Neurovascular Photoacoustic Tomography

Neurovascular coupling refers to the relationship between neuronal activities and downstream hemodynamic responses. Photoacoustic tomography (PAT), enabling comprehensive label-free imaging of hemodynamic activities with highly scalable penetration and spatial resolution, has great potential in the study of neurovascular coupling. In this review, we first introduce the technical basis of hemodynamic PAT – including label-free quantification of total hemoglobin concentration, blood oxygenation, and blood flow – as well as its applications in hemodynamic monitoring. Then, we demonstrate the potential application of PAT in neurovascular imaging by highlighting representative studies on cerebral vascular responses to whisker stimulation and Alzheimer's disease. Finally, potential research directions and associated technical challenges are discussed

Deep reflection-mode photoacoustic imaging of biological tissue

A reflection-mode photoacoustic (PA) imaging system was designed and built to image deep structures in biological tissues. We chose near-infrared laser pulses of 804-nm wavelength for PA excitation to achieve deep penetration. To minimize unwanted surface signals, we adopted dark-field ring-shaped illumination. This imaging system employing a 5-MHz spherically focused ultrasonic transducer provides penetration up to 38mm in chicken breast tissue. At the 19-mm depth, the axial resolution is 144μm and the transverse resolution is 560μm. Internal organs of small animals were imaged clearly

Deep reflection-mode photoacoustic imaging of internal organs

A deep reflection-mode photoacoustic imaging system was developed and demonstrated to possess a maximum imaging depth up to 38 mm in chicken breast tissue. Using this system, structures in the thoracic cavity and vasculature in cervical area of rats were clearly imaged. Particularly, part of the heart was imaged. In the thoracic cavity, the right atrium imaged, which is one of deepest, was situated ~7 mm deep. In the cervical area, common carotid artery and jugular vein were imaged, which are appropriate for the study of oxygenation between artery and vein. In the abdominal cavity, the embedded structures of a kidney, spinal cord, and vena cava inferior were also clearly imaged in situ and in vivo. The depth of the vena cava inferior was as deep as ~15 mm in vivo. This study shows the depth capability of the system in animals. This imaging modality can be a useful tool to diagnose the disease of organs by assessing the morphological and functional changes in the blood vessels and the organs

Existence of Solutions for Nonlinear Impulsive Fractional Differential Equations of Order α

We investigate the existence and uniqueness of solutions to the nonlocal boundary value problem for nonlinear impulsive fractional differential equations of order α∈(2,3]. By using some well-known fixed point theorems, sufficient conditions for the existence of solutions are established. Some examples are presented to illustrate the main results

From Early Curiosity to Space Wide Web: Emergence of the Small Satellite Innovation Ecosystem

Research Questions: How did the small satellite ecosystem emerge and evolve? Although the first modern small satellite UoSat-1 was successfully launched in 1981, and the CubeSat dominant design was introduced in 1999, the sales takeoff of small satellites did not occur until the early 2010s. What explains this long time period

A Study on the Problems and Countermeasures of Oral English Teaching in Rural Junior Middle Schools under the Background of Man-machine Dialogue Examination in China

English is a main subject of high school entrance examination in China. Many Students have learned English for more than ten years, but they are still unable to communicate with others in English after they graduate from middle school or even high school because of the poor oral English. With the advocacy of the new curriculum reform and quality-oriented education, many provinces and municipalities in China have introduced oral English test into the English exam of high school entrance examination. However, comparing with urban students, students’ oral English in rural areas is relatively weak, which is undoubtedly a huge challenge for rural junior middle schools. Hence, rural junior middle schools need to take measures to improve the oral English of students. This paper analyses the problems of oral English teaching in rural junior middle schools from the aspects of teaching facilities, teachers and students, putting forward some suggestions accordingly

Do political connections foster or hamper firm environmental investment?

Extant studies of environmental investment determinants have not distinguished between different types of political connections. This study tries to close this gap by employing an extensive dataset based on the four-yearly Chinese Private Enterprises Survey conducted between 2006 and 2012. The central question in this paper asks whether different political connections (ascribed vs. achieved) are fostering or hindering environmental protection expenditures in private enterprises. The results show that achieved political connections serve as binds of promoting firm environmental investment while ascribed political connections act as buffers, hampering firm environmental expenditures. The moderating roles of environmental regulation and innovation capability demonstrate heterogeneous effects: environmental regulation stringency strengthens the positive impact of achieved political connections only. In contrast, innovation capability enhances the negative impact of ascribed political connections