No abstract

Frequency agile radar (FAR) is known to have excellent electronic counter-countermeasures (ECCM) performance and the potential to realize spectrum sharing in dense electromagnetic environments. Many compressed sensing (CS) based algorithms have been developed for joint range and Doppler estimation in FAR. This paper considers theoretical analysis of FAR via CS algorithms. In particular, we analyze the properties of the sensing matrix, which is a highly structured random matrix. We then derive bounds on the number of recoverable targets. Numerical simulations and field experiments validate the theoretical findings and demonstrate the effectiveness of CS approaches to FAR.

A radiative vapor condenser sheds heat in the form of infrared radiation and cools itself to below the ambient air temperature to produce liquid water from vapor. This effect has been known for centuries, and is exploited by some insects to survive in dry deserts. Humans have also been using radiative condensation for dew collection. However, all existing radiative vapor condensers must operate during the nighttime. Here, we develop daytime radiative condensers that continue to operate 24 h a day. These daytime radiative condensers can produce water from vapor under direct sunlight, without active consumption of energy. Combined with traditional passive cooling via convection and conduction, radiative cooling can substantially increase the performance of passive vapor condensation, which can be used for passive water extraction and purification technologies.

Using a combination of synchrotron radiation based magnetic imaging and high-resolution transmission electron microscopy we reveal systematic correlations between the magnetic switching field and the internal nanoscale structure of individual islands in bit patterned media fabricated by Co/Pd-multilayer deposition onto pre-patterned substrates. We find that misaligned grains at the island periphery are a common feature independent of the island switching field, while irregular island shapes and misaligned grains specifically extending into the center of an island are systematically correlated with a reduced island reversal field.

(0.96‐x)K0.48Na0.52NbO3‐0.04Bi0.5Na0.5ZrO3‐xLaFeO3 ceramics (abbreviated as KNN‐BNZ‐LF1000x) with enhanced piezoelectric performance and temperature stability were prepared by the conventional solid‐state sintering method. It was found that the incorporation of LaFeO3 gradually shifted the O‐T phase boundary toward room temperature, while maintaining the Curie temperature above 300°C. The optimal piezoelectricity was found at x = 0.006, with relatively high piezoelectric constant d33 of 345 pC/N as well as a high level of unipolar strain (0.126% at 3 kV/mm). Benefiting from the diffused phase transition induced by appropriate amount of LaFeO3 content, the KNN‐BNZ‐LF6 sample possessed greatly enhanced the temperature stability of d33∗, which varied less than 8% in the temperature range of 20°C‐100°C.