bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cluster expansion of the wave function. Valence excitations and ionizations of pyridine
Authors: Kitao O. , Nakatsuji H. 
Published: July 2002

The SAC (symmetry-adapted cluster) and SAC-CI theories are applied to the calculations of the valence excitations and the ionizations of pyridine. The active space consists of 85 MOs (35π and 50 σ MOs). For the valence π→π* and n→π* excited states, S1(1 1B2), S2(1 1A1), S3(2 1B2), Sn(1 1B1), T1(1 3A1), and Tn(1 3B1), the calculated excitation energies are higher than the experimental values by within ∼0.7 eV. Although the S4(2 1A1) state is experimentally considered not to be split from S3, the present calculation predicted it to be higher than S3 by 0.31 eV. The average discrepancy from the experimental data is 0.55 eV without including S4. The transition energies and some other properties are predicted for the valence π→π* excited states, T2(1 3B2), T3(2 3A1), T4(2 3B2) and for the n→π* excited states, S′n(1 1A2) and Tn(1 3A2), for which the experimental values are unavailable so far. The following two observations seem to be interesting. (i) The valence π→π* excited states of pyridine are understood from those of benzene, reported previously, as a result of perturbation, an alteration of one C–H group to an isoelectronic nitrogen atom. The typical V states, S3 and S4, show large σ-reorganization effect, which is detected as the change in the transition energy and some one electron properties. (ii) For the relative positions between the π→π* and n→π* excitations, our results are as follows. The lowest singlet excited state is n→π*[Sn(1 1B2)]. The lowest triplet state is
π→π*[T1(1 3A1)] and n→π*[Tn(1 3B1)] exists higher than T1 by 0.15 eV. Experimentally, the lowest singlet excitation is confirmed to be n→π*, but two controversial assignments exist for the lowest triplet state: π→π* or n→π*. For the ionization potential, the experimental spectra is reproduced to within ∼0.6 eV. The nature of the first three peaks are calculated as nππ, which is supported by some recent experimental studies. The similarity and difference in the satellite peaks of benzene and pyridine are pointed out.
Intracavity, laser absorption spectroscopy of Ar2: Aπu5p and Aσu5p Rydberg states
Authors: Shannon D. C. , Eden J. G. 
Published: July 2002

Inter-Rydberg transitions of Ar2 in the green (∼460–530 nm) have been studied by intracavity, laser absorption spectroscopy. All five Hund’s case (c) members of the Aπu5p manifold, predicted by the guidelines established by Mulliken [J. Chem. Phys. 52, 5170 (1970)] for Xe2 and later adapted by Chang and Setser [J. Chem. Phys. 69, 3885 (1978)] for Ar2, have been observed. The molecular transitions originate from Aσg4s(1u,0−u) and terminate on the A2 Σ+ 1/2  u ion core, 3Πg on the A2 Σ+ 1/2  u ion co-derived (5p Rydberg electron 0−g, 0+g, 2g, 1g, and 1g. Transitions involving three of these are strongly red degraded [revealing that Re4s(1u, 0−u) &lt;Re5p(0−g) ≲Re(0+g)&lt;Re(1g upper)] whereas the bands associated with the 2g and lowest 1g levels are not. Analysis of newly observed hot bands (Δv≡v′−v″&lt;0) yields the following vibrational constants for ω″e =297.2±1.0 cm−1, ω″e x″e =3.3±0.4 cm−1, and ω″e y″e =0.08±0.05 cm−1. Several clear vibrational sequences are observed and tentative assignments for the Aπu5p separated atom limits are reported. The 0−g, 0+g, (2g, 1g), and 1g (upper) states apparently correlate (in the separated atom limit) with Ar(1S0)+Ar 5p[ 1/2 ]1, [ (5)/(2)
]2, [ (5)/(2) ]3, and [ (3)/(2) ]1, respectively, which is consistent with the known 4p, 5p→4s oscillator strengths, the Ar 3p5 5p fine structure splittings, and the measured energy defects between the Aπu5p substrates. Rather than being degenerate at small R, the 0−g and 0+g states of the πu5p manifold are split by 247 cm−1 near Re. Bandheads arising from the Aσu5p(0−g)←Aσg4s (1u, 0−u) transition have also been observed. Calculations show that the Aσu5p(0−g) state dissociation energy (D0≂1.0 eV) is noticeably smaller than that for the Aπu5p levels (D0=1.26±0.01 eV).
Energy transfer and reaction dynamics of matrix-isolated 1,2-difluoroethane-d4
Authors: Raff Lionel M. 
Published: July 2002

The molecular dynamics of vibrationally excited 1,2-difluoroethane-d4 isolated in Ar, Kr, and Xe matrices at 12 K are investigated using trajectory methods. The matrix model is an fcc crystal containing 125 unit cells with 666 atoms in a cubic (5×5×5) arrangement. It is assumed that 1,2-difluoroethane-d4 is held interstitially within the volume bounded by the innermost unit cell of the crystal. The transport effects of the bulk are simulated using the velocity reset method introduced by Riley, Coltrin, and Diestler [J. Chem. Phys. 88, 5934 (1988)]. The system potential is written as the separable sum of a lattice potential, a lattice–molecule interaction and a gas-phase potential for 1,2-difluoroethane. The first two of these are assumed to have pairwise form while the molecular potential is a modified form of the global potential previously developed for 1,2-difluoroethane [J. Phys. Chem. 91, 3266 (1987)]. Calculated sublimation energies for the pure crystals are in good accord with the experimental data.
The distribution of metastable-state energies for matrix-isolated 1,2-difluoroethane-d4 is Gaussian in form. In krypton, the full width at half maximum for the distribution is 0.37 eV. For a total excitation energy of 6.314 eV, the observed dynamic processes are vibrational relaxation, orientational exchange, and four-center DF elimination reactions. The first of these processes is characterized by a near linear, first-order decay curve with rate coefficients in the range 1.30–1.48×1011 s−1. The average rates in krypton and xenon are nearly equal. The process is slightly slower in argon. The decay curves exhibit characteristic high-frequency oscillations that are generally seen in energy transfer studies. It is demonstrated that these oscillations are associated with the frequencies for intramolecular energy transfer so that the entire frequency spectrum for such transfer processes can be obtained from the Fourier transform of the decay curve. Orientational exchange is shown to occur with much greater frequency as the unit cell spacing decreases. The occurrence of orientational exchange generally results in a very rapid dissipation of molecular rotational energy to the lattice which causes a characteristic break to occur in the decay curve. It is shown that 16% of the total energy transfer to the lattice in argon is a result of such rotational energy transfer. The propensity for four-center DF elimination is found to be greater in argon than in either krypton or xenon. The relaxation data show that this effect is not the result of different energy transfer rates but is probably associated with steric effects resulting from the smaller lattice dimensions in argon. Isotope effects upon the energy partitioning in unimolecular reactions of 1,2-difluoroethane and upon the energy transfer dynamics under matrix-isolation conditions are also reported.
Comment concerning the optimum control of transformations in an unbounded quantum system
Authors: Zhao Meishan , Rice Stuart A. 
Published: July 2002

We discuss the achievability of optimal control of the evolution of an unbounded quantum system by the action of external fields. Previous work has established that the evolution of a quantum system with a nondegenerate discrete and bounded spectrum of states can, in principle, be fully controlled, i.e., that the system wave function can be guided by external fields to approach arbitrarily closely a selected target state wave function. The optimal control of the evolution of a quantum system with a discrete and bounded spectrum of states has also been studied, using a method of analysis that depends on the localized character of bound state wave functions and the fact that the spectrum of states is bounded. In this paper, we examine whether it is possible to control, partially or fully, the evolution of an unbounded quantum system. We show that optimal control of the evolution of an unbounded quantum system is possible, in the sense that it is possible to minimize the difference between the product function formed at time t0 from a localizing function and a continuum wave function and a similarly defined target function at time tf.
We have not been able to establish that such optimal control is equivalent to full control, i.e., that the difference between the initial and target functions can be made arbitrarily small, which would require showing that the set of control functions is complete with respect to the function space of the system. Our analysis establishes the existence of external fields that can optimally guide the unbounded system evolution in the absence of other constraints than the Schrödinger equation of motion, but does not provide an algorithm for the construction of such fields. The relationship between optimal control of the evolution of a quantum system and the existence of chaotic dynamics in the continuum domain is briefly discussed. We argue that the optimally controlled system cannot have chaotic dynamics even if the bare system does. As illustrations of the results obtained, we discuss briefly the optimal control of evolution in the subset of discrete states from a spectrum with both discrete and continuum states, the optimal control of evolution in resonant states, and the inversion of the optimally controlled localized product continuum target function to yield the corresponding system wave function.
Common microscopic origin of superconductivity and unusual temperature dependence of the dc electrical conductivity in strongly correlated organic donor–acceptor salts
Authors: Böhm Michael C. 
Published: July 2002

Material properties of low-dimensional organic donor–acceptor (DA) metals are comparatively discussed. It is shown that the low-temperature superconductivity in organic solids and the nonconventional temperature dependence of the dc electrical conductivity σ have the same microscopic precursor, softening of lattice modes caused by a divergence of the generalized susceptibility on effectively flat Fermi surfaces (FS) (T dependence of σ), as well as the resulting enhancement of the electron–phonon coupling (superconductivity). Prerequisite for this behavior are sizeable electronic charge fluctuations 〈(Δn2i)〉 in the strongly correlated organic DA salts at any temperature. Nonvanishing fluctuations, which are maintained also in the limit of almost perfect interatomic correlations, are possible as a result of nonintegral effective electron densities n̄i≠1.0. The electronic charge fluctuations at T=0 K and finite temperature are studied by an analytic many-body model. The T dependence of the fluctuations is discussed as a function of the accessible electron density n̄i.
Charge densities n̄i≠1.0 as realized in the highly conducting organic metals attenuate a possible temperature control on the fluctuations. For the integral 1:1 charge transfer salts of D+A− stoichiometry, negligible fluctuations (insulating Mott configurations) for temperatures &lt;500 K are predicted. In addition to the T dependence of the electronic fluctuations, the mean-squared atomic fluctuations are studied as a function of temperature. The fluctuation amplitude diverges with increasing mode softening. Experimental consequences of this behavior are touched. A Kubo–Mori projector technique in a single-particle approximation is adopted to quantify the strong interrelation between the T variation of σ and FS properties (mode softening). Boundary expressions following a T−2 and T−1 law of σ(T) are formulated. The first relation is valid for systems with sizeable frequency renormalization; the second one for conventional metals with vanishing mode softening. The theoretical results suggest a new subclassification of the DA salts into two classes; FS properties serve as underlying criterion. The validity of the transport theory is demonstrated for the two-dimensional (BEDT-TTF)2ClO4 system. A two-mode model in the strong-coupling approximation is used to calculate superconducting transition temperatures TC of organic superconductors in the presence of Kohn mode softening. A remarkable influence of the frequency renormalization on the magnitude of TC is evaluated. An additional enhancement of TC is possible due to the divergence of the mean-squared atomic (lattice) displacement. Calculated TC numbers of (BEDT-TTF)2A superconductors are in fair agreement with experimental results.
How to grow large clusters from SixD+y ions in silane or disilane: Water them!
Authors: Mandich M. L. , Reents W. D. 
Published: July 2002

Growth of large cationic clusters is observed in real time for subsilane and subdisilane cations in the presence of silane/disilane–water mixtures. SiD+0–3 and Si2D+0–6 are created by electron impact in the trapped ion cell of a Fourier transform mass spectrometer and their sequential clustering reactions with 5% water: 95% silane/disilane are monitored for up to 80 s at total pressures of 10−7–10−5 Torr. Formation of SixDyO+z clusters out to at least 450 amu in silane and 650 amu in disilane can be seen on the available experimental time scales. The early portion of the sequence leading to large clusters has been elucidated for silane. Amazingly, of the possible subsilane cations, only SiD+ reacts with silane and water to form increasingly larger cluster sizes. Reactions of the other subsilane cations, SiD+0,2–3, do not continue without apparent limit. Initial growth of SiD+ proceeds in a highly specific fashion involving the formation of two critical doorway ions, Si4D+7 followed by Si4D7O+.
The growth pattern then fans out to include numerous alternating and parallel reactions with both SiD4 and D2O. Several general features of the growth reactions are seen. Reactions with SiD4 are noticeably slower than reactions with D2O. Cluster growth by bimolecular reaction with SiD4 and D2O occurs by addition of SiD2 and addition of an oxygen atom, respectively, accompanied by elimination of D2. Loss of additional molecules of D2 sometimes occurs, particularly as clustering proceeds to large sizes. Cluster growth by termolecular attachment of SiD4 or D2O is also seen. This process results in the formation of SixDyO+z complexes with SiD4 and D2O that appear to serve as important intermediates which enhance cluster growth rates as the total pressure is increased. Sequential clustering without apparent limit is only observed for subsilane and subdisilane cations with silane and disilane when water is present. On this basis, it is proposed that low levels of water contamination can provide a key ingredient for the chemistry which leads to the formation of the hydrogenated silicon particles found ubiquitously in silane plasmas.
Effects of lattice morphology upon reaction dynamics in matrix-isolated systems
Authors: Raff Lionel M. 
Published: July 2002

The dynamics of the cis-d2-ethylene+F2 addition reaction and the subsequent reaction dynamics of the products isolated in vapor-deposited Ar matrices at 12 K are investigated using trajectory methods that incorporate nonstatistical sampling to enhance the reaction probabilities. The matrix-isolated cis-d2-ethylene+F2 system is generated using a combination of Monte Carlo, damped trajectory, and volume contraction methods. Transport effects of the bulk are simulated using the velocity reset procedure developed by Riley et al. [J. Chem. Phys. 88, 5934 (1988)]. The potential-energy hypersurface is the same as that employed in our previous investigations of the matrix-isolated, decomposition dynamics of 1,2-difluoroethane-d4 and the bimolecular cis-d2-ethylene+F2 system in face-centered-cubic (fcc) matrices [J. Chem. Phys. 93, 3160 (1990); 95, 8901 (1991)]. It is found that matrices generated by these methods are amorphous with numerous vacancies and other imperfections. On the average, there are approximately three vacancies about each lattice atom compared to the fcc crystal.
The calculated lattice density is about 82% that for a bulk fcc Ar solid. Computed radial distribution functions resemble those expected for a liquid which exhibits some short-range order. The imperfections of the lattice remain even after substantial annealing at 50 K. The calculated energy relaxation rate to the lattice phonon modes in these amorphous matrices is about a factor of 4 less than that for a close-packed fcc lattice. The 1,2-difluoroethane product is formed primarily via an αβ-addition process, as is the case for fcc matrices. However, the prominence of this pathway is greatly reduced. The major process leading to a fluoroethylene elimination product in amorphous matrices involves an atomic addition mechanism. Such a reaction path accounts for 94% of the elimination reactions. The probability of internal rotation about the C■C double bond in the fluoroethylene product is increased fivefold over that for fcc lattices. The calculated stabilization/elimination product ratio, the cis/trans ratios of fluoroethylene products, and the HF/DF elimination ratio are all found to be in fair to good accord with the reported experimental data. It is concluded that accurate simulation of matrix-isolation experiments requires a matrix model that properly represents the lattice structure present in the experiments.
Every complete doubling metric space carries a doubling measure
Authors: Luukkainen Jouni , Saksman Eero 
Published: July 2002

We prove that a complete metric space

X
X

carries a doubling measure if and only if

X
X

is doubling and that more precisely the infima of the homogeneity exponents of the doubling measures on

X
X

and of the homogeneity exponents of

X
X

are equal. We also show that a closed subset

X
X

of

R

n

\mathbf {R}^{n}

carries a measure of homogeneity exponent

n
n

. These results are based on the case of compact

X
X

due to Vol

′

^{\prime }

berg and Konyagin.
The art of pedigree drawing: algorithmic aspects
Authors: Tores Frédéric , Barillot Emmanuel 
Published: July 2002

Abstract
Motivation: Giving a meaningful representation of a pedigree is not obvious when it includes consanguinity loops, individuals with multiple mates or several related families.
Results: We show that finding a perfectly meaningful representation of a pedigree is equivalent to the interval graph sandwich problem and we propose an algorithm for drawing pedigrees.
Contact: Emmanuel.Barillot@infobiogen.fr
* To whom correspondence should be addressed.
Perceptions of Breast Cancer Risks Among Women Receiving Mammograph Screening
Authors: Beidler Laura B. , Kressin Nancy R. , Wormwood Jolie B. , Battaglia Tracy A. , Slanetz Priscilla J. , Gunn Christine M. 
Published: January 2023

ImportanceBreast density is an independent risk factor for breast cancer. Despite the proliferation of mandated written notifications about breast density following mammography, there is little understanding of how women perceive the relative breast cancer risk associated with breast density.ObjectiveTo assess women’s perception of breast density compared with other breast cancer risks and explore their understanding of risk reduction.Design, Setting, and ParticipantsThis mixed-methods qualitative study used telephone surveys and semistructured interviews to investigate perceptions about breast cancer risk among a nationally representative, population-based sample of women. Eligible study participants were aged 40 to 76 years, reported having recently undergone mammography, had no history of prior breast cancer, and had heard of breast density. Survey participants who had been informed of their personal breast density were invited for a qualitative interview. Survey administration spanned July 1, 2019, to April 30, 2020, with 2306 women completing the survey. Qualitative interviews were conducted from February 1 to May 30, 2020.Main Outcomes and MeasuresRespondents compared the breast cancer risk associated with breast density with 5 other risk factors. Participants qualitatively described what they thought contributed to breast cancer risk and ways to reduce risk.ResultsOf the 2306 women who completed the survey, 1858 (166 [9%] Asian, 503 [27%] Black, 268 [14%] Hispanic, 792 [43%] White, and 128 [7%] other race or ethnicity; 358 [19%] aged 40-49 years, 906 [49%] aged 50-64 years, and 594 [32%] aged ≥65 years) completed the revised risk perception questions and were included in the analysis. Half of respondents thought breast density to be a greater risk than not having children (957 [52%]), having more than 1 alcoholic drink per day (975 [53%]), or having a prior breast biopsy (867 [48%]). Most respondents felt breast density was a lesser risk than having a first-degree relative with breast cancer (1706 [93%]) or being overweight or obese (1188 [65%]). Of the 61 women who were interviewed, 6 (10%) described breast density as contributing to breast cancer risk, and 43 (70%) emphasized family history as a breast cancer risk factor. Of the interviewed women, 17 (28%) stated they did not know whether it was possible to reduce their breast cancer risk.Conclusions and RelevanceIn this qualitative study of women of breast cancer screening age, family history was perceived as the primary breast cancer risk factor. Most interviewees did not identify breast density as a risk factor and did not feel confident about actions to mitigate breast cancer risk. Comprehensive education about breast cancer risks and prevention strategies is needed.
Moderate‐Intensity Exercise Maintains Redox Homeostasis for Cardiovascular Health
Authors: Jiang Jizong , Ni Lingyan , Zhang Xinxin , Gokulnath Priyanka , Vulugundam Gururaja , Li Guoping , Wang Hongyun , Xiao Junjie 
Published: January 2023

AbstractIt is well known that exercise is beneficial for cardiovascular health. Oxidative stress is the common pathological basis of many cardiovascular diseases. The overproduction of free radicals, both reactive oxygen species and reactive nitrogen species, can lead to redox imbalance and exacerbate oxidative damage to the cardiovascular system. Maintaining redox homeostasis and enhancing anti‐oxidative capacity are critical mechanisms by which exercise protects against cardiovascular diseases. Moderate‐intensity exercise is an effective means to maintain cardiovascular redox homeostasis. Moderate‐intensity exercise reduces the risk of cardiovascular disease by improving mitochondrial function and anti‐oxidative capacity. It also attenuates adverse cardiac remodeling and enhances cardiac function. This paper reviews the primary mechanisms of moderate‐intensity exercise‐mediated redox homeostasis in the cardiovascular system. Exploring the role of exercise‐mediated redox homeostasis in the cardiovascular system is of great significance to the prevention and treatment of cardiovascular diseases.