Accurate high level ab initio-based global potential energy surface and dynamics calculations for ground state of CH2(+).

A global many-body expansion potential energy surface is reported for the electronic ground state of CH2 (+) by fitting high level ab initio energies calculated at the multireference configuration interaction level with the aug-cc-pV6Z basis set. The topographical features of the new global potential energy surface are examined in detail and found to be in good agreement with those calculated directly from the raw ab initio energies, as well as previous calculations available in the literature. In turn, in order to validate the potential energy surface, a test theoretical study of the reaction CH(+)(X(1)Σ(+))+H((2)S)→C(+)((2)P)+H2(X(1)Σg (+)) has been carried out with the method of time dependent wavepacket on the title potential energy surface. The total integral cross sections and the rate coefficients have been calculated; the results determined that the new potential energy surface can both be recommended for dynamics studies of any type and as building blocks for constructing the potential energy surfaces of larger C(+)/H containing systems.

Terahertz response in single-walled carbon nanotube transistor: a real-time quantum dynamics simulation.

We use time-dependent quantum wavepacket methods to simulate ballistic electron transport in a single-walled carbon nanotube field-effect transistor at terahertz frequencies ( approximately 100 GHz-10 THz). We observe an electron resonance phenomenon in a sub-picosecond-scale time domain. Our simulation results clearly show that the electron resonance corresponds to the formation of the resonance cavity and the interference of the electron wavepackets, which is directly supported by recent experimental measurements (Zhong et al 2008 Nat. Nanotechnol. 3 201).

Integral and differential cross sections for the S(1D)+HD reaction employing the ground adiabatic electronic state.

We present converged quantum mechanical calculations for the title reaction employing a time-dependent wavepacket method. We obtained integral and differential cross sections over an energy range from 0.23 to 0.35 eV total energy as well as product state distributions for both product channels. The excitation functions decrease with energy and point to statistical dynamics as do the cold vibrational distributions and highly inverted rotational distributions. The differential cross sections oscillate strongly with energy for both product channels. Our differential cross sections for both product channels at 2.5 kcal/mol, one of the experimental energies, compare well to the experimental results. The quantum results obtained in this study are similar to what has been found employing QCT methods, implying that the differences between the experimental and theoretical results are due to the potential energy surface or non-adiabatic effects rather than due to quantum effects or the methods employed.

[Ventilator-associated pneumonia among premature infants <34 weeks' gestational age in neonatal intensive care unit in China: a multicenter study].

Objective: To investigate the incidence and pathogen distribution of ventilator-associated pneumonia (VAP) among preterm infants admitted to level Ⅲ neonatal intensive care units (NICU) in China. Method: A prospective study was conducted in 25 level Ⅲ NICU, enrolling all preterm infants <34 weeks gestational age admitted to the participating NICU within the first 7 days of life from May 2015 to April 2016. Chi-square test, t test and Mann-Whitney U test were used for statistical analysis. Result: A total of 7 918 patients were enrolled, within whom 4 623(58.4%) were males. The birth weight was (1 639±415) g and the gestational age was (31.4±2.0) weeks; 4 654(58.8%) infants required non-invasive mechanical ventilation and 2 154(27.2%) required intubation. Of all the mechanically ventilated patients, VAP occurred in 95 patients. The overall VAP rate was 7.0 episodes per 1 000 ventilator days, varying from 0 to 34.4 episodes per 1 000 ventilator days in different centers. The incidence of VAP was 9.6 and 6.0 per 1 000 ventilator days in children's hospitals and maternity-infant hospitals respectively, without significant differences (t=1.002, P=0.327). Gram-negative bacilli (76 strains, 91.6%) were the primary VAP microorganisms, mainly Acinetobacter baumannii (24 strains, 28.9%), Klebsiella pneumonia (23 strains, 27.7%), and Pseudomonas aeruginosa (10 strains, 12.0%). Conclusion: The incidence of VAP in China is similar to that in developed counties, with substantial variability in different NICU settings. More efforts are needed to monitor and evaluate the preventable factors associated with VAP and conduct interventions that could effectively reduce the occurrence of VAP.

Dynamics of X+CH4 (X=H,O,Cl) reactions: how reliable is transition state theory for fine-tuning potential energy surfaces?

Trajectory calculations run on global potential energy surfaces have shown that the topology of the entrance channel has strong implications on the dynamics of the title reactions. This may explain why huge differences are observed between the rate constants calculated from global dynamical methods and those obtained from local methods that employ the same potential energy surfaces but ignore such topological details. Local dynamics approaches such as transition state-based theories should then be used with caution for fine-tuning potential energy surfaces, especially for fast reactions with polyatomic species since the key statistical assumptions of the theory may not be valid for all degrees of freedom.

Life-course predictors of ultrasonic heel measurement in a cross-sectional study of immigrant women from Southeast Asia.

Few studies address chronic disease risk for Southeast Asians in the United States. In 1999, the authors conducted a cross-sectional study of bone mineral density (BMD) estimated from ultrasonic calcaneal measurements in women born in Southeast Asia who then lived in Chicago, Illinois. The study addressed three questions: Do Southeast-Asian women have relatively low BMD? What factors before and after immigration are associated with BMD? Are factors that reflect the childhood/adolescent environment equally associated with BMD for postmenopausal and premenopausal women? An interviewer-administered bilingual questionnaire collected immigration, reproductive, and lifestyle data from 213 women (aged 20--80 years) born in Vietnam, Cambodia, or Laos. The authors found that the estimated mean BMD of postmenopausal Southeast-Asian women was lower than the reference values for White women. Four summary indicators of childhood/adolescent environment were predictive of higher BMD: more years of education, earlier age at menarche, lower height, and coastal birth; these indicators were more strongly associated with BMD for premenopausal (multiple-partial R(2) = 0.21) than postmenopausal (R(2) = 0.06) women. Young-adult exposures (e.g., early first pregnancy and age at immigration) and proximal lifestyle factors (e.g., smoking, physical inactivity, vegetarian diet, and betel nut use) were also assessed as potential predictors of BMD.