6.4 GHz Acoustic Sensor for In-situ Monitoring of AFM Tip Wear

This paper demonstrates an acoustic sensor that can resolve atomic force microscopy (AFM) tip blunting with a frequency sensitivity of 0.007%. The AFM tip is fabricated on a thin film piezoelectric aluminum nitride (AlN) membrane that is excited as a film bulk acoustic resonator (FBAR). We demonstrate that cutting 0.98 μm off of the tip apex results in a resonance frequency change of 0.4MHz at 6.387GHz. This work demonstrates the potential for in-situ monitoring of AFM tip wear

Nano-electromechanical Zero-dimensional Freestanding Nanogap Actuator

Micromachined free standing nanogap with metal electrodes is presented. The gap size is as small as 17 nm, and can be reduced further with electrostatic or piezoelectric actuation. The nanoscale gap is fabricated by industrial standard optical lithography and anisotropic wet chemical Si etching. Electron transport between the metal electrodes with optical stimulus enhancing photon-electron coupling (plasmon) is presented

Improving estimation efficiency for regression with MNAR covariates

For regression with covariates missing not at random where the missingness depends on the missing covariate values, complete‐case (CC) analysis leads to consistent estimation when the missingness is independent of the response given all covariates, but it may not have the desired level of efficiency. We propose a general empirical likelihood framework to improve estimation efficiency over the CC analysis. We expand on methods in Bartlett et al. (2014, Biostatistics 15, 719–730) and Xie and Zhang (2017, Int J Biostat 13, 1–20) that improve efficiency by modeling the missingness probability conditional on the response and fully observed covariates by allowing the possibility of modeling other data distribution‐related quantities. We also give guidelines on what quantities to model and demonstrate that our proposal has the potential to yield smaller biases than existing methods when the missingness probability model is incorrect. Simulation studies are presented, as well as an application to data collected from the US National Health and Nutrition Examination Survey.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/154274/1/biom13131-sup-0002-web_supp.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/154274/2/biom13131_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/154274/3/biom13131.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/154274/4/biom13131-sup-0003-supmat.pd

On the low frequency acoustic properties of novel multifunctional honeycomb sandwich panels with micro-perforated faceplates

This paper explores further possibilities of structurally-efficient honeycomb sandwich panels by replacing one of the faceplates with the perforated faceplate from the viewpoint of sound absorption coefficient (SAC) as well as sound transmission loss (STL). An analytical model is presented to calculate both the STL and SAC, with the displacements of the two faceplates assumed identical at frequencies below the faceplate resonance frequency. Influences of core configuration are investigated by comparing different honeycomb core designs. Finite element (FE) models are subsequently developed to validate the proposed analytical model, with agreement achieved. Subsequently, parametric surveys, including the influences of perforation ratio, pore size and core configuration on STL and SAC, are conducted based on the analytical model. Unlike classical honeycomb sandwich panels which are poor sound absorbers, honeycomb sandwiches with perforated faceplates lead to high SAC at low frequencies, which in turn brings about increment in the low frequency STL. Moreover, sandwich panels with triangular cores are found to have the lowest peak frequency in the STL and SAC curves compared with the other kinds of sandwich panels having the same effective mass and perforations

Anisotropic acoustical properties of sintered fibrous metals

A combined theoretical and experimental study is carried out to investigate the anisotropic acoustic properties of sintered fibrous metals. In the theoretical model, based on the transversal and longitudinal dynamic mass densities and effective bulk modulus of randomly placed parallel fibers, the dynamic mass densities and effective dynamic bulk modulus of a sintered fibrous metal in the direction normal and parallel to its surface are obtained. Sound absorption coefficient, sound speed and attenuation coefficient in each of the two directions are calculated once the dynamic mass densities and effective dynamic bulk modulus are determined. For validation, experimental measurements are performed, with good agreement between theoretical prediction and measurement data achieved. Subsequent numerical investigations focus on the influence of fiber diameter and porosity on the anisotropic acoustical properties of the sintered fibrous metal. The sintered fibrous metal exhibits better sound absorption/attenuation performance in the parallel direction than in the normal direction. The anisotropy in acoustical properties increases with decreasing fiber diameter and porosity due mainly to increasing interactions between adjacent fibers

Small perforations in corrugated sandwich panel significantly enhance low frequency sound absorption and transmission loss

Numerical and experimental investigations are performed to evaluate the low frequency sound absorption coefficient (SAC) and sound transmission loss (STL) of corrugated sandwich panels with different perforation configurations, including perforations in one of the face plates, in the corrugated core, and in both the face plate and the corrugated core. Finite element (FE) models are constructed with considerations of acoustic-structure interactions and viscous and thermal energy dissipations inside the perforations. The validity of FE calculations is checked against experimental measurements with the tested samples provided by additive manufacturing. Compared with the classical corrugated sandwich without perforation, the corrugated sandwich with perforated pores in one of its face plate not only exhibits a higher SAC at low frequencies but also a better STL as a consequence of the enlarged SAC. The influences of perforation diameter and perforation ratio on the vibroacoustic performance of the sandwich are also explored. For a corrugated sandwich with uniform perforations, the acoustical resonance frequencies and bandwidth in its SAC and STL curves decrease with increasing pore diameter and decreasing perforation ratio. Non-uniform perforation diameters and perforation ratios result in larger bandwidth and lower acoustical resonance frequencies relative to the case of uniform perforations. The proposed perforated sandwich panels with corrugated cores are attractive ultralightweight structures for multifunctional applications such as simultaneous load-bearing, energy absorption, sound proofing and sound absorption

Translational groups as generators of gauge transformations

We examine the gauge generating nature of the translational subgroup of Wigner's little group for the case of massless tensor gauge theories and show that the gauge transformations generated by the translational group is only a subset of the complete set of gauge transformations. We also show that, just like the case of topologically massive gauge theories, translational groups act as generators of gauge transformations in gauge theories obtained by extending massive gauge noninvariant theories by a Stuckelberg mechanism. The representations of the translational groups that generate gauge transformations in such Stuckelberg extended theories can be obtained by the method of dimensional descent. We illustrate these with the examples of Stuckelberg extended first class versions of Proca, Einstein-Pauli-Fierz and massive Kalb-Ramond theories in 3+1 dimensions. A detailed analysis of the partial gauge generation in massive and massless 2nd rank symmetric gauge theories is provided. The gauge transformations generated by translational group in 2-form gauge theories are shown to explicitly manifest the reducibility of gauge transformations in these theories.Comment: Latex, 20 pages, no figures, Version to appear in Physical Review

Stability of Negative Image Equilibria in Spike-Timing Dependent Plasticity

We investigate the stability of negative image equilibria in mean synaptic weight dynamics governed by spike-timing dependent plasticity (STDP). The neural architecture of the model is based on the electrosensory lateral line lobe (ELL) of mormyrid electric fish, which forms a negative image of the reafferent signal from the fish's own electric discharge to optimize detection of external electric fields. We derive a necessary and sufficient condition for stability, for arbitrary postsynaptic potential functions and arbitrary learning rules. We then apply the general result to several examples of biological interest.Comment: 13 pages, revtex4; uses packages: graphicx, subfigure; 9 figures, 16 subfigure

Evaluation in vitro and in rats of161Tb-DTPA-octreotide, a somatostatin analogue with potential for intraoperative scanning and radiotherapy

The characteristics of terbium-161 diethylene triamine penta-acetic acid (DTPA) labelled octreotide with respect to specific binding to somatostatin (octreotide) receptors on rat brain cortex membranes, biological activity, uptake and excretion by isolated perfused rat livers and metabolism in vivo in normal and tumour-bearing rats were determined and compared to those of indium-111 DTPA-octreotide. The results of the binding studies demonstrate that161Tb-DTPA-octreotide is a high-affinity radioligand for somatostatin receptors, with an affinity comparable to that of111In-DTPA-octreotide. Rat growth hormone secretion inhibition experiments showed that161Tb-DTPA-octreotide has a similar potency to111In-DTPA-octreotide.161Tb-DTPA-octreotide appeared to be taken up even less by the isolated perfused rat liver than111In-DTPA-octreotide, as almost no tracer disappeared from the perfusion medium. Furthermore, hardly any radioactivity was found in the liver, and excretion into the bile was negligible. The biodistribution studies showed that for octreotide receptor-positive organs, such as pancreas and adrenals, uptake of161Tb-DTPA-octreotide is lower then that of111In-DTPA-octreotide. However, as the clearance from the blood of the former compound is faster than that of the latter, the tissue/blood ratio is higher in the case of161Tb-DTPA-octreotide than with111In-DTPA-octreotide. Furthermore, these studies demonstrated that the uptake of161Tb-DTPA-octreotide by the renal tubular cells after glomerular filtration can be reduced by administration of lysine or sodium maleate. Increase in urine production before and during the experiment had no effect on the kidney uptake of161Tb-DTPA-octreotide. Finally, it appeared that a maximal labelling efficiency of161Tb-DTPA-octreotide is essential, as with decreasing efficiency the uptake in the octreotide receptor-positive organs decreased, whereas non-specific uptake in the other organs was increased. It is concluded that, on the basis of the favourable physical characteristics of161Tb combined with the in vitro and in vivo studies performed with161Tb-DTPA-octreotide, the latter is a promising radiopharmaceutical for both intraoperative scanning and radiotherapy. Studies in patients need to be performed now to see whether161Tb-DTPA-octreotide can indeed open new therapeutic applications for patients bearing octreotide receptor-positive tumours

Radioiodinated somatostatin analogue RC-160: preparation, biological activity, in vivo application in rats and comparison with [123I-Tyr3]octreotide

We have evaluated the potential usefulness of the radioiodinated octapeptide RC-160, a somatostatin analogue, which might serve as a radiopharmaceutical for the in vivo detection of somatostatin receptor-positive tumours. For this purpose, iodine-123 and iodine-125 labelled RC-160 was tested for biological activity and applied in vivo in rats bearing the transplantable rat pancreatic tumour CA20948, which expresses somatostatin receptors. Our group has recently described the in vivo visualization of such tumours in rats and in humans with the radioiodinated somatostatin analogue [Tyr3]octreotide. Like [123I-Tyr3]octreotide, 123I-RC-160 showed uptake in and specific binding in vivo to somatostatin receptor-positive organs and tumours. However, blood radioactivity (background) was higher, resulting in a lower tumour to blood (background) ratio. We therefore conclude that in this animal model 123I-RC-160 has no advantage over [123I-Tyr3]octreotide as a radiopharmaceutical for the in vivo use as a somatostatin receptor imager, although, like [123I-Tyr3]octreotide, 123I-RC-160 shows specific binding to different somatostatin receptor-positive organs. Recently differences were reported in affinity between somatostatin and its analogues for somatostatin receptors expressed in different human cancers, like those of the breast, ovary, exocrine pancreas, prostate and colon. Therefore 123I-RC-160 might be of interest for future use in humans as a radiopharmaceutical for imaging octreotide receptor-negative tumours