Radiative cooling is a passive cooling method by emitting heat to outer space without energy input. In this work we propose a cost effective double-layer coating embedded with nanoparticles for both nighttime and daytime radiative cooling. The top and bottom layers are acrylic resin embedded with titanium dioxide and carbon black particles, respectively responsible for reflecting the solar irradiation and emitting the heat in the atmospheric transparency window. The carbon black layer is considered as the black substrate. For the top layer, different sizes of titanium dioxide particles are examined, and 0.2 µm radius is found to give the best cooling performance. More than 90% of the solar irradiation can be reflected, and the average emissivity in the atmospheric transparency window is larger than 0.9 in most directions. A daytime net cooling power over 100 W/m 2 is predicted at the ambient temperature. The cooling effect persists even if significant conduction and convection heat exchange is considered.

Mammography is the primary imaging tool for screening and diagnosis of human breast cancers, but ∼10-20% of palpable tumors are not detectable on mammograms and only about 40% of biopsied lesions are malignant. Here we report a high-resolution, low-dose phase contrast X-ray tomographic method for 3D diagnosis of human breast cancers. By combining phase contrast X-ray imaging with an image reconstruction method known as equally sloped tomography, we imaged a human breast in three dimensions and identified a malignant cancer with a pixel size of 92 μm and a radiation dose less than that of dual-view mammography. According to a blind evaluation by five independent radiologists, our method can reduce the radiation dose and acquisition time by ∼74% relative to conventional phase contrast X-ray tomography, while maintaining high image resolution and image contrast. These results demonstrate that high-resolution 3D diagnostic imaging of human breast cancers can, in principle, be performed at clinical compatible doses.radiation dose reduction | iterative algorithm | analyzer based imaging M ammography is a widely used imaging technique for early detection of human breast cancers. Although more advanced technologies such as digital mammography have been developed to improve its image quality (1), there are three potential risks associated with mammography. First, mammograms miss up to 20% of breast cancers that are present during the time of screening (2). Second, in some cases mammograms appear abnormal, but no breast cancers are actually present (3). Third, repeated mammography examinations have the potential of causing cancers (4). Dedicated breast computed tomography (CT) can reduce some of these risks, but its spatial resolution (∼400 μm) is mainly limited by the X-ray dose deliverable to the radiationsensitive human breast and its detection of microcalcifications is inferior to mammography (5). Furthermore, some tumors are not visible in CT because its image contrast is based on the X-ray absorption coefficient and is intrinsically low between tumors and normal tissues. A very promising approach to significantly improve the image resolution, image contrast and detectability is the use of phase contrast x-ray tomography (PCT) (6-8) (Materials and Methods). Compared with absorption-based CT, PCT is sensitive to the refraction (i.e., "phase shift") of X-rays in matter. In soft tissues, phase variations can be two to three orders of magnitude larger than the absorption ones (9), and thus an increased image contrast can be achieved. Over the past few decades, phase contrast X-ray imaging has been under rapid development and various X-ray phase contrast methods have been implemented, including X-ray interferometry (6, 7), analyzer-based (or diffraction-enhanced) imaging (10, 11), propagation-based imaging (12, 13), grating-based imaging (14, 15), and grating noninterferometric methods (16). A large number of X-ray phase contrast imaging results has been reported on both technical developments and biomedical applications ...

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