Cosmic-ray-mediated Formation of Benzene on the Surface of Saturn's Moon Titan

The aromatic benzene molecule (C_6H_6)—a central building block of polycyclic aromatic hydrocarbon molecules—is of crucial importance for the understanding of the organic chemistry of Saturn's largest moon, Titan. Here, we show via laboratory experiments and electronic structure calculations that the benzene molecule can be formed on Titan's surface in situ via non-equilibrium chemistry by cosmic-ray processing of low-temperature acetylene (C_2H_2) ices. The actual yield of benzene depends strongly on the surface coverage. We suggest that the cosmic-ray-mediated chemistry on Titan's surface could be the dominant source of benzene, i.e., a factor of at least two orders of magnitude higher compared to previously modeled precipitation rates, in those regions of the surface which have a high surface coverage of acetylene

Chemical dynamics of triacetylene formation and implications to the synthesis of polyynes in Titan's atmosphere

For the last four decades, the role of polyynes such as diacetylene (HCCCCH) and triacetylene (HCCCCCCH) in the chemical evolution of the atmosphere of Saturn's moon Titan has been a subject of vigorous research. These polyacetylenes are thought to serve as an UV radiation shield in planetary environments; thus, acting as prebiotic ozone, and are considered as important constituents of the visible haze layers on Titan. However, the underlying chemical processes that initiate the formation and control the growth of polyynes have been the least understood to date. Here, we present a combined experimental, theoretical, and modeling study on the synthesis of the polyyne triacetylene (HCCCCCCH) via the bimolecular gas phase reaction of the ethynyl radical (CCH) with diacetylene (HCCCCH). This elementary reaction is rapid, has no entrance barrier, and yields the triacetylene molecule via indirect scattering dynamics through complex formation in a single collision event. Photochemical models of Titan's atmosphere imply that triacetylene may serve as a building block to synthesize even more complex polyynes such as tetraacetylene (HCCCCCCCCH)

Double Blind Study Investigating the Effect of Different Voice Prostheses on Ease of Swallowing and Residue Post Laryngectomy.

Voice prostheses have been examined for their effect on voice production but there is little datum on their effect on swallow function. This study investigated the difference between six commonly available voice prostheses in terms of swallowing. Laryngectomy patients had up to six voice prostheses placed in a random order over two visits. Swallowing was evaluated for each prosthesis using FEES (Fibreoptic Endoscopic Evaluation of Swallowing). After each prosthesis trial, patients self-evaluated their experience of swallowing. Three independent experts indicated which prosthesis they considered best for swallowing for each patient and judged residue on the voice prosthesis and in the upper esophagus. Raters were blinded to participant details, voice prosthesis type and scores of other raters. On patient self-evaluation, scores were equally distributed across all prostheses for swallowing. Experts most frequently chose the Blom Singer Low pressure and Blom Singer Classic Indwelling voice prostheses as best for swallowing but consensus was poor for most patients. Experts found that the Blom Singer Classic Indwelling and the Provox Vega had least residue on the voice prosthesis on thin liquid (p ≤ 0.001) and soft (p = 0.001), respectively. Experts also found that the Blom Singer Low Pressure had least residue in the upper esophagus on soft consistency (p ≤ 0.001). While self-evaluation by patients did not identify a consistently preferred prosthesis for swallow, many patients expressed personal preferences, suggesting benefits to involving patients in the choice of prosthesis. Some voice prostheses may be associated with lower levels of residue on the prosthesis and upper esophagus with certain consistencies

Clinical Practices in Head and Neck Cancer: A Speech-Language Pathologist Practice Pattern Survey

Objective: Clinical practices of speech-language pathologists (SLP) treating head and neck cancer (HNC) patients range widely despite literature trending toward best practices. This survey study was designed to identify current patterns and assess for gaps in clinical implementation of research evidence. Method: A web-based survey was distributed to SLPs via listserv and social media outlets. Descriptive statistics and group calculations were completed to identify trends and associations in responses. Results: Of 152 received surveys, the majority of respondents were hospital-based (86%) and had greater than 5 years of experience (65%). There was group consensus for the use of prophylactic exercise programs (95%), recommendations for SLP intervention during HNC treatment (75%), and use of maintenance programs post-treatment (97%). Conversely, no group consensus was observed for use of pre-treatment swallow evaluations, frequency of service provision, and content of therapy sessions. Variation in clinical decision making was noted in use of prophylactic feeding tubes and number of patients taking nothing by mouth during treatment. No associations were found between years of experience and decision-making practices, nor were any associations found between practice setting and clinical decision making. Conclusion: Despite the growing body of literature outlining evidence-based treatment practices for HNC patients, clinical practice patterns among SLPs continue to vary widely resulting in inconsistent patient care across practice settings. As compared to prior similar data, increased alignment with best practices was observed relative to early referrals, implementation of prophylactic intervention programs, and intervention with the SLP during the period of HNC treatment

Comparison of Maximum Power Point Tracking Techniques Used in Photovoltaic System

Among the various renewable energy sources, photovoltaic (PV) systems are experiencing a great expansion, due to their low polluting levels, the abundance of solar energy and the cost decreasing of PV technologies, attracting research and investments in the field. The maximum power generated in a PV panel varies according to irradiation and temperature. Since the conversion efficiency of photovoltaic modules is low, it is necessary to implement sophisticated control techniques for monitoring the maximum power point (MPPT). Maximum power point tracking techniques are automatic control algorithms that adjust power interfaces to achieve the maximum power generation, during variations in irradiation, temperature, and characteristics of the photovoltaic module. The purpose of the MPPT is to adjust the solar panel operating voltage near the maximum power point (MPP) according to environmental conditions. This technique has become an essential component in photovoltaic power system designs. This article presents comparison of the performance of various MPPT tracking methods in photovoltaic systems using the MATLAB/Simulink software and a comparative approach

Formation Mechanisms of Naphthalene and Indene: From the Interstellar Medium to Combustion Flames

The article addresses the formation mechanisms of naphthalene and indene, which represent prototype polycyclic aromatic hydrocarbons (PAH) carrying two six-membered and one five- plus a six-membered ring. Theoretical studies of the relevant chemical reactions are overviewed in terms of their potential energy surfaces, rate constants, and product branching ratios; these data are compared with experimental measurements in crossed molecular beams and the pyrolytic chemical reactor emulating the extreme conditions in the interstellar medium (ISM) and the combustion-like environment, respectively. The outcome of the reactions potentially producing naphthalene and indene is shown to critically depend on temperature and pressure or collision energy and hence the reaction mechanisms and their contributions to the PAH growth can be rather different in the ISM, planetary atmospheres, and in combustion flames at different temperatures and pressures. Specifically, this paradigm is illustrated with new theoretical results for rate constants and product branching ratios for the reaction of phenyl radical with vinylacetylene. The analysis of the formation mechanisms of naphthalene and its derivatives shows that in combustion they can be produced via hydrogen-abstraction-acetylene-addition (HACA) routes, recombination of cyclopentadienyl radical with itself and with cyclopentadiene, the reaction of benzyl radical with propargyl, methylation of indenyl radical, and the reactions of phenyl radical with vinylacetylene and 1,3-butadiene. In extreme astrochemical conditions, naphthalene and dihydronaphthalene can be formed in the C₆H₅ + vinylacetylene and C₆H₅ + 1,3-butadiene reactions, respectively. Ethynyl-substituted naphthalenes can be produced via the ethynyl addition mechanism beginning with benzene (in dehydrogenated forms) or with styrene. The formation mechanisms of indene in combustion include the reactions of the phenyl radical with C₃H₄ isomers allene and propyne, reaction of the benzyl radical with acetylene, and unimolecular decomposition of the 1-phenylallyl radical originating from 3-phenylpropene, a product of the C₆H₅ + propene reaction, or from C₆H₅ + C₃H₅

Quantifying Subjective and Objective Measures of Singing After Different Warm-Up Durations

Performing vocal warm-ups prior to singing repertoire has been shown to change the perceived quality and acoustic parameters of the voice. To date, there are no studies that specifically compare singers’ and listeners’ perceptions of vocal quality after various warm-up durations. To determine if specific warm-up durations (0, 5, 10, or 15 minutes) change subjective and objective measures of voice. Prospective cohort study. Information related to demographics, singing practice, medical history, and vocal hygiene were collected. First- and second-year collegiate classical voice majors completed a series of four warm-up times, 1 week apart, prior to singing Caro mio ben in a standard key for their voice type. A modified Voice Range Profile (mVRP), and the Evaluation of the Ability to Sing Easily (EASE) scale were completed. Participants blindly rated 30-second recorded audio clips using the Auditory-Perceptual Rating Instrument for Operatic Singing. Four independent expert blinded listeners rated all audio clips for each participant in random order. Six first-year and three second-year classical vocal performance majors completed all measures. Results of the EASE scale showed decreased scores with 5- and 10-minute warm-up duration, compared to 0 and 15 minutes of warm-up (P = 0.029 for the total EASE score and P = 0.044 for Rasch score). Delayed perceptual analysis of voice yielded nearly equal medians between warm-up durations for both self and expert-listener ratings. The mVRP showed that both 5 and 10 minutes of warm-up duration led to increased highest fundamental frequency for females (P = 0.017). This pilot study demonstrates the immediate self-perceived benefit for all participants and increased frequency range for females after performing 5 and 10 minutes of vocal warm-up. No significant differences were found in delayed perceptual analyses completed by the participants or the expert raters after the different warm-up durations. Future investigations should include a larger population and different levels of education and genres of singing

Prevalence of Vocal Fold Pathologies Among First-Year Singing Students Across Genres

The purpose of the study was to compare the prevalence of vocal fold pathologies among first-year singing students from the classical, musical theatre, and contemporary commercial music (CCM) genres. Prospective cohort study. Videostroboscopic examinations were rated by blinded expert raters. Vocal pathology was defined as a vocal fold abnormality on the membranous or cartilaginous portions of the vocal folds or hypomobility. Consensus among three of four raters confirmed presence of pathology. Association between genre of singer and presence of pathology, interrater reliability, and intrarater reliability were calculated. Differences in singing voice handicap, and voice use and vocal hygiene were compared. Fifty-seven participants were included. Seventeen percent of CCM, 40% of musical theatre, and 0% of classical singers were found to have vocal fold pathology. Interrater reliability was 0.522 between all four raters, 0.591 between the two laryngologists, and 0.581 between the two speech-language pathologists, showing a moderate agreement (P < .0001). Intrarater reliability was 1.000 (P < .0001) for the two laryngologists and 0.452 (P = .949) and 0.622 (P = .828) for the two speech-language pathologists. Singing Voice Handicap Index-10 data across genre showed differences between CCM and classical singers. No significant differences were found in voice usage or vocal hygiene. No classical students were found to have vocal fold pathology, whereas CCM and musical theatre students had significantly higher prevalence of pathologies. Voice use, vocal hygiene, and physiologic phonatory differences among classical, musical theatre, and CCM genres may be risk factors for development of vocal pathology. 2b Laryngoscope, 2019