studies, “for the most part, Chinese diets are adequate in calories, but deficient in animal protein, vitamins, and certain salts.”[5] He stated that several years prior, the Nutritional Committee of the Chinese Medical Association had recommended an increase in animal protein for Chinese diets, “but it has not been possible to follow this recommendation.”[6] Chiao then told the Americans that Chinese soldiers “received animal food usually once, or at most twice, a month.”[7] The idea that meat was an imperative ingredient to a daily diet played directly to American audience’s own understanding of food. Perhaps coincidently, over the next two years, the American military spent considerable resources attempting to rectify this lack of meat in Chinese soldiers’ daily diet. In researching this attempt, it appears that while certain aspects of China’s military food system changed, these were far from universal, were reliant on a local populace, and were unsustainable beyond America’s direct intervention.
By the end of World War II, the Americans had felt that their nutritional experiment with the Chinese soldiers had had some limited success. American Colonel Charles F. Kearney, who was a liaison officer to the Chinese Army logistics unit, believed that “the Chinese were shown that armies on the march could be given an adequate, balanced diet,” which was based on “what the Americans thought to be effective procedures.”[8]Kearney, however, concluded in his report that he did not believe permanent or lasting changes had occurred in the Chinese military before the end of World War II.[9] Indeed, the research into American and Chinese archives suggests that there was a gap between what American military leaders tried to change and what actually occurred on the ground.
[1] Chang, David Cheng. The Hijacked War: The Story of the Chinese POWs in the Korean War. Stanford University Press: Stanford. 2020. Page 79.
[2] “Text of Secretary Acheson\u27s Letter Transmitting White Paper on China to President Truman.” The New York Times. August 6, 1949. Page 4.
[3] The foundation was a trust fund given to the University of Chicago in 1923, for the promotion of knowledge of an interest in international affairs. As such, it held annual Harris Institutes, composed of a private round table and a series of public lectures on international affairs. The annual institutes lasted until 1956. https://www.lib.uchicago.edu/e/scrc/findingaids/view.php?eadid=ICU.SPCL.HARRISNW.
[4] Harley Farnsworth MacNair. “Synthesis Out of Analysis.” Voices from Unoccupied China. Ed. By Harley Farnsworth MacNair. University of Chicago Press: Chicago. 1944. Page x.
[5] Tsai Chiao. “Problems of Nutrition in Present Day China.” Voices from Unoccupied China. Ed. By Harley Farnsworth MacNair. University of Chicago Press: Chicago. 1944. Page 16.
[6] Ibid. Page 17. I was not able to find the report Chiao cited other than what was presented at the conference.
[7] Ibid.
[8] Quoted in Romanus, Charles F. and Riley Sunderland. China, Burma, India Theater: Time Runs Out in CBI. Center of Military History. United States Army: Washington, D.C. 1999. Page 243.
[9] Ibid. Page 246