Exchange Phase Research Articles

Calculation of photoionization differential cross sections using complex Gauss-type orbitals.

Accurate theoretical calculation of photoelectron angular distributions for general molecules is becoming an important tool to image various chemical reactions in real time. We show in this article that not only photoionization total cross sections but also photoelectron angular distributions can be accurately calculated using complex Gauss-type orbital (cGTO) basis functions. Our method can be easily combined with existing quantum chemistry techniques including electron correlation effects, and applied to various molecules. The so-called two-potential formula is applied to represent the transition dipole moment from an initial bound state to a final continuum state in the molecular coordinate frame. The two required continuum functions, the zeroth-order final continuum state and the first-order wave function induced by the photon field, have been variationally obtained using the complex basis function method with a mixture of appropriate cGTOs and conventional real Gauss-type orbitals (GTOs) to represent the continuum orbitals as well as the remaining bound orbitals. The complex orbital exponents of the cGTOs are optimized by fitting to the outgoing Coulomb functions. The efficiency of the current method is demonstrated through the calculations of the asymmetry parameters and molecular-frame photoelectron angular distributions of H2+ and H2. In the calculations of H2, the static exchange and random phase approximations are employed, and the dependence of the results on the basis functions is discussed. © 2017 Wiley Periodicals, Inc.

Design and analysis of pairing protocol for bluetooth enabled devices using R-LWE Lattice-based cryptography

Secure Simple Pairing protocol of Bluetooth introduced in Bluetooth version 2.1+EDR has security issues. Shared secret key using Elliptic Curve Diffie–Hellman algorithm generated in public key exchange phase, is subsequently used for authentication of devices and for computing Link key. The stability of Elliptic-Curve-Diffie–Hellman is based on the determination of order and structure of a finite Abelian group and computation of Elliptic Curve Discrete Logarithm (ECDLP) in a cyclic group. An algorithm for a quantum computers exists, that can figure out the inverse of Elliptic Curve Discrete Logarithm in polynomial time. Therefore, it demands a safe and sound cryptosystem for quantum computers. A revision to boost the security of pairing and authentication process in the Secure Simple Pairing (SSP) protocol of Bluetooth intended for classical and quantum computers is proposed called as Classiquantum Resistance Secure Simple Pairing protocol. On simulating the proposed protocol, it is studied that the proposed protocol is superior over SSP, as far as security performance by enhancement of key strength and by wrapping link key with two R-LWE secret key, is concerned.

Hb Amsterdam-A1 [α32(B13)Met→Ile; HBA1: c.99G>A]: A Hyperunstable Variant Due to a New Mutation on the α1 Gene

Patients with hyperunstable α chain variants usually present with a thalassemic, rather than hemolytic, phenotype. Electrophoretic, ion exchange and reverse phase separations usually fail to detect the variant and when DNA sequencing identifies a ‘silent’ substitution it is usually presumed to be hyperunstable. We report the identification of such a variant, α32(B13)Met→Ile; HBA1: c.99G>A, arising from a new mutation on the α1 gene. The hemoglobin (Hb) was unequivocally detected by the isopropanol stability test and confirmed as hyperunstable by mass spectrometry (MS) of the precipitate and lysate, which showed proportions of 55% and 2.5% of α chains, respectively. The instability appears to be driven by perturbation of globin-heme, and possibly α1β1 subunit, interactions.

Class Type Separation of the Polar and Apolar Components of Petroleum.

Identification of the heteroatom (nitrogen, sulfur, and oxygen)-containing compounds of petroleum is of key importance when considering industrial and environmental issues associated with crude oil production. The more commonly performed methods of crude oil fractionation are often insufficient in the extent to which they separate oils, not allowing defined "molecular" fractions to be obtained. Methods capable of performing a class type separation are uncommon and are often extensive and resource and time intensive. Here we report a method for the separation of crude oils into discrete compound classes. The method utilizes both ion exchange and normal phase chromatography to generate fractions of saturated hydrocarbons, aromatic hydrocarbons, basic compounds, naphthenic acids, and other oxygen-containing species, carbazoles, sulfones, and thiophenes from small crude oil samples (∼0.5 g). Assessment of method selectivity with a suite of model compounds has shown the fractions to be well-defined, with classes of model compounds isolated within discrete fractions. Application of the method to five crude oils of varying API gravity (12.1-38.3°) demonstrates a potential for wide-ranging use. Sample recoveries were high (77-98%) with simple evaporative losses correlating closely with total sample loss. Repeatability was also high, demonstrated by triplicate analyses of model compound mixtures, oils spiked with model compounds and oils alone. Separation selectivity was further demonstrated by application of the scheme to the Alaska North Slope (ANS) crude oil and analysis of fractions by comprehensive two-dimensional gas-chromatography mass-spectrometry (GC × GC/MS) and/or liquid-chromatography high-resolution accurate-mass mass-spectrometry methods (LC-HRAM-MS). Isolation of discrete fractions then allowed excellent separation (by LC and GC methods) of carbazole, dibenzothiophene, fluorenones, xanthones, and quinoline fractions. Individual parent and C1-5 alkyl homologues were easily separated (GC × GC/MS), allowing high-quality mass spectra (EI) to be obtained for the individual compounds in many cases. Analysis of fractions by GC × GC/MS also allowed a series of thioxanones to be identified.

Solid cation exchange phase to remove interfering anthocyanins in the analysis of other bioactive phenols in red wine.

Bioactive phenols (BPs) are often targets in red wine analysis. However, other compounds interfere in the liquid chromatography methods used for this analysis. Here, purification procedures were tested to eliminate anthocyanin interference during the determination of 19 red-wine BPs. Liquid chromatography, coupled to a diode array detector (HPLC-DAD) and a mass spectrometer (UPLC-MS), was used to compare the direct injection of the samples with solid-phase extractions: reversed-phase (C18) and strong cation-exchange (SCX). The HPLC-DAD method revealed that, out of 13BPs, only six are selectively analyzed with or without C18 treatment, whereas SCX enabled the detection of all BPs. The recovery with SCX was above 86.6% for eight BPs. Moreover, UPLC-MS demonstrated the potential of SCX sample preparation for the determination of 19BPs. The developed procedure may be extended to the analysis of other red wine molecules or to other analytical methods where anthocyanins may interfere.

Determination of inosine 5'-monophosphate dehydrogenase activity in red blood cells of thiopurine-treated patients using HPLC.

Thiopurine drugs are commonly used in immune diseases and to a lesser extent, in transplant rejection prophylaxis: however interindividual variability in drug response and in the occurrence of adverse events is observed. Genetic variation in thiopurine S-methyltransferase (TPMT) doesn't completely explain the occurrence of all adverse events and drug response variability. The potential implication of other enzymes involved in thiopurine metabolism, such as ITPA, has been investigated over the last decade but little data is available on inosine 5'-monophosphate dehydrogenase (IMPDH) in patients treated with thiopurine drugs. The authors reported a HPLC method to determine IMPDH activity in the red blood cells (RBCs) of thiopurine-treated patients. IMPDH activity was evaluated by enzymatic conversion of inosine 5'-monophosphate (IMP) to xanthosine 5'-monophosphate (XMP). The XMP formed was analyzed on a Luna® NH2 stationary phase, a weak anion exchange phase that exhibits both ionic and hydrophobic properties. XMP was eluted below 15min. Intra-assay and inter-assay precisions were below 9% for RBCs supplemented with 2, 40 and 80μmol/L of XMP. IMPDH activity was measured in adults without thiopurine treatment as well as in adult and paediatric patients treated with thiopurines. A wide interindividual variability in IMPDH activity in RBCs was observed. No difference in IMPDH activity was found between untreated subjects and adult and paediatric patients on thiopurine therapy (median value 11.8, 7.9 and 7.7nmol XPM/g Hb/h respectively). The method described is useful in the determination of IMPDH phenotype from patients on thiopurine therapy and in the investigation of the potential relationship between IMPDH activity in RBCs and the occurrence of adverse events and drug response variability.

Evaluation and application of a targeted SPE-LC-MS method for quantifying plant hormones and phenolics in Arabidopsis.

Application of metabolomics techniques to plant physiology is now considerable, and LC-MS is often being used for non-targeted, semi-quantitative analysis of effects caused by mutations or environmental conditions. However, examination of signalling metabolites like hormones require absolute rather than semi-quantitative quantitation, since their effect in planta is strongly dependent upon concentration. Further, plant hormones belong to different chemical classes and thus simultaneous quantitation remains highly challenging. Here we present an LC-MS method that allows the simultaneous absolute quantitation of six hormone families as well as selected phenolics. The technique requires solid phase extraction with a sulfonated cation exchange phase before analysis, and use calibration curves instead of isotopically labelled standards, which are indeed not commercially available for many hormonal molecules. The use of the total signal (including adducts) rather than a single quantifying mass appears to be crucial to avoid quantification errors because the ion distribution between adducts is found to be concentration-dependent. The different hormones considered appear to have contrasted ionisation efficiency due to their physical properties. However, the relatively low variability and the satisfactory response to standard additions show that the technique is accurate and reproducible. It is applied to Arabidopsis plants subjected to water stress, using either the wild-type or lines with altered NAD biosynthesis causing changes in salicylate signalling and phenylpropanoid levels. As expected, analyses show an increase in abscisic acid upon water stress and a consistent modification of phenolic compounds (including salicylate) in mutants.

Experimental evaluation of sampling, storage and analytical protocols for measuring arsenic speciation in sulphidic hot spring waters

Recently developed analytical techniques allowed for the detection of a range of dissolved arsenic-sulphur species in sulphur-rich environments. These so called thioarsenates are unstable, however, and can degrade upon handling and storage. An experiment evaluating the effect of exposure to air on arsenic and sulphur-enriched geothermal waters demonstrated a near to complete loss of thioarsenate species to arsenite or arsenate during short oxidation times. In contrast, thioarsenic standards were stable for the duration of analysis in spite of exposure to air. For samples containing thio-methylated arsenic species, the extent of oxidation varied for different methylated arsenic species. This study recommends flash freezing of samples in liquid nitrogen immediately after recovery and further storage under anaerobic conditions at −80°C. A second experiment to test the efficiencies of different HPLC columns for separating arsenic species resulted in the preference for an IonPac column with NaOH as the mobile phase when analysing arsenic thioanions, over the commonly used PEEK PRP-X100 anion exchange and Atlantis C18 reverse phase column with ammonium phosphate mobile phases. Distinct separation of thio-methylated arsenic species with the IonPac column, however, was not successful potentially due to matrix components. Acceptable detection, separation and quantification of thio-methylated arsenic species were only achieved with the Atlantis C18 column. This study shows that preservation and analysis of samples is matrix dependent, which holds important implications for efforts to interpret arsenic speciation in geothermal waters, especially those of low pH (2–3), low oxygen (≤49% saturation), low iron (≤5mgL−1) and high sulphur concentrations (≥91mgL−1).

Insights into the spurious long-range nature of local r-dependent non-local exchange-correlation kernels.

A systematic route to go beyond the exact exchange plus random phase approximation (RPA) is to include a physical exchange-correlation kernel in the adiabatic-connection fluctuation-dissipation theorem. In the previous study [D. Lu, J. Chem. Phys. 140, 18A520 (2014)], we found that non-local kernels with a screening length depending on the local Wigner-Seitz radius, rs(r), suffer an error associated with a spurious long-range repulsion in van der Waals bounded systems, which deteriorates the binding energy curve as compared to RPA. We analyze the source of the error and propose to replace rs(r) by a global, average rs in the kernel. Exemplary studies with the Corradini, del Sole, Onida, and Palummo kernel show that while this change does not affect the already outstanding performance in crystalline solids, using an average rs significantly reduces the spurious long-range tail in the exchange-correlation kernel in van der Waals bounded systems. When this method is combined with further corrections using local dielectric response theory, the binding energy of the Kr dimer is improved three times as compared to RPA.

Long-term experiments to investigate irreversibility in sorption of pesticides to soil

Experiments investigated irreversibility in pesticide sorption to soil. Sorption behaviour under abiotic conditions was quantified for chlorotoluron, prometryn and hexaconazole in three soils over periods of up to 274 days. An isotope-exchange procedure was used whereby sorption of 12C- and 14C-pesticide isotopes in shaken suspensions of three soils (56–168 days shaking) was followed by substitution of the isotopes in the liquid phase and a 14-day exchange phase. This was followed by forced isotope exchange where the sorbed 14C material was exchanged by adding an excess of non-radiolabelled compound. Experiments were concluded with solvent extraction and soil combustion to determine remaining radioactivity. Under conditions of continuous shaking, the pesticide-soil systems took around four months to approach sorption equilibrium, resulting in strong asymmetry between the profiles of exchange for isotopes of all three compounds. Physically entrapped residues were released back into solution under the steep concentration gradient of forced isotope exchange and small amounts of radioactivity were still being released at the termination of the experiment. The profiles of exchange did not deviate markedly from ideal behaviour based on the assumption that sorption is fully reversible. Whilst the timescales for release of sorbed residues back into solution were very long, soil combustion at study termination only yielded <1–2% of applied radioactivity; this confirms that sorption processes under abiotic soil conditions were overwhelmingly reversible for this set of compounds and soils.

A Novel Unique Parameter for Increasing of Security in GPON Networks

Passive optical networks are widely used because of their sufficient bandwidth and low price of individual elements.Based on the European Commission, The Czech Republic ISPs have to ensure 30 Mbit/s (in existing networks) and 100 Mbit/s (in new constructed networks) for each customer in selected areas till 2020. Nowadays, the GPON standard is dominating in the Europe due to its low price and maturity. In general, the passive optical networks are based on P2MP (Point to Multipoint) physical topology. Therefore each end unit receives data meant for all units. To mitigate this, the standard defines an encryption method (authentication and key exchange phase) but the key exchange phase relies only on a single unique parameter (serial number of an end unit). A new unique parameter for the key exchange phase is proposed. No modification of the transmission convergence layer in GPON is considered. A measuring scheme for determining of accuracy of our new unique parameter, called Tprop, is also proposed.

Different Boosting Systems and their Control Strategies for a Spark Ignition Internal Combustion Engine

Abstract This research uses 1-D simulation in GT-Power for evaluation of boosting systems for a spark ignition engine. Exhaust gas driven (waste-gated turbocharger) and mechanical driven (Roots blower) boosting systems are assessed in both steady state and transient modes in terms of performance, efficiency, fuel consumption, drivability, energy distribution and other aspects that influence gas exchange phase. Moreover, different boost control strategies, particularly at partial load, are also evaluated. Results of the research are aimed at helping identify an optimal boosting system for standardized or real-world drive cycles.

Dynamic analysis and control strategy of wet clutches during torque phase of gear shift

Control over the clutch during gear shift is the key technique in automatic transmission shift control and this control largely decides the shift quality. The engagement of the on-coming clutch and the disengagement of the off-going clutch should be controlled synchronously and accurately to achieve a smooth shift. Optimal control of clutch torque exchange phase is required to achieve this synchronous and accurate control. Shift quality can be easily influenced with inappropriate control parameters because of the many factors that affect the torque phase, as well as the use of closed-loop control. In this study, a dynamic model of frictional clutch with electro-hydraulic shift control is built. On the basis of the study of the influence of clutch-related parameters, an optimal control model is proposed with the closed-loop control together with an adaptive control method based on micro-slip clutch control. This control method can continually self-adjust control parameters to prevent shock, improve control precision and effectively reduce the calibration work after. Test result shows that this closed loop with adaptive method ensures consistently good shift quality.

Charge ordering in Nd2/3Ca1/3MnO3: ESR and magnetometry study

The evolution of magnetic and electric properties of the narrow-band manganite Nd2/3Ca1/3MnO3 was studied by the electron-spin resonance (ESR), static magnetic field (dc) and resistivity techniques in the temperature range of 100–380K. It was found that below the charge ordering temperature, TCO≈212K, the compound is a mixture of the charge ordered and charge disordered phases in varying proportions depending on the temperature. The exchange phase process, when the amount of the charge ordered phase increases under cooling, while the amount of the charge disordered phase decreases is the most intense between ∼220K and 180K. At low temperatures, T<160K, the charge ordered to the charge disordered phase ratio is about 4:1, which is in excellent agreement with previous neutron diffraction data. Both a sharp decrease of the magnetic susceptibility and a huge resistivity increase are evident of the weakening of ferromagnetic correlations and suppression of the double exchange interaction across the charge ordering due to the localization of the charge carriers.

Isolation, structural and functional characterization of a new Lys49 phospholipase A2 homologue from Bothrops neuwiedi urutu with bactericidal potential

Snake venom is a complex mixture of active compounds consisting of 80–90% proteins and peptides that exhibit a variety of biological actions that are not completely clarified or identified. Of these, phospholipase A2 is one of the molecules that has shown great biotechnological potential. The objectives of this study were to isolate, biochemically and biologically characterize a Lys49 phospholipase A2 homologue from the venom of Bothrops neuwiedi urutu. The protein was purified after two chromatographic steps, anion exchange and reverse phase. The purity and relative molecular mass were assessed by SDS-PAGE, observing a molecular weight typical of PLA2s, subsequently confirmed by mass spectrometry obtaining a mass of 13,733 Da. As for phospholipase activity, the PLA2 proved to be enzymatically inactive. The analyses by Edman degradation and sequencing of the peptide fragments allowed for the identification of 108 amino acid residues; this sequence showed high identity with other phospholipases A2 from Bothrops snake venoms, and identified this molecule as a novel PLA2 isoform from B. neuwiedi urutu venom, called BnuTX-I. In murine models, both BnuTX-I as well as the venom induced edema and myotoxic responses. The cytotoxic effect of BnuTX-I in murine macrophages was observed at concentrations above 12 μg/mL. BnuTX-I also presented antimicrobial activity against gram-positive and negative bacterial strains, having the greatest inhibitory effect on Pseudomonas aeruginosa. The results allowed for the identification of a new myotoxin isoform with PLA2 structure with promising biotechnological applications.

Incorporation of tryptophan analogues into the lantibiotic nisin.

Lantibiotics are posttranslationally modified peptides with efficient inhibitory activity against various Gram-positive bacteria. In addition to the original modifications, incorporation of non-canonical amino acids can render new properties and functions to lantibiotics. Nisin is the most studied lantibiotic and contains no tryptophan residues. In this study, a system was constructed to incorporate tryptophan analogues into nisin, which included the modification machinery (NisBTC) and the overexpression of tryptophanyl-tRNA synthetase (TrpRS). Tryptophan and three different tryptophan analogues (5-fluoroTrp (5FW), 5-hydroxyTrp (5HW) and 5-methylTrp (5MeW)) were successfully incorporated at four different positions of nisin (I1W, I4W, M17W and V32W). The incorporation efficiency of tryptophan analogues into mutants I1W, M17W and V32W was over 97 %, while the mutant I4W showed relatively low incorporation efficiency (69–93 %). The variants with 5FW showed relatively higher production yield, while 5MeW-containing variants showed the lowest yield. The dehydration efficiency of serines or threonines was affected by the tryptophan mutants of I4W and V32W. The affinity of the peptides for the cation-ion exchange and reverse phase chromatography columns was significantly reduced when 5HW was incorporated. The antimicrobial activity of IIW and its 5FW analogue both decreased two times compared to that of nisin, while that of its 5HW analogue decreased four times. The 5FW analogue of I4W also showed two times decreased activity than nisin. However, the mutant M17W and its 5HW analogue both showed 32 times reduced activity relative to that of nisin.

A new relay attack on distance bounding protocols and its solution with time-stamped authentication for RFID

Relay attack is one of the most threatening challenges against radio frequency identification(RFID) now. Distance bounding protocols have been introduced to thwart relay attacks. They form a family of challenge-response authentication protocols and confirm the round-trip time at the Rapid Bit Exchange phase. They enable a reader to authenticate and to establish an upper bound on the physical distance to an entrusted tag. We design an effective attack against a family of such protocols to launch the spoofing attacks within effective distance successfully, which demonstrates that existing protocols cannot eliminate such attacks completely. The thesis proposes a new program with time- stamping verification to correct the defect and verify the effectiveness.

Detecting the Exchange Phase of Majorana Bound States in a Corbino Geometry Topological Josephson Junction.

A phase from an adiabatic exchange of Majorana bound states (MBS) reveals their exotic anyonic nature. For detecting this exchange phase, we propose an experimental setup consisting of a Corbino geometry Josephson junction on the surface of a topological insulator, in which two MBS at zero energy can be created and rotated. We find that if a metallic tip is weakly coupled to a point on the junction, the time-averaged differential conductance of the tip-Majorana coupling shows peaks at the tip voltages eV=±(α-2πl)ℏ/T_{J}, where α=π/2 is the exchange phase of the two circulating MBS, T_{J} is the half rotation time of MBS, and l an integer. This result constitutes a clear experimental signature of Majorana fermion exchange.

Structure, dynamical stability, and electronic properties of phases inTaS2from a high-level quantum mechanical calculation

${\mathrm{TaS}}_{2}$ is a transition-metal dichalcogenide having an exceptionally rich phase diagram, which includes exotic phenomena such as a charge density wave. We analyzed the structure, bonding, ground state, and dynamical stability of $1T, 2H$, and $3R$ phases of ${\mathrm{TaS}}_{2}$, and a commensurate charge density wave phase from the first principles. Van der Waals interaction among layers and strong electron-electron interactions were included by using the exact exchange plus random phase approximation, a high-level quantum mechanical approach. The calculated structural parameters agree well with the available experimental data. The individual sheets of ${\mathrm{TaS}}_{2}$ are bound by dispersive forces, which are stronger than dispersive forces in graphite and fluorographite. $1T\ensuremath{-}{\mathrm{TaS}}_{2}$ is dynamically unstable at low temperature, which leads to the formation of charge density wave and opening of the in-plane band gap. Anharmonic phonon-phonon interactions stabilize the $1T$ structure at elevated temperatures. The calculated phase diagram of ${\mathrm{TaS}}_{2}$ reveals that the $1T$ phase is the ground state at temperatures above 1300 K, $2H$ below this point, and the charge density wave phase becomes more stable than the perfect $1T$ structure below 480 K.

Determination of sulfonamides in beeswax by liquid chromatography coupled to tandem mass spectrometry.

The manuscript presents the development of a new method for the quantification of 16 sulfonamides in beeswax. Different sample preparation techniques were tested and modified to maximise the recovery of the target analytes and minimise the amount of coeluted impurities under conditions that provide reproducible results. The proposed method consisted of melting and dilution of beeswax in a mixture of n-hexane and isopropanol followed by extraction with 2% acetic acid. The extract was cleaned up by solid-phase extraction using strong cation exchange phase. Determination of the sulfonamides was achieved by liquid chromatography coupled to tandem mass spectrometry with the use of a pentafluorophenyl analytical column and applying a gradient elution with acetonitrile and 0.01% acetic acid as mobile phases. The limits of detection and limits of quantification ranged from 1 to 2μg/kg and from 2 to 5μg/kg, respectively. The recoveries varied between 65.2% and 117.8% while coefficient of variation of the method was less than 24.2% under intermediate precision conditions. Finally, the method was applied to the analysis of real samples of beeswax from beekeepers and commercial foundations manufacturers.