Latvian Academy of Sciences

Abstract The current understanding of the complex role of ROS in the organism and pathological sequelae of oxidative stress points to the necessity of comprehensive studies of antioxidant reactivities and interactions with cellular constituents. Studies of antioxidants performed within the COST B-35 action has concerned the search for new natural antioxidants, synthesis of new antioxidant compounds and evaluation and elucidation of mechanisms of action of both natural and synthetic antioxidants. Representative studies presented in the review concern antioxidant properties of various kinds of tea, the search for new antioxidants of herbal origin, modification of tocopherols and their use in combination with selenium and properties of two promising groups of synthetic antioxidants: derivatives of stobadine and derivatives of 1,4-dihydropyridine.

The solutions of the Hamilton-Jacobi equation and of the continuity equation for electron-atom ionization problem at zero total angular momentum are investigated in the neighbourhood of saddle points of the potential. Solutions are found which describe sets of orbits whose points of condensation coincide with the saddle points of the potential. The asymptotic behaviour of solutions corresponds to a spherically outgoing wave or to a plane wave. The energy dependence of WKB wave functions is determined and by means of a matching procedure the Wannier ionization threshold law has been confirmed. The connection between the WKB approximation and the asymptotic expansion of the zero- energy wave function has been considered.

The modified close-coupling approximation for e-H scattering is proposed, which exactly accounts for dipole and quadrupole polarization without losing the extremal properties for phase.

Some forms of asymptotic expansions are suggested for wavefunctions of charged particles scattering on systems with charge, multipole moments and inner degrees of freedom. The recurrence relations necessary for the calculations are obtained. Formulae are written for collisions of electrons with ions or atoms. The methods suggested may also be used in the investigation of collisions between other particles.

A recombinant baculovirus expressing the M2 protein from influenza A/Ann Arbor/6/60 (H2N2) virus (AA60 virus) was constructed. The expressed M2 protein was recognized by a monoclonal antibody specific for the M2 protein and comigrated with the M2 protein from cells infected with AA60 virus on SDS-polyacrylamide gels. Immunofluorescence studies indicated that the expressed M2 protein was present on the surface of Spodoptera frugiperda (Sf9) cells infected with the recombinant baculovirus. Immunoassays using the expressed M2 protein were able to detect antibodies to the M2 protein in serum samples from humans and ferrets infected with influenza A viruses.

An asymptotic method is presented for solving the problem of a hydrogen atom perturbed by a uniform electric field F considered as a weak field. An asymptotic expansion for the level width Gamma is obtained. A comparison is given of the values of Gamma obtained using the asymptotic formulae with exact numerical results.

The response of a magnetic fluid microdrop to a rotating magnetic field is studied for the first time. An unexpected shape instability is observed, leading to the formation of a spiny starfish shape that slowly corotates with the field. A simple model accounts for (i) the stability range of an oblate ellipsoidal shape that is a precursor to the starfish, (ii) the rotational frequency which is substantially lower than that of the applied magnetic field, and (iii) a lateral peak instability that is responsible for growth of the spiny arms of the starfish.

The behaviour of electronic terms and wave functions of the molecular ion H2+ for large internuclear separations is considered. Comparisons of asymptotic formulae with numerical calculations are presented.

We study a nonlocal Frenkel-Kontorova model that describes a one-dimensional chain of atoms moving in a periodic external potential and repulsing one another according to a long-range law, e.g., the power law \ensuremath{\sim}${\mathit{x}}^{\mathrm{\ensuremath{-}}\mathit{n}}$. The investigation is carried out both numerically and analytically in approximations of a weak or strong bond between atoms. Static characteristics of kinks (topological solitons) such as the effective mass, shape, and amplitude of the Peierls potential, the interaction energy of kinks, and the creation energy of kink-antikink pairs are calculated for different (exponential and power with n=1 and 3) laws of the interparticle interaction and various concentrations of atoms, i.e., ratio between the external potential period and the average spacing of atoms in the chain. The anharmonicity of the interaction potential between atoms is shown to result in differences between kink and antikink parameters, which are proportional to the value of the anharmonicity that rises with increasing exponent n of the interaction potential as well as at a changeover from a complex to a simpler unit cell. It is noted that at a power law of the interparticle repulsion this law describes also the asymptotics of the kink shape as well as the interaction energy of the kinks. Because of this, the dependence of, e.g., the amplitude of the Peierls potential versus the atom concentration, is similar to the ``devil's staircase.'' The applicability of the extended Frenkel-Kontorova model for describing diffusion characteristics of a quasi-one-dimensional layer adsorbed on a crystal surface is discussed.

Two methods of determination of the surface tension at the interface of a magnetic liquid and another fluid, in a confined two-dimensional geometry, are presented. The first is based upon a surface instability under the action of a vertical magnetic field and the second uses the deformation of a magnetic droplet in plane layer under the influence of a horizontal magnetic field. Theoretical calculations and experimental results are presented in both cases. Both determinations lead to comparable values of the surface tension $\ensuremath{\sigma}\ensuremath{\approx}3$ mN ${\mathrm{m}}^{\ensuremath{-}1}$.

OBJECTIVE: A meta-analysis was made of studies addressing occupational exposure to vinyl chloride in relation to cancer mortality. METHODS: Two recently updated multicenter cohort studies and six smaller studies were identified. For selected neoplasms, standardized mortality ratios (SMR) and 95% confidence intervals (95% CI) were abstracted (or calculated from raw data). In cases of lack of heterogeneity (P-value > or = 0.01), meta-analyses were conducted using a random-effects model. RESULTS: With SMR values ranging from 1.63 to 57.1, all six studies for which these ratios could be obtained suggested an increased risk of liver cancer. For four of these studies, excesses persisted when known cases of angiosarcoma of the liver (ASL) were excluded. The meta-SMR for liver cancers other than ASL (based on the 2 large cohorts) was 1.35 (95% CI 1.04-1.77). The meta-SMR for lung cancer was 0.90 (95% CI 0.77-1.00, based on 5 studies), although higher SMR values were reported in early studies. The meta-SMR for brain cancer, based on 5 studies, was 1.26 (95% CI 0.98-1.62). For soft tissue sarcomas, the meta-SMR based on 4 studies was 2.52 (95% CI 1.56-4.07). The meta-SMR for lymphatic and hematopoietic neoplasms in the 2 large studies was 0.90 (95% CI 0.75-1.01), although 3 of the smaller studies reported significant excesses. CONCLUSIONS: Apart from the known risk of ASL, workers exposed to vinyl chloride may experience an increased risk of hepatocellular carcinoma and soft-tissue sarcoma; however, these results may have been influenced by the underdiagnosis of true ASL. Increased mortality from lung and brain cancers and from lymphatic and hematopoietic neoplasms cannot be excluded; mortality from other neoplasms does not appear to be increased.

Using undoped hydrogenated amorphous silicon (a-Si: H) containing ND = 6.7 × 1015cm-3 native dangling bond (DB) defects we found that metastable DB defects can be created with comparable efficiency at 4.2 K and 300 K by exposure to bandgap light. This shows that the creation mechanism is not thermally activated and that only rather local changes in bonding can be involved. The dependence of the metastable defect concentration ΔND on photocarrier generation rate G at 4.2 K is G0.44, its dependence on exposure time te is tme with m = 0.35 ± 0.01 at 4.2 K, 80 K and 300 K. For a given te there are about 0.7 times fewer defects created at 4.2 K and about 0.3 times fewer at 80 K than at 300 K. Defects created at 4.2 K have a spread of relaxation barriers. About 30% of the metastable defects anneal between 150 K and 300 K, the remainder below 460 K according to subgap absorption measurements. Strong effects of metastable defects on the photoconductivity [sgrave]p and its temperature dependence were observed. ΔND = 1016cm-3 additional metastable defects decrease [sgrave]p by two to three orders of magnitude between 150 K and 300 K. The relation between ND and [sgrave]p is not single-valued. Metastable defects having small anneal energies reduce [sgrave]p more strongly than more stable defects. We discuss how the properties of the defects depend on the way they were produced.

The energy of any bound state of the hydrogen molecule ion ${\mathrm{H}}_{2}$${\mathrm{}}^{+}$ has an expansion in inverse powers of the internuclear distance R of the form Rayleigh-Schr\"odinger perturbation theory (RSPT) gives the coefficients ${E}^{(N)}$ but is otherwise unable to treat the exponentially small series, which in part are characteristic of the double-well aspect of ${\mathrm{H}}_{2}$${\mathrm{}}^{+}$. (Here n denotes the hydrogenic principal quantum number.) We develop a quasisemiclassical method for solving the Schr\"odinger equation that gives all the exponentially small subseries.The RSPT series diverges: for the ground state ${E}^{(N)}$\ensuremath{\sim}-(N+1)!/${e}^{2}$ for large N. The ${E}^{(N)}$ asymptotics are governed via a dispersion relation by the imaginary ${e}^{\mathrm{\ensuremath{-}}2R/n}$ series, which itself is given by the square of the ${e}^{\mathrm{\ensuremath{-}}R/n}$ series times a ``normalization integral.'' That the expansion itself contains imaginary terms might seem inconsistent with the reality of the ${\mathrm{H}}_{2}$${\mathrm{}}^{+}$ eigenvalues. In fact, the RSPT series is Borel summable for R complex. The Borel sum has a cut on the real R axis, and its limit from above or below the positive R axis is complex. The imaginary ${e}^{\mathrm{\ensuremath{-}}2R/n}$ (and higher) series consist of just the counterterms to cancel the imaginary part of the Borel sum.Extensive numerical examples are given. Of interest is a weak (down by a factor ${N}^{\mathrm{\ensuremath{-}}6}$) alternating-sign contribution to ${E}^{(N)}$, which is uncovered both theoretically and numerically. Also of interest is the identification of the Borel sum of the RSPT series with nonphysical boundary conditions. This too is illustrated both theoretically and numerically.

OBJECTIVES AND METHODS: Clinical features of 50 adults with diphtheritic polyneuropathy (DP) were studied in Riga, Latvia and compared with 21 patients with Guillain-Barré syndrome (GBS). RESULTS: Neurological complications occurred in 15% of patients admitted to hospital with diphtheria and usually after severe pharyngeal infection. Bulbar dysfunction occurred in 98% of patients with DP and only 10% of patients with GBS. Limb weakness was mild or absent in 30% of patients with DP. Ventilation dependent respiratory failure occurred in 20% of patients with DP. The first symptoms of DP occurred 2-50 days after the onset of local diphtheria infection. Neurological deterioration in DP continued for a median of 49 (range 15-83) days and improvement started 73 (range 20-115) days after onset. In 66% of patients with DP, the neuropathy was biphasic with a secondary worsening after 40 days. By contrast patients with GBS worsened for only 10 days on average (range 2-28 days) and improved after 21 (range 4-49) days. Eight patients with DP died, four from severe cardiomyopathy and four from multiple diphtheritic organ failure. Prolonged distal motor latencies (DMLs) were common to both DP and GBS, and more pronounced than motor conduction slowing. Limb symptoms continued after 1 year in 80% of the patients with DP, 6% were unable to walk independently, but independent respiratory and bulbar function had returned in all survivors. By comparison no patients with GBS died and none were severely disabled after 1 year. No death, in patients with DP occurred after antitoxin on days 1 or 2 after onset of diphtheria symptoms, whereas identical rates of death and peak severity of DP were seen both in those who received antitoxin on days 3-6 and those who did not receive it at all. CONCLUSION: Diphtheric polyneuropathy is much more likely than GBS to have a bulbar onset, to lead to respiratory failure, to evolve more slowly, to take a biphasic course, and to cause death or long term disability. Antitoxin seems ineffective if administered after the second day of diphtheritic symptoms.

PURPOSE: Although alcohol dependence causes marked mortality and disease burden in Europe, the treatment rate is low. Primary care could play a key role in reducing alcohol-attributable harm by screening, brief interventions, and initiating or referral to treatment. This study investigates identification of alcohol dependence in European primary care settings. METHODS: Assessments from 13,003 general practitioners, and 9,098 interviews (8,476 joint number of interviewed patients with a physician's assessment) were collected in 6 European countries. Alcohol dependence, comorbidities, and health service utilization were assessed by the general practitioner and independently using the Composite International Diagnostic Interview (CIDI) and other structured interviews. Weighted regression analyses were used to compare the impact of influencing variables on both types of diagnoses. RESULTS: The rate of patients being identified as alcohol dependent by the CIDI or a general practitioner was about equally high, but there was not a lot of overlap between cases identified. Alcohol-dependent patients identified by a physician were older, had higher rates of physicial comorbidity (liver disease, hypertension), and were socially more marginalized, whereas average consumption of alcohol and mental comorbidity were equally high in both groups. CONCLUSION: General practitioners were able to identify alcohol dependence, but the cases they identified differed from cases identified using the CIDI. The role of the CIDI as the reference standard should be reexamined, as older alcohol-dependent patients with severe comorbidities seemed to be missed in this assessment.

BACKGROUND AND PURPOSE: The intravenous use of recombinant tissue-type plasminogen activator (rTPA) in acute ischemic stroke has been investigated in three large trials. Limited series have reflected outcome after local intraarterial thrombolysis (LIT) in the cerebral territory. The purpose of this study was to evaluate the safety and efficacy of combined intraarterial/intravenous thrombolysis using rTPA (actilyse) for acute ischemic stroke. METHODS: Forty-five patients with acute onset of severe hemispheric stroke and without signs of major cerebral infarction on early CT scans were randomized by order of admission. Twelve patients were treated with 50 mg actilyse (maximal dose, 0.7 mg/kg); three had occlusion of the internal carotid artery and nine had occlusion of the middle cerebral artery. Thrombolysis was started by LIT and continued intravenously within 6 hours of stroke onset. Outcome, assessed after 1 and 12 months according to the modified Rankin scale (MRS), was considered good (MRS score, 0-3) for patients who were functionally independent and poor (MRS score, 4-5) for those who were dependent or had died. RESULTS: In the thrombolysis group, outcome was good in eight patients at 1 month and in 10 patients at 12 months; in the control group, outcome was good in seven (21%) and 11 (33%) patients, respectively. Of the eight patients with a good outcome after thrombolysis, four had complete and one had partial recanalization. In the control group, the rate of intracerebral hemorrhage was 6%. Mortality at 1 month in the thrombolysis and control groups was 17% and 48%, respectively. CONCLUSIONS: Combined intraarterial/intravenous thrombolysis with low-dose rTPA may be a safe and effective treatment for acute ischemic stroke within 6 hours in carefully selected patients.

Periodic branched columns are observed for the first time in a layer of phase-separated magnetic colloid confined in a cell. The periodicity \ensuremath{\lambda} scales with the layer thickness L. In the thin limit, where no branching occurs, \ensuremath{\lambda}\ensuremath{\propto}${\mathit{L}}^{1/2}$. In the thick limit, each column develops a tree structure with branches and roots, and the columns are separated by shrubs while the scaling relation crosses over to \ensuremath{\lambda}\ensuremath{\propto}${\mathit{L}}^{2/3}$.

Small-angle neutron scattering is used to measure the two-dimensional diffraction pattern of a monophasic magnetic colloid, under an applied magnetic field. This dipolar system presents in zero field a fluidlike structure. It is well characterized by an interaction parameter K(0)(T) proportional to the second virial coefficient, which is here positive, expressing a repulsion of characteristic length kappa-10. Under the field a strong anisotropy is observed at the lowest q vectors. The length kappa-10 remains isotropic, but the interaction parameter K(T) becomes anisotropic due to the long-range dipolar interaction. However, the system remains stable, the interaction being repulsive in all directions. Thus we do not observe any chaining of the nanoparticles under magnetic field. On the contrary, the revealed structure of our anisotropic colloid is a lowering of the concentration fluctuations along the field while the fluidlike structure, observed without field, is roughly preserved perpendicularly to the field. It expresses a strong anisotropy of the Brownian motion of the nanoparticles in the solution under applied field.

Diffusion processes in a magnetic colloid are studied by a forced Rayleigh scattering technique under an applied static magnetic field. A periodic spatial modulation of the particle concentration (transient grating) is induced in the colloid with three different field geometries, B being either parallel or perpendicular to the grating direction. The value of the translational diffusion coefficient of the particles is given by the transient grating relaxation time. It depends on the magnetic field strength and on the field geometry. A theoretical model based on a mean field approximation taking magnetic interactions of particles under a field into account is given which agrees with experimental results.

The electric properties of the neutron have been deduced from precise measurements of coherent scattering lengths and of total cross sections of Pb, of its isotopes with A=208, 207, and 206, and of Bi. Their energy dependences are due to nuclear properties, to nuclear and atomic charges as well as to the neutron's electric polarizability and to the neutron-electron interaction. We investigated in detail the different evaluations used in the past by German and Russian scientist groups. By means of both data handling methods we found consistent results of ${\mathrm{\ensuremath{\alpha}}}_{\mathit{n}}$=(0.0\ifmmode\pm\else\textpm\fi{}0.5)${10}^{\mathrm{\ensuremath{-}}3}$ ${\mathrm{fm}}^{3}$ for the electric polarizability and of ${\mathit{b}}_{\mathit{n}\mathit{e}}$=-(1.32\ifmmode\pm\else\textpm\fi{}0.03)${10}^{\mathrm{\ensuremath{-}}3}$ fm for the neutron-electron scattering length. This result agrees with quark-core models of the neutron.