Ultrafast relaxation of photoexcited superfluid He nanodroplets.

The relaxation of photoexcited nanosystems is a fundamental process of light-matter interaction. Depending on the couplings of the internal degrees of freedom, relaxation can be ultrafast, converting electronic energy in a few fs, or slow, if the energy is trapped in a metastable state that decouples from its environment. Here, we study helium nanodroplets excited resonantly by femtosecond extreme-ultraviolet (XUV) pulses from a seeded free-electron laser. Despite their superfluid nature, we find that helium nanodroplets in the lowest electronically excited states undergo ultrafast relaxation. By comparing experimental photoelectron spectra with time-dependent density functional theory simulations, we unravel the full relaxation pathway: Following an ultrafast interband transition, a void nanometer-sized bubble forms around the localized excitation (He[Formula: see text]) within 1 ps. Subsequently, the bubble collapses and releases metastable He[Formula: see text] at the droplet surface. This study highlights the high level of detail achievable in probing the photodynamics of nanosystems using tunable XUV pulses.

Resolving multi-exciton generation by attosecond spectroscopy.

We propose an experimentally viable attosecond transient absorption spectroscopy scheme to resolve controversies regarding multiexciton (ME) generation in nanoscale systems. Absence of oscillations indicates that light excites single excitons, and MEs are created by incoherent impact ionization. An oscillation indicates the coherent mechanism, involving excitation of superpositions of single and MEs. The oscillation decay, ranging from 5 fs at ambient temperature to 20 fs at 100 K, gives the elastic exciton-phonon scattering time. The signal is best observed with multiple-cycle pump pulses.

Comment on "Characterization of excess electrons in water-cluster anions by quantum simulations".

The conclusion by Turi et al. (Reports, 5 August 2005, p. 914) that all experimental spectral and energetic data on water-cluster anions point toward surface-bound electrons is overstated. Comparison of experimental vertical detachment energies with their calculated values for (H2O)n- clusters with surface-bound and internalized electrons supports previous arguments that both types of clusters exist.

Photofragment translation spectroscopy of ClN3 at 248 nm: determination of the primary and secondary dissociation pathways.

Photofragmentation translational spectroscopy was used to identify the primary and secondary reaction pathways in the KrF laser (248 nm) photodissociation of chlorine azide (ClN(3)) under collision-free conditions. Both the molecular channel producing NCl (X (3)Sigma,a (1)Delta) + N(2) and the radical channel producing Cl ((2)P(J)) + N(3) were analyzed in detail. Consistent with previously reported velocity map ion imaging experiments [N. Hansen and A. M. Wodtke, J. Phys. Chem. A 107, 10608 (2003)] a bimodal translational energy distribution is seen when Cl atoms are monitored at mz = 35(Cl(+)). Momentum-matched N(3) counterfragments can be seen at mz = 42(N(3) (+)). The characteristics of the observed radical-channel data reflect the formation of linear azide radical and another high-energy form of N(3) (HEF-N(3)) that exhibits many of the characteristics one would expect from cyclic N(3). HEF-N(3) can be directly detected by electron-impact ionization more than 100 mus after its formation. Products of the unimolecular dissociation of HEF-N(3) are observed in the mz = 14(N(+)) and mz = 28(N(2) (+)) data. Anisotropy parameters were determined for the primary channels to be beta = -0.3 for the NCl forming channel and beta = 1.7 and beta = 0.4 for the linear N(3) and HEF-N(3) forming channels, respectively. There is additional evidence for secondary photodissociation of N(3) and of NCl.

Observation of large water-cluster anions with surface-bound excess electrons.

Anionic water clusters have long been studied to infer properties of the bulk hydrated electron. We used photoelectron imaging to characterize a class of (H2O)n- and (D2O)n- cluster anions (n

Experimental and theoretical study of the infrared spectra of BrHI- and BrDI-.

Gas phase vibrational spectra of BrHI- and BrDI- have been measured from 6 to 17 microm (590-1666 cm(-1)) using tunable infrared radiation from the free electron laser for infrared experiments in order to characterize the strong hydrogen bond in these species. BrHI-.Ar and BrDI-.Ar complexes were produced and mass selected, and the depletion of their signal due to vibrational predissociation was monitored as a function of photon energy. Additionally, BrHI- and BrDI- were dissociated into HBr (DBr) and I- via resonant infrared multiphoton dissociation. The spectra show numerous transitions, which had not been observed by previous matrix studies. New ab initio calculations of the potential-energy surface and the dipole moment are presented and are used in variational ro-vibrational calculations to assign the spectral features. These calculations highlight the importance of basis set in the simulation of heavy atoms such as iodine. Further, they demonstrate extensive mode mixing between the bend and the H-atom stretch modes in BrHI- and BrDI- due to Fermi resonances. These interactions result in major deviations from simple harmonic estimates of the vibrational energies. As a result of this new analysis, previous matrix-isolation spectra assignments are reevaluated.

Hydrated electron dynamics: from clusters to bulk.

The electronic relaxation dynamics of size-selected (H2O)n-/(D2O)n[25 eaq-(s(dagger)) internal conversion lifetime.

Research design and subject characteristics predicting nonparticipation in a panel survey of older families with cancer.

BACKGROUND: While recognized that loss of subjects over time may introduce bias and complicate statistical analysis in panel studies, it is seldom acknowledged that sampling bias starts with subjects who are eligible but do not participate. OBJECTIVES: Community-based recruiters identified 1,948 subjects as eligible to participate in a descriptive panel survey of older families with cancer. Focusing on the time between identification of eligible subjects until contact for the first interview for consenting subjects, the purpose of this study was to determine if subject or research design factors predicted who was more prone to nonparticipation. METHOD: A multivariate model explored the simultaneous effects of subject and research design characteristics on nonparticipation. Demographic and cancer characteristics, as well as features of the study protocol, were used as predictors in a multinomial logit regression model to enable a three-way comparison between nonconsenters (n = 748), consenters who dropped out prior to data collection (n = 208), and consenters who participated in the intake interview (n = 992). RESULTS: Age and cancer diagnosis played roles in whether consent was obtained, whereas race did not affect consent but raised odds of drop out after consent. Powerful evidence emerged that design features, such as if a caregiver participated, recruitment staff roles, and payment to recruiters, affected the probability of subjects not participating or dropping out before being interviewed. CONCLUSIONS: Findings suggest that both subject and research design characteristics affect the likelihood of nonparticipation in a panel study of older cancer patients and family caregivers. Future research involving testing of strategies addressing access and accrual issues, research staff roles, reimbursements, and responsiveness to the needs of research personnel, ill participants, and family members is warranted.

Transition state spectroscopy of the I + HI reaction in clusters: photoelectron spectroscopy of IHI-.Arn (n = 1-15).

We have investigated effects of solvation on the transition state spectroscopy and dynamics of the I + HI reaction by measuring the anion photoelectron (PE) spectra of the clusters IHI-.Arn (n = 1-5). Argon clustering results in a successive shift of the PE spectra to lower electron kinetic energies with increasing cluster size. It also leads to significant vibrational cooling in the PE spectra and facilitates the observation of features associated with symmetric stretch vibrations and hindered rotational motions of the transition state complex IHI. The shifts in electron binding energy suggest that the first six argon atoms form a ring around the waist of the IHI- anion, just as in I2-.Arn. The spacing of the antisymmetric stretch features evolves with cluster size and is attributed at least in part to perturbation of the IHI- geometry in larger argon clusters. Intensities of features due to hindered rotation are enhanced for larger clusters, possibly due to solvent perturbation of the neutral transition state region.

Time-resolved photoelectron spectroscopy of molecules and clusters.

Time-resolved photoelectron spectroscopy (TRPES) has become a powerful new tool in studying the dynamics of molecules and clusters. It has been applied to processes ranging from energy flow in electronically excited states of molecules to electron solvation dynamics in clusters. This review covers experimental and theoretical aspects of TRPES, focusing on studies of neutral and negatively charged species.

Occupational impairment and disability among applicants for Social Security disability benefits in Pennsylvania.

OBJECTIVE: The study goal was to assess the extent of workplace-related disease and injury among Social Security Disability Insurance applicants. METHODS: A convenience sample of 240 consecutive applicants to the Pennsylvania Bureau of Disability Determination was studied to assess the prevalence of work-related disorders. An applicant had a work-related condition if there was a clear statement of a workplace illness or injury associated with the impairment, or if the applicant had worked at an occupation with a high likelihood of exposures known or suspected to contribute to the condition of interest. RESULTS: Of the 240 applicants, 166 (69%) were awarded disability insurance benefits; a total of 27 (11%) had work-related conditions, including 14 of the 166 (8%) who were found to be disabled. Forty percent of the 27 had a disorder that was musculoskeletal in origin. Of 59 applicants with cancer, 10.2% had some work-related etiological component. Of an estimated 71,680 adult disability insurance applicants in Pennsylvania in 1990, 5134 new insurance beneficiaries had a projected occupationally related disability. CONCLUSIONS: A substantial number of applicants for disability insurance benefits suffer from an impairment caused or exacerbated by prior workplace exposures. These individuals may serve as sentinel events for initiating follow-up surveillance and prevention activities.

Providing information about advance directives to patients in ambulatory care and their families.

PURPOSE/OBJECTIVES: To devise a teaching pamphlet on advance directives. DATA SOURCES: Published articles, professional publications, books. DATA SYNTHESIS: Content was designed to educate, increase awareness of the topic, and encourage dialogue among caregivers, patients, and families prior to the onset of a health crisis. The tool is written at a fifth-grade reading level. CONCLUSIONS: The booklet can achieve its goals. Dissemination strategies still are under discussion. IMPLICATIONS FOR NURSING PRACTICE: Helping patients and their families explore end-of-life decisions is vital to providing comprehensive care for patients with cancer. Tools such as this can facilitate that process.

The transition state of the f + h2 reaction.

The transition state region of the F + H(2) reaction has been studied by photoelectron spectroscopy of FH(2)(-). New para and normal FH(2)(-)photoelectron spectra have been measured in refined experiments and are compared here with exact three-dimensional quantum reactive scattering simulations that use an accurate new ab initio potential energy surface for F + H(2). The detailed agreement that is obtained between this fully ab initio theory and experiment is unprecedented for the F + H(2) reaction and suggests that the transition state region of the F + H(2) potential energy surface has finally been understood quantitatively.

Fertility timing, wages, and human capital.

PIP: This theoretical model posits that women who delay child bearing will be more likely to invest in human capital (training that enhances productivity but is costly). This investment is conditioned by a greater discount rate than an economy-wide growth rate of wages for non-human capital investor women. The aim of the model is to present a more unified view of relationships between wages and fertility timing identified in earlier research. The empirical analyses, using ordinary least squares techniques, was based on data from the National Longitudinal Survey of Young Women, 1968-82 annually, for a sample of 1817 White working women aged 28-38 in 1982. Data were available for wages, education, work experience, age, number of children, and the percentage in occupations (manager, professional, administrative, service, and blue collar). First wages of women not in school and without a first birth were obtained for 991 women in the sample. Descriptive statistics revealed that the average early wage of late child bearers was 37% higher than the average early wage of early child bearers and 43% higher for 1982 wages. Childless women, compared to early child bearers, experienced a growth in wages from 31-38%. The assumptions in the theoretical model were 1) that all women were equally productive in the labor market in the beginning; 2) that women bore only one child; 3) that women worked continuously for a period of time, except for time out for child bearing; 4) that all women had the option of investing in one type of human capital, which cost the same for all women; 5) that the only source of income was the woman's own earnings; and 6) that a woman's lifetime utility was a function of the present value of her lifetime income and the intervening time period for child birth. Differences in education, experience, tenure, and wages were strongly associated with differences in fertility timing. The results revealed that wages were higher for delayed child bearers, primarily because of larger accumulations of human capital, assuming joint human capital and fertility timing decisions. The interpretation of regressions to test family influence was that unobserved heterogeneity partly explained the empirical relationship. Wages were affected by education, experience, and tenure, as proxies for human capital. Results were consistent with the hypothesis but did not confirm the theory.^ieng

Interpreting demographic effects in duration analyses of first birth intervals.

"Estimated demographic effects in proportional hazard models of first birth intervals could reflect time-invariant differences in the risk of a birth, or differences in the timing of a shift in the risk, or both. This paper attempts to distinguish between these possibilities. The procedure is to estimate a more general model than the proportional hazard specification, in which the evolution of the risk of a birth can differ with demographic characteristics. The proportional hazard specification is nested within this more general model. Consequently, the consistency of the data with the 'risk' or the 'timing' interpretation of demographic effects can be tested. The data studied do not lead to a rejection of the proportional hazard specification." Data are from the 1984 U.S. National Longitudinal Survey Youth Cohort and concern 670 women aged 16 or 17 in 1979.

Costs of occupational injury and illness in Pennsylvania.

A variety of state and federal data sources are used to estimate two critical components of the annual economic costs of occupational injuries and illnesses in Pennsylvania: foregone earnings of affected workers and medical costs. Foregone earnings costs resulting from occupational injuries and illnesses are estimated at between $1.22 billion and $2.02 billion in 1988. A number of potential adjustments to these estimates widen the range considerably. Estimates of medical costs range from $740 million to $797 million. Combining these two estimates gives total estimated costs of $1.96 billion to $2.82 billion.