Near-Infrared Kinetic Spectroscopy of the HO_2 and C_2H_5O_2 Self-Reactions and Cross Reactions

The self-reactions and cross reactions of the peroxy radicals HO_2 and C_2H_5O_2 and HO_2 were monitored using simultaneous independent spectroscopic probes to observe each radical species. Wavelength modulation (WM) near-infrared (NIR) spectroscopy was used to detect HO_2, and UV absorption monitored HO_2 and C_2H_5O_2. The temperature dependences of these reactions were investigated over a range of interest to tropospheric chemistry, 221−296 K. The Arrhenius expression determined for the cross reaction, k_2(T) = (6.01^(+1.95)_(−1.47)) × 10^(−13) exp((638 ± 73)/T) cm^3 molecules^(−1) s^(−1) is in agreement with other work from the literature. The measurements of the HO_2 self-reaction agreed with previous work from this lab and were not further refined.(1) The C_2H_5O_2 self-reaction is complicated by secondary production of HO_2. This experiment performed the first direct measurement of the self-reaction rate constant, as well as the branching fraction to the radical channel, in part by measurement of the secondary HO_2. The Arrhenius expression for the self-reaction rate constant is k_3(T) = (1.29^(+0.34)_(−0.27)) × 10^(−13)exp((−23 ± 61)/T) cm^3 molecules^(−1) s^(−1), and the branching fraction value is α = 0.28 ± 0.06, independent of temperature. These values are in disagreement with previous measurements based on end product studies of the branching fraction. The results suggest that better characterization of the products from RO_2 self-reactions are required

A combined HST and XMM-Newton campaign for the magnetic O9.7 V star HD 54879: towards constraining the weak-wind problem of massive stars

Context: HD 54879 (O9.7 V) is one of a dozen O-stars for which an organized atmospheric magnetic field has been detected. To gain insights into the interplay between atmospheres, winds, and magnetic fields of massive stars, we acquired UV and X-ray data of HD 54879 using the Hubble Space Telescope and the XMM-Newton satellite. In addition, 35 optical amateur spectra were secured to study the variability of HD 54879. A multiwavelength (X-ray to optical) spectral analysis is performed using the Potsdam Wolf-Rayet (PoWR) model atmosphere code and the xspec software. Results: The photospheric parameters are typical for an O9.7 V star. The microturbulent, macroturbulent, and projected rotational velocities are lower than previously suggested (<4 km/s). An initial mass of 16$\,M_\odot$ and an age of 5 Myr are inferred from evolutionary tracks. We derive a mean X-ray emitting temperature of $\log T_{\rm X} = 6.7\,$[K] and an X-ray luminosity of $\log L_\text{X} = 32\,$[erg/s]. Short- and long-scale variability is seen in the H-alpha line, but only a very long period of $P \approx 5\,$yr could be estimated. Assessing the circumstellar density of HD 54879 using UV spectra, we can roughly estimate the mass-loss rate HD 54879 would have in the absence of a magnetic field as $\log \dot{M}_{B=0}\approx -9.0\,[{M_\odot}/{\rm yr}]$. The magnetic field traps the stellar wind up to the Alfv\'en radius > $12\,R_\odot$, implying that its true mass-loss rate is $\log \dot{M}< -10.2\,[{M_\odot}/{\rm yr}]$. Hence, density enhancements around magnetic stars can be exploited to estimate mass-loss rates of non-magnetic stars of similar spectral types, essential for resolving the weak wind problem. Conclusions: Our study confirms that strongly magnetized stars lose little or no mass, and supplies important constraints on the weak-wind problem of massive main sequence stars.Comment: Accepted for publication in A&A on Aug. 9, 2017, 12 + 1 pages, 15 figures. Paper replaced due to typos and missing acknowledgment

Traditional practices and perceptions of epilepsy among people in Roma communities in Bulgaria

PURPOSE: We attempted to identify cultural aspects of epilepsy among the Roma community in Bulgaria by elucidating cultural beliefs, traditional treatments, and potential markers of stigma. METHODS: We established representative discussion groups among five distinct Roma subgroups (Lom, Kalderas, Thracian Tinsmiths (Tinkers), Kyustendil Xoroxane and Kopanari) from different Bulgarian regions. Data about local beliefs and treatment strategies were gathered. RESULTS: Most people were familiar with convulsions but non-convulsive focal seizures were seen not as epileptic but mainly as a "mental problem". Beliefs about putative etiologies for epilepsy were not uniform as some considered environmental and external factors such as high environmental temperatures, electric shocks, loud music, and fever as causes of seizures while others listed bad experiences, stress, trauma, and fear as possible causes. Epilepsy was seen by some as a divine punishment or resulting from black magic. Most considered epilepsy shameful and an obstacle to children attending school. Despite local differences, there was a uniform belief that epilepsy is incurable by Western medicine and people usually resort to traditional healers. A variety of rituals performed by local healers to treat epilepsy were described. DISCUSSION: Misconceptions about epilepsy may contribute to stigmatization in this population; this may in turn contribute to a high treatment gap in this group. As a result, the majority of Roma children with epilepsy are likely to leave school early, are greatly limited in their choice of spouse (particularly girls), and marriages often occur between people with epilepsy or those with a family history of epilepsy

First principles calculation of structural and magnetic properties for Fe monolayers and bilayers on W(110)

Structure optimizations were performed for 1 and 2 monolayers (ML) of Fe on a 5 ML W(110) substrate employing the all-electron full-potential linearized augmented plane-wave (FP-LAPW) method. The magnetic moments were also obtained for the converged and optimized structures. We find significant contractions ($\sim$ 10 %) for both the Fe-W and the neighboring Fe-Fe interlayer spacings compared to the corresponding bulk W-W and Fe-Fe interlayer spacings. Compared to the Fe bcc bulk moment of 2.2 $\mu_B$, the magnetic moment for the surface layer of Fe is enhanced (i) by 15% to 2.54 $\mu_B$ for 1 ML Fe/5 ML W(110), and (ii) by 29% to 2.84 $\mu_B$ for 2 ML Fe/5 ML W(110). The inner Fe layer for 2 ML Fe/5 ML W(110) has a bulk-like moment of 2.3 $\mu_B$. These results agree well with previous experimental data

Atmospheric Bromine and Ozone Perturbations in the Lower Stratosphere

The role of bromine compounds in the photochemistry of the natural and perturbed stratosphere has been reexamined using an expanded reaction scheme and the results of recent laboratory studies of several key reactions. The most important finding is that through the reaction BrO + CIO → Br + Cl + O2, there is a synergistic effect between bromine and chlorine which results in an efficient catalytic destruction of ozone in the lower stratosphere. One-dimensional photochemical model results indicate that BrO is the major bromine species throughout the stratosphere, followed by BrONO2, HBr, HOBr and Br. We show from the foregoing that bromine is more efficient than chlorine as a catalyst for destroying ozone, and discuss the implications for stratospheric ozone of possible future growth in the industrial and agricultural use of bromine. Bromine concentrations of 20 pptv (2 × 10^−11), as suggested by recent observations, can decrease the present-day integrated ozone column density by 2.4%, and can enhance ozone depletion from steady-state chlorofluoromethane release at 1973 rates by a factor of 1.1–1.2

Multiscale Kinetic Monte-Carlo for Simulating Epitaxial Growth

We present a fast Monte-Carlo algorithm for simulating epitaxial surface growth, based on the continuous-time Monte-Carlo algorithm of Bortz, Kalos and Lebowitz. When simulating realistic growth regimes, much computational time is consumed by the relatively fast dynamics of the adatoms. Continuum and continuum-discrete hybrid methods have been developed to approach this issue; however in many situations, the density of adatoms is too low to efficiently and accurately simulate as a continuum. To solve the problem of fast adatom dynamics, we allow adatoms to take larger steps, effectively reducing the number of transitions required. We achieve nearly a factor of ten speed up, for growth at moderate temperatures and large D/F.Comment: 7 pages, 6 figures; revised text, accepted by PR

Marriage in epilepsy: The impact of the question in knowledge, attitude, and practice surveys.

BACKGROUND: Knowledge, attitudes, and practice (KAP) questionnaire-based surveys have captured negative attitudes towards marriage involving people with epilepsy (PWE). The attitudes may vary according to the nature of the question posed, whether personal or generic, in addition to many other covariates. METHODS: We carried out meta-proportion and -regression analyses of epilepsy-related KAP surveys published between 1970 and 2016 in the medical literature analysis retrieval system online (MEDLINE) database. RESULTS: The pooled estimate of the proportion of those responding positively to the marriage question was 0.45 (95% confidence interval (95%CI): 0.35 to 0.54; I2res = 99.89%). The pooled proportion of positive responders to a personal question (0.40; 95%CI: 0.35 to 0.46) was significantly lower than those responding positively to a generic question (0.64; 95%CI: 0.57 to 0.70) (P = 0.001). When modeled individually in regression analyses, only the continent of origin of the survey (P = 0.001; tau2: 0.06; I2res: 99.8%; adjusted R2: 11.4%) and subject population type (P = 0.02; tau2: 0.07; I2res: 99.9%; adjusted R2: 4.2%) were associated with the pooled estimate of positive responders to the question on marriage. CONCLUSIONS: Personal questions probing the possibility of marriage of self or family members to someone with epilepsy bring about negative attitudes more often than generic questions inquiring the marriage-worthiness of PWE