Standing and travelling waves in the shallow-water circular hydraulic jump

A wave equation for a time-dependent perturbation about the steady shallow-water solution emulates the metric an acoustic white hole, even upon the incorporation of nonlinearity in the lowest order. A standing wave in the sub-critical region of the flow is stabilised by viscosity, and the resulting time scale for the amplitude decay helps in providing a scaling argument for the formation of the hydraulic jump. A standing wave in the super-critical region, on the other hand, displays an unstable character, which, although somewhat mitigated by viscosity, needs nonlinear effects to be saturated. A travelling wave moving upstream from the sub-critical region, destabilises the flow in the vicinity of the jump, for which experimental support has been given.     

Apparent diffusion coefficient (ADC) measurements may be more reliable and reproducible than lesion volume on diffusion-weighted images from patients with acute ischaemic stroke-implications for study design

Early ischemic change after stroke can be demonstrated with diffusion-weighted imaging (DWI) and quantified by measuring the apparent diffusion coefficient (ADC) and/or lesion volume. We examined the reliability and reproducibility of lesion volume and ADC measurement on DWI images, and discuss the implications for clinical studies. Using 38 DWI scans from 15 stroke patients, two observers (a physicist and a neuroscience graduate) blind to each other, recorded the lesion volume on DWI sequences, measured the ADC values in this volume and calculated the ratio of ischemic: control ADC (ADCr). One observer repeated his measurements blind to his first, and also examined the effect on lesion volume and ADC of deliberately varying by only one pixel, the outline of the visible boundary of the lesion. The inter and intra-rater reliability were worse for lesion volume than ADC or ADCr measurements: lesion volume, inter-rater coefficient of variation (CoV) 85 +/- 130%, intra-rater CoV 20+/-SD80% (p < 0.05); ADC inter-rater CoV 7.7 +/- SD 19%, intra-rater CoV 0.2 +/- SD 12% (p = NS); and ADCr inter-rater CoV 8 +/- SD27%, intra-rater CoV 0.8 +/- SD73% (p = NS). Altering the position of the outline tracing of the lesion boundary by one pixel altered the measured volumes by 22 +/- SD25% (p < 0.05), but ADC values were altered by only 2.9 +/- SD4.9% and ADCr by 2.7 +/- SD4.8% (p = NS). ADC and ADCr values are more reliable and reproducible than DWI lesion size in acute ischemic stroke because altering where the lesion boundary is measured has a much greater impact on lesion volume than on the ADC or ADCr. This effect is greatest in large lesions.     

Biomolecular hybrid of a conducting polymer with DNA: morphology, structure, and doping behavior

A poly(o-methoxyaniline) (POMA)/DNA [weight fraction of DNA (W(DNA)) = 0.45] hybrid was prepared by mixing their solutions in sterilized double distilled water. The solution turned green upon aging for a longer time, and the doping of POMA by DNA was complete after about 15 d of aging. The doping was confirmed from the UV-vis spectra where the 599 nm peak of POMA(EB) disappeared and a new peak for a pi to localized polaron band-transition appeared. With increasing aging time the new peak gradually shifted from 674 nm at 3 h to 820 nm at 15 d of mixing and thereafter it remained constant. The absence of a free carrier tail in the UV-vis spectra indicated a coiled structure of POMA in the complex. Circular dichroism spectra of the hybrid solution indicated that the DNA conformation (double helical structure) remained unchanged in the hybrid. The SEM micrograph of the freeze-dried hybrid showed a needle-like morphology of the DNA dispersed in a polymer matrix and it was completely different from the fibrillar network morphology of pure DNA in the solid state. The TEM micrograph indicated a homogeneous dispersion of DNA fibrils in the POMA matrix. The melting temperature of the POMA-DNA hybrid showed an increase compared to that of pure DNA by 5 degrees C, probably caused by an electrostatic interaction between the DNA anion and the POMA radical cation generated in the doping process. WAXS investigations revealed that the DNA crystal structure remained unchanged in the hybrid whereas the POMA crystal structure might be lost. An FT-IR study suggested that interaction occurred between the phosphoric acid group of DNA and a nitrogen atom of POMA through proton transfer from the OH group of the former. A schematic model of the POMA-DNA complex randomly anchoring POMA chains with the DNA molecule was proposed. The dc conductivity of the POMA-DNA complex was found to be ca. 10(-7) S . cm(-1). Hence, this work describes a procedure for making a DNA-conducting polymer hybrid without changing the conformation and structure of DNA. [Diagram: see text]     

Volume holographic telescope

We have developed a novel imaging instrument, the volume holographic telescope, which is capable of returning high-resolution depth information about remote objects. We present a theoretical analysis of the instrument's performance and an experimental demonstration with a microfabricated object.     

Exquisite 1D Assemblies Arising from Rationally Designed Asymmetric Donor–Acceptor Architectures Exhibiting Aggregation‐Induced Emission as a Function of Auxiliary Acceptor Strength

One‐dimensional nanostructures with aggregation‐induced emission (AIE) properties have been fabricated to keep the pace with growing demand from optoelectronics applications. The compounds 2‐[4‐(4‐methylpiperazin‐1‐yl)benzylidene]malononitrile ( PM1 ), 2‐{4‐[4‐(pyridin‐2‐yl)piperazin‐1‐yl]‐benzylidene}malononitrile ( PM2 ), and 2‐{4‐[4‐(pyrimidin‐2‐yl)piperazin‐1‐yl]benzylidene}malononitrile ( PM3 ) have been designed and synthesized by melding piperazine and dicyanovinylene to investigate AIE in an asymmetric donor–acceptor (D–A) construct of A′–D–π–A‐ topology. The synthetic route has been simplified by using phenylpiperazine as a weak donor (D), dicyanovinylene as an acceptor (A), and pyridyl/pyrimidyl groups ( PM2/PM3 ) as auxiliary acceptors (A′). It has been established that A′ plays a vital role in triggering AIE in these compounds because the same D–A construct led to aggregation‐caused quenching upon replacing A′ with an electron‐donating ethyl group ( PM1 ). Moreover, the effect of restricted intramolecular rotation and twisted intramolecular charge transfer on the mechanism of AIE has also been investigated. Furthermore, it has been clearly shown that the optical disparities of these A′–D–π–A architectures are a direct consequence of comparative A′ strength. Single‐crystal X‐ray analyses provided justification for role of intermolecular interactions in aggregate morphology. Electrochemical and theoretical studies affirmed the effect of the A′ strength on the overall properties of the A′–D–π–A system.