Broadband transparent ultrasound transducer with polymethyl methacrylate as matching layer for in vivo photoacoustic microscopy.

Photoacoustic imaging (PAI) uniquely combines optics and ultrasound, presenting a promising role in biomedical imaging as a non-invasive and label-free imaging technology. As the traditional opaque ultrasound (US) transducers could hinder the transportation of the excitation light and limit the performance of PAI system, piezoelectric transparent ultrasonic transducers (TUTs) with indium tin oxide (ITO) electrodes have been developed to allow light transmission through the transducer and illuminate the sample directly. Nevertheless, without having transparent matching materials with appropriate properties, the bandwidth of those TUTs was generally narrow. In this work, we propose to employ polymethyl methacrylate (PMMA) as the matching layer material to improve the bandwidth of lithium niobate (LN)-based TUTs. The effects of PMMA matching layer on the performance of TUTs have been systematically studied. With the optimized PMMA matching layer, the very wide bandwidth of > 50 % could be achieved for the TUTs even with different transducer frequencies, leading to the great enhancement of axial resolution when compared to the similar reported work. In addition, the imaging performance of the developed TUT prototype has been evaluated in a PAI system and demonstrated by both phantom and in vivo small animal imaging.

Three-dimensional Budyko framework incorporating terrestrial water storage: Unraveling water-energy dynamics, vegetation, and ocean-atmosphere interactions.

The two-dimensional steady-state Budyko framework, widely used to study water-energy dynamics in landscapes, primarily focused on the partitioning of precipitation into evapotranspiration (ET) and water yield. Though this framework has been extended by incorporating water storage changes into precipitation input for non-steady state conditions, the interactions among water-energy dynamics, vegetation covers, and ocean-atmosphere oscillations within the Budyko framework at finer spatial and temporal scales have been unexplored. This study aims to investigate the interactions of regional hydroclimatic conditions, vegetation, and climate teleconnections over the Indo-China Peninsula (ICP), a region highly vulnerable to climate change. To achieve the objective, we propose a three-dimensional Budyko framework that incorporates the ratio of Gravity Recovery and Climate Experiment (GRACE)-based terrestrial water storage (TWS) or its changes (TWSC) to precipitation (SI/SCI) as the third dimension alongside the traditional two-dimensional Budyko framework. Our findings reveal that TWS has a significant impact on the Budyko framework, particularly during the dry season. The dryness index (DI)/evaporative index (EI) and SI/SCI exhibit positive (strongly negative) linear relationships in the wet (dry) season, respectively. Vegetation covers strongly influence the three-dimensional Budyko framework, with poor performance observed in highly vegetated regions due to high ET demand. Through relative importance analysis, we identify the Silk Road Pattern (SRP) as the most influential climate teleconnection among nine different teleconnections, affecting hydroclimatic conditions over the ICP. Positive (negative) phases of SRP encourage water-limited (energy-limited) ET conditions. This demonstrates that the Budyko parameter is influenced not only by landscapes but also by climate teleconnections, offering potential benefits for Budyko parameter estimation. Furthermore, the linear relationships between DI/EI and SI/SCI in three-dimensional Budyko framework can provide a promising alternative method for evapotranspiration and groundwater estimation.

Cable-free brain imaging for multiple free-moving animals with miniature wireless microscopes.

Significance: Although several miniature microscope systems have been developed to allow researchers to image brain neuron activities of free moving rodents, they generally require a long cable connecting to the miniature microscope. It not only limits the behavior of the animal, but also makes it challenging to study multiple animals simultaneously. Aim: The aim of this work is to develop a fully wireless miniature microscope that would break constraints from the connecting cables so that the animals could move completely freely, allowing neuroscience researchers to study more of animals' behaviors simultaneously, such as social behavior. Approach: We present a wireless mini-microscope (wScope) that enables simultaneously real-time brain imaging preview from multiple free-moving animals. The wScope has a mass of 2.7 g and a maximum frame rate of 25 Hz at 750 µ m × 450 µ m field of view with 1.8 - µ m resolution. Results: The performance of the wScope is validated via real-time imaging of the cerebral blood flow and the activity of neurons in the primary visual cortex (V1) of different mice. Conclusions: The wScope provides a powerful tool for brain imaging of multiple free moving animals in their much larger spaces and more naturalistic environments.

Gravimetry-based terrigenous freshwater extension in the southwestern South China Sea and its response to monsoon under ENSO.

Terrigenous discharge represents a mass movement from land to oceanic environment. While previous studies characterized terrigenous freshwater via oceanographic (physical and biochemical) data, the persistent fresh water in the far-field ocean via satellite-gravimetric observation has been rarely explored. This paper aims to characterize the spatiotemporal extension of Mekong freshwater and the interchangeable role of runoff and climatic factors in the southwestern South China Sea. Employing wavelet coherence analysis between the in situ runoff and oceanic freshwater variations inferred from satellite gravimetry, the coherence and transport duration were obtained at annual, intra- and inter-annual time scales during 2003-2015. Despite weak relationship at 6-month and 24-month scales in regions away from the estuary, the two time series remained significantly correlated at the 12-month scale with a highly positive coherence over 0.97. Spatial pattern of the annual transport duration further indicated that freshwater firstly flowed alongshore before turning eastward offshore, qualitatively consistent with the northeastward western boundary current and an anticyclonic eddy during the summertime generated from the ocean circulation model. Using partial wavelet coherence, the time-variable relationship at all these three scales was found closely related to the Indian Monsoon and Western North Pacific Monsoon. A series of alternating ENSO events during 2007-2011 were responsible for the inter-annual variations, contributing <5 % to the seasonal freshwater extension. Compared with the averaged transport duration of the isotope method (i.e., 21.5 days) and the geostrophic current computation (i.e., 38.8 days) in the summer of 2007, our method yielded a comparable transport duration of 23.9 days with smaller uncertainties. The wind-driven Ekman transport, however, was primarily responsible for the anticyclonic movement of freshwater transport in the southwestern South China Sea during late summer.

Improved Remotely Sensed Total Basin Discharge and Its Seasonal Error Characterization in the Yangtze River Basin.

Total basin discharge is a critical component for the understanding of surface water exchange at the land-ocean interface. A continuous decline in the number of global hydrological stations over the past fifteen years has promoted the estimation of total basin discharge using remote sensing. Previous remotely sensed total basin discharge of the Yangtze River basin, expressed in terms of runoff, was estimated via the water balance equation, using a combination of remote sensing and modeled data products of various qualities. Nevertheless, the modeled data products are presented with large uncertainties and the seasonal error characteristics of the remotely sensed total basin discharge have rarely been investigated. In this study, we conducted total basin discharge estimation of the Yangtze River Basin, based purely on remotely sensed data. This estimation considered the period between January 2003 and December 2012 at a monthly temporal scale and was based on precipitation data collected from the Tropical Rainfall Measuring Mission (TRMM) satellite, evapotranspiration data collected from the Moderate Resolution Imaging Spectroradiometer (MODIS) satellite, and terrestrial water storage data collected from the Gravity Recovery and Climate Experiment (GRACE) satellite. A seasonal accuracy assessment was performed to detect poor performances and highlight any deficiencies in the modeled data products derived from the discharge estimation. Comparison of our estimated runoff results based purely on remotely sensed data, and the most accurate results of a previous study against the observed runoff revealed a Pearson correlation coefficient (PCC) of 0.89 and 0.74, and a root-mean-square error (RMSE) of 11.69 mm/month and 14.30 mm/month, respectively. We identified some deficiencies in capturing the maximum and the minimum of runoff rates during both summer and winter, due to an underestimation and overestimation of evapotranspiration, respectively.

Far-field correlation of bidirectional tracking beams due to wave-front deformation in inter-satellites optical communication links.

In some applications of optical communication systems, such as inter-satellites optical communication, the correlation of the bidirectional tracking beams changes in far-field as a result of wave-front deformation. Far-field correlation model with wave-front deformation on tracking stability is established. Far-field correlation function and factor have been obtained. Combining with parameters of typical laser communication systems, the model is corrected. It shows that deformation pointing-tracking errors θ(A) and θ(B), far-field correlation factor δ depend on RMS of deformation error rms, which decline with a increasing rms including Tilt and Coma. The principle of adjusting far-field correlation factor with wave-front deformation to compensate deformation pointing-tracking errors has been given, through which the deformation pointing-tracking error is reduced to 18.12″ (Azimuth) and 17.65″ (Elevation). Work above possesses significant reference value on optimization design in inter-satellites optical communication.