Agency for Defense Development

Silica aerogels have drawn a lot of interest both in science and technology because of their low bulk density (up to 95% of their volume is air), hydrophobicity, low thermal conductivity, high surface area, and optical transparency. Aerogels are synthesized from molecular precursors by sol‐gel processing. Special drying techniques must be applied to replace the pore liquid with air while maintaining the solid network. Supercritical drying is most common; however, recently developed methods allow removal of the liquid at atmospheric pressure after chemical modification of the inner surface of the gels, leaving only a porous silica network filled with air. Therefore, by considering the surprising properties of aerogels, the present review addresses synthesis of silica aerogels by the sol‐gel method, as well as drying techniques and applications in current industrial development and scientific research.

OVER the past few years, there have been significant efforts devoted to the research and development of cooperative unmannedsystems [1–3].The formationflyingofmultipleunmanned aerial vehicles (UAVs) has been studied for radar deception, reconnaissance, surveillance, and surface-to-air-missile jamming in military operations. An example of a cooperative operational scenario of multiple vehicles is that of a small UAV flying over an urban area, dispensingmultiplemicro aerial vehicles to examinepointsof interest fromclosedistances [4].Agroupofwell-organized low-costmultiple vehicles can be far superior to a single high-technology and high-cost UAV in effectiveness. Tactical missile systems as well as UAVs provide more capabilities when they are organized as a coordinated group than when they are operated independently. Modern antiship missiles need to be able to penetrate the formidable defensive systems of battleships such as antiair defense missile systems and close-in weapon system (CIWS). CIWS is a naval shipboard weapon system for detecting and destroying incoming antiship missiles and enemy aircraft at short range. These defensive weapons with powerful fire capability and various strategies seriously intimidate the survivability of the conventional antiship missiles. Hence, antiship missile developers have made great efforts to develop a high-performance missile system with ultimate sea-skimming flight and terminal evasive maneuvering capabilities despite a huge cost. On the other hand, cooperative attack strategies have been studied to enhance survivability of the conventional ones. Here, a cooperative attack means that multiple missiles attack a single target or multiple targets cooperatively or, in a specific case, simultaneously [5,6]. Clearly, it is difficult to defend a group of attackers bursting into sight at the same time, even though each member is the conventional one in performance. So the simultaneous attack ofmultiple missiles is a cost-effective and efficient cooperative attack strategy. A simultaneous attack of a group of missiles against a single common target can be achieved by two ways. The first approach is individual homing, inwhich a common impact time is commanded to all members in advance, and thereafter each missile tries to home on the target on time independently. The second is cooperative homing, inwhich themissiles communicate among themselves to synchronize the arrival times. In other words, the missiles with larger times-to-go try to take shortcuts, whereas others with shorter times-to-go take detours to delay the arrival times. The first concept requires determination of a suitable common impact time before homing, but the second needs online data links throughout the engagement. Despite a number of studies on guidance problems related to timeto-go [7–10], studies on guidance laws to control impact time for a simultaneous attack are rare, except a few recent works by the authors. An impact-time-control guidance law (ITCG) for antiship missiles was developed in [5] and, as an extension of this study, a guidance law to control both impact time and angle (ITACG) was presented in [11]. These individual homing methods are based on optimal control theory, providing analytical closed-loop guidance laws. Herein, the desired impact time is assumed to be prescribed before the homing phase starts. Alternatively, this Note is concerned with a new guidance law based on the second approach, cooperative homing, for a simultaneous attack of multiple missiles. Proportional navigation (PN) is a well-known homing guidance method in which the rate of turn of the interceptor is made proportional with a navigation ratio N to the rate of turn of the line of sight (LOS) between the interceptor and the target. The navigation constant N is a unitless gain chosen in the range from 3 to 5 [12]. Although PNwithN 3 is known to be energy-optimal, an arbitrary N > 3 is also optimal if a time-varying weighting function is included into the cost function of the linear quadratic energy-optimal problem [13,14]. In general, the navigation ratio is held fixed. In some cases, however, it can be considered as a control parameter to achieve a desired terminal heading angle [15].Although PN results in successful intercepts under a wide range of engagement conditions, its control-efficiency is not optimal, in general, especially for the case of maneuvering targets [16]. Augmented proportional navigation, a variant of PN, is useful in cases in which target maneuvers are significant [12]. Biased proportional navigation is also commonly used to compensate for target accelerations and sensor noises or to achieve a desired attitude angle at impact [17]. Even if PN and its variants are alreadywell known andwidely used, they are not directly applicable to many-to-one engagements. This Note proposes a homing guidance law called cooperative proportional navigation (CPN) for many-to-one engagements: CPN has the same structure as conventional PN except that it has a time-varying navigation gain that is adjusted based on the onboard time-to-go and the times-to-go of the other missiles. CPN uses the time-varying navigation gain as a control parameter for reducing the variance of times-on-target of multiple missiles. This Note begins with the formulation of the homing problem of multiple missiles against a single target, subject to constraints on the impact time. Next, preliminary concepts such as the relative time-togo error and the variance of times-to-go of multiple missiles are introduced and a new guidance law is proposed. Then the major property of the law is investigated and the characteristics of the law for the case of twomissiles are examined in detail. Finally, numerical simulation results illustrate the performances of the proposed law.

Optimal guidance laws providing the specified impact angle as well as zero terminal miss distance are generalized for arbitrary missile dynamics. The optimal guidance command is represented by a linear combination of the ramp and the step responses of the missile’s lateral acceleration. Optimal guidance laws in the form of the state feedback for the lag-free and the first-order lag system are derived, and their characteristics are investigated. Practical timeto-go calculation methods, which are important for the implementation of the optimal guidance laws, are proposed to consider the path curvature. Nonlinear and adjoint simulations are performed to investigate the performance of the proposed laws.

In this work, we demonstrate that gas adsorption is significantly higher in edge sites of vertically aligned MoS2 compared to that of the conventional basal plane exposed MoS2 films. To compare the effect of the alignment of MoS2 on the gas adsorption properties, we synthesized three distinct MoS2 films with different alignment directions ((1) horizontally aligned MoS2 (basal plane exposed), (2) mixture of horizontally aligned MoS2 and vertically aligned layers (basal and edge exposed), and (3) vertically aligned MoS2 (edge exposed)) by using rapid sulfurization method of CVD process. Vertically aligned MoS2 film shows about 5-fold enhanced sensitivity to NO2 gas molecules compared to horizontally aligned MoS2 film. Vertically aligned MoS2 has superior resistance variation compared to horizontally aligned MoS2 even with same surface area exposed to identical concentration of gas molecules. We found that electrical response to target gas molecules correlates directly with the density of the exposed edge sites of MoS2 due to high adsorption of gas molecules onto edge sites of vertically aligned MoS2. Density functional theory (DFT) calculations corroborate the experimental results as stronger NO2 binding energies are computed for multiple configurations near the edge sites of MoS2, which verifies that electrical response to target gas molecules (NO2) correlates directly with the density of the exposed edge sites of MoS2 due to high adsorption of gas molecules onto edge sites of vertically aligned MoS2. We believe that this observation extends to other 2D TMD materials as well as MoS2 and can be applied to significantly enhance the gas sensor performance in these materials.

The complex permeability ( mu /sub r/) and permittivity ( epsilon /sub r/) spectra at X-band frequencies and their relationship with microwave absorbing properties are investigated in ferrite-rubber composite material. Multifrequency measurements of mu /sub r/ and epsilon /sub r/ are made by the reflection/transmission technique. The theoretical determination of matching frequency and matching thickness and minimum reflection loss can be made by plotting the observed mu /sub r/ and epsilon /sub r/ spectra on the solution map of wave-impedance-matching. It is found that a proper combination of mu /sub r/ and epsilon /sub r/ is necessary to produce the zero-reflection absorber at a given frequency and thickness.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The use of self‐reinforcement by larger elongated grains in silicon nitride ceramics requires judicious control of the microstructure to achieve high steady‐state toughness and high fracture strength. With a distinct bimodal distribution of grain diameters, such as that achieved by the addition of 2% rodlike seeds, the fracture resistance rapidly rises with crack extension to steady‐state values of up to 10 MPam 1/2 and is accompanied by fracture strengths in excess of 1 GPa. When the generation of elongated reinforcing grains is not regulated, a broad grain diameter distribution is typically generated. While some toughening is achieved, both the plateau (steady‐state) toughness and the R ‐curve response suffer, and the fracture strength undergoes a substantial reduction. Unreinforced equiaxed silicon nitride exhibits the least R ‐curve response with a steady‐state toughness of only 3.5 MPam 1/2 coupled with a reduced fracture strength.

Superior chemical sensing performance of black phosphorus (BP) is demonstrated by comparison with MoS2 and graphene. Dynamic sensing measurements of multichannel detection show that BP displays highly sensitive, selective, and fast-responsive NO2 sensing performance compared to the other representative 2D sensing materials. As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Recently, hybrid supercapacitors (HSCs), which combine the use of battery and supercapacitor, have been extensively studied in order to satisfy increasing demands for large energy density and high power capability in energy-storage devices. For this purpose, the requirement for anode materials that provide enhanced charge storage sites (high capacity) and accommodate fast charge transport (high rate capability) has increased. Herein, therefore, a preparation of nanocomposite as anode material is presented and an advanced HSC using it is thoroughly analyzed. The HSC comprises a mesoporous Nb2O5/carbon (m-Nb2O5-C) nanocomposite anode synthesized by a simple one-pot method using a block copolymer assisted self-assembly and commercial activated carbon (MSP-20) cathode under organic electrolyte. The m-Nb2O5-C anode provides high specific capacity with outstanding rate performance and cyclability, mainly stemming from its enhanced pseudocapacitive behavior through introduction of a carbon-coated mesostructure within a voltage range from 3.0 to 1.1 V (vs Li/Li(+)). The HSC using the m-Nb2O5-C anode and MSP-20 cathode exhibits excellent energy and power densities (74 W h kg(-1) and 18,510 W kg(-1)), with advanced cycle life (capacity retention: ∼90% at 1000 mA g(-1) after 1000 cycles) within potential range from 1.0 to 3.5 V. In particular, we note that the highest power density (18,510 W kg(-1)) of HSC is achieved at 15 W h kg(-1), which is the highest level among similar HSC systems previously reported. With further study, the HSCs developed in this work could be a next-generation energy-storage device, bridging the performance gap between conventional batteries and supercapacitors.

Chameleons use a non-close-packed array of guanine nanocrystals in iridophores to develop and tune skin colors in the full visible range. Inspired by the biological process uncovered in panther chameleons, we designed photonic films containing a non-close-packed face-centered-cubic array of silica particles embedded in an elastomer. The non-close-packed array is formed by interparticle repulsion exerted by solvation layers on the particle surface, which is rapidly captured in the elastomer by photocuring of the dispersion medium. The artificial skin exhibits a structural color that shifts from red to blue under stretching or compression. The separation between inelastic particles enables tuning without experiencing significant rearrangement of particles, providing elastic deformation and reversible color change, as chameleons do. The simple fabrication procedure consists of film casting and UV irradiation, potentially enabling the continuous high-throughput production. The mechanochromic property of the photonic films enables the visualization of deformation or stress with colors, which is potentially beneficial for various applications, including mechanical sensors, sound-vision transformers, and color display.

In this paper, the optimal guidance law with terminal constraints of miss distance and impact angle is presented for a constant speed missile against the stationary target. The proposed guidance law is obtained as the solution of a linear quadratic optimal control problem with the energy cost weighted by a power of the time-to-go. Systematic selection of guidance gains and trajectory shaping are possible by adjusting the exponent of the weighting function. A new time-to-go calculation method taking account of the trajectory curve is also proposed for implementation of the proposed law. Nonlinear and adjoint simulations are performed to investigate the performance of the proposed guidance law and time-to-go calculation method.

Solid oxide fuel cells (SOFC) are the cleanest, most efficient, and cost-effective option for direct conversion to electricity of a wide variety of fuels. While significant progress has been made in anode materials with enhanced tolerance to coking and contaminant poisoning, cathodic polarization still contributes considerably to energy loss, more so at lower operating temperatures. Here we report a synergistic effect of co-doping in a cation-ordered double-perovskite material, PrBa0.5Sr0.5Co(2-x)Fe(x)O(5+δ), which has created pore channels that dramatically enhance oxygen ion diffusion and surface oxygen exchange while maintaining excellent compatibility and stability under operating conditions. Test cells based on these cathode materials demonstrate peak power densities ~2.2 W cm(-2) at 600°C, representing an important step toward commercially viable SOFC technologies.

This letter reports a performance analysis of a dual-hop relay system composed of asymmetric radio-frequency and free-space optics (RF/FSO) links. This approach is based on the fact that FSO links can provide even wider bandwidths as compared to RF ones. In particular, an exact closed-form expression for the end-to-end outage probability of the RF/FSO relay links is derived. Overall, the RF/FSO links show a slightly worse performance than the RF/RF links, but the performance gap is gradually reduced as the signal-to-noise ratio (SNR) increases. Our mathematical analysis results were verified by exactly matching Monte Carlo simulation results.

Vaccines and therapeutics are urgently needed for the pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Here, we screen human monoclonal antibodies (mAb) targeting the receptor binding domain (RBD) of the viral spike protein via antibody library constructed from peripheral blood mononuclear cells of a convalescent patient. The CT-P59 mAb potently neutralizes SARS-CoV-2 isolates including the D614G variant without antibody-dependent enhancement effect. Complex crystal structure of CT-P59 Fab/RBD shows that CT-P59 blocks interaction regions of RBD for angiotensin converting enzyme 2 (ACE2) receptor with an orientation that is notably different from previously reported RBD-targeting mAbs. Furthermore, therapeutic effects of CT-P59 are evaluated in three animal models (ferret, hamster, and rhesus monkey), demonstrating a substantial reduction in viral titer along with alleviation of clinical symptoms. Therefore, CT-P59 may be a promising therapeutic candidate for COVID-19.

A novel algorithm to remove rain or snow streaks from a video sequence using temporal correlation and low-rank matrix completion is proposed in this paper. Based on the observation that rain streaks are too small and move too fast to affect the optical flow estimation between consecutive frames, we obtain an initial rain map by subtracting temporally warped frames from a current frame. Then, we decompose the initial rain map into basis vectors based on the sparse representation, and classify those basis vectors into rain streak ones and outliers with a support vector machine. We then refine the rain map by excluding the outliers. Finally, we remove the detected rain streaks by employing a low-rank matrix completion technique. Furthermore, we extend the proposed algorithm to stereo video deraining. Experimental results demonstrate that the proposed algorithm detects and removes rain or snow streaks efficiently, outperforming conventional algorithms.

One-dimensional electromagnetic bandgap (1-D EBG) and split ring resonator (SRR) structures were inserted between two closely located monopole antennas to suppress mutual coupling. The 1-D EBG and SRR structures in these planar multiple antennas function as a reflector and wave trap, respectively. With the effect of these two structures, the mutual coupling between the two antennas is reduced by more than 42 dB and the back lobes are reduced by 6 dB. Thereby, the radiation efficiency of the antenna is also improved. The two fabricated antennas with 0.19λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> spacing exhibit mutual coupling (S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">21</sub> , S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sub> ) of less than -30 dB from 2.43 to 2.54 GHz. A minimum correlation coefficient of 0.002 and maximum radiation efficiency of 82% are also demonstrated.

In this paper, we introduce a new high-resolution reflectometry technique that operates simultaneously in both the time and frequency domains. The approach rests upon time-frequency signal analysis and utilizes a chirp signal multiplied by a Gaussian time envelope. The Gaussian envelope provides time localization, while the chirp allows one to excite the system under test with a swept sinewave covering a frequency band of interest. This latter capability is of particular interest when testing communication cables and systems. Sensitivity in detecting the reflected signal is provided by a time-frequency cross-correlation function. The approach is verified by experimentally locating various types of faults, located at various distances, in RG 142 and RG 400 coaxial cables.

A nanohybridization strategy is presented for the fabrication of high performance lithium ion batteries based on redox-active organic molecules. The rearrangement of electroactive aromatic molecules from bulk crystalline particles into molecular layers is achieved by non-covalent nanohybridization of active molecules with conductive scaffolds. As a result, nano-hybrid organic electrodes in the form of a flexible self-standing paper-free of binder/additive and current collector-are synthesized, which exhibit high energy and power densities combined with excellent cyclic stability.

In this work, a modified polyol synthesis by adding KBr and by replacing the AgCl with NaCl seed was used to obtain high quality silver nanowires with long aspect ratios with an average length of 13.5 μm in length and 62.5 nm in diameter. The Ag nanowires suspended in methanol solution after removing any unwanted particles using a glass filter system were then deposited on a flexible polycarbonate substrate using an electrostatic spray system. Transmittance of 92.1% at wavelength of 550 nm with sheet resistance of 20 Ω/sq and haze of 4.9% were measured for the electrostatic sprayed Ag nanowire transparent electrode.

Calibration between color camera and 3D Light Detection And Ranging (LIDAR) equipment is an essential process for data fusion. The goal of this paper is to improve the calibration accuracy between a camera and a 3D LIDAR. In particular, we are interested in calibrating a low resolution 3D LIDAR with a relatively small number of vertical sensors. Our goal is achieved by employing a new methodology for the calibration board, which exploits 2D-3D correspondences. The 3D corresponding points are estimated from the scanned laser points on the polygonal planar board with adjacent sides. Since the lengths of adjacent sides are known, we can estimate the vertices of the board as a meeting point of two projected sides of the polygonal board. The estimated vertices from the range data and those detected from the color image serve as the corresponding points for the calibration. Experiments using a low-resolution LIDAR with 32 sensors show robust results.

The mobile inverted pendulum is developed and tested for an intelligent control experiment of control engineers. Intelligent control algorithms are tested for the control experiment of a low cost mobile inverted pendulum system. Online learning and control using neural network of a wheel-driven mobile inverted pendulum system is presented. Neural network learning algorithm is embedded on a digital signal processing board along with primary proportional-integral-differential controllers to achieve real time control. Without knowing dynamics of the system, uncertainties in system dynamics are compensated by neural network in an online fashion. Digital filters are designed for a gyro sensor to compensate for a phase lag. Experimental studies of balancing the pendulum and tracking the desired trajectory of the cart for one dimensional motion are conducted. Results show the robustness of the proposed controller even when outer impacts as disturbance are present.