Development of a 64 channel ultrasonic high frequency linear array imaging system

In order to improve the lateral resolution and extend the field of view of a previously reported 48 element 30 MHz ultrasound linear array and 16-channel digital imaging system, the development of a 256 element 30 MHz linear array and an ultrasound imaging system with increased channel count has been undertaken. This paper reports the design and testing of a 64 channel digital imaging system which consists of an analog front-end pulser/receiver, 64 channels of Time-Gain Compensation (TGC), 64 channels of high-speed digitizer as well as a beamformer. A Personal Computer (PC) is used as the user interface to display real-time images. This system is designed as a platform for the purpose of testing the performance of high frequency linear arrays that have been developed in house. Therefore conventional approaches were taken it its implementation. Flexibility and ease of use are of primary concern whereas consideration of cost-effectiveness and novelty in design are only secondary. Even so, there are many issues at higher frequencies but do not exist at lower frequencies need to be solved. The system provides 64 channels of excitation pulsers while receiving simultaneously at a 20–120 MHz sampling rate to 12-bits. The digitized data from all channels are first fed through Field Programmable Gate Arrays (FPGAs), and then stored in memories. These raw data are accessed by the beamforming processor to re-build the image or to be downloaded to the PC for further processing. The beamformer that applies delays to the echoes of each channel is implemented with the strategy that combines coarse (8.3 ns) and fine delays (2 ns). The coarse delays are integer multiples of the sampling clock rate and are achieved by controlling the write enable pin of the First-In-First-Out (FIFO) memory to obtain valid beamforming data. The fine delays are accomplished with interpolation filters. This system is capable of achieving a maximum frame rate of 50 frames per second. Wire phantom images acquired with this system show a spatial resolution of 146 μm (lateral) and 54 μm (axial). Images with excised rabbit and pig eyeball as well as mouse embryo were also acquired to demonstrate its imaging capability.     

SERS nanosensors that report pH of endocytic compartments during FcεRI transit

Recently, the development of an IgE receptor (FcεRI)-targeted, pH-sensitive, surface-enhanced Raman spectroscopy (SERS) nanosensor has been demonstrated by Nowak-Lovato and Rector (Appl Spectrosc 63:387–395, 2009). The targeted nanosensor enables spatial and temporal pH measurements as internalized receptors progress through endosomal compartments in live cells. Trafficking of receptor-bound nanosensors was compared at physiological temperature (37 °C) versus room temperature (25 °C). As expected, we observed markedly slower progression of receptors through low-pH endocytic compartments at the lower temperature. We also demonstrate the utility of the nanosensors to measure directly changes in the pH of intracellular compartments after treatment with bafilomycin or amiloride. We report an increase in endosome compartment pH after treatment with bafilomycin, an H⁺ ATPase pump inhibitor. Decreased endosomal luminal pH was measured in cells treated with amiloride, an inhibitor of Na⁺/H⁺ exchange. The decrease in amiloride-treated cells was transient, followed by a recovery period of approximately 15–20 min to restore endosomal pH. These experiments demonstrate the novel application of Raman spectroscopy to monitor local pH environment in live cells with the use of targeted SERS nanosensors.     

Pseudospectra and stability radii for analytic matrix functions with application to time-delay systems

Definitions for pseudospectra and stability radii of an analytic matrix function are given, where the structure of the function is exploited. Various perturbation measures are considered and computationally tractable formulae are derived. The results are applied to a class of retarded delay differential equations. Special properties of the pseudospectra of such equations are determined and illustrated.     

Plane wave source with minimal harmonic distortion for investigating nonlinear acoustic properties

The objective of this investigation is to introduce and validate a practical ultrasound source to be used in the investigation of the nonlinear material properties of liquids and soft tissues studied in vitro. Methods based on the progressive distortion of finite amplitude ultrasonic waves in the low megahertz frequency range are most easily implemented under the assumption of plane wave propagation. However, achieving an approximately planar ultrasonic field over substantial propagation distances can be challenging. Furthermore, undesired harmonic distortion of the ultrasonic field prior to insonification of the specified region of interest represents another serious limitation. This paper introduces an approach based on the use of the ultrasonic field emanating from a stainless-steel delay line. Both simulation and direct experimental measurement demonstrate that such a field exhibits relatively planar wave fronts to a good approximation (such that a 3-mm-diam receiver would be exposed to no more than 3 dB of loss across its face) and is free from the significant harmonic distortion that would occur in a conventional water path.     

Passive combination of multiple beams in an optical fiber via stimulated Brillouin scattering

We demonstrate passive combination of multiple beams in an optical fiber via stimulated Brillouin scattering (SBS). Four off-axis beams are combined in a long multimode optical fiber using a novel all-optical mount. The combined beam has the high spatial coherence properties of the LP(01) mode owing to the beam cleanup properties of SBS. The threshold for SBS when off-axis pumps are used is shown to be a factor of 13 times higher than for on-axis pump beams. We propose this method would improve the brightness of an array of fiber amplifiers.     

Effective transformation of cellulose to 5-hydroxymethylfurfural catalyzed by fluorine anion-containing ionic liquid modified biochar sulfonic acids in water

This article first discloses that the fluorine anion-containing ionic liquids-functionalized biochar sulfonic acids (BCSA-IL-F_1–3s), which were simply synthesized by an ionic exchange of 1-trimethoxysilylpropyl-3-methylimidazolium chloride (IL-Cl) grafted on the BCSA with CF₃SO₃H (HF₁), HBF₄ (HF₂), HPF₆ (HF₃), respectively, can efficiently catalyze cellulose hydrolysis into reducing sugars (RSs) and 5-hydroxymethyl furfural (HMF) in water under microwave irradiation. This process provides a very high catalysis efficiency (turnover numbers, 4.03–4.89) at mild temperature (80 °C) for 3 h, but also possesses an excellent repeatability. More outstandingly, they can achieve much higher HMF yields (12.70–27.94%) compared to the IL-Cl-functionalized BCSA catalyst (HMF yields are lower than 0.1%) under the same reaction conditions. This is likely because the introduction of IL-F_1–3s groups can significantly improve the accessibility, acidity and thermal stability of BCSA’s SO₃H sites, as supported by evidence from a solid ³¹P NMR spectrum and thermogravimetric analysis. It is proposed that the good selectivity for HMF perhaps originates from a co-catalysis action of the IL-F_1–3s and SO₃H groups on BCSA-IL-F_1–3s in the further conversion of RSs to HMF.     

Synthesis, self-assembly, and photophysical properties of cationic oligo(p-phenyleneethynylene)s

Three series of cationic oligo p-phenyleneethynylenes (OPEs) have been synthesized to study their structure-property relationships and gain insights into the transition from molecular to macromolecular properties. The absorbance maxima and molar extinction coefficients in all three sets increase with increasing number of repeat units; however, the increase in λ(max) between the oligomers having 2 and 3 repeat units is very small, and the oligomer having 3 repeat units shows virtually the same spectra as a p-phenyleneethynylene polymer having 49 repeat units. A computational study of the oligomers using density functional theory calculations indicates that while the simplest oligomers (OPE-1) are fully conjugated, the larger oligomers are nonplanar and the limiting "segment chromophore" may be confined to a near-planar segment extending over three or four phenyl rings. Several of the OPEs self-assemble on anionic "scaffolds", with pronounced changes in absorption and fluorescence. Both experimental and computational results suggest that the planarization of discrete conjugated segments along the phenylene-ethynylene backbone is predominantly responsible for the photophysical characteristics of the assemblies formed from the larger oligomers. The striking differences in fluorescence between methanol and water are attributed to reversible nucleophilic attack of structured interfacial water on the excited singlet state.