Stealth materials

A major contribution from chemistry and chemical engineering has been the development of materials with important military applications. Chemists and chemical engineers, working with experts from areas such as electronics, materials science, and physics, have contributed to such developments as new explosives and propellants, reactive armor (a complex material with an explosive layer that can reduce the penetration of an incoming projectile), and stealth materials that reduce the detectability of aircraft by radar. 

It is hypothesized that nonordered protein adsorption on materials begins the cascade leading to the foreign body reaction, since all normal biological events operate on a system based on specific recognition of proteins and polysaccharides [62,63]. To control nonspecific adsorption, several surface modification approaches have been explored stealth materials are designed to decrease nonspecific protein adsorption while others promote adsorption of specific proteins in an effort to direct biological processes [63,64]. 

There are three main methods used in the development of protein-resistant stealth materials, also referred to as nonfouling or noninteractive surfaces [65] ... 

Immobilization of proteins to control tissue-surface interaction represents a more biomimetic approach to material development, in contrast to stealth materials that prevent interaction. Natural biomolecules have the dual capability of triggering specific cellular responses while their presence can prevent nonspecific adsorption. The techniques used to append biologically active moieties on surfaces can be grouped into three main categories physical micro/nanofabrication, imprinting, and direct chemical immobilization. 

Non-interacting surfaces are designed to adsorb a minimum amoimt of proteins on their surfaces. These materials can be divided into two general categories low energy surfaces such as fluorinated surfaces or extremely hydrophilic and mobile surfaces such as hydrogels which result in less conformational changes in absorbed proteins than hard surfaces. In all these cases the lack of non-specific interactions results in stealth materials. 

The present study focuses on elucidating and quantifying the physical changes in the polymers that were induced by the PEG-modulation of the PHB-synthesis. PEG is a polyether that is known for its exceptional blood and tissue compatibility, it is used extensively as stealth material in a variety of drug delivery vehicles and is also under investigation as surface coating for biomedical implants. PEG, when dissolved in water, has a low interfacial free ener, exhibits rapid chain motion, and its lai e excluded volume leads to steric repulsion of approaching molecules (16, 17). These properties are responsible for the superb biocompatibility of PEG. However, PEG is not a thermoplastic material and therefore not moldable. Furthermore, a PEG-modified alizarin dye is used for modulated fermentation in order to synthesize colored bacterial PHB. 

The B-2 stealth bomber in Figure 1-38 is made by Northrop Grumman. Virtually all external parts are made of various composite materials because of their radar-absorption characteristics and/or their capability to be formed to shapes that naturally lower the radar cross section of the plane. However, the details are not publicly available, nor are they for the Lockheed Martin F-117A stealth fighter. 

The most common mode of aircraft detection is radar. Essentially, radar is the detection of radio waves that have been thrown out and which bounce off objects returning to the site of origin. Today s radar, if properly used, can help identify the location, speed, and identity of the aircraft. The radar cross-section (RCS) of an aircraft is how much echo the plane sends from radar. Birds have an RCS of about 0.01 m. The Stealth Bomber has an RCS of 0.75 m. The Stealth Bomber and many stealth aircraft gain their stealth character from both the shape of the aircraft and the presence of radar absorbing material (RAM), which is made to absorb and eliminate radio waves rather than reflect them. Most of the RAM materials are polymeric. 

Composite materials have been acclaimed as the Materials of the Future. A key question is whether composite materials will always remain the materials of the future or if the future is here. Advanced polymer composites, once destined for stealth military aircraft or aerospace uses, are beginning to be used in down-to-earth structures, such as bridges, buildings, and highways. However, there are still considerable impediments to wider use, and composite manufacturers need to make great strides in the development and manufacturing of composite materials. 

Cough A cough is a sudden and noisy expulsion of air from the lungs to keep the respiratory passages free of irritating material. -5 penalty on any attempts to perform Skills or Feats that require stealth, silence or a clear voice, such as Move Silently or Intimidate. Verbal spell casting is not possible. 

In modern construction materials, such as the advanced composites from which the American Stealth bomber has been built, the subterfuge of invisibility is achieved in a different way. fl he characteristics of these materials permit the virtual elimination of an electronic signature resulting in near absence of a radar screen image. Coupled with extreme high speed and low altitude heneath-radar manoeuvrability, such vehicles can operate unseen. 

The destabilization (mixing) of a jet flow is desirable in many applications, including combustion, noise suppression at jet engine exhaust, infrared signature reduction of engine exhaust for platform stealth, and employment of a lighter and cheaper material for the lift flap such as that used in C-17 aircraft. 

Composites. Composites are materials that contain strong fibers or reinforcement embedded in a continuous phase called a matrix. They are found in jet fighters such as stealth fighters and bombers, in the reusable space shuttle, in graphite golf clubs, in synthetic human body parts, and for many years in marine craft (fibrous glass). 

Nevertheless, several general papers have been published on stealth technology applied to aircraft such as LOCKHEED F 117 [5,6] or others [7,8,9]. The description of radar absorbing materials is restricted to iron or ferrite loaded paints or elastomers except the case of retinyl Schiff base salts [10,11]. This molecule attracted interest of many scientists in 1987. In fact this material which is a charge transfer salt derived from the A vitamin, never exhibited high-frequency dielectric constant due to its intrinsic conductivity, despite its beautiful orange colour Moreover, reference books as the one of Knott el al. [12] do not mention the use of conductive polymers for this purpose. 

Stealth technologies are very complex due to the important number of involved scientific fields. Only the combination of materials improvement, numerical simulation and new stealth concepts can lead to improvements in this new science. 

It is now possible to design materials possessing permittivities which have low variation with the frequency (e"a(w ) or high (e"ao) ) directly correlated to the intrinsic conductivity of the polymer. To obtain the best performance (large bandwidth) these materials have to be associated in multilayer structures. Moreover, the use of structural laminates allows the integration of two functions (stealth and mechanical). 

It should be noted that to date, such radar absorbing structural materials (glass or Kevlar -F carbon) could not be processed by conventional weaving techniques. A brief calculation shows that the addition of a stealth function to conventional composites only results in a 50% mass uptake. For example, the architecture of... 

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