Disentangling conical intersection and coherent molecular dynamics in methyl bromide with attosecond transient absorption spectroscopy

Attosecond probing of core-level electronic transitions provides a sensitive tool for studying valence molecular dynamics with atomic, state, and charge specificity. In this report, we employ attosecond transient absorption spectroscopy to follow the valence dynamics of strong-field initiated processes in methyl bromide. By probing the 3d core-to-valence transition, we resolve the strong field excitation and ensuing fragmentation of the neutral σ* excited states of methyl bromide. The results provide a clear signature of the non-adiabatic passage of the excited state wavepacket through a conical intersection. We additionally observe competing, strong field initiated processes arising in both the ground state and ionized molecule corresponding to vibrational and spin-orbit motion, respectively. The demonstrated ability to resolve simultaneous dynamics with few-femtosecond resolution presents a clear path forward in the implementation of attosecond XUV spectroscopy as a general tool for probing competing and complex molecular phenomena with unmatched temporal resolution

Electron affinity of Li: A state-selective measurement

We have investigated the threshold of photodetachment of Li^- leading to the formation of the residual Li atom in the $2p ^2P$ state. The excited residual atom was selectively photoionized via an intermediate Rydberg state and the resulting Li^+ ion was detected. A collinear laser-ion beam geometry enabled both high resolution and sensitivity to be attained. We have demonstrated the potential of this state selective photodetachment spectroscopic method by improving the accuracy of Li electron affinity measurements an order of magnitude. From a fit to the Wigner law in the threshold region, we obtained a Li electron affinity of 0.618 049(20) eV.Comment: 5 pages,6 figures,22 reference

Spectroscopy of free radicals and radical containing entrance-channel complexes in superfluid helium nano-droplets

The spectroscopy of free radicals and radical containing entrance-channel complexes embedded in superfluid helium nano-droplets is reviewed. The collection of dopants inside individual droplets in the beam represents a micro-canonical ensemble, and as such each droplet may be considered an isolated cryo-reactor. The unique properties of the droplets, namely their low temperature (0.4 K) and fast cooling rates ($\sim10^{16}$ K s$^{-1}$) provides novel opportunities for the formation and high-resolution studies of molecular complexes containing one or more free radicals. The production methods of radicals are discussed in light of their applicability for embedding the radicals in helium droplets. The spectroscopic studies performed to date on molecular radicals and on entrance / exit-channel complexes of radicals with stable molecules are detailed. The observed complexes provide new information on the potential energy surfaces of several fundamental chemical reactions and on the intermolecular interactions present in open-shell systems. Prospects of further experiments of radicals embedded in helium droplets are discussed, especially the possibilities to prepare and study high-energy structures and their controlled manipulation, as well as the possibility of fundamental physics experiments.Comment: 25 pages, 12 figures, 4 tables (RevTeX

Classical interventions in quantum systems. I. The measuring process

The measuring process is an external intervention in the dynamics of a quantum system. It involves a unitary interaction of that system with a measuring apparatus, a further interaction of both with an unknown environment causing decoherence, and then the deletion of a subsystem. This description of the measuring process is a substantial generalization of current models in quantum measurement theory. In particular, no ancilla is needed. The final result is represented by a completely positive map of the quantum state $\rho$ (possibly with a change of the dimensions of $\rho$). A continuous limit of the above process leads to Lindblad's equation for the quantum dynamical semigroup.Comment: Final version, 14 pages LaTe

Language barrier and its relationship to diabetes and diabetic retinopathy

10.1186/1471-2458-12-781BMC Public Health121

Measured body mass index, body weight perception, dissatisfaction and control practices in urban, low-income African American adolescents

<p>Abstract</p> <p>Background</p> <p>Current understanding of the associations between actual body weight status, weight perception, body dissatisfaction, and weight control practices among low-income urban African American adolescents is limited. The knowledge can help direct future intervention efforts.</p> <p>Methods</p> <p>Cross-sectional data including measured weight and height and self-reported weight status collected from 448 adolescents in four Chicago Public Schools were used.</p> <p>Results</p> <p>The prevalence of overweight and obesity (BMI ≥ 85^thpercentile) was 39.8%, but only 27.2% considered themselves as obese, although 43.4% reported trying to lose weight. Girls were more likely to express weight dissatisfaction than boys, especially those with BMI ≥ 95^thpercentile (62.9% vs. 25.9%). BMI ≥ 85^thpercentile girls were more likely to try to lose weight than boys (84.6% vs. 66.7%). Among all adolescents, 27.2% underestimated and 67.2% correctly judged their own weight status. Multinomial logistic models show that those with BMI ≥ 85^thpercentile, self-perceived as obese, or expressed body dissatisfaction were more likely to try to lose weight; adjusted odds ratios and 95% confidence intervals were 4.52 (2.53–8.08), 18.04 (7.19–45.30), 4.12 (1.64–10.37), respectively. No significant differences were found in diet and physical activity between those trying to lose weight and those not trying, but boys who reported trying to lose weight still spent more television time (P < 0.05).</p> <p>Conclusion</p> <p>Gender differences in weight perception, body dissatisfaction, and weight control practices exist among African American adolescents. One-third did not appropriately classify their weight status. Weight perception and body dissatisfaction are correlates of weight control practices. Adolescents attempting to lose weight need be empowered to make adequate desirable behavioral changes.</p

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 pho- toelectron 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 ) within 1 ps. Subsequently, the bubble collapses and releases metastable He at the droplet surface. This study highlights the high level of detail achievable in probing the photodynamics of nanosystems using tunable XUV pulses

Gender and ethnic disparities contributing to overweight in California adolescents

To explore differences in health behaviors and factors contributing to overweight among 12 to 17 year olds in California. Data from the 2005 California Health Interview Survey for 3,315 adolescents self-identified as Latino, Asian, or white were reviewed. Adolescents reported their weight, height, gender, ethnicity, parents’ educational level, household income, physical activity, sedentary activity, breakfast consumption, and family meals. Overall 34% of boys and 22% of girls in this study were overweight (&gt;85th percentile for age and gender). Approximately 38% of Latinos, 25% of whites, and 16% of Asians were overweight. Latinos were more than twice as likely to be overweight as whites (2.07) and Asians (2.53). Younger adolescents (12–13 years old) and adolescents whose family income is less than 200% of the federal poverty level were more likely to be overweight. Low level of parental education is a risk factor for Latino and Asian girls and white and Latino boys. White girls with a lower socioeconomic status and white boys with more than 2 h daily of television, video, and computer time were more likely to be overweight. Results suggest gender and ethnic variations in factors that contribute to overweight in California adolescents. To influence the current overweight epidemic, clinicians must develop culturally sensitive and gender-specific interventions that address the unique needs of an ethnically diverse adolescent population

Alcohol dehydrogenase 1B (ADH1B) genotype, alcohol consumption and breast cancer risk by age 50 years in a German case–control study

In a population-based study of 613 cases and 1082 controls, alcohol dehydrogenase 1B (ADH1B) genotype was not an independent risk factor for breast cancer, athough the possibility was raised that it modifies risk associated with high levels of alcohol consumption (OR 1.1, 95% confidence interval (CI) 0.8–1.6 for ADH1B*1/*1 genotype vs 0.2, 95% CI 0.1–1.0 for ADH1B*2 carriers)