Prediction of surface temperature rise of ultrasonic diagnostic array transducers

Temperature rise at the surface of an ultrasound transducer used for diagnostic imaging is an important factor in patient safety and regulatory compliance. This paper presents a semianalytical model that is derived from first principles of heat transfer and is simple enough to be implemented in a commercial ultrasound scanner for real-time forecasting of transducer surface temperature. For modeling purposes, one-dimensional array transducers radiating into still air are considered. Promising experimental verification data are shown and practical implementation benefits of the model for thermal design and management of ultrasonic array transducers are discussed. In particular, the reduction in the amount of thermal characterization data required, compared to empirical models, shows promise.     

Synthesis and characterization of cadmium telluride nanowire

CdTe nanowires with controlled composition were cathodically electrodeposited using track-etched polycarbonate membrane as scaffolds and their material and electrical properties were systematically investigated. As-deposited CdTe nanowires show nanocrystalline cubic phase structures with grain sizes of up to 60 nm. The dark-field images of nanowires reveal that the crystallinity of nanowires was greatly improved from nanocrystalline to a few single crystals within nanowires upon annealing at 200?°C for 6?h in a reducing environment (5%?H(2)+95%?N(2)). For electrical characterization, a single CdTe nanowire was assembled across microfabricated gold electrodes using the drop-casting method. In addition to an increase in grain size, the electrical resistivity of an annealed single nanowire (a few 10(5)?Ω?cm) was one order of magnitude greater than in an as-deposited nanowire, indicating that crystallinity of nanowires improved and defects within nanowires were reduced during annealing. By controlling the dopants levels (e.g.?Te content of nanowires), the resistivity of nanowires was varied from 10(4) to 10(0)?Ω?cm. Current-voltage (I-V) characteristics of nanowires indicated the presence of Schottky barriers at both ends of the Au/CdTe interface. Temperature-dependent I-V measurements show that the electron transport mode was determined by a thermally activated component at T>-50?°C and a temperature-independent component below -50?°C. Under optical illumination, the single CdTe nanowire exhibited enhanced conductance.     

Model-based analysis of the silica glass film etch mechanism in CF4/O2 inductively coupled plasma

The analysis of the Er-doped silica glass films (62%SiO₂–30%B₂O₃–8%P₂O₅ + 0.2 wt%. Er₂O₃) etch mechanism in the CF₄/O₂ inductively coupled plasma was carried out using the combination of simplified models for plasma chemistry and etch kinetics. As the O₂ mixing ratio in the CF₄/O₂ plasma increases from 0% to 30%, the etch rate decreases monotonically in the range of 385–190 nm/min that contradicts with the behavior of F atom density and flux. From the model-based analysis, it was found that, at low ion bombardment energies, the etch process followed the formal kinetics of ion-assisted chemical reaction and was controlled by both neutral and ion fluxes.     

IZO/Al/GZO multilayer films to replace ITO films

Multilayer transparent conducting oxide (TCO) film structures have been designed and fabricated to achieve both high conductivity and high transmittance. In this article we report a buffering method and introduction of an aluminum (Al) interlayer to enhance the electrical conductivity of the IZO/Al/GZO/ZnO multilayer film on glass. Hall measurement results show that this multilayer film has a remarkable increase in mobility compared to those without using an Al interlayer. The surface morphology shows a decrease in surface roughness as the Al layer thickness increases. We have shown that the use of a thin Al interlayer enhances the electrical conductivity without sacrificing its optical transmittance much. By optimizing the thickness of the Al layer, the lowest resistivity of 2.2 × 10⁻⁴ Ω cm and an average transmittance higher than 75% in a range from 400 to 800 nm have been achieved. These properties are acceptable for future TCO applications.     

Facile synthesis of highly faceted multioctahedral Pt nanocrystals through controlled overgrowth

Highly faceted Pt nanocrystals with a large number of interconnected arms in a quasi-octahedral shape were synthesized simply by reducing H2PtCl6 precursor with poly(vinyl pyrrolidone) in aqueous solutions containing a trace amount of FeCl3. The iron species (Fe(3+) or Fe(2+)) play a key role in inducing the formation of the multioctahedral structure by decreasing the concentration of Pt atoms and keeping a low concentration for the Pt seeds during the reaction. This condition favors the overgrowth of Pt seeds along their corners and thus the formation of multiarmed nanocrystals. Electron microscopy studies revealed that the multioctahedral Pt nanocrystals exhibit a large number of edge, corner, and surface step atoms. The size of the multioctahedral Pt nanocrystals can be controlled by varying the concentration of FeCl3 added to the reaction and/or the reaction temperature. These multioctahedral Pt nanocrystals were tested as electrocatalysts for the oxygen reduction reaction in a proton exchange membrane fuel cell and exhibited improved specific activity and durability compared to commercial Pt/C catalyst.     

Pulse-loaded ferroelectric nanowire as an alternating current source

The behavior of an uniaxially pulse-loaded ferroelectric nanowire is simulated using a Landau-Ginzburg type thermodynamic model. Our results show that under a load of suitable magnitude and frequency, an appropriately dimensioned ferroelectric nanowire can produce a sizable alternating current voltage, sufficient for applications as a nanopower source for energy harvesting, or as an effective nanomechanical sensor.     

Negative differential resistance in carbon atomic wire-carbon nanotube junctions

Negative differential resistance (NDR) was recently observed in carbon nanotube junctions just before breaking and hypothesized to arise from the formation of monatomic carbon wires in the junction. Motivated by these results, a first-principles scattering-state approach, based on density functional theory, is used to study the transport properties of carbon chains covalently connecting metallic carbon nanotube leads at finite bias. The I- V characteristics of short carbon chains are predicted to exhibit even-odd behavior, and NDR is found for both even and odd chain junctions in our calculations.     

Structural engineering of nanoporous anodic aluminium oxide by pulse anodization of aluminium

Nanoporous anodic aluminium oxide has traditionally been made in one of two ways: mild anodization or hard anodization. The first method produces self-ordered pore structures, but it is slow and only works for a narrow range of processing conditions; the second method, which is widely used in the aluminium industry, is faster, but it produces films with disordered pore structures. Here we report a novel approach termed "pulse anodization" that combines the advantages of the mild and hard anodization processes. By designing the pulse sequences it is possible to control both the composition and pore structure of the anodic aluminium oxide films while maintaining high throughput. We use pulse anodization to delaminate a single as-prepared anodic film into a stack of well-defined nanoporous alumina membrane sheets, and also to fabricate novel three-dimensional nanostructures.     

Ka-band oscillator integrating a high-Q low-temperature co-fired ceramic circular resonator using zigzagged via posts and a λ/4 short stub

A Ka-band oscillator with a high-Q low-temperature co-fired ceramic circular resonator is presented. The resonator, including zigzagged dual-row via posts for tightly confined electromagnetic power as a metallic boundary wall, is presented. The unloaded-Q of the proposed resonator is improved by 22.1% compared to that of a conventional one with vertical via posts. Another resonator is fed with a lambda/4 short stub on a feeding via post in the circular resonator for effectively power transmission in the resonator to the output load without radiation loss. The measured unloaded-Q of the proposed resonator with zigzagged dual-row via posts and a lambda/4 short stub is improved by 45.1% compared with that of a conventional one. Approaches for enhancing Q-factors using two techniques are demonstrated. The Ka-band oscillator integrating a negative resistance generator monolithic microwave integrated circuit and the resonator with zigzagged dual-row via posts and the lambda/4 short stub shows an output power of 19.34 dBm at 26.98 GHz and phase noise of -102.17 dBc/Hz at 1 MHz offset. The figure-of-merit is -164.1 dBc/Hz, and the DC-to-RF conversion efficiency is 18.28%. It can be easily implemented without any additional processes to achieve the high resonator Q-factor. At the same time, it is also very suitable to implement in high-integrated systems for millimeter-wave applications.     

实践型服装与纺织设计

在人文领域,学术界的研究通常都是理论与文字性的,也因此,艺术和设计的博士研究都是更多的注重理论分析的。然而,艺术家和设计师都是通过动手实践来获取知识的,而这些知识,很难仅靠语言和文字来传达与吸收。设计史学家Clive Dilnot曾指出：“在与创意有关的学科中,人类的语言不足以来传达其想要表达的所有内涵。现有的（在这方面的学术研究）,包含了太多的预设先决概念。”