Approximate KKT points and a proximity measure for termination

Karush–Kuhn–Tucker (KKT) optimality conditions are often checked for investigating whether a solution obtained by an optimization algorithm is a likely candidate for the optimum. In this study, we report that although the KKT conditions must all be satisfied at the optimal point, the extent of violation of KKT conditions at points arbitrarily close to the KKT point is not smooth, thereby making the KKT conditions difficult to use directly to evaluate the performance of an optimization algorithm. This happens due to the requirement of complimentary slackness condition associated with KKT optimality conditions. To overcome this difficulty, we define modified ${\epsilon}$ -KKT points by relaxing the complimentary slackness and equilibrium equations of KKT conditions and suggest a KKT-proximity measure, that is shown to reduce sequentially to zero as the iterates approach the KKT point. Besides the theoretical development defining the modified ${\epsilon}$ -KKT point, we present extensive computer simulations of the proposed methodology on a set of iterates obtained through an evolutionary optimization algorithm to illustrate the working of our proposed procedure on smooth and non-smooth problems. The results indicate that the proposed KKT-proximity measure can be used as a termination condition to optimization algorithms. As a by-product, the method helps to find Lagrange multipliers correspond to near-optimal solutions which can be of importance to practitioners. We also provide a comparison of our KKT-proximity measure with the stopping criterion used in popular commercial softwares.     

Ruthenium(II) mediated C-H activation of substituted acetophenone thiosemicarbazones: Synthesis, structural characterization, luminescence and electrochemical properties

Treatment of [RuHCl(CO)(AsPh₃)₃] with 4′-substituted acetophenone thiosemicarbazone derivatives in methanol under reflux afford a series of air stable new ruthenium(II) cyclometalated complexes containing thiosemicarbazone of general formula [Ru(L)(CO)(AsPh₃)₂]. The 4′-substituted acetophenone thiosemicarbazone ligands behave as a dianionic terdentate C, N and S donors (L) and coordinates to ruthenium via aromatic carbon, the imine nitrogen and thiol sulfur. The compositions of the complexes have been established by elemental analysis, and spectral methods (FT-IR, UV-Vis, ¹H NMR, ESI-MS) and X-ray crystallography. In chloroform solution all the complexes exhibit metal-to-ligand charge transfer transitions (MLCT) in the visible region and are emissive at room temperature with quantum yield of 0.001-0.005. The crystal structure of one of the complexes [Ru(4CAP-PTSC)(CO)(AsPh₃)₂] (4) has been solved by single crystal X-ray crystallography and it indicates the presence of a distorted octahedral geometry in these complexes. All the complexes exhibit a quasi reversible one electron reduction (Ru^II/Ru^I) in the range −0.83 to −0.86 V. The formal potential of all the couples correlate linearly with the Hammett constant of the para substituent in phenyl fragment of the acetophenone thiosemicarbazone ligands.     

A simple internal charge transfer probe offering dual optical detection of Co (II) via color and fluorescence modulations

A newly designed internal charge transfer chemosensor, DIPZON exhibits Co²⁺ selective optical responses, which include 112 nm red shift in absorption and a dramatic 37-fold enhancement in the fluorescence output in the buffer CH₃OH/H₂O (1:1 v/v) system. By contrast, the optical responses were not as sensitive with several other biologically relevant metal ions examined with the binding interactions following the sequence Co²⁺ > Cu²⁺ > Zn²⁺ > Cd²⁺ >> Ba²⁺ ≈ Ca²⁺ ≈ Mg²⁺ ≈ K⁺ ≈ Na⁺ ≈ Li⁺.     

Capacitance of graphene films: effect of the number of layers of the constituent graphene flakes

Journal of Solid State Electrochemistry - Assembly of graphene flakes into a film for an electric double-layer capacitor electrode causes restacking and aggregation of the constituent flakes that...     

Nonlinear vibration of symmetrically laminated composite skew plates by finite element method

Here, the large amplitude free flexural vibration behavior of symmetrically laminated composite skew plates is investigated using the finite element method. The formulation includes the effects of shear deformation, in-plane and rotary inertia. The geometric non-linearity based on von Kármán's assumptions is introduced. The nonlinear matrix amplitude equation obtained by employing Galerkin's method is solved by direct iteration technique. Time history for the nonlinear free vibration of composite skew plate is also obtained using Newmark's time integration technique to examine the accuracy of matrix amplitude equation. The variation of nonlinear frequency ratios with amplitudes is brought out considering different parameters such as skew angle, fiber orientation and boundary condition.     

A label free aptasensor for Ochratoxin A detection in cocoa beans: An application to chocolate industries

Contamination of food by mycotoxin occurs in minute/trace quantities. Nearly 92.5% of the cocoa samples present Ochratoxin A (OTA) levels at trace quantity. Hence, there is a necessity for a highly sensitive and selective device that can detect and quantify these organic toxins in various matrices such as cocoa beans. This work reports for the first time, a facile and label-free electrochemical impedimetric aptasensor for rapid detection and quantitation of OTA in cocoa beans. The developed aptasensor was constructed based on the diazonium-coupling reaction mechanism for the immobilization of anti-OTA-aptamer on screen printed carbon electrodes (SPCEs). The aptasensor exhibited a very good limit of detection (LOD) as low as 0.15 ng/mL, with added advantages of good selectivity and reproducibility. The increase in electron transfer resistance was linearly proportional to the OTA concentration in the range 0.15–2.5 ng/mL, with an acceptable recovery percentage (91–95%, RSD = 4.8%) obtained in cocoa samples. This work can facilitate a general model for the detection of OTA in cocoa beans based on the impedimetric aptasensor. The analysis can be performed onsite with pre-constructed and aptamer modified electrodes employing a portable EIS set up.     

Cloning, expression, and sequence analysis of diaminopropionate ammonia lyase gene from a nonvirulentsalmonella typhimurium PU011

Background: Seeds ofLathyrus sativus, a legume plant, contain 3-oxalyl and 2,3-dioxalyl DAP (O-DAP), neurotoxins which when consumed causes Neurolathyrism or Osteolathyrism, in humans, affecting nervous system and bone formation respectively. Some microorganisms viz virulent and non-virulentSalmonella typhimurium, Salmonella typhi and Pseudomonad have been shown to detoxifyL-α,β-diaminopropionate (DAP), the immediate precursor of O-DAP. Result: The gene coding for diaminopropionate ammonia lyase (DAPAL) which detoxifies DAP was cloned from nonvirulentS. typhimurium PU011 intoEscherichia coli DH5α and the nucleotides sequenced (1212 bp). Whereas the specific enzyme activity of DAPAL obtained from recombinantE. coli PU018 was 0.346 U/mg, the specific activity of the enzyme from nonvirulentS. typhimurium PU011 was 0.351 U/mg. The DAPAL corresponding to 43 kDa protein was found both in nonvirulentS. typhimurium PU011 andE. coli PU018. The Km value was found to be 0.740 mM and 0.680 mM forS. typhimurium PU011 and 0.741 mM and 0.683 mM forE. coli PU018 when grown in minimal medium (MM+DAP) andL. sativus seed extracts respectively, indicating that both of them were capable of utilizing the neurotoxins present inL. sativus seeds. The biomass, enzyme production and the effect of pH and temperature on DAPAL enzyme activity from both non-virulentS. typhimurium PU011 andE. coli PU018 were found to be similar. Conclusion: The recombinantE. coli PU018 as well as non-virulentS. typhimurium PU011 are as good as pathogenicS. typhimurium in detoxifying DAP, the immediate precursor of O-DAP present inL. sativus seeds.     

Oxidative Products of Curcumin Rather Than Curcumin Bind to Helicobacter Pylori Virulence Factor VacA and Are Required to Inhibit Its Vacuolation Activity

Curcumin is a hydrophobic polyphenol derived from turmeric with potent anti-oxidant, anti-microbial, anti-inflammatory and anti-carcinogenic effects. Curcumin is degraded into various derivatives under in vitro and in vivo conditions, and it appears that its degradation may be responsible for the pharmacological effects of curcumin. The primary risk factor for the cause of gastric cancer is Helicobacter pylori (H. pylori). A virulence factor vacuolating cytotoxic A (VacA) is secreted by H. pylori as a 88 kDa monomer (p88), which can be fragmented into a 33 kDa N-terminal domain (p33) and a 55 kDa C-terminal domain (p55). Recently it has been reported that curcumin oxidation is required to inhibit the activity of another major H.pylori toxin CagA. We performed molecular docking of curcumin and its oxidative derivatives with p33 and p55 domains of VacA. Further, we have examined the effect of the oxidation of curcumin on the vacuolation activity of VacA protein. We observed the binding of curcumin to the p55 domain of VacA at five different sites with moderate binding affinities. Curcumin did not bind to p33 domain of VacA. Remarkably, cyclobutyl cyclopentadione and dihydroxy cyclopentadione, which are oxidized products of curcumin, showed a higher binding affinity with VacA protein at all sites except one as compared to parent curcumin itself. However, cyclobutyl cyclopentadione showed a significant binding affinity for the active site 5 of the p55 protein. Active site five (312–422) of p55 domain of VacA plays a crucial role in VacA-mediated vacuole formation. Invitro experiments showed that curcumin inhibited the vacuolation activity of H. pylori in human gastric cell line AGS cells whereas acetyl and diacetyl curcumin, which cannot be oxidized, failed to inhibit the vacuolation in AGS cells after H. pylori infection. Here our data showed that oxidation is essential for the activity of curcumin in inhibiting the vacuolation activity of H. pylori. Synthesis of these oxidized curcumin derivatives could potentially provide new therapeutic drug molecules for inhibiting H. pylori-mediated pathogenesis.     

Octahedral Cuprous Oxide Decorated Flexible Reduced Graphene Oxide Paper for Food Sensing Application

This work presents a simple method to fabricate an octahedral cuprous oxide (Cu₂O) decorated two-dimensional (2D) flexible rGOP electrode with filtration and electrodeposition strategies. The characteristic of the Cu₂O/rGOP electrodes was recorded by SEM, EDX, XPS, XRD, and Raman spectroscopy. The results clearly showed that Cu₂O was successfully electrodeposited on the surface of rGOP by controlling the electrodeposition potential without the introduction of any template or surfactant. The electrochemical characterizations of the Cu₂O/rGOP exhibited high electrocatalytic activity toward the reduction of H₂O₂. The linear detection range for the Cu₂O/rGOP flexible sensor was 5.0 μM to 5.5 mM, with a limit of detection of 1.27 μΜ. Subsequently, the developed flexible rGOP sensor was extended for H₂O₂ detection in milk samples for avoiding milk spoilage_. Such judicial preparation of rGOP as a sensing device will certainly pave the way for various other sensing applications including environmental and biomedical applications.     

Anthracene-tethered aminomethyl oxadiazole chemosensor: a probe offering selective chromo- and fluorogenic signalings for targeting Cu(II)

A new optical chemosensor featuring anthracene as a fluorophore and an aminomethyl oxadiazole moiety as a bidentate chelate has been synthesized. From photophysical studies, we find the probe to offer remarkably selective chromo- and fluorogenic signaling responses towards biologically and environmentally significant Cu²⁺. In the presence of Cu²⁺, fluorescence is quenched to the extent of 95%, while the absorbance due to the anthracene chromophore is nearly completely bleached out. On the other hand, Li⁺, Na⁺, K⁺, Ba²⁺, Ca²⁺, Zn²⁺, Mg²⁺, Cd²⁺, Co²⁺, Ni²⁺, Ag⁺, Pb²⁺ and Hg²⁺ even at 10 times higher concentration than Cu²⁺ do not cause detectable photophysical perturbations. The stability constants, logK for Cu²⁺ were calculated to be 4.36 and 4.76 on the basis of spectrophotometric and fluorimetric titrations, respectively. However, logKs for other metal ions are too low (<0.1) to pose any interferences in the optical detection of Cu²⁺. Though, not fully defined, the uncommon phenomenon of the absorbance bleaching by Cu²⁺ is tentatively explained by invoking the involvement of non-covalent anthracene-Cu²⁺ complex.