A lumped-parameter model of the free-flooded ring transducer array.

The free-flooded ring (FFR) transducer is an extensively used ring-type acoustic transducer in underwater environments owing to its broad operating frequency bandwidth and small size. However, achieving high sound pressure levels with a single FFR transducer is often difficult, thus necessitating the construction of vertically arranged FFR transducer arrays. This study presents a comprehensive analysis of the electrical and acoustic characteristics of an FFR transducer array by considering the mutual radiation load and the effects of gaps between adjacent piezoelectric rings. The lumped-parameter models of the piezoelectric ring, cylindrical cavity, cylindrical gap, and radiation impedance constitute an entire impedance matrix. The radiation impedance matrix for the FFR transducer array is calculated using the Helmholtz-Kirchhoff integral formula by considering the interaction of the FFR surfaces with the surrounding fluid medium. The proposed model predicts the resonance peaks in the admittance and transmitted voltage response (TVR) with a relative error of 5%, and the TVR level within a 3 dB range. Detailed analyses of a four-FFR transducer array reveal that a wider gap between each FFR leads to a decreased chance of negative conductance and broader operating bandwidth. The proposed model offers valuable insights into the design of FFR transducer arrays.

Epigenetic MicroRNAs as Prognostic Markers of Postoperative Atrial Fibrillation: A Systematic Review.

Postoperative atrial fibrillation (POAF) is a common complication after cardiac surgery, increasing the risk for adverse outcomes such as perioperative and long-term mortality, stroke, myocardial infarction, and other thromboembolic events. Epigenetic biomarkers show promise as prognostic tools for POAF. Epigenetic changes, such as DNA methylation, histone modification, and microRNAs (miRNA), can result in altered gene expression and the development of various pathological conditions. This systematic review aims to present the current literature on the association between various epigenetic markers and the development of POAF following cardiac surgery. Here, an electronic literature search was performed using MEDLINE, EMBASE, Cochrane Central Register of Controlled Trials, ClinicalTrials.gov, and Google Scholar to identify studies that reported the role of epigenetic markers in the development of POAF. Five of the 6 studies focused on miRNAs and their association with POAF. In POAF patients, the expression of miR-1 and miR-483-5p were upregulated in the right atrial appendage (RAA), while the levels of miR-133A, miR-208a, miR-23a, miR-26a, miR-29a, miR-29b, and miR-29c were decreased in the RAA and venous blood. One study examined cytosines followed by guanines (CpGs) as DNA methylation markers. Across all studies, 488 human subjects who had undergone cardiac surgery were investigated, and 195 subjects (39.9%) developed new-onset POAF. The current literature suggests that miRNAs may play a role in predicting the development of atrial fibrillation after cardiac surgery. However, more robust clinical data are required to justify their role in routine clinical practice.

Yb Substitution and Ultralow Thermal Conductivity of the Ca3-xYbxAlSb3 (0 ≤ x ≤ 0.81(1)) System.

A series of Yb-substituted Zintl phases in the Ca3-xYbxAlSb3 (0 ≤ x ≤ 0.81(1)) system has been synthesized by initial arc melting and post-heat treatment, and their isotypic crystal structures were characterized by both powder and single crystal X-ray diffraction analysis. All four title compounds adopted the Ca3AlAs3-type structure (space group Pnma, Pearson code oP28, Z = 4). The overall structure can be described as a combination of the 1-dimensional (1D) infinite chain of ∞1[Al(Sb2Sb2/2)] formed by two vertices sharing [AlSb4] tetrahedral moieties and three Ca2+/Yb2+ mixed sites located in between these 1D chains. The charge balance and the resultant independency of the 1D chains in the title system were explained by the Zintl-Klemm formalism [Ca2+/Yb2+]3[(4b-Al1-)(1b-Sb2-)2(2b-Sb1-)2/2]. A series of DFT calculations proved that (1) the band overlap between the d-orbital states from two types of cations and the p-orbital states from Sb at the high symmetry Γ point implied a heavily doped degenerate semiconducting behavior of the quaternary Ca2YbAlSb3 model and (2) the site preference of Yb for the M1 site was due to the electronic-factor criterion based on the Q values of each atomic site. The electron localization function calculations also proved that the two different shapes of lone pairs of the Sb atoms─the "umbrella-shape" and the "C-shape"─are determined by local geometry and the coordination environment on the anionic frameworks. Thermoelectric measurements of the quaternary title compound Ca2.19(1)Yb0.81AlSb3 showed an approximately two times larger ZT value than that of ternary Ca3AlSb3 at 623 K due to increased electrical conductivity and ultralow thermal conductivity originated from Yb substitution for Ca.

Opioids-induced inhibition of HERG ion channels and sudden cardiac death, a systematic review of current literature.

BACKGROUND: It is estimated that over 60 million individuals regularly use opioids globally, with opioid use disorder increasing substantially in the past decade. Several reports have linked sudden cardiac death, QTc prolongation, and other adverse cardiovascular outcomes with opioid use through their inhibitory effect on the human ether-a-go-go-related gene (HERG) ion channel. Therefore, understanding this underlying mechanism may be critical for risk prevention and management in prescribing opioids and treating patients with opioid dependency. AIM: The present systematic review summarizes the current literature on the impact of opioids-induced inhibition of HERG channel function and its relationship with sudden cardiac death, QTc prolongation, and other cardiovascular adverse effects. METHODS: A systematic review was conducted of the databases PubMed, EMBASE, Cochrane, and ClinicalTrials.gov of primary studies that reported the effects of opioids on HERG channel function and associated cardiovascular outcomes. RESULTS: The search identified 1,546 studies, of which 12 were finally included for data extraction. Based on the current literature, methadone, oliceridine, l-α-acetylmethadol (LAAM), and fentanyl were found to inhibit the HERG channel function and were associated with QTc prolongation. However, other opioids such as morphine, codeine, tramadol, and buprenorphine were not associated with inhibition of HERG channels or QTc prolongation. Additional cardiac outcomes associated with opioid related HERG channels dysfunction included sudden cardiac death and Torsade de Pointes. CONCLUSION: Our findings suggest that certain opioid consumption may result in the inhibition of HERG channels, subsequently prolonging the QTc interval and increasing patient susceptibility to sudden cardiac death.

Pseudo-Hydrodynamic Flow of Quasiparticles in Semimetal WTe2 at Room Temperature.

Recently, much interest has emerged in fluid-like electric charge transport in various solid-state systems. The hydrodynamic behavior of the electronic fluid reveals itself as a decrease of the electrical resistance with increasing temperature (the Gurzhi effect) in narrow channels, polynomial scaling of the resistance as a function of the channel width, violation of the Wiedemann-Franz law supported by the emergence of the Poiseuille flow. Similar to whirlpools in flowing water, the viscous electronic flow generates vortices, resulting in abnormal sign-changing electrical response driven by backflow. However, the question of whether the long-ranged sign-changing electrical response can be produced by a mechanism other than hydrodynamics has not been addressed so far. Here polarization-sensitive laser microscopy is used to demonstrate the emergence of visually similar abnormal sign-alternating patterns in semi-metallic tungsten ditelluride at room temperature where this material does not exhibit true hydrodynamics. It is found that the neutral quasiparticle current consisting of electrons and holes obeys an equation remarkably similar to the Navier-Stokes equation. In particular, the momentum relaxation is replaced by the much slower process of quasiparticle recombination. This pseudo-hydrodynamic flow of quasiparticles leads to a sign-changing charge accumulation pattern via different diffusivities of electrons and holes.

Reduction in Biogenic Amine Content in Baechu (Napa Cabbage) Kimchi by Biogenic Amine-Degrading Lactic Acid Bacteria.

This study was performed to mine biogenic amine (BA)-degrading lactic acid bacteria (LAB) from kimchi and to investigate the effects of the LAB strains on BA reduction in Baechu kimchi fermentation. Among 1448 LAB strains isolated from various kimchi varieties, five strains capable of considerably degrading histamine and/or tyramine were selected through in vitro tests and identified as Levilactobacillus brevis PK08, Lactiplantibacillus pentosus PK05, Leuconostoc mesenteroides YM20, L. plantarum KD15, and Latilactobacillus sakei YM21. The selected strains were used to ferment five groups of Baechu kimchi, respectively. The LB group inoculated with L. brevis PK08 showed the highest reduction in tyramine content, 66.65% and 81.89%, compared to the control group and the positive control group, respectively. Other BA content was also considerably reduced, by 3.76-89.26% (five BAs) and 7.87-23.27% (four BAs), compared to the two control groups, respectively. The other inoculated groups showed similar or less BA reduction than the LB group. Meanwhile, a multicopper oxidase gene was detected in L. brevis PK08 when pursuing the BA degradation mechanism. Consequently, L. brevis PK08 could be applied to kimchi fermentation as a starter or protective culture to improve the BA-related safety of kimchi where prolific tyramine-producing LAB strains are present.

740-watt level optical tap coupler using side-polished large-mode-area double clad fibers for a high power fiber laser.

We fabricated a fiber-optic directional coupler based on evanescent field coupling between side-polished large mode area (LMA) double clad fibers (DCFs) for a high power fiber laser. The tapping ratio of the fabricated coupler was measured to be - 32 dB. The fundamental mode coupled in a core of the lower side-polished fiber (SPF) was transferred to the upper SPF without clad-mode coupling. Two SPFs were directly faced to increase an optical handling power up to 740 W. The tapping ratio of the coupler was constantly maintained at the applied laser output. The beam quality of the laser including the fabricated coupler was maintained to be 1.22, without mode distortion by the coupler.

p-Type Double Doping and the Diamond-like Morphology Shift of the Zintl Phase Thermoelectric Materials: The Ca11-xAxSb10-yGez (A = Na, Li; 0.06(3) ≤ x ≤ 0.17(5), 0.19(1) ≤ y ≤ 0.55(1), 0.13(1) ≤ z ≤ 0.22(1)) System.

Five ternary and quaternary Zintl phases in the solid-solution Ca11-xAxSb10-yGez (A = Na, Li; 0.06(3) ≤ x ≤ 0.17(5), 0.19(1) ≤ y ≤ 0.55(1), 0.13(1) ≤ z ≤ 0.22(1)) system have been successfully synthesized by both of the arc-melting and the molten Pb metal-flux reactions. The crystal structure of these title compounds was characterized by powder and single-crystal X-ray diffractions analyses, and all title compounds crystallized in the Ho11Ge10-type phase in the tetragonal space group I4/mmm (Z = 4, Pearson code tI84). The complex crystal structure can be described as an assembly of 1) three kinds of cationic polyhedra centered by three different Sb and 2) the cage-shaped anionic frameworks built through the connection of two types of Sb. The newly substituted p-type double dopants of the cationic (Na and Li) and anionic (Ge) elements displayed particular site preferences, which were successfully explained by either the size-factor criterion based on the atomic size or the electronic-factor criterion based on the electronegativity of an element. Quite interestingly, as the reaction conditions were changed, the morphology shift of single crystals in Ca10.94(3)Na0.06Sb9.58(1)Ge0.21 occurred from a cubic-shaped to a hummocky-type, to a hopper-type, and eventually to an octahedral-shaped crystal, just like the Yakutian kimberlite diamonds. Moreover, we firmly believe that the inclusion of the p-type Ge dopant for Sb was crucial to trigger this type of morphology shift and complete the octahedral-shaped morphology in the overall crystal-growth mechanism. The theoretical calculations using a DFT method rationalized the observed site preference of Na and the electronic effect of the p-type Ge dopants. The Seebeck coefficient measurements for Ca10.88(4)Li0.12Sb9.45(1)Ge0.21 indicated that some portions of electron charge carriers were effectively eliminated by the p-type double dopants using Li and Ge.

Effectiveness of synthetic aperture focusing and coherence factor weighting for intravascular ultrasound imaging.

Synthetic aperture focusing (SAF) and coherence factor weighting (CFW) have been used to improve the lateral resolution of ultrasound images. Although the two methods are effective for array-based ultrasound imaging, many researchers have also employed the methods for single-element-based imaging including intravascular ultrasound (IVUS) imaging. For single-element-based imaging, CFW is generally calculated from the scanlines obtained by SAF and applied to the scanline obtained after coherent summation of the SAF delayed scanlines, which is called a SAF-CFW method. In the paper, a theoretical model was derived to explore the effectiveness of SAF and CFW for single-element-based imaging, and the model was used to explain that SAF is not effective for IVUS imaging in terms of enhancing the spatial resolution, although it has the advantage of improving a contrast-to-noise ratio (CNR). This means that the SAF-CFW method is not optimal for improving the spatial resolution of IVUS imaging. In contrast, it was found in simulations and experiments that applying CFW to the target scanline itself is beneficial for the spatial resolution rather than a coherent summed scanline for IVUS SAF imaging, but CNR was not as good as SAF and SAF-CFW. As a result of both simulation and experimentation, it could be concluded that focused IVUS transducers without the application of those methods may be more advantageous to improve the spatial and contrast resolution simultaneously, considering the system complexity in the implementation of such imaging methods.

Centrosome defects cause microcephaly by activating the 53BP1-USP28-TP53 mitotic surveillance pathway.

Mutations in centrosome genes deplete neural progenitor cells (NPCs) during brain development, causing microcephaly. While NPC attrition is linked to TP53-mediated cell death in several microcephaly models, how TP53 is activated remains unclear. In cultured cells, mitotic delays resulting from centrosome loss prevent the growth of unfit daughter cells by activating a pathway involving 53BP1, USP28, and TP53, termed the mitotic surveillance pathway. Whether this pathway is active in the developing brain is unknown. Here, we show that the depletion of centrosome proteins in NPCs prolongs mitosis and increases TP53-mediated apoptosis. Cell death after a delayed mitosis was rescued by inactivation of the mitotic surveillance pathway. Moreover, 53BP1 or USP28 deletion restored NPC proliferation and brain size without correcting the upstream centrosome defects or extended mitosis. By contrast, microcephaly caused by the loss of the non-centrosomal protein SMC5 is also TP53-dependent but is not rescued by loss of 53BP1 or USP28. Thus, we propose that mutations in centrosome genes cause microcephaly by delaying mitosis and pathologically activating the mitotic surveillance pathway in the developing brain.

Two Steps to Improve the Thermoelectric Performance of the Ca5-xYbxAl2-yInySb6 System.

A series of quaternary and quinary Zintl phase thermoelectric (TE) compounds, Ca5-xYbxAl2-yInySb6 (3.07(1) ≤ x ≤ 4.88(2); 0.16(2) ≤ y ≤ 2.00), containing Al/In mixed sites as well as Ca/Yb mixed sites has been successfully synthesized by a direct arc-melting method, and the X-ray diffraction analyses indicated that the products initially adopted an orthorhombic Ba5Al2Bi6-type structure (space group Pbam, Z = 2). However, after a postannealing process at 973 K for 1 month, the particular Yb rich compounds underwent a transformation of the original structure type to a Ca5Ga2Sb6-type phase regardless of the In substitution for Al. The noticeable site preference of cationic Ca and Yb in the three available cationic sites could be understood on the basis of a size match between the central cation and the volume of the anionic polyhedra. The observed phase transition was nicely explained by DFT calculations, proving that the Ca5Ga2Sb6-type phase was energetically more favorable than the Ba5Al2Sb6-type phase for the particular Yb-rich compound. Moreover, this energy difference between the two title phases was originally the result of both the site energy in the Ca site and the bond energies in the [(Al/In)2Sb8] anionic building blocks. A series of thermoelectric property data indicated that a two-step process involving a partial/full In substitution for Al and a phase transition from the Ba5Al2Sb6-type to the Ca5Ga2Sb6-type phase successfully enhanced the electrical conductivities and the Seebeck coefficients of the title compounds. This kind of combined effect eventually resulted in a ZT improvement for the quinary compound Ca1.14(2)Yb3.86Al1.68(1)In0.32Sb6 by approximately 4 times in comparison to its quaternary predecessor Ca1.55(1)Yb3.45Al2Sb6.

The Role of Enterococcus faecium as a Key Producer and Fermentation Condition as an Influencing Factor in Tyramine Accumulation in Cheonggukjang.

The study evaluated the role of Enterococcus faecium in tyramine production and its response to fermentation temperature in a traditional Korean fermented soybean paste, Cheonggukjang. Tyramine content was detected in retail Cheonggukjang products at high concentrations exceeding the recommended limit up to a factor of 14. All retail Cheonggukjang products contained Enterococcus spp. at concentrations of at least 6 Log CFU/g. Upon isolation of Enterococcus strains, approximately 93% (157 strains) produced tyramine at over 100 µg/mL. The strains that produced the highest concentrations of tyramine (301.14-315.29 µg/mL) were identified as E. faecium through 16S rRNA sequencing. The results indicate that E. faecium is one of the major contributing factors to high tyramine content in Cheonggukjang. During fermentation, tyramine content in Cheonggukjang groups co-inoculated with E. faecium strains was highest at 45 °C, followed by 37 °C and 25 °C. The tyramine content of most Cheonggukjang groups continually increased as fermentation progressed, except groups fermented at 25 °C. At 45 °C, the tyramine content occasionally exceeded the recommended limit within 3 days of fermentation. The results suggest that lowering fermentation temperature and shortening duration may reduce the tyramine content of Cheonggukjang, thereby reducing the safety risks that may arise when consuming food with high tyramine concentrations.

Magnetically Actuated Forward-Looking Interventional Ultrasound Imaging: Feasibility Studies.

OBJECTIVE: Interventional ultrasound imaging is a prerequisite for guiding implants and treatment within the hearts and blood vessels. Due to limitations on the catheter's diameter, interventional ultrasonic transducers have side-looking structures although forward-looking imaging may provide more intuitive and real time guidance in treating diseased sites ahead of catheters. To address the issue, a magnetically actuated forward-looking interventional ultrasound imaging device is implemented for the first time. METHODS: A forward-looking catheter containing a 1 mm ring type focused 35 MHz ultrasound transducer and a micro magnet, was fabricated. For imaging, the transducer was placed at the center of four electromagnetic coils positioned on four sides of a squared acrylic housing. By modifying the magnetic field, the catheter tip could be remotely translated for sector scanning. RESULTS: The scanning angle could reach up to 3° in 1 Hz with 15 mT, while wider angles of 5° could be achieved with a higher magnetic field of 25 mT for ex-vivo imaging. The position of the transducer could be detected by monitoring the motion with a CCD camera, mimicking clinical X-ray imaging. In the wire target and tissue mimicking phantom studies, the measured hole size, spatial resolution and distance between wires by the proposed system were comparable with the values from a linear scanner. Multi-frame real time data acquisition was demonstrated via ex-vivo imaging on a pig's coronary artery. CONCLUSION/SIGNIFICANCE: The feasibility of magnetically actuated forward-looking interventional ultrasound imaging was demonstrated. The remote-controlled scanning method may allow to simplify the structures of forward-looking interventional ultrasound imaging catheters.

2.05 kW all-fiber high-beam-quality fiber amplifier with stimulated Brillouin scattering suppression incorporating a narrow-linewidth fiber-Bragg-grating-stabilized laser diode seed source.

We experimentally demonstrate an all-fiber high-power fiber amplifier with high beam quality and a slope efficiency of 81.8%, using a fiber-Bragg-grating-stabilized laser diode as a narrow spectral linewidth (0.08 nm) seed source. During amplification, the spectral linewidth of the laser output is broadened from 0.08 to 0.24 nm due to nonlinear phenomena. To the best of our knowledge, we report the first experimental observation of the suppression of stimulated Brillouin scattering (SBS), with increased output power. In addition, we investigated the SBS suppression by simultaneously measuring the optical backscattered power, backscattered spectrum, and output spectrum at different values of output power. The beam quality, M2, was measured to be ∼1.28 at the maximum output power of 2.05 kW, and modal instability was not observed.

Dual-Element Intravascular Ultrasound Transducer for Tissue Harmonic Imaging and Frequency Compounding: Development and Imaging Performance Assessment.

OBJECTIVE: For accurate diagnosis of atherosclerosis, the high spatial and contrast resolutions of intravascular ultrasound (IVUS) images are a key requirement. Increasing the center frequency of IVUS is a simple solution to meet this requirement. However, this leads to a reduction in imaging depth due to the frequency-dependent attenuation of ultrasound. Here, we report a recently developed dual-element IVUS transducer for tissue harmonic imaging (THI) and frequency compounding to increase the spatial and contrast resolutions of IVUS images, while maintaining the imaging depth to assess the overall morphological change of blood vessels. METHODS: One 35-MHz element is used for producing general IVUS images and the other 70-MHz element is for receiving the second harmonic signals induced by the 35-MHz ultrasound. The fundamental and second harmonic signals can also be used for frequency compound imaging to further improve contrast resolution. The spatial and contrast resolutions achieved by the developed transducer were evaluated through wire and tissue-mimicking phantom imaging tests. Additionally, the images of a stent deployed in a tissue-mimicking phantom and an excised pig artery were acquired to assess clinical usefulness of the transducer. RESULTS: The results demonstrated that the developed IVUS transducer enables us to simultaneously examine the overall morphological change of blood vessels by the 35-MHz ultrasound images and the near vessel layers such as the intima, the media, and the adventitia by either THI or compound images with high spatial and contrast resolutions. In addition, the developed transducer facilitates the simultaneous acquisition of 35- and 70-MHz fundamental images when needed. CONCLUSION: The developed dual-element IVUS transducer makes it possible to fully realize the potential benefits of IVUS in the diagnosis of atherosclerosis.

Layered Bismuth Oxyfluoride Nitrates Revealing Large Second-Harmonic Generation and Photocatalytic Properties.

Two novel bismuth oxyfluoride nitrates, Bi2OF3(NO3) and Bi6O6F5(NO3), have been synthesized via hydrothermal reactions. Whereas Bi2OF3(NO3) crystallizes in the centrosymmetric (CS) hexagonal space group, P63/ m, Bi6O6F5(NO3) crystallizes in the polar noncentrosymmetric (NCS) trigonal space group, R3. The backbones of the title compounds reveal double layered structures composed of asymmetric BiF3(O/F)3 or BiO3F2 polyhedra and NO3 trigonal planar groups. The diffuse reflectance spectra indicate that Bi2OF3(NO3) and Bi6O6F5(NO3) contain wide band gaps of 3.5 and 4.0 eV, respectively. Powder second-harmonic generation (SHG) measurements suggest that NCS Bi6O6F5(NO3) is Type-I phase-matchable and has a large SHG response of ca. 3 times that of KH2PO4 (KDP). Electron localization function (ELF) analysis indicates that the large SHG efficiency of Bi6O6F5(NO3) is attributed to the synergistic effect of the alignment of NO3- trigonal planar groups and strong interactions between highly polarizable lone pair electrons on Bi3+ and π-delocalized electrons in NO3- groups. Bi2OF3(NO3) also exhibits a very good photocatalytic degradation efficiency of Rhodamine B (RhB) under the UV light irradiation.

A 40-MHz Ultrasound Transducer with an Angled Aperture for Guiding Percutaneous Revascularization of Chronic Total Occlusion: A Feasibility Study.

Complete blockage of a coronary artery, called chronic total occlusion (CTO), frequently occurs due to atherosclerosis. To reopen the obstructed blood vessels with a stent, guidewire crossing is performed with the help of angiography that can provide the location of CTO lesions and the image of guidewire tip. Since angiography is incapable of imaging inside a CTO lesion, the surgeons are blind during guidewire crossing. For this reason, the success rate of guidewire crossing relies upon the proficiency of the surgeon, which is considerably reduced from 69.0% to 32.5% if extensive calcification, not penetrated by a guidewire, exists in CTO lesions. In this paper, a recently developed 40-MHz forward-looking intravascular ultrasound (FL⁻IVUS) transducer to visualize calcification within CTO lesions is reported. This transducer consists of a single element angled aperture and a guidewire passage. The aperture is spherically deformed to have a focal length of 3 mm in order to improve spatial resolution of FL⁻IVUS images. The angle between the beam direction and the axis of rotation is designed to be 30° to effectively visualize calcification within a CTO lesion as well as the blood vessel wall. The experimental results demonstrated that the developed FL⁻IVUS transducer facilitates visualization of calcification within CTO lesions and makes it possible to help the surgeon make decisions about whether to push the guidewire in order to cross the lesion or to change the surgical procedure.

A 35 MHz/105 MHz Dual-Element Focused Transducer for Intravascular Ultrasound Tissue Imaging Using the Third Harmonic.

The superharmonic imaging of tissue has the potential for high spatial and contrast resolutions, compared to the fundamental and second harmonic imaging. For this technique, the spectral bandwidth of an ultrasound transducer is divided for transmission of ultrasound and reception of its superharmonics (i.e., higher than the second harmonic). Due to the spectral division for the transmission and reception, transmitted ultrasound energy is not sufficient to induce superharmonics in media without using contrast agents, and it is difficult that a transducer has a -6 dB fractional bandwidth of higher than 100%. For the superharmonic imaging of tissue, thus, multi-frequency array transducers are the best choice if available; transmit and receive elements are separate and have different center frequencies. However, the construction of a multi-frequency transducer for intravascular ultrasound (IVUS) imaging is particularly demanding because of its small size of less than 1 mm. Here, we report a recently developed dual-element focused IVUS transducer for the third harmonic imaging of tissue, which consists of a 35-MHz element for ultrasound transmission and a 105-MHz element for third harmonic reception. For high quality third harmonic imaging, both elements were fabricated to have the same focus at 2.5 mm. The results of tissue mimicking phantom tests demonstrated that the third harmonic images produced by the developed transducer had higher spatial resolution and deeper imaging depth than the fundamental images.

Development of Dual-Frequency Oblong-Shaped-Focused Transducers for Intravascular Ultrasound Tissue Harmonic Imaging.

Tissue harmonic imaging (THI), an essential mode of commercial ultrasound imaging scanners, can provide images with high spatial and contrast resolutions. For THI, the frequency spectrum of a transducer is generally divided for the transmission of fundamental signal and the reception of its second harmonic. Therefore, it is difficult to use the THI mode for intravascular ultrasound (IVUS) imaging because typical IVUS transducers have a narrow -6-dB fractional bandwidth of about 50%. Due to its small aperture (about 0.5 mm) and the strength of IVUS being too weak, it is difficult to construct a high-quality tissue harmonic image. In this paper, we report a recently developed dual-frequency oblong-shaped-focused IVUS transducer for high-quality intravascular THI; the transducer consists of three elements arranged side by side in the horizontal (i.e., elevation) direction. The two outer elements with a center frequency of 35 MHz are responsible for ultrasound transmission and the center element has a center frequency of 70 MHz for the reception of the second-harmonic signals. All three elements have a spherical shape with a radius of 3 mm to efficiently generate harmonics in the region of interest. This configuration of the developed IVUS transducer was determined to facilitate high-quality THI, which was based on the results of Field II simulation and finite-element analysis. The images of wires and a tissue-mimicking phantom indicated that the tissue harmonic images produced by the developed transducer have not only a high spatial resolution but also a deep imaging depth, compared to the 35- and 70-MHz fundamental images.

Structure and Chemical Bonding of the Li-Doped Polar Intermetallic RE2In1-xLixGe2 (RE = La, Nd, Sm, Gd; x = 0.13, 0.28, 0.43, 0.53) System.

Four polar intermetallic compounds belonging to the RE2In1-xLixGe2 (RE = La, Nd, Sm, Gd; x = 0.13(1), 0.28(1), 0.43(1), 0.53(1)) system have been synthesized by the traditional solid-state reaction method, and their crystal structures have been characterized by single-crystal X-ray diffraction (SXRD) analyses. The isotypic crystal structures of four title compounds adopt the Mo2FeB2-type structure having the tetragonal space group P4/mbm (Z = 2, Pearson code tP40) with three crystallographically independent atomic sites and can be simply described as a pile of the identical 2-dimensioanl (2D) RE2In1-xLixGe2 slabs stacked along the c-axis direction. The substituting Li atom shows a particular site preference for replacing In at the Wyckoff 2a site rather than Ge at the Wyckoff 4g in this crystal structure. As the size of a used rare-earth metal decreases from La3+ to Gd3+ throughout the title system, the Ge-Ge and Ge-In/Li bond distances, both of which consist of the 2D anionic Ge2(In/Li) layer, gradually decrease resulting in the reduction of a unit cell volume. A series of theoretical investigations has been performed using a hypothetical structure model Gd2In0.5Li0.5Ge2 by tight-binding linear muffin-tin orbital (TB-LMTO) method. The resultant densities of states (DOS) value at the Fermi level (EF) suggests a metallic conductivity for this particular composition, and this calculation result is in a good agreement with the formal charge distribution assigning two extra valence electrons for a metal-metal bond in the conduction band. The thorough analyses of six crystal orbital Hamilton population (COHP) curves representing various interatomic interactions and an electron localization function (ELF) diagram indicating the locations of paired-electron densities are also provided in this article.