An effective deep learning model for grading abnormalities in retinal fundus images using variational auto-encoders

Diabetic retinopathy (DR) and Diabetic Macular Edema (DME) are severe diseases that affect the eyes due to damage in blood vessels. Computer-aided automated grading will help clinicians conduct disease diagnoses at ease. Experiments of automated image processing with deep learning techniques using CNN produce promising results, especially in the medical imaging domain. However, the disease grading tasks in retinal images using CNN struggle to retain high-quality information at the output. A novel deep learning model based on variational auto-encoder to grade DR and DME abnormalities in retinal images is proposed. The objective of the proposed model is to extract the most relevant retinal image features efficiently. It focuses on addressing less relevant candidate region generation and translational invariance present in images. The experiments are conducted in IDRID dataset and evaluated using accuracy, U-kappa, sensitivity, specificity and precision metrics. The results outperform compared with other state-of-art techniques.     

Molecular relaxation in cross-linked poly(ethylene glycol) and poly(propylene glycol) diacrylate networks by dielectric spectroscopy

The molecular relaxation characteristics of rubbery amorphous crosslinked networks based on poly(ethylene glycol) diacrylate [PEGDA] and poly(propylene glycol) diacrylate [PPGDA] have been investigated using broadband dielectric spectroscopy. Dielectric spectra measured across the sub-glass transition region indicate the emergence of an intermediate “fast” relaxation in the highly crosslinked networks that appears to correspond to a subset of segmental motions that are more local and less cooperative as compared to those associated with the glass transition. This process, which is similar to a distinct sub-T_g relaxation detected in poly(ethylene oxide) [PEO], may be a general feature in systems with a sufficient level of chemical or physical constraint, as it is observed in the crosslinked networks, crystalline PEO, and PEO-based nanocomposites.     

Dynamic relaxation characteristics of thermally rearranged aromatic polyimides

The glass–rubber and sub-glass relaxation characteristics of ortho-functionalized aromatic polyimides and thermally rearranged polymers were investigated by dynamic mechanical and dielectric methods. Soluble polyimides (HAB–6FDA; APAF–ODPA) were synthesized by chemical and thermal imidization and subject to thermal rearrangement at elevated temperature. For the thermal exposure histories investigated, mass loss studies indicated partial conversion of the polyimide precursor, suggesting the formation of TR copolymers containing both benzoxazole units and residual imide segments. Measurement of storage modulus and loss tangent was used to follow the thermal rearrangement process in-situ as reflected in the suppression of the polyimide glass transition as a function of precursor structure, the nature of the ortho functional groups and prior thermal exposure. In addition, changes in the position and intensity of local relaxations detected across the sub-glass temperature range were correlated with the degree of thermal rearrangement in these polymers.     

Palladacycle‐Catalyzed Tandem Allylic Amination/Allylation Protocol for One‐Pot Synthesis of 2‐Allylanilines from Allylic Alcohols

An efficient methodology involving the predominant formation of C C bonds is described for the first direct synthesis of 2‐allylanilines from allylic alcohols via a one‐pot tandem allylic amination/allylation protocol catalyzed by a palladacycle under mild conditions without the requirement for additional activators.     

Evaluation of Palladacycles as a Non‐Rhodium Based Alternative for the Asymmetric Conjugate 1,4‐Addition of Arylboronic Acids to α,β‐Unsaturated Enones

The asymmetric conjugate 1,4‐addition of arylboronic acids to α,β‐unsaturated carbonyl compounds is an extremely versatile and widely used organic transformation. While the rhodium(I)‐catalysed reaction has been thoroughly explored, the asymmetric palladium‐catalysed protocol is far less developed and understood, particularly with acyclic enones as substrates. Herein, we report the systematic evaluation of a series of metallacycles for this reaction and the conjugate addition of arylboronic acids to a wide range of α,β‐unsaturated enones, catalysed by an easily accessible and robust chiral phosphapalladacycle in high yields and enantioselectivities.

     

Dynamic mechanical and dielectric relaxation characteristics of poly(trimethylene terephthalate)

The dynamic mechanical and dielectric relaxation properties of a commercial poly(trimethylene terephthalate) [PTT] have been investigated for both quenched and isothermally melt-crystallized specimen films. The relaxation characteristics of PTT were consistent with those of other low-crystallinity semiflexible polymers, e.g. PET and PEEK. While the sub-glass relaxation was largely unperturbed by the presence of the crystalline phase, both calorimetric and broadband dielectric measurements across the glass transition indicated the existence of a sizeable rigid amorphous phase (RAP) fraction in melt-crystallized PTT owing to the constraining influence of the crystal surfaces over the crystal-amorphous interphase region. A strong increase in measured dielectric relaxation intensity (Δ?) with temperature above T_g indicated the progressive mobilization of the RAP material, as well as an overall loss of correlation amongst the responding dipoles.     

Enantioselective Addition of Diphenylphosphine to 3‐Methyl‐4‐nitro‐5‐alkenylisoxazoles

An enantioselective Michael addition reaction of diphenylphosphine to substituted alkenylisoxazoles has been developed. The reaction proceeds efficiently under mild conditions with high yields (up to 99%) and moderate to excellent enantioselectivities (up to 92%) thus providing a hitherto unavailable direct access to a library of chiral tertiary phosphine‐functionalized isoxazoles.     

Relation between structure and gas transport properties of polyethylene oxide networks based on crosslinked bisphenol A ethoxylate diacrylate

Poly(ethylene oxide) (PEO) networks prepared from the photopolymerization of bisphenol A ethoxylate diacrylate (BPA-EDA) have been investigated as a function of crosslinker molecular weight and copolymer composition. Dynamic mechanical and dielectric methods have been used to elucidate the thermal relaxation characteristics of the polymers as a function of network composition and architecture, and these properties were related to measured gas transport for CO₂ separations. Copolymerization strategies involving the insertion of flexible PEG side chains along the network backbone proved effective in enhancing network free volume and increasing permeability. The gas transport performance of rubbery amorphous membranes based on the n=15 BPA-EDA crosslinker (i.e., crosslinker encompassing 30 ethylene oxide repeat units between crosslinks) compared favorably to model polymers synthesized from poly(ethylene glycol) diacrylate.     

Crystallization,melting, and rheology of reactive polyamide blends

The crystallization and melting characteristics of a series of polyamide blends based on PA 4,6 and PA 6I were investigated by calorimetric methods; preparation of the samples was conducted so as to control the extent of transamidation occurring in the melt before crystallization. Blend samples with minimal prior thermal history displayed a modest degree of melting point depression compared to the equilibrium melting temperature of PA 4,6 (T = 309.5°C). Application of the Nishi–Wang equation indicated a value of χ = ?0.25 for the blends. PA 4,6 and the blends followed Avrami crystallization kinetics with exponents in the range 2.0 to 2.5; no systematic variation of n with blend composition was observed. The influence of transamidation was investigated for samples exposed to varying melt temperatures and melt times with the extent of transreaction quantified using ¹³C‐NMR. Increasing extents of transreaction led to a decrease in both the rate of crystallization and the overall bulk crystallinity of the blends owing to a reduction in the length and number of crystallizable blocks present along the polymer chains. Capillary rheometry studies indicated a strong sensitivity to time in the melt for the PA 4,6 homopolymer, and the mechanism responsible for the observed decrease in apparent viscosity was also operative in the blend samples. As such, it was not possible to independently assess the influence of transreaction on the rheology of the blends. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1245–1252, 2004