Temporary States Research Articles

A study of the molecular structure and spectroscopic properties of benzo- and pyrido-tetraazapentalenes

The equilibrium structures of Y- and Z-dibenzotetraazapentalene and some pyridyl derivatives were fully optimized by the density functional method B3LYP/6-31+G(d,p). For all the molecules, the results predict a fully conjugated planar geometry. The NMR 13C chemical shifts were recorded and analyzed by means of ab initio continuous set of gauge transformations calculations performed with the B3LYP/6-311+G(2d,p) DFT–HF hybrid model, which account for the different displacements of the resonances in the NMR spectra. The He(I) photoelectron spectra were measured and interpreted by means of ab initio outer valence Green function calculations, which give an overall consistent description of the energies, sequence and splitting of the uppermost bands. These are mainly associated with the π and n(N) orbitals of the central tetraaza fragment and with the n(N) lone pairs of the pyridyl rings. Electron transmission spectroscopy was employed to characterize the low-lying temporary anion states of the Y- and Z-isomers.

Quality adjusted life years as expected utilities

Abstract. This article is intended to systematicaly show all the conditions that the Quality Adjusted Life Year (QALY) must satisfy so that it can be interpreted as a von Newman-Morgenstern utility. Such conditions cover two cases. When health states are chronic, we shall be referring to the conditions inferred by Pliskin, Shepard and Weinstein (1980). Likewise, we will devote our attention to commenting on the characterization of Bleichrodt (1996), pointing out that its condition 0 is a bit artificial. In turn, for temporary health states, we will remark that the characterization of Bleichrodt (1995) appears to be incomplete. We shall provide a complete derivation of QALYs. In this way, QALYs can be derived from an individual's preference relation that satisfies the von Newman-Morgenstern axioms by imposing additive independence, absence of contradictory trade-offs and partial symmetry. Moreover, the two last conditions conditions can be replaced by a single condition that we call general symmetry.

A time-tradeoff method for cost-effectiveness models applied to radiology.

The wait tradeoff (WTO) is a simple time-tradeoff method designed for temporary health states that uses a realistic and intuitive interface for the patient/subject. This method was tested by assessing patients' preferences for magnetic resonance angiography (MRA) versus x-ray angiography (XRA). The WTO was tested by telephone interview in 38 patients with atherosclerotic peripheral vascular disease, all having previously undergone both MRA and XRA. At indifference point, patients were ambivalent about having MRA or XRA and immediate treatment, versus having a waiting period for test results and treatment after a hypothetical "ideal test" that entailed no pain or risk. The patients were willing to wait a mean of 42.1 days after the ideal test for results and treatment, as opposed to XRA. They were willing to wait only 16.1 days as opposed to MRA. This difference in waiting times was significant (p = 0.0001) and indicates a clear preference for MRA, in agreement with known literature. The WTO method assesses preferences for these radiologic tests in an intuitive fashion that does not invoke artificial or irrelevant health states. This approach may also prove useful for other testing situations or short-term treatments being evaluated for cost-effectiveness.

The Calculation of the Electron Affinity of Atoms and Molecules

Non-local density functional theory, as implemented in the code DMol, has been used to calculate the electron affinity of a set of 44 small atoms and molecules. A judicious choice of basis sets produces a root mean square deviation from recommended values of 0.1 eV and 0.3 eV for atoms and small molecules (with positive electron affinities) respectively. Applying DMol to calculations of temporary anion states or resonances of linear alkanes to n = 36 (where n is the number of carbon atoms) a gradual increase in electron affinity is predicted which appears to have converged by n = 36 to -0.75 eV (in agreement with experimental data for C36 and polyethylene).

Calculation of temporary anion states using density functional theory

Density functional theory (DFT) was examined for computing energies of temporary anions having negative electron affinities ranging from −8.0 to −0.2 eV. The calculated electron affinities are in good agreement with experiment for π ∗ states and low-energy σ ∗ states. The dependence of the DFT results on basis set was investigated. Comparisons are made with results from traditional ab initio molecular orbital theory based on Koopmans' theorem (KT) and energy difference methods (ΔHF and ΔMP2). It is shown that DFT methods provide an improvement over use of ab initio molecular orbital methods.

A study of the molecular structure and spectroscopic properties of tetrahydro[4]beltene and related compounds

The equilibrium structure of hexacyclo[8.7.0.0 3,8.0 5,15.0 6,13.0 12,16]heptadeca-1(10),5-diene-3,8-dicarboxylic anhydride, a tetrahydro[4]beltene with two σ-conjugated double bonds, and of two derivatives, the first with only one double bond and the second with a closed annular belt, was calculated at the RHF/6-31G ** ab initio level of theory. The results, consistent with the available X-ray experimental data, account for an efficient homoconjugation in the two compounds with an open belt. The NMR 13 C chemical shifts were analyzed by means of ab initio CSGT (continuous set of gauge transformations) calculations performed with the B3LYP/6-311+G(2d, p) DFT-HF hybrid functional model. The He(I) photoelectron spectra were measured and interpreted by means of ab initio OVGF (outer valence Green function) calculations, which give an overall consistent reproduction of the energies and splittings of the uppermost bands. These are associated with the π(CC) and/or Walsh orbitals of the equatorial belt and with the n(CO) lone pair orbitals of the anhydridic moiety. Electron transmission spectroscopy was employed to characterize the low-lying temporary anion states of tetrahydro[4]beltene. The single-crystal X-ray structure was also determined for the tris(demethano)pagodane derivative.

Ab initio investigation of the temporary anion states of silane and the linear silanes: (Si nH 2 n+2 ), n=2–5

The stabilization method is used in conjunction with Koopmans' theorem to calculate the energies of the unfilled molecular orbitals appropriate for describing the low-lying anion states of the linear silanes, Si n H 2 n+2 , with n=1–5. In agreement with earlier studies, the lowest energy unfilled molecular orbital for each member of the n⩾3 silanes is found to be largely SiH 2 σ * in character.

特殊条件下の構造研究の新展開 高圧，応力過程での相転移の動的観察

Lattice instability due to plastic and elastic deformation under pressure induces many types of structure transformations, including changes of coordination number, cation ordering, electronic state such as charge disproportionation, charge transfer and electron density of state, and spin-lattice interaction. Nonhydrostaticity of compression brings metastable states or intermediate states, which are different from the thermo-dynamically stable phases, because they are temporary states in the dynamical process. Kinetic study of the pressure-induced transition is discussed in accordance with the in situ observation of time-resolved diffraction measurement. Besides the stress-strain relation, the crystallite size is an effective parameter of phase transition under pressure. Molecular dynamical calculation simulates the high-pressure phase transition.

Electron spectroscopy of resonance-enhanced vibrational excitations of gaseous and solid tetrahydrofuran

We report intramolecular vibrational excitation of tetrahydrofuran (THF) in both the gas and solid phase induced by 1–30 eV electrons. High-resolution electron-energy-loss spectra reveal selective vibrational enhancement of THF for different impact energies, indicating the presence of at least three resonances (i.e., temporary anion states), located near 4, 7.5, and 10 eV, as well as many possibly overlapping higher-lying resonances. We also report electron-energy-loss spectra for different THF film thicknesses. Besides fundamental vibrational excitation, we observe several energy loss peaks due to overtones and combination vibrational modes. The present vibrational losses are assigned in compliance with published optical measurements. The similarities between the solid THF and gaseous cyclopentane spectra suggest that the resonances in both molecules could have a common origin and hence need not be attributed to the presence of the oxygen nonbonding electrons in THF.

Patients' utilities for cancer treatments: a study of the chained procedure for the standard gamble and time tradeoff.

Temporary health states cannot be measured in the traditional way by means of techniques such as the time tradeoff (TTO) and the standard gamble (SG), where health states are chronic and are followed by death. Chained methods have been developed to solve this problem. This study assesses the feasibility of a chained TTO and a chained SG, and the consistency and concordance between the two methods. Seventy female early-stage breast cancer patients were interviewed. In using both chained methods, the temporary health state to be evaluated was weighed indirectly with the aid of a temporary anchor health state. The patients were asked to evaluate their actual health states, a hypothetical radiotherapy scenario, and a hypothetical chemotherapy scenario. Sixty-eight patients completed the interview. The use of the anchor health state yielded some problems. A significant difference between the means of the TTO and the SG was found for the anchor health state only. For the other health states, the results were remarkably close, because the design avoided some of the bias effects in traditional measurements. The feasibility and the consistency of the chained procedure were satisfactory for both methods. The problems regarding the anchor health state can be solved by adapting the methods and by the use of a carefully chosen anchor health state. The chained method avoids biases present in the conventional method, and thereby the TTO and the SG may be reconciled. Moreover, there are several psychological advantages to the method, which makes it useful for diseases with uncertain prognoses.

Valuing temporary and chronic health states associated with breast screening

The aim of this study was to derive quality of life values for the four key breast screening outcomes (true negative, false positive, true positive and false negative), including the quality of life effects of the screening and treatment processes. In doing so, methodological issues in health status measurement were explored, in particular the valuation of temporary health states. The true negative and false positive descriptions were temporary health states, lasting for short term durations (12 months) and the true positive and false negative outcomes were chronic health states lasting for long term durations (rest of life). Descriptions of breast screening outcomes were valued using the time trade-off technique and the visual analogue scale. Paired comparisons between TTO values for states with the same duration found a difference between the true negative and the false positive time trade-off values but no difference for true positive and false negative descriptions. The TTO values for the false positive were low. The study highlights several important methodological issues such as the use of the two stage procedure for valuing temporary health states, the impact of duration on values, the impact of anchor points, and the importance of qualitative analysis of respondents values. Further empirical testing of all these issues is recommended.

Potential energy curves for the HF − and CH 3F − anions: a coupled cluster study

Very accurate ab initio calculations using the single-reference (SR) coupled cluster (CC) theory were performed for HF, CH 3F and their negative ions. The CC theory with singly and doubly excited clusters (CCSD approach) and its non-iterative counterpart accounting for connected triexcited components (CCSD(T) approach) were used as primary theoretical methods, and the HF and HF − systems were also investigated using the complete active space self-consistent field (CASSCF) approach. Emphasis was placed on the stability of the negatively charged ions and the potential energy curves for dissociative electron attachment in HF and CH 3F. In agreement with the majority of earlier calculations, the HF − and CH 3F − anions are unstable (i.e. have negative electron affinities) and can only capture an electron when the HF and CF bonds are significantly stretched. It is demonstrated that electron capture by HF and CH 3F correlates quite well with the maxima in the corresponding dipole moment functions. The potential energy curve for HF − is attactive, i.e. without a barrier for electron attachment, representing the HF molecule plus free electron near the equilibrium geometry of HF and crossing the neutral HF curve at the HF internuclear separation of 2.2 bohr in order to reach the H(1 s 2S) + F − (2 6 p 1S) limit (the equilibrium HF bond length is 1.733 bohr). The stretching of the HF bond and the energy required to capture an electron, resulting from CC calculations, are lower than in earlier calculations. The potential energy curve for CF bond breaking in CH 3F − has barriers for the dissociative electron attachment ( ΔE ‡ a ) and associative electron detachment ( ΔE ‡ d ) at the CF distance of approximately 3.7 bohr (the equilibrium CF separation is 2.612 bohr). Both barriers resulting from CC calculations, which are lower than in earlier calculations (CCSD method gives ΔE ‡ a = 1.67 eV , ΔE ‡ d = 0.28 eV ; CCSD(T) results are ΔE ‡ a = 1.56 eV , ΔE ‡ d = 0.20 eV ), are sensitive to many-electron correlation effects. The dissociative electron attachment in methyl fluoride is accompanied by a strong variation of the angle describing the umbrella motion of the methyl group and the appearance of a shallow (approximately 2 kcal mol −1) van der Waals' minimum in the corresponding CH 3F − curve representing the CH 3·F − complex. The implications of our findings for electron transfer phenomena, in particular for the photoinitiated charge transfer processes of the harpooning type, are discussed. The role of diffuse functions in the calculations for the temporary anion states and the role of the basis set and the theoretical approach in the modelling of potentials for electron attachment to a molecule are also briefly discussed.

Health-related quality of life during post-induction chemotherapy in children with acute lymphoblastic leukemia in remission

Using a multi-attribute approach, we and others have reported on the comprehensive health status of survivors of cancer in childhood, after completion of therapy. However, there is a dearth of information about health status and associated health-related quality of life (HRQL) in children and adults with cancer, during the treatment process; a deficit which this study was intended to redress. All children (n=18) receiving 'maintenance' chemotherapy for acute lymphoblastic leukemia (ALL) at a single institution were assessed prospectively through a single cycle of therapy. Patients, family members and health care professionals used global ratings, the health utilities index mark 2 (HUI2) and mark 3 (HUI3) classification systems, and detailed descriptions of temporary states of health, to provide independent assessments of health status at weekly intervals. Utility scores were derived for each comprehensive health state and for single attribute levels of the HUI2 system, and for the temporary health state descriptions. The classification of the subjects into the most appropriate temporary health states was challenging even for older children and some of the parents. The HUI instruments were used much more easily and produced highly comparable information. The most frequently affected attributes were pain, emotion and mobility/ambulation; in that order. The global (p=0.005) and specific morbidity burdens were, as predicted, greatest in the middle of the cycle of chemotherapy, reflecting the toxicity of steroid use. HUI2 global utility scores demonstrated moderate responsiveness with an intra-class correlation coefficient of 0.43. Cyclical administration of therapy, in particular corticosteroids, produces important changes in health status and HRQL in children with ALL. The HUI are valid and responsive systems for quantifying the burden of morbidity during the treatment of cancer in childhood. These are sensitive tools which can be used in a wide array of other circumstances to quantify changes in health status.

Intersubjectivity in Mathematics Learning: A Challenge to the Radical Constructivist Paradigm?

Radical constructivism is currently a major, if not the dominant, theoretical orientation in the mathematics education community, in relation to children's learning. There are, however, aspects of children's learning that are challenges to this perspective, and what appears to be “at least temporary states of intersubjectivity” (Cobb, Wood, & Yackel, 1991, p. 162) in the classroom is one such challenge. In this paper I discuss intersubjectivity and through it offer an examination of the limitations of the radical constructivist perspective. I suggest that the extension of radical constructivism toward a social constructivism, in an attempt to incorporate intersubjectivity, leads to an incoherent theory of learning. A comparison of Piaget's positioning of the individual in relation to social life with that of Vygotsky and his followers is offered, in support of the claim that radical constructivism does not offer enough as an explanation of children's learning of mathematics.

Resonance-assisted, hot-electron-induced desorption

The phenomenon of resonance-assisted hot-electron-induced desorption of adsorbed atoms or molecules is considered in terms of a semi-classical Gaussian wavepacket model. Inelastic scattering of hot electrons, forming temporary negative ion adsorbate states, gives rise to enhanced energy transfer between the hot electron and the adsorption complex. The numerical implications of the wavepacket model, which follows in the spirit of past theory of resonance Raman processes, suggests a very simple and intuitive analytic representation of the resonance desorption process providing a clear connection between the three independent timescales of the process and observable quantities such as desorption probabilities and rates. The timescales are identified as the vibrational period associated with the negative-ion-surface bond, that portion of the vibrational period within which desorption is possible, and the resonance lifetime of the intermediate negative ion state.

Theoretical investigation on the acceptor role of [formula omitted] MOs in three and four-membered ring thio compounds and their open chain analogues. Comparison of ground state, lowest energy triplet state and anion properties

Ab initio SCF-CI (6-31G ∗∗/MP2 and 6-31G ∗∗/MP4) computation of the singlet ground state, lowest energy triplet and anion states have been carried out for a series of divalent sulfur compounds. The aim of this study was to provide an insight into the acceptor capacity of σ ∗ MOs involved in the temporary states created in X-ray photoabsorption and electron transmission spectroscopies. A roughly parallel behavior is observed between triplet and anion species, either for vertical (GS geometry) or relaxed moieties. Qualitative correlations are presented between the calculated energies and molecular properties such as the CS bond length or the energy of the first virtual σ ∗ MO.

Time preference, duration and health state valuations.

There is increasing interest in health status measurement and the relative weights that people attach to different states of health and illness. One important issue which has been raised is the effect that the time spent in a health state may have on the way that state is perceived. Previous studies have suggested that the worse a state is, the more intolerable it becomes as it lasts longer. However, for most of these studies, it is impossible to determine how much of what was observed is attributable to the time spent in the state and how much is attributable to when it was occurring. This paper reports on a pilot study designed to test the feasibility of using the Time Trade-Off (TTO) method to isolate the effect of pure time preference from the effect of duration per se. Interviews were conducted with 39 members of the general population who were asked to rate 5 health states for durations of one month, one year and ten years. In aggregate, rates of time preference were very close to zero which suggests that the implicit assumption of the TTO method that there is no discounting may be a valid one. However, that more respondents had negative (rather than positive) rates, casts some doubt on the axions of discounted utility theory. In addition, implied valuations for states lasting for short periods were often counter-intuitive which questions the feasibility of using the TTO method to measure preferences for temporary health states.

Coupling of the dissociative electron attachment resonances of CO 2 to anionic excitations in rare gas solids

Significant sharp enhancements (FWHM ≤ 0.5 eV) are observed in electron stimulated desorption O − yields, obtained from small quantities of CO 2 physisorbed on thick rare gas substrate films. The enhancement are positioned 0.3–0.4 eV below the lowest substrate exciton energy, and are attributed to a coupling of the (electron plus exciton) core-excited anion resonances of the rare gas atoms to the dissociative temporary molecular anion states of the co-adsorbed CO 2 at the solid's surface. This causes a transfer of the charge and excitation energy to the co-adsorbate.

Temporary negative-ion states of Na, K, Rb, and Cs.

Electron-transmission spectroscopy is used to observe structure in the electron-scattering cross section associated with the formation of temporary negative ions and channel-opening effects. A strong ``family'' resemblance is apparent among the resonances of the alkali metals. From published calculations and angular scattering studies, the lower-lying features are known with some confidence. Based on these, plausible assignments for some of the higher-lying resonances are put forth. We propose that the absence of resonances near the Cs 5 $^{2}$D and possibly the Na 4 $^{2}$P and 5 $^{2}$P thresholds is associated with the negative polarizabilities of these excited states.

Multireference configuration interaction study of temporary anion states in haloforms

Multireference configuration interaction study of potential energy curves for the ground and lowest excited states for dissociative electron attachment are presented for CHCl 3/CHCl − 3, CHBr 3/CHBr − 3 and CHI 3/CHI − 3 systems. Reasonable agreement has been found with available experimental data for electron affinities, and comparison with other theoretical data is also made.