Measurement and analysis of species distribution in laser-induced ablation plasma of an aluminum-magnesium alloy

We proposed a theoretical spatio-temporal imaging method, which was based on the thermal model of laser ablation and the two-dimensional axisymmetric multi-species hydrodynamics model. By using the intensity formula, the integral intensity of spectral lines could be calculated and the corresponding images of intensity distribution could be drawn. Through further image processing such as normalization, determination of minimum intensity, combination and color filtering, a relatively clear species distribution image in the plasma could be obtained. Using the above method, we simulated the plasma ablated from Al-Mg alloy by different laser energies under 1 atm argon, and obtained the theoretical spatio-temporal distributions of Mg I, Mg II, Al I, Al II and Ar I species, which are almost consistent with the experimental results by differential imaging. Compared with the experimental decay time constants, the consistency is higher at low laser energy, indicating that our theoretical model is more suitable for the plasma dominated by laser-supported combustion wave.

Narrowing the Pipe: Different Etiologies of Tracheal Stenosis

The trachea serves as the conduit for passage of air between the larynx and the lung bronchi. The tracheal luminal caliber may be narrowed in adults by extrinsic mass effect from adjacent structures; intrinsic stenosis secondary to intubation, inflammatory, systemic, or idiopathic disorders; and benign or malignant masses. Contrast-enhanced CT accurately depicts the source of the stenosis and can measure the length and cross-sectional area of the stenosis and evaluate the extent of locoregional spread with malignancies. In addition, the data are capable of being reformatted by several techniques, including virtual endoscopy and surface-rendered reconstruction. Certain imaging characteristics such as the presence of calcifications and involvement or sparing of the posterior membrane can be useful to suggest a particular diagnosis or differential. Imaging, however, is not usually pathognomonic for a specific benign or malignant tracheal stenotic lesion, and ultimately biopsy is needed to establish a definitive histopathologic diagnosis.Learning Objective: To describe the different etiologies of tracheal stenosis

Ultrasonic Ring Array-Based Transient Triplet Differential Photoacoustic Imaging for Strong Background Removal

Photoacoustic imaging (PAI) is a fast evolving imaging technology enabling in vivo imaging with high specificity and spatial resolution. However, due to strong background signals from various intrinsic chromospheres such as melanin, photoacoustic imaging of targeting objects labeled by contrast agents remain a challenge. The transient triplet differential (TTD) method has shown a significant potential for background-free photoacoustic imaging. Here, we develop a photoacoustic system using an ultrasonic semicircular ring array for transient triplet differential imaging. Pt(II) Octaethylporphine (PtOEP) and black ink are used as the contrast agent and the phantom of melanoma, respectively. Using the TTD method, we could remove the strong background signal from black ink. The ratio between contrast agent signal and background signal is increased to about 10 times the previous one. Our finding demonstrates the potential of the TTD method on molecular imaging for strong background removal.

On Differential Imaging Using Electromagnetic Simulation for Vehicular Antenna Signature Analysis

The current trend in vehicles is to integrate a wide number of antennae and sensors operating at a variety of frequencies for sensing and communications. The integration of these antennae and sensors in the vehicle platform is complex because of the way in which the antenna radiation patterns interact with the vehicle structure and other antennae/sensors. Consequently, there is a need to study the radiation pattern of each antenna or, alternatively, the currents induced on the surface of the vehicle to optimize the integration of multiple antennae. The novel concept of differential imaging represents one method by which it is possible to obtain the surface current distribution without introducing any perturbing probe. The aim of this study was to develop and confirm the assumptions that underpin differential imaging by means of full-wave electromagnetic simulation, thereby providing additional verification of the concept. The simulation environment and parameters were selected to replicate the conditions in which real measurements were taken in previous studies. The simulations were performed using Ansys HFSS simulation software. The results confirm that the approximations are valid, and the differential currents are representative of the induced surface currents generated by a monopole positioned on the top of a vehicle.