Biomedical subjects

Hans Agren

Publications and source records attributed to Hans Agren.

At least 19 recordsLinked to original sources

PubMed2006

Detection of major depression in Ugandan primary health care settings using simple questions from a subjective well-being (SWB) subscale.

OBJECTIVE: To explore whether the 4-item subjective well-being subscale could be used to detect a major depressive illness. Secondly, to describe the prevalence and characteristics of depressed health care attendees at primary healthcare centres. METHOD: Using a descriptive, cross-sectional study design, we interviewed 199 consecutive patients about their socio-demographics, subjective well-being (SWB), major depressive illness symptoms and depression severity. The instruments used were translated into Luganda. RESULTS: Point prevalence of a current Major Depressive Episode (MDE) was 31.6%. Using a one week reference period, we found that experiencing a lot of distress, having less energy or poor health, having poor emotional and psychological adjustment and not being satisfied with life were significantly more common among patients with a current MDE. The 4-item SWB subscale detected depression of up to 87.1% (95% CI: 0.818-0.923). In logistic regression, all four SWB items predicted a current MDE. CONCLUSION: Major depressive illness is a common at primary healthcare level in Uganda. Four simple questions reflecting SWB items have potential to detect diagnosable patients likely to have a current MDE, making general screening procedures less necessary.

Adolescent↗

PubMed2006

Theoretical simulations of clamping levels in optical power limiting.

Multiphysics modeling, combining quantum mechanical and classical wave mechanical theories, of clamping levels has been performed for a platinum(II) organic compound in a sol-gel glass matrix. A clamping level of 2.5 microJ is found for a pulse duration of 10 ns. The excited-state absorption in the triplet manifold is shown to be crucial for clamping to occur.

Journal Article↗

PubMed2006

Density functional theory study of vibronic structure of the first absorption Qx band in free-base porphin.

Harmonic vibrational frequencies and vibronic intensities in the first S(0)-->S(1) (pipi( *)) absorption band of free-base porphin (H(2) P) are investigated by hybrid density functional theory (DFT) with the standard B3LYP functional. The S(0)-S(1) transition probability is calculated using time-dependent DFT with account of Franck-Condon (FC) and Herzberg-Teller (HT) contributions to the electric-dipole transition moments including displacements along all 108 vibrational modes. Two weak wide bands observed in the gas phase absorption spectra of the H(2) P molecule at 626 and 576 nm are interpreted as the 0-0 band of the X(1) A(g)-->1B(3u) transition and the 0-1 band with largest contributions from the nu(10)(a(g))=1610 cm(-1) and nu(19)(b(1g))=1600 cm(-1) modes, respectively, in agreement with previous tentative assignments. Both bands are induced by the HT mechanism, while the FC contributions are negligible. A number of fine structure bands, including combination of two vibrational quanta, are obtained and compared with available spectra from supersonic jet and Shpolskij matrices. Both absorption and fluorescence spectra are interpreted on ground of the linear coupling model and a good fulfillment of the mirror-symmetry rule.

Chemical Phenomena↗

PubMed2006

Origin invariant approaches to the calculation of two-photon circular dichroism.

The origin dependence of the expression of two-photon circular dichroism in the length formulation employed by the authors in a recent computational study [B. Jansik et al., Chem. Phys. Lett. 414, 461 (2005)] is discussed in detail, and some inherently origin invariant alternative formulations are introduced. Extensive computational tests on a small reference chiral system, namely, a chiral form of H(2)O(2), are performed at the density functional theory (DFT)/B3LYP level of theory with large diffuse correlation consistent basis sets. The results indicate that the velocity formulation originally proposed by Tinoco, Jr. [J. Chem. Phys. 62, 1006 (1975)] provides the most convenient approach for an origin invariant calculation of two-photon circular dichroism.

Journal Article↗

PubMed2006

Hydrogen bonding effects on infrared and Raman spectra of drug molecules.

Infrared and Raman spectra of three drug molecules, aspirin, caffeine and ibuprofen, in gas phase and in aqueous solution have been simulated using hybrid density functional theory. The long range solvent effect is modelled by the polarizable continuum model, while the short range hydrogen bonding effects are taken care of by the super-molecular approach with explicit inclusion of water molecules. The calculated spectra are found to compare well with available experimental results. The agreement obtained make grounds for proposing theoretical modeling as a tool for characterizing changes in the bonding environments of drug molecules in terms of particular variations in their IR and Raman spectra.

Aspirin↗

PubMed2006

Optical properties of two-dimensional negative-phase-velocity-medium photonic crystals.

By an extended plane-wave-based transfer-matrix method, the photonic band structure and the corresponding transmission spectrum have been calculated for a two-dimensional photonic crystal composed of negative-phase-velocity-medium (NPVM) cylindrical rods. Dispersionless anticrossing bands in the two-dimensional NPVM periodic structure are generated by the couplings among surface polaritons localized in the NPVM rods. In part of the negative-phase-velocity frequency region, the photonic band structures of the NPVM photonic crystal are characterized by a topographical continuous dispersion relationship accompanied by many anticrossing bands. The effect of the filling fraction of the NPVM rods on the optical properties of photonic crystals has also been studied.

Journal Article↗

PubMed2006

Solvation of N3- at the water surface: the polarizable continuum model approach.

We present a new quantum mechanical model to introduce Pauli repulsion interaction between a molecular solute and the surrounding solvent in the framework of the Polarizable Continuum Model. The new expression is derived in a way to allow naturally for a position-dependent solvent density. This development makes it possible to employ the derived expression for the calculation of molecular properties at the interface between two different dielectrics. The new formulation has been tested on the azide anion (N3-) for which we have calculated the solvation energy, the dipole moment, and the static polarizability at the interface as a function of the ion position. The calculations have been carried out for different ion-surface orientations, and the results have also been compared with the parallel electrostatic-only solvation model.

Models, Theoretical↗

PubMed2006

Molecular dynamics simulations applied to electric field induced second harmonic generation in dipolar chromophore solutions.

Electric field induced second harmonic generation (EFISH) is an important experimental technique in extracting the first hyperpolarizability of an organic chromophore molecule. Such experiments are carried out in solutions with chromophore molecules dissolved in some common solvents. A known fact is that the first hyperpolarizabilities extracted from EFISH experiments are subject to the use of local field factors. In this work, we apply simulations to study the EFISH properties of chromophore solutions. By combining quantum chemistry calculations with the results derived from molecular dynamics simulations, we show how macroscopic EFISH properties can be modeled, using 4-(dimethylamino)-4'-nitroazobenzene dissolved in chloroform as a demonstration case. The focus of the study is on deriving accurate local field factors. We find that the local field approach applies very well to dipolar solutions, such as the one studied here, but that the local field factors derived are much smaller than the commonly used Onsager or Lorentz local field factors. Our study indicates that many of the reported first hyperpolarizabilities for dipolar molecules from EFISH experiments are most probably underestimated because the Onsager/Lorentz approach, commonly used in extracting the molecular first hyperpolarizability, neglects the effects of the shapes of dipolar chromophore molecules on the local field factors.

Journal Article↗

PubMed2006

Time-dependent density functional theory with the generalized restricted-unrestricted approach.

This work presents the derivation, implementation, and first applications of the generalized restricted-unrestricted method based on the density functional Kohn-Sham formalism. By using a spin-restricted Kohn-Sham representation for the reference state the well-known spin contamination problem is avoided, while the unrestricted representation of the perturbation response retains a proper description of spin polarization. The formulation is a generalization of our previous implementation of the restricted-unrestricted method [Z. Rinkevicius et al., J. Chem. Phys. 121, 7614 (2004)], as it accounts for the full unrestricted response instead of describing the spin polarization in terms of triplet operators only. The purpose of this paper is to investigate the role of the generalization employed and demonstrate its numerical performance. For this purpose we focus on isotropic hyperfine coupling constants of a set of organic radicals and transition metal compounds. For both classes of molecules we observe that the effect of neglecting singlet excitation operators in the response part of restricted-unrestricted formalism changes the calculated hyperfine coupling parameters by a few MHz. The obtained results confirm the validity of the approximation used in the simplified restricted-unrestricted approach, i.e. spin polarization can, in most cases, be adequately described by an account of only triplet operators in the response term.

Journal Article↗

PubMed2006

Quantum-classical modeling of nonlinear pulse propagation in a dissolved two-photon active chromophore.

In the present work we outline the implications of a quantum-classical approach for modeling two-photon absorption of organic chromophores in solution. The approach joins many-photon absorption dynamic simulations with quantum chemical first principles calculations of corresponding excitation energies and transition matrix elements. Among a number of conclusions of the study, we highlight three: (i) The use of either short- or long-pulse excitation is demonstrated to switch the absorptive capacity of the nonlinear medium owing to enhancement of the nonlinear stepwise processes; (ii) The two-photon cross section strongly depends on the way in which the dephasing rate decays when the laser frequency is tuned off-resonant with the corresponding molecular transition; (iii) The results of the pulse propagation simulations based on electronic structure data obtained with a new Coulomb attenuated functional is shown to be in much better agreement with the experimental results than those based on data received with traditional density functionals.

Absorption↗

PubMed2006

Evaluation of low-scaling methods for calculation of phosphorescence parameters.

In order to find a methodology that is a compromise between favorable computational scaling and tolerable errors, a series of nonrelativistic approaches for the calculation of radiative phosphorescence lifetimes are benchmarked against fully relativistic four-component results. The study of the a 3A2-X 1A1 transition intensity in the series of H2CX molecules, where X is a chalcogene atom, X={O,S,Se,Te}, indicates a general good agreement between fully relativistic four-component and nonrelativistic perturbation-theoretical calculations. Among the nonrelativistic approaches, the scaled-charge spin-orbit operator approach is recognized as to provide transition matrix elements that are in good agreement with those obtained with the more elaborate Breit-Pauli and atomic mean field spin-orbit operators. This finding supports phosphorescence calculations using the available linear scaling technology for large complexes and, together with effective-core potentials, large complexes including heavy elements.

Journal Article↗

PubMed2006

A longitudinal study of PTSD in a sample of adult mass-evacuated Kosovars, some of whom returned to their home country.

PTSD among a sample of mass-evacuated adults from Kosovo was studied using a prospective design with a baseline study and follow-ups at 3 and 6 months in Sweden, and with an additional follow-up after 1.5 years in both Sweden and Kosovo. Trauma events and PTSD-related symptoms were measured by the Harvard Trauma Questionnaire (HTQ). At the additional follow-up after 1.5 years the same measure (HTQ) was used as well as clinical diagnostic interviews with the SCID instrument and measurement of saliva cortisol levels. Thirty-seven percent had PTSD-related symptoms at baseline. Morbidity increased at the three follow-ups. About 80% of the participants had PTSD at the additional follow-up after 1.5 years. The HTQ results were confirmed by clinical diagnoses and the participants diagnosed with PTSD also had low saliva cortisol levels. The results are discussed in terms of trauma, time needed to develop PTSD, post-migration stress and selection mechanisms.

Adolescent↗

PubMed2006

Effects of conjugation length, electron donor and acceptor strengths on two-photon absorption cross sections of asymmetric zinc-porphyrin derivatives.

Exceptionally large two-photon absorption cross sections at the infrared region have been revealed by time-dependent density functional theory calculations for asymmetric charge-transfer conjugated zinc-porphyrin derivatives. The largest two-photon cross section is found to be more than one order of magnitude larger than for the conventional two-photon active organic molecules. The calculations show that the formation of strong charge-transfer states depends on the length of the conjugation bridge between the zinc-porphyrin core and the electron donor/acceptor. The two-photon absorption cross section can be greatly enhanced by increasing the strengths of the electron donor/acceptor.

Electrons↗

PubMed2006

Mood changes correlate to changes in brain serotonin precursor trapping in women with premenstrual dysphoria.

The cardinal mood symptoms of premenstrual dysphoria can be effectively treated by serotonin-augmenting drugs. The aim of the study was to test the serotonin hypothesis of this disorder, i.e. of an association between premenstrual decline in brain serotonin function and concomitant worsening of self-rated cardinal mood symptoms. Positron emission tomography was used to assess changes in brain trapping of 11C-labeled 5-hydroxytryptophan, the immediate precursor of serotonin, in the follicular and premenstrual phases of the menstrual cycle in eight women with premenstrual dysphoria. Changes in mood and physical symptoms were assessed from daily visual analog scale ratings. Worsening of cardinal mood symptoms showed significant inverse associations with changes in brain serotonin precursor trapping; for the symptom "irritable", r(s)=-0.83, and for "depressed mood" r(s)=-0.81. Positive mood variables showed positive associations, whereas physical symptoms generally displayed weak or no associations. The data indicate strong inverse associations between worsening of cardinal symptoms of premenstrual dysphoria and brain serotonin precursor (11C-labeled 5-hydroxytryptophan) trapping. The results may in part support a role for serotonin in premenstrual dysphoria and may provide a clue to the effectiveness of serotonin-augmenting drugs in this disorder but should, due to small sample size and methodological shortcomings, be considered preliminary.

5-Hydroxytryptophan↗

PubMed2006

Model to assess the cost-effectiveness of new treatments for depression.

OBJECTIVES: The objective of this study was to develop a model to assess the cost-effectiveness of a new treatment for patients with depression. METHODS: A Markov simulation model was constructed to evaluate standard care for depression as performed in clinical practice compared with a new treatment for depression. Costs and effects were estimated for time horizons of 6 months to 5 years. A naturalistic longitudinal observational study provided data on costs, quality of life, and transition probabilities. Data on long-term consequences of depression and mortality risks were collected from the literature. Cost-effectiveness was quantified as quality-adjusted life-years (QALYs) gained from the new treatment compared with standard care, and the societal perspective was taken. Probabilistic analyses were conducted to present the uncertainty in the results, and sensitivity analyses were conducted on key parameters used in the model. RESULTS: Compared with standard care, the new hypothetical therapy was predicted to substantially decrease costs and was also associated with gains in QALYs. With an improved treatment effect of 50 percent on achieving full remission, the net cost savings were 20,000 Swedish kronor over a 5-year follow-up time, given equal costs of treatments. Patients gained .073 QALYs over 5 years. The results are sensitive to changes in assigned treatment effects. CONCLUSIONS: The present study provides a new model for assessing the cost-effectiveness of treatments for depression by incorporating full remission as the treatment goal and QALYs as the primary outcome measure. Moreover, we show the usefulness of naturalistic real-life data on costs and quality of life and transition probabilities when modeling the disease over time.

Cost-Benefit Analysis↗

PubMed2006

Efficacy and tolerability of reboxetine compared with citalopram: a double-blind study in patients with major depressive disorder.

The objective of this study was to compare efficacy and tolerability of the selective noradrenaline reuptake inhibitor reboxetine with the selective serotonin reuptake inhibitor citalopram, in the treatment of major depressive disorder (MDD). In total, 357 outpatients with MDD were randomized to treatment with reboxetine 8-10 mg or citalopram 20-40 mg per day during 24 weeks. Primary end-point was change from baseline in the Hamilton Depression Rating Scale (HAM-D, 21 items). Sexual function/dysfunction was measured by the Sexual Function scale (SF). Observed case analysis showed that both treatments yielded a gradual reduction of HAM-D scores: reboxetine with -21.4 and citalopram with -22.1 points (NS). LOCF analysis showed a greater reduction of the HAM-D scores with citalopram compared with reboxetine (-19.6 vs. -17.8; P = 0.034). The response rate was 90.3% for reboxetine and 92.7% for citalopram (NS). The most common side effect in the reboxetine group was dry mouth, and in the citalopram group sexual dysfunction. At week 24, anorgasmia was reported by 5.9% of the sexually active women in the reboxetine group vs 39% in the citalopram group. The dropout number was 91 in the reboxetine group, and 54 in the citalopram group. To summarize, both treatments gave a satisfactory antidepressant effect. The side effect profile differed between the groups, with a notably high prevalence of sexual dysfunctions in the citalopram group. The high number of dropouts in the reboxetine group, is considered as a result of the non-titration starting dose of 8 mg reboxetine per day, which gave a high incidence of early side-effects.

Adolescent↗

PubMed2005

Quantum chemical studies of three-photon absorption of some stilbenoid chromophores.

Three-photon absorption of a series of donor-acceptor trans-stilbene derivatives is studied by means of density functional theory applied to the third-order response function and its residues. The results obtained by using different functionals are compared with experimental data for similar systems obtained from the literature. With a Coulomb attenuated, asymptotically corrected functional, the excitation energy to the first resonance state is much improved. Comparison with experiment indicates that this is the case for the three-photon cross section as well. In particular, the overestimation of the cross sections and underestimation of excitation energies offered by the density functional theory using common density functionals is corrected for. It is argued that a reliable theory for three-photon absorption in charge transfer and other chromophore systems thereby has been obtained. Further elaboration of the theory and its experimental comparison call for explicit inclusion of solvent polarization and pulse propagation effects.

Journal Article↗

PubMed2005

Calculations of two-photon charge-transfer excitations using Coulomb-attenuated density-functional theory.

In this work, we show that an implementation of Coulomb-attenuated density-functional theory leads to considerably better prospects than hitherto for modeling two-photon absorption cross sections for charge-transfer species. This functional, which corrects for the effect of poor asymptotic dependence of commonly used functionals, essentially brings down the widely different results for larger charge-transfer species between Hartree-Fock and density-functional theory (DFT)-B3LYP into a closer range. The Coulomb-attenuated functional, which retains the best aspects of the Hartree-Fock and DFT-B3LYP methods, proves to be very promising for further modeling design of multiphoton materials with technical applications.

Journal Article↗