Inspection of a magneto-optical trap via electromagnetically induced absorption

Electromagnetically induced absorption (EIA) was observed for the first time on a sample of ⁸⁵Rb in a magneto-optical trap using low intensity cw copropagating pump and probe optical fields. Narrow resonances revealing the dependence of the ground-state Zeeman sublevels energy structure on the quadrupolar magnetic field and the trapping optical field intensity at different trap positions, were observed. Coherence resonances as narrow as 30 kHz were obtained under low trapping field intensities. The use of EIA spectroscopy for the magnetic field mapping of cold atomic samples is illustrated.     

A column-switching method for quantification of the enantiomers of omeprazole in native matrices of waste and estuarine water samples

This work reports the use of a two-dimensional liquid chromatography (2D-LC) system for quantification of the enantiomers of omeprazole in distinct native aqueous matrices. An octyl restricted-access media bovine serum albumin column (RAM-BSA C₈) was used in the first dimension, while a polysaccharide-based chiral column was used in the second dimension with either ultraviolet (UV-vis) or ion-trap tandem mass spectrometry (IT-MS/MS) detection. An in-line configuration was employed to assess the exclusion capacity of the RAM-BSA columns to humic substances. The excluded macromolecules had a molecular mass in the order of 18 kDa. Good selectivity, extraction efficiency, accuracy, and precision were achieved employing a very small amount (500 μL or 1.00 mL) of native water sample per injection, with detection limits of 5.00 μg L⁻¹, using UV-vis, and 0.0250 μg L⁻¹, using IT-MS/MS. The total analysis time was only 35 min, with no time spent on sample preparation. The methods were successfully applied to analyze a series of waste and estuarine water samples. The enantiomers were detected in an estuarine water sample collected from the Douro River estuary (Portugal) and in an influent sample from the wastewater treatment plant (WWTP) of São Carlos (Brazil). As far as we are concerned, this is the first report of the occurrence of (+)-omeprazole and (−)-omeprazole in native aqueous matrices.     

Water-based enhancement of the resonant photoacoustic signal from methane–air samples excited at 3.3 μm

Photoacoustic spectroscopy is widely applied for trace-gas detection because of its sensitivity and low detection limit. In a previous work, where we studied the potential application to methane monitoring under a resonant excitation at 3.3???m, we showed that the signal from methane?Cnitrogen mixtures decreases with the addition of oxygen. This effect is due to an energy exchange between the ?? ₄ asymmetric stretching mode of methane and the first metastable level of oxygen. This process makes oxygen accumulate energy, thus hindering the generation of the photoacoustic signal. In this work, we study the possible addition of water, as a good collisional partner of oxygen, in order to obtain a greater sensitivity. We develop a model based on rate equations and find good agreement between theory and measurements. The experiment is carried out with a novel cell of rectangular cross section and a Q factor of 165±1. We find that 0.7?% water content is large enough to obtain a signal as high as in the methane?Cnitrogen case at atmospheric pressure.     

Kinetics and Mechanism of the Reaction between an Arenediazonium Ion and Methyl Gallate (=Methyl 3,4,5‐Trihydroxybenzoate) in Aqueous Solution: Evidence for Diazo Ether Formation through an O‐Coupling Reaction

We have investigated the kinetics and mechanism of the reaction between 3‐methylbenzenediazonium ions (3MBD) and methyl gallate (=methyl 3,4,5‐trihydroxybenzoate; MG), in aqueous buffer solution by employing spectrophotometric (UV/VIS) and electrochemical (linear‐sweep voltammetry, LSV) techniques and computational methods. Because the absorption band of MG overlaps that of 3MBD, the reaction was monitored spectrophotometrically by measuring the changes in absorbance with time due to product formation, and biphasic kinetic profiles, indicative of accumulation of an intermediate in the course of the reaction, were obtained. The formation of an intermediate was confirmed by LSV. The observed rate constants k_obs for 3MBD disappearance were obtained by fitting the decrease in the peak current of the first reduction peak of 3MBD with time to the integrated first‐order equation. The variation of k_obs with [MG] was determined at different pH values and follows a saturation kinetic pattern. Alternatively, at a fixed [MG], k_obs values show an inverse dependence on [H⁺], suggesting that the reactive species is the anion and not the neutral form of MG. To discern which of the three OH groups of MG is the first one undergoing deprotonation, the geometries of the resulting anions were optimized by using B3LYP hybrid density functional theory (DFT) and a 6‐31G(++d,p) basis set. The deprotonation energies suggest that the OH group at the 4‐position is first deprotonated. The kinetic results can be accommodated, therefore, by assuming two competitive mechanisms, the spontaneous D_N+A_N decomposition involving 3MBD, and a mechanism involving an electrophilic attack at the O‐atom at C(4) in a pre‐equilibrium step, leading to the formation of a transient diazo ether of the type Ar? N?N? O? R which further decomposes. All attempts to isolate and characterize the diazo ether failed.     

NLO predictions for the growth ofF 2 at smallx and comparison with experimental data

We present parametrizations for the proton structure functionF ₂ in the next to leading order in perturbative QCD. We consider that the dominant term toF ₂(x, Q ²) should grow asx ^?ψ _s for smallx values, with the exponentλ _S being essentially independent ofQ ². Comparisons with the most recent H1 and ZEUS data confirm the valueλ _S ～0.35 obtained previously from fits to low energy data.     

Influence of oxygen on the resonant photoacoustic signal from methane excited at the <Emphasis Type="Italic">ν</Emphasis><Subscript>3</Subscript> mode

This paper shows that, when samples of methane in dry air are irradiated with an OPO tuned at the ν ₃ mode at 3019 cm⁻¹, the photoacoustic signal is lower than in mixtures in pure nitrogen. In order to explain this change, we developed a rate-equation-based model which describes the methane excitation and relaxation to heat by collisions with the buffer. In particular, we reduced the problem to a system of six energy levels taking into account the fast energy exchange between methane and oxygen resonant states and the slow relaxation rate of oxygen. Thus, the photoacoustic signal is calculated for methane–nitrogen and methane–air systems and a very good agreement is found with the experimental results.     

Inferring interdependencies in climate networks constructed at inter-annual, intra-season and longer time scales

We study global climate networks constructed by means of ordinal time series analysis. Climate interdependencies among the nodes are quantified by the mutual information, computed from time series of monthly-averaged surface air temperature anomalies, and from their symbolic ordinal representation (OP). This analysis allows identifying topological changes in the network when varying the time-interval of the ordinal pattern. We consider intra-season time-intervals (e.g., the patterns are formed by anomalies in consecutive months) and inter-annual time-intervals (e.g., the patterns are formed by anomalies in consecutive years). We discuss how the network density and topology change with these time scales, and provide evidence of correlations between geographically distant regions that occur at specific time scales. In particular, we find that an increase in the ordinal pattern spacing (i.e., an increase in the timescale of the ordinal analysis), results in climate networks with increased connectivity on the equatorial Pacific area. On the contrary, the number of significant links decreases when the ordinal analysis is done with a shorter timescale (by comparing consecutive months), and interpret this effect as due to more stochasticity in the time-series in the short timescale. As the equatorial Pacific is known to be dominated by El Niño-Southern Oscillation (ENSO) on scales longer than several months, our methodology allows constructing climate networks where the effect of ENSO goes from mild (monthly OP) to intense (yearly OP), independently of the length of the ordinal pattern and of the thresholding method employed.     

Improved sensitivity to charged Higgs searches in top quark decays t→bH+→b(τ+ντ) at the LHC using τ polarisation and multivariate techniques

We present an analysis with improved sensitivity to the light charged Higgs (m_H⁺ < m_t-m_bm_{H^{+}} < m_{t}-m_{b}) searches in the top quark decays t→bH ⁺→b(τ ⁺ ν _τ )+c.c. in the t[`(t)]t\bar{t} and single t/[`(t)]t/\bar{t} production processes at the LHC. In the Minimal Supersymmetric Standard Model (MSSM), one anticipates the branching ratio B (H⁺ ?t⁺n_t) @ 1{\mathcal{B}} (H^{+} \to\tau^{+}\nu_{\tau})\simeq1 over almost the entire allowed tanb\tan\beta range. Noting that the τ ⁺ arising from the decay H ⁺→τ ⁺ ν _τ are predominantly right-polarized, as opposed to the τ ⁺ from the dominant background W ⁺→τ ⁺ ν _τ , which are left-polarized, a number of H ⁺/W ⁺→τ ⁺ ν _τ discriminators have been proposed and studied in the literature. We consider hadronic decays of the τ ^±, concentrating on the dominant one-prong decay channel τ ^±→ρ ^± ν _τ . The energy and p _T of the charged prongs normalised to the corresponding quantities of the ρ ^± are convenient variables which serve as τ ^± polariser. We use the distributions in these variables and several other kinematic quantities to train a boosted decision tree (BDT). Using the BDT classifier, and a variant of it called BDTD, which makes use of decorrelated variables, we have calculated the BDT(D)-response functions to estimate the signal efficiency vs. the rejection of the background. We argue that this chain of analysis has a high sensitivity to light charged Higgs searches up to a mass of 150 GeV in the decays t→bH ⁺ (and charge conjugate) at the LHC. For the case of single top production, we also study the transverse mass of the system determined using Lagrange multipliers.     

Expanding the carbo‐Benzene Chemical Space for Electron‐Accepting Ability: Trifluorotolyl/Tertiobutyl Substitution Balance

With the view to altering the lipophilicity and electron accepting ability of the tetraphenyl‐carbo‐benzene scaffold, peripheral fluorination of the C₁₈ ring through aromatic linkers was envisaged from the C₁₈Ph₆ and o‐^tBu₂C₁₈Ph₄ references, by replacement of two Ph substituents with two p‐CF₃‐C₆H₄ counterparts (^FTol). The synthesis relied on a [8+10] macrocyclization involving a common bis(trifluorotolyl)‐tetraynedione, followed by reductive aromatization of the resulting [6]pericyclynediols. While p‐^FTol₂C₁₈Ph₄ proved to be hardly tractable due to an extremely low solubility, p‐^FTol₂‐o‐^tBu₂C₁₈Ph₂ could be extensively studied by X‐ray crystallography, NMR and UV/Vis spectroscopy, voltammetry, STM imaging of monolayers, and AFM imaging of binary films with P3HT or PC₇₁BM fabricated by spin‐coating for organic photovoltaic cells and J?V curve measurement thereof. The electronic and polarity properties are correlated with moderate but consistent electron‐withdrawing effects of the CF₃ groups, in agreement with the DFT‐calculated frontier orbitals and multipole moments. The results provide guidelines for optimization of fluorinated carbo‐benzene targets.