On removable circuits in graphs and matroids

Mader proved that every 2‐connected simple graph G with minimum degree d exceeding three has a cycle C, the deletion of whose edges leaves a 2‐connected graph. Jackson extended this by showing that C may be chosen to avoid any nominated edge of G and to have length at least d − 1. This article proves an extension of Jackson's theorem. In addition, a conjecture of Goddyn, van den Heuvel, and McGuinness is disproved when it is shown that a natural matroid dual of Mader's theorem fails. © 1999 John Wiley & Sons, Inc. J Graph Theory 30: 51–66, 1999     

On energy pumping, synchronization and beat phenomenon in a nonideal structure coupled to an essentially nonlinear oscillator

In this paper, we investigated the effectiveness of the linear electromechanical vibration absorber (LEVA) and a nonlinear electromechanical vibration absorber (NEVA) in the vibration attenuation for nonideal structures (NIS). This electromechanical damping device consists of an electrical system coupled magnetically to a mechanical structure under a nonideal excitation. An analysis of the effects of the parameters of coupling and of nonlinear coefficients with increasing of constant torque of the DC motor is presented.     

Screening ofBothrops snake venoms forl-amino acid oxidase activity

Applied Biochemistry and Biotechnology - Toxins, enzymes, and biologically active peptides are the main components of snake venoms from the genusBothrops. Following the venom inoculation, the local...     

1H and 13C NMR spectra of 3,8-dimethoxyfuro[3,2-g]coumarin and maculine from Esenbeckia grandiflora Martius (Rutaceae)

One- and two-dimensional NMR experiments were used for the unambiguous assignment of the (1)H and (13)C NMR chemical shifts of the furoquinoline alkaloid maculine (1) and the new furanocoumarin 3,8-dimethoxyfuro[3,2-g]coumarin (2).     

Antifungal activity, toxicity and chemical composition of the essential oil of Coriandrum sativum L. fruits

The aims of this study were to test the antifungal activity, toxicity and chemical composition of essential oil from C. sativum L. fruits. The essential oil, obtained by hydro-distillation, was analyzed by gas chromatography/mass spectroscopy. Linalool was the main constituent (58.22%). The oil was considered bioactive, showing an LC?? value of 23 μg/mL in the Artemia salina lethality test. The antifungal activity was evaluated against Microsporum canis and Candida spp. by the agar-well diffusion method and the minimum inhibitory concentration (MIC) and the minimum fungicidal concentration (MFC) were established by the broth microdilution method. The essential oil induced growth inhibition zones of 28 ± 5.42 and 9.25 ± 0.5 for M. canis and Candida spp. respectively. The MICs and MFCs for M. canis strains ranged from 78 to 620 and 150 to 1,250 μg/mL, and the MICs and MFCs for Candida spp strains ranged from 310 to 620 and 620 to 1,250 μg/mL, respectively. C. sativum essential oil is active in vitro against M. canis and Candida spp. demonstrating good antifungal activity.     

Determination of pesticide residues and related compounds in water and industrial effluent by solid-phase extraction and gas chromatography coupled to triple quadrupole mass spectrometry

Pollution of drinking water supplies from industrial waste is a result of several industrial processes and disposal practices, and the establishment of analytical methods for monitoring organic compounds related to environmental and health problems is very important. In this work, a method using solid-phase extraction (SPE) and gas chromatography coupled to triple quadrupole tandem mass spectrometry (GC-QqQ-MS/MS) was developed and validated for the simultaneous determination of pesticide residues and related compounds in drinking and surface water as well as in industrial effluent. Optimization of the method was achieved by using a central composite design approach on parameters such as the sample pH and SPE eluent composition. A single SPE consisting of the loading on a polymeric sorbent of 100 mL of sample adjusted to pH 3 and elution with methanol/methylene chloride (10:90, v/v) permitted the obtaining of acceptable recoveries in most cases. The concentration factor associated with sensitivity of the chromatographic analysis permitted the achievement of the method limit of detection values between 0.01 and 0.25 μg L^?1. Recovery assays presented mean recoveries between 70 and 120 % for most of the compounds with very good precision, despite the different chemical nature of the compounds analyzed. The selectivity of the method, evaluated through the relative intensity of quantification and qualification ions obtained by GC-QqQ-MS/MS, was considered adequate. The developed method was finally applied to the determination of target analytes in real samples. River water and treated industrial effluent samples presented residues of some compounds, but no detectable residues were found in the drinking water samples evaluated.     

Excited State Properties and Energy Transfer within Dipyrrin‐Based Binuclear Iridium/Platinum Dyads: The Effect of ortho‐Methylation on the Spacer

Luminescent cyclometalated iridium complexes based on pyridyl appended dipyrrin ligands were prepared and characterized both in the solid state and in solution. The functionalization of the peripheral pyridyl moiety causes dramatic changes on the emission properties of both mono‐ and hetero‐ binuclear complexes. A detailed photophysical investigation of the two mononuclear derivatives of the [(Ppy)₂Ir(dpm‐py)] family (Ppy=2‐phenylpyridine, dpm‐py=5‐(4‐pyridyl)dipyrrin) was carried out. Introduction of methyl groups at the 3 and 5 positions on the pyridyl unit diminishes the non‐radiative rate constant by locking the peripheral pyridyl group orthogonally to the dipyrrinato plane. Thus, they limit the rotational degree of freedom, as well as the charge‐transfer character of the excited state. The coordination of these two complexes to a cyclometalated [(dppy)Pt] fragment (dppy=2,6‐diphenylpyridine) led to the formation of binuclear species in which the iridium and platinum complexes behave as acceptors and donors, respectively. In these heterobinuclear compounds, the methyl groups do not influence the energy transfer efficiency, which is estimated to be above 90 %. However, they do limit the charge‐transfer character of the acceptor’s excited state, as well as its rotational degree of freedom, thus avoiding the detrimental effect upon the photophysical performance.     

An antimicrobial diketopiperazine alkaloid and co-metabolites from an endophytic strain of Gliocladium isolated from Strychnos cf. toxifera

From an endophytic strain of Gliocladium sp. isolated from the Amazonian plant Strychnos cf. toxifera, we obtained the diketopiperazine alkaloid cyclo-(glycyl-L-tyrosyl)-4,4-dimethylallyl ether (1), the steroids ergosterol (2), ergosterol peroxide (3), cerevisterol (4) and the citric acid (5). The AcOEt extract of the fermented broth by Gliocladium sp. showed potent activity against the cancer cell lines MDA-MB435 (human breast cancer cells), HCT-8 (human colorectal cancer cells) and SF-295 (human glioblastoma cancer cells). Compound 1 exhibited a strong antimicrobial activity against Micrococcus luteus at a concentration of 43.4?μM.     

Phase-Locked loops lock-in range in Frequency Modulated-Atomic Force Microscope nonlinear control system

Since the mid 1980s the Atomic Force Microscope is one the most powerful tools to perform surface investigation, and since 1995 Non-Contact AFM achieved true atomic resolution. The Frequency-Modulated Atomic Force Microscope (FM-AFM) operates in the dynamic mode, which means that the control system of the FM-AFM must force the microcantilever to oscillate with constant amplitude and frequency. However, tip-sample interaction forces cause modulations in the microcantilever motion. A Phase-Locked loop (PLL) is used to demodulate the tip-sample interaction forces from the microcantilever motion. The demodulated signal is used as the feedback signal to the control system, and to generate both topographic and dissipation images. As a consequence, a proper design of the PLL is vital to the FM-AFM performance. In this work, using bifurcation analysis, the lock-in range of the PLL is determined as a function of the frequency shift (Ω) of the microcantilever and of the other design parameters, providing a technique to properly design the PLL in the FM-AFM system.     

Simple and highly diastereoselective access to 3,4-substituted tetrahydro-1,8-naphthyridines from Morita-Baylis-Hillman adducts

We disclose herein a facile and straightforward method to access 3,4-substituted tetrahydro-1,8-naphthyridines from Morita-Baylis-Hillman. The strategy is based on a tandem sequence involving a Michael addition reaction followed by an intramolecular S_NAr reaction on a silylated-Morita-Baylis-Hillman adduct. In a single step, a new cycle is formed and the relative stereochemistry of two new centers is controlled with good to excellent diastereoselectivity.