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Topic Review
Semiconductor Gas Sensors
Semiconductor materials include metal oxides, conducting polymers, carbon nanotubes, and 2D materials. Metal oxides are most often the first choice due to their ease of fabrication, low cost, high sensitivity, and stability. Some of their disadvantages are low selectivity and high operating temperature. Conducting polymers have the advantage of a low operating temperature and can detect many organic vapors. They are flexible but affected by humidity. Carbon nanotubes are chemically and mechanically stable and are sensitive towards NO and NH3, but need dopants or modifications to sense other gases. Graphene, transition metal chalcogenides, boron nitride, transition metal carbides/nitrides, metal organic frameworks, and metal oxide nanosheets as 2D materials represent gas-sensing materials of the future, especially in medical devices, such as breath sensing.
  • 2.5K
  • 10 Dec 2020
Topic Review
Satellite Constellations
The New Space Economy encourages constellations of satellites that are being proposed in large numbers by private companies. They will provide communication, enable global monitoring of Earth, and enhance space observation. Mostly enabled by technology miniaturization, satellite constellations require a coordinated effort to face the technological limits in spacecraft operations and space traffic. In this Topic Review, we provide a survey of the upcoming satellite constellations and an overview of future challenges to be faced.
  • 2.5K
  • 27 Oct 2020
Topic Review
Abiotic and Biotic Polymer Degradation Mechanisms
Polymer degradation is defined as an irreversible change of the chemical structure, physical properties, and visual appearance due to the chemical cleavage of the polymer’s constitutive macromolecules by one or more mechanism. More than one mechanism can simultaneously take place due to the action of external factors, and one mechanism can be more dominant than others at any time. External factors associated with the environment, such as heat, humidity, radiation, and acidic or alkaline conditions, could modify the degradation process and its rate. The degradation process can alter polymer properties such as mechanical, optical, electrical, discoloration, phase separation or delamination, erosion, cracking, and crazing. The four main abiotic mechanisms associated with polymer degradation are mechanical, thermal (or thermo-oxidative), photo (photo-oxidative), and hydrolytic (chemical) degradation, some of which can be assisted by catalysis. In addition, ozone degradation (chemical) is considered a mechanism of degradation for polymers but is less common. The biotic degradation involves the action of microorganisms by enzymatic action.
  • 2.5K
  • 27 Oct 2022
Topic Review
Stereolithography
Being the earliest form of Additive manufacturing, Stereolithography (SLA) fabricates 3D objects by selectively solidifying the liquid resin through photopolymerization reaction. The ability to fabricate objects with high accuracy as well as a wide variety of materials brings much attention to stereolithography. Since its invention in 1980s, SLA underwent four generations of major technological innovation over the past 40 years. These innovations have thus result in a diversifies range of stereolithography systems with dramatically improved resolution, throughput, and materials selection for creating complex 3D objects and devices. In this paper, we review the four generations stereolithography processes, which are scanning, projection, continuous and volumetric stereolithography. For each generation, representative stereolithography system configurations are also discussed in detail. In addition, other derivative technologies, such as scanning-projection, multi-material, and magnetically assisted stereolithography processes, are also included in this review.
  • 2.5K
  • 16 Sep 2020
Topic Review
Out-of-Autoclave Process for Composite Manufacturing
Composite materials have gained increased usage due to their unique characteristic of a high-stiffness-to-weight ratio. High-performing composite materials are produced in the autoclave by applying elevated pressure and temperature. The process is characterized by numerous disadvantages, such as long cycle time, massive investment, costly tooling, and excessive energy consumption. As a result, composite manufacturers seek a cheap alternative to reduce cost and increase productivity. The out-of-autoclave (OoA) process manufactures composites by applying vacuum, pressure, and heat outside of the autoclave.
  • 2.5K
  • 20 Jul 2022
Topic Review
Acer Aspire Laptops
Acer Aspire (stylized as Λspire or ΛSPIRE) is a series of personal computers by Acer Inc. aimed at the casual household user or for small business use. The Aspire series covers both desktop computers and laptops. Acer developed the series in order to cover from essentials to high performances. Many of the Aspire laptops, such as model 8920G, have built in Blu-ray drives, 5.1 audio outputs and transflective displays. Acer was the first to include these drives in laptops. Most Aspire laptops have water-resistant screens, such as the 1410 and the 5741 Z. In 2007, Acer introduced the Gemstone series that marked a milestone in the Acer Aspire line. As with many Windows laptops, different models may have different specification in different parts of the world.
  • 2.5K
  • 20 Oct 2022
Topic Review
Messerschmitt Me 323
The Messerschmitt Me 323 Gigant ("Giant") was a German military transport aircraft of World War II. It was a powered variant of the Me 321 military glider and was the largest land-based transport aircraft of the war. A total of 213 are recorded as having been made, 15 being converted from the Me 321.
  • 2.5K
  • 17 Oct 2022
Topic Review
Wind Turbine Blade Failures
The wind turbine is a complex structure. Although there is no single approach and there is variability in the commercial designs, a typical WTB is a thin-walled multi-cellular hollow airfoil shaped cross-section. For its manufacture, a number of materials and material systems are used for structural purposes (fibre composites and sandwich composite systems) as well as aesthetic purposes (primers, UV gel coats, paint, etc). The potential causes of wind turbine blade failures can be classified into the following four categories:1. damage from lightning;2. failures due to fatigue;3. leading edge erosion;4. damage from icing.The types of damage caused to wind turbine blades—originating from the above four different sources—along with their significance to the turbine’s performance and secure operation, are detailed in the following sub-sections.
  • 2.5K
  • 11 Oct 2021
Topic Review
Ghazal
The ghazal (Bengali: গজল, Sylheti: ꠊꠏꠟ, Punjabi: ਗ਼ਜ਼ਲ, Urdu: غزَل , Hindi: ग़ज़ल, Persian: غزل‎, Azerbaijani: qəzəl, Turkish: gazel, Uzbek: gʻazal, Pashto: غزل‎, Template:Lang-gu,) is a form of amatory poem or ode, originating in Arabic poetry. A ghazal may be understood as a poetic expression of both the pain of loss or separation and the beauty of love in spite of that pain. The ghazal form is ancient, tracing its origins to 7th-century Arabic poetry. The ghazal spread into South Asia in the 12th century due to the influence of Sufi mystics and the courts of the new Islamic Sultanate, and is now most prominently a form of poetry of many languages of the Indian subcontinent and Turkey. A ghazal commonly consists of between five and fifteen couplets, which are independent, but are linked – abstractly, in their theme; and more strictly in their poetic form. The structural requirements of the ghazal are similar in stringency to those of the Petrarchan sonnet. In style and content, due to its highly allusive nature, the ghazal has proved capable of an extraordinary variety of expression around its central themes of love and separation.
  • 2.5K
  • 24 Nov 2022
Topic Review
Drone Detection and Defense Systems
Drones are small and low-cost unmanned aerial vehicles (UAVs). With the decrease in the cost and size of drones in recent years, their number has also increased exponentially. As such, the concerns regarding security aspects that are raised by their presence are also becoming more serious.
  • 2.5K
  • 10 Mar 2022
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