Flow injection analysis methods for determination of diffusion coefficients

Two flow injection analyses (FIA) methods for the determination of diffusion coefficients in a straight single tube FIA system were developed. Based on the analytical solution of the convection-diffusion equation, linear relationships of the logarithmic values of the dispersion coefficient (D) and the half-peak width (W_1/2) with the diffusion coefficient (D_m) were obtained. Experiments were designed to verify these methods. For example, for potassium hexacyanoferrate (III) a D_m value of 0.72 × 10⁵ cm² s⁻¹ was found versus a literature value of 0.76 × 10⁵ cm² s⁻¹ (error, 5%). For potassium hexacyanoferrate (II) a D_m value of 0.67 × 10⁵ cm² s⁻¹ was obtained versus a literature value of 0.63 × 10⁵ cm² s⁻¹ (error, 6%). The diffusion coefficients of some important biomedical compounds, such as dopamine, epinephrine, norepinephrine and ascorbic acid, were then determined. The values of 10⁵ D_m/cm² s⁻¹ are 0.60 ± 0.03, 0.44 ± 0.02, 0.60 ± 0.01 and 0.68 ± 0.06, respectively.     

Water diffusion in polyethylene modified by ion irradiation

Water diffusion in polyethylene (PE) modified by irradiation with 40keV Ar⁺ ions to fluences of 1 × l0¹² to 1 × l0¹⁵cm⁻² was studied. The diffusion experiments were performed in a temperature interval from 25 to 100 °C and for diffusion times of up to 3 h. The water incorporated was detected by infra-red spectroscopy, microgravimetry and by measuring contact angles. Maximum water uptake observed for the ion fluence of 1 × 10¹³cm⁻² may be connected with an increase in free volume fraction and oxidative processes in the PE surface layer modified by ion irradiation. For higher ion fluences, the available free volume is reduced owing to carbonization and crosslinking of the polymer and, accordingly, the water content decreases. The water incorporated in PE is mostly in the form of isolated molecules. At elevated temperature rediffusion of water is observed.     

Effect of dose rate of gamma irradiation on biochemical quality and browning of mushrooms Agaricus bisporus

In order to enhance the shelf-life of edible mature mushrooms Agaricus bisporus, 2 kGy ionising treatments were applied at two different dose rates: 4.5 kGy/h (I⁻) and 32 kGy/h (I⁺). Both I⁺ and I⁻ showed 2 and 4 days shelf-life enhancement compared to the control (C). Before day 9, no significant difference (p>0.05) in L^* value was detected in irradiated mushrooms. However, after day 9, the highest observed L^* value (whiteness) was obtained for the mushrooms irradiated in I⁻. Analyses of phenolic compounds revealed that mushrooms in I⁻ contained more phenols than I⁺ and C, the latter containing the lower level of phenols. The polyphenol oxidase (PPO) activities of irradiated mushrooms, analysed via catechol oxidase and dopa oxidase substrates, resulted in being significantly lowered (p0.05) compared to C, with a further decrease in I⁺. Analyses of the enzymes indicated that PPO activity was lower in I⁺, contrasting with its lower phenol concentration. Ionising treatments also increased significantly (p0.05) the phenylalanine ammonia-lyase (PAL) activity. The observation of mushrooms cellular membranes, by electronic microscopy, revealed a better preserved integrity in I⁻ than in I⁺. It is thus assumed that the browning effect observed in I⁺ was caused by both the decompartimentation of vacuolar phenol and by the entry of molecular oxygen into the cell cytoplasm. The synergetic effect of the residual active PPO and the molecular oxygen, in contact with the phenols, allowed an increased oxidation rate and, therefore, a more pronounced browning in I⁺ than in I⁻.     

Electron delocalization of metal electrons in Fe complexes by positronium spin conversion reactions

The rate constants, k_CR, of conversion reactions, CR, of ortho- into para-positronium atoms promoted by 3d paramagnetic complexes of V^II, Cr^II, Cr^III, Mn^II, Co^II and Ni^II ions are linearly correlated with the electron delocalization β caused by the ligands. β's may be evaluated by means of the empirical equation β=1−th, where t and h are constants characteristic of the ion and ligands, respectively. The determination of the unknown t(Fe^II) value is here described. It was derived by means of the rate constants of the CR caused by some Fe^II complexes. It was found that t(Fe^II)=0.14±0.01. A relationship between t and the oxidation number of the metal ions is suggested.     

On the multiple peaks in charge-transfer probability versus laser frequency in the theory of laser assisted surface ion neutralization

Some aspects of the theory of LASIN (laser assisted surface ion neutralization) are discussed, with emphasis on the physical origins of the so-called double-peak structures found in some calculations of the charge-transfer (neutralization) probability, P, as a function of the laser frequency η. These two peaks have been called the first peak at η ≈ η_m = _O − _m (in a.u.), where _o(_m) is the electronic energy level of the ion/atom (middle of the solid's valence band) and the second peak, a much larger peak at η ≈ 1.3 η_m, respectively.

We show that these double-peak structures are all special cases of multiple-peak structures which result from quantum interference effects, and that, in fact, the second peak is to be regarded as the main resonance peak. This result is interesting in itself, because it is the first peak which has heretofore been considered the main resonance peak.

To simplify the discussion, a two-level model is adapted, which represents the solid valence band by a single level at _m. Clarification of the physical reason for the multiple peaks is based on the semiclassical theory of nonadiabatic transitions, in which the peaks are due to the phase difference between the two adiabatic paths that arise from the diagonalization of the two-level hamiltonian.

With the electronic hopping potential modelled by V(t) = V_osech(λt), and the laser potential by W(t) = W_osech(λt) cos(πt + δ), in the usual notation, an approximate analytical expression for P(η) is presented for the case W_o/V_o < 1, which covers most of the previous treatments, and is in good agreement with the exact results.     

Recent progress of high-power negative ion beam development for fusion plasma heating

A negative-ion-based neutral beam injector (N-NBI) has been constructed for JT-60U. The N-NBI is designed to inject 500 keV, 10 MW neutral beams using two ion sources, each producing a 500 keV, 22 A D⁻ ion beam. In the preliminary experiment using one ion source, a D⁻ ion beam of 13.5 A has been successfully accelerated with an energy of 400 keV (5.4 MW) for 0.12 s at an operating pressure of 0.22 Pa. This is the highest D⁻ beam current and power in the world. Co-extracted electron current was effectively suppressed to the ratio of Ie/I_D⁻ < 1. The highest energy beam of 460 keV, 2.4 A, 0.44 s has also been obtained. To realize 1 MeV class NBI system for ITER (International Thermonuclear Experimental Reactor), demonstration of ampere class negative ion beam acceleration up to 1 MeV is an important mile stone. To achieve the mile stone, a prototype accelerator and a 1 MV, 1 A test facility called MeV Test Facility (MTF) were constructed. Up to now, an H⁻ ion beam was accelerated up to the energy of 805 keV with an acceleration drain current of 150 mA for 1 s in a five stage electrostatic multi-aperture accelerator.     

The first measured Ag I, Ag II and Ag III Stark broadening parameters

The Stark widths (W) and shifts (d) of two neutral (520.908 and 546.550 nm), eleven singly (211.382, 224.643, 224.874, 232.029, 232.468, 233.140, 241.141, 241.323, 243.781, 244.793 and 276.754 nm) and three doubly (216.189, 231.004 and 239.569 nm) ionized silver (Ag I, Ag II and Ag III, respectively) spectral lines have been measured in nitrogen plasma at about 18,000 K electron temperature and electron density ranged between 0.65 × 10²³ and 1.15 × 10²³ m^− 3. They are the first measured W and d values while those of the Ag II and Ag III lines are the first published data in these spectra. The modified version of the linear, low-pressure, pulsed arc was used as a plasma source operated in nitrogen with silver atoms, as impurities, evaporated from silver cylindrical plates located in the homogeneous part of the discharge. No theoretical predictions exist for W and d values of above mentioned spectral lines. Besides, we have checked the transition probability ratio of two investigated Ag I lines. An agreement with theoretical predictions was found.     

Predicted radiolysis yield in a Fricke solution irradiated with various heavy ions

Experimental data on the spatial distribution of the energy deposited around an energetic heavy ion, from 1 MeV proton to 5.9 MeV/n uranium ion, which have been reported in the literature were documented to obtain a scaled radial dose distribution; (β/Z*)² D(Z*, β,t)=200 (for t=0–1), 200/t² (for t=1t_c), and 200 t_c/t³ (for t>t_c) where Z* and β are the effective charge and velocity relative to c, the velocity of light, of the incident ion, respectively, D the dose in unit of Gy, t the radial distance in unit of nm, t_c the critical distance empirically determined.

Then, if we know the yield of any chemical reaction as a function of dose from the results of experiments using γ-radiations or fast electrons or theoretical calculations, we can calculate the probability for the yield of the chemical reaction in the system bombarded with a heavy ion of the effective charge Z* and velocity β. The results of the present calculation of the LET-values and of G(Fe³⁺) in the ferrous sulfate acidic solution are presented and compared with reported experimental results.     

The compton defect in ammonia as observed using 35 keV incident electrons

Using a 35 keV electron beam incident on NH₃, precision measurements of the energy loss position of the Compton peak have been performed. The observed Compton peak is found to be at larger energy losses than predicted for an electron scattered through the same angle from a stationary unbound electron. This defect has been studied for the momentum transfer range 0.5 au < K < 11 au, and is shown to be nonzero even at large K values. A sudden increase in the magnitude of the defect is observed when the inner electrons start contributing to the maximum of the Compton profile. This could suggest the possibility that the defect is related to the binding energies of the target electrons.     

Energetic distribution of the electrons from a 200 keV beam in polyurethane layers : EGS4 calculation and FTIR analysis

The aim of this study is to characterize the chemical transformation of a polymer resulting from irradiation by a 200 keV electron beam. Thermoplastic PU polyetherurethane material was used and irradiation was performed with applied electron fluences in the range of 10¹⁴–10¹⁷ electron cm⁻² at 77 K.

The chemical changes have been observed by FTIR analysis of irradiated layers. A NH bond evolution study has allowed us to follow polymer degradation versus depth and fluence. The results have been compared to a simulation of electronic energy loss and to the energy spectrum of the generated electrons in the polymer using EGS4 code.     

聚-4-乙基苯酚抗氧剂对聚丙烯结晶行为的影响

通过差示扫描量热仪(DSC)和X射线粉末衍射仪(XRD)研究了聚-4-乙基苯酚抗氧剂对聚丙烯结晶行为的影响。 分别用Jeziorny法和Mo法处理非等温结晶动力学。 同时用Friedman法和Kissinger法计算其结晶活化能。 最后由结晶活化能与结晶温度的变化曲线求得Hoffman-Lauritzen参数成核速率常数(K_g)和迁移活化能(U^*)值,进而求得折叠链端表面自由能(σ_e)和分子链段折叠功(q)。 结果表明,抗氧剂的加入,使聚丙烯的结晶峰温度向低温区移动,结晶半峰宽变大,半结晶时间(t_1/2)增大,Jeziorny法所得的结晶速率常数(Z)降低,Mo法所得反映结晶速率快慢的参数F(T)提高,在相同结晶转化率下,结晶活化能负值变小。 Hoffman-Lauritzen参数K_g、U^*、σ_e和q值均增大。 所有变化均表明聚-4-乙基苯酚抗氧剂对PP的结晶有抑制作用。     

Pyrolysis of N-acryloyl, N′cyanoacetohydrazide and its polymer

The rate of the gas-phase thermolysis of N-acryloyl, N′acetohydrazide has been measured in the gas phase in the range 482–517 K. This is believed to be a first order elimination reaction for which log A = 10.8 s⁻¹ and the activation energy E_n = 132 kJ mol⁻¹. Product analysis for the monomer and polymer were used for the elucidation of the thennolysis mechanism. It has been concluded that pyrolysis of the polymer occurs by depolymerization reaction followed by the pyrolysis of the monomer produced.     

TEMPO-initiated oxidation of 2-aminophenol to 2-aminophenoxazin-3-one

The oxidation reaction of 2-aminophenol (OAP) to 2-aminophenoxazin-3-one (APX) initiated by 2,2,6,6-tetramethyl-1-piperidinyloxyl (TEMPO) has been investigated in methanol at ambient temperature. The oxidation of OAP was followed by electronic spectroscopy and the rate constants were determined according to the rate law −d[OAP]/dt=k_obs[OAP][TEMPO]. The rate constant, activation enthalpy and entropy at 298 K are as follows: k_obs (dm³ mol⁻¹ s⁻¹)=(1.49±0.02)×10⁻⁴, E_a=18±5 kJ mol⁻¹, ΔH^‡=15±4 kJ mol⁻¹, ΔS^‡=−82±17 J mol⁻¹ K⁻¹. The results of oxidation of OAP show that the formation of 2-aminophenoxyl radical is the key step in the activation process of the substrate.     

Kinetic study of a thermal dechlorination and oxidation of neodymium oxychloride

This study investigated the kinetics of a thermal dechlorination and oxidation of neodymium oxychloride (NdOCl) by using a non-isothermal thermogravimetric (TG) analysis under various oxygen partial pressures. The results of the isoconversional analysis of the TG data suggests that the dechlorination and oxidation of NdOCl follows a single step reaction and the observed activation energy was determined as 228.3 ± 6.1 kJ mol⁻¹. A kinetic rate equation was derived for a conversion of the NdOCl into Nd₂O₃ with a power law model, f() = 2/3^−1/2. The oxygen power dependency and the pre-exponential factor were determined as 0.315 and 3.55 × 10⁵ s⁻¹ Pa^−0.315, respectively.     

Dynamics of electronic polarization in molecular crystals

Dynamics of electronic polarization in the vicinity of charge carriers in molecular crystals is for the first time investigated here in connection with the carrier transport and intramolecular vibronic polarization. According to standard picture it has been assumed that the electronic polarization relaxation time is extremely short, as estimated from the relation τ_c = τ_d1 ≈ h/E_exc, where E_exc is the energy of the first single exciton state. In the case of anthracene (Ac) crystals, the value of τ_e is about 2 × 10⁻¹⁶ s, i.e. by several orders of magnitude shorter than a typical hopping (residence) time of charge carriers τ_h = 10⁻¹⁴ -10⁻¹³ s. It is argued that typical time of full reconstruction of the electronic polarization after individual carrier hops equals, in the slow carrier regime, approximately to t_d2 ≈ h/ΔE_exc is the width of the lowest singlet-exciton band. In Ac, this means t_d2 ≈ 0.73 × 10⁻¹⁴ s. Physical implications of this relatively high value of t_d2 in connection with carrier transport and molecular (vibronic) polarization are discussed.     

The mean-free-path of monochromatic hadronic axions

We have calculated the mean-free-path (mfp) of near-monochromatic hadronic axions produced in the solar core during M1 transitions between the first, thermally excited state of ⁵⁷Fe, at 14.4 keV, and the ground state. Solar absorption of axions of mass 1 keV has been found to be insignificant (<10⁻⁷) with the implication of free escape from the solar interior.     

Direct evaluation of meat spoilage and the progress of aging using biosensors

A direct sensing method for monitoring meat quality was developed. The sensor is composed of an Ag/AgCl electrode and a platinum electrode on which putrescine oxidase or xanthine oxidase were immobilized to estimate bacterial spoilage or the progress of aging, respectively. A potential-step chronoamperometric method was applied in which the potential was stepped from 300 mV to 600 mV. A linear relationship was obtained between 5 and 60 nmol g⁻¹ for putrescine (Put) and 0.05 and 1.0 μmol g⁻¹ for hypoxanthine (Hx). The coefficient of variation was 0.75% for 20 nmol ml⁻¹ Put solution and 2.2 for a meat sample using the putrescine sensor, and 1.09% for 0.25 μmol ml⁻¹ Hx solution and 2.6% for a meat sample using the xanthine sensor. The pH requirements and substrate selectivity were suitable for the direct measurement of substrates on the surface of meat. From the results of practical experiments, the direct sensing method was indicated to be useful with some modifications for the estimation of meat quality during aging.     

Electrokinetic characterization of a microporous non-commercial polysulfone membrane: phenomenological coefficients and transport parameters

Electrical and electrokinetic phenomena (electrical resistance, streaming potential and membrane potential) in a porous polysulfone membrane was studied in the framework of the linear thermodynamics of irreversible processes and the phenomenological coefficients were determined for different concentrations of NaCl and MgCl₂ solutions (10⁻³M<5×10⁻²M). From experimental values, other characteristic membrane parameters such as the concentration of fixed charge in the membrane (=−3×10⁻³M), the ionic transport numbers and permeabilities through the membrane (t(Na⁺)=0.392 and t(Mg⁺²)=0.363; P(Na⁺)=3.5×l0⁻⁸m/sec and P(Mg⁺²)=2.9×10⁻⁸m/sec) were also obtained. Membrane surface-electrolyte solution interface was characterized by zeta potential values. The effect of both salt concentration and pH on zeta potential results was also studied.     

Phosphorescence of biacetyl sensitized by benzene in gas phase pulse radiolysis

The phophorescence of biacetyl induced by an energy transfer to biacetyl from triplet benzene produced in the pulse radiolysis of benzene-biacetyl mixtures has been studied. The time required to reach the maximum intensity of phosphorescence, t_max, after the electron pulse, varies as a function of biacetyl pressure at constant benzene pressure (40 torr), which gives the lifetime of triplet benzene τ = (6.7 ± 3.2) × 10⁻⁶ s and the rate constant of the energy transfer k_{C6H6^*(T1) + biacetyl} = (1.6 ± 0.7) × 10⁻¹⁰ cm³ molecule⁻¹ s⁻¹.