Practical thermodynamics of Yukawa systems at strong coupling

Simple practical approach to estimate thermodynamic properties of strongly coupled Yukawa systems, in both fluid and solid phases, is presented. The accuracy of the approach is tested by extensive comparison with direct computer simulation results (for fluids and solids) and the recently proposed shortest-graph method (for solids). Possible applications to other systems of softly repulsive particles are briefly discussed.Comment: Published in J. Chem. Phy

Collective modes of two-dimensional classical Coulomb fluids

Molecular dynamics simulations have been performed to investigate in detail collective modes spectra of two-dimensional Coulomb fluids in a wide range of coupling. The obtained dispersion relations are compared with theoretical approaches based on quasi-crystalline approximation (QCA), also known as the quasi-localized charge approximation (QLCA) in the plasma-related context. An overall satisfactory agreement between theory and simulations is documented for the longitudinal mode at moderate coupling and in the long-wavelength domain at strong coupling. For the transverse mode, satisfactory agreement in the long-wavelength domain is only reached at very strong coupling, when the cutoff wave-number below which shear waves cannot propagate becomes small. The dependence of the cutoff wave-number for shear waves on the coupling parameter is obtained.Comment: 10 pages, 6 figure

Detection of an atmosphere around the super-Earth 55 Cancri e

We report the analysis of two new spectroscopic observations of the super-Earth 55 Cancri e, in the near infrared, obtained with the WFC3 camera onboard the HST. 55 Cancri e orbits so close to its parent star, that temperatures much higher than 2000 K are expected on its surface. Given the brightness of 55 Cancri, the observations were obtained in scanning mode, adopting a very long scanning length and a very high scanning speed. We use our specialized pipeline to take into account systematics introduced by these observational parameters when coupled with the geometrical distortions of the instrument. We measure the transit depth per wavelength channel with an average relative uncertainty of 22 ppm per visit and find modulations that depart from a straight line model with a 6$\sigma$ confidence level. These results suggest that 55 Cancri e is surrounded by an atmosphere, which is probably hydrogen-rich. Our fully Bayesian spectral retrieval code, T-REx, has identified HCN to be the most likely molecular candidate able to explain the features at 1.42 and 1.54 $\mu$m. While additional spectroscopic observations in a broader wavelength range in the infrared will be needed to confirm the HCN detection, we discuss here the implications of such result. Our chemical model, developed with combustion specialists, indicates that relatively high mixing ratios of HCN may be caused by a high C/O ratio. This result suggests this super-Earth is a carbon-rich environment even more exotic than previously thought.Comment: 10 pages, 10 figures, 4 tables, Accepted for publication in Ap

ОПТИМІЗАЦІЯ ПРОТИЕПІДЕМІЧНОГО ЗАБЕЗПЕЧЕННЯ У ДИНАМІЦІ ПАНДЕМІЇ COVID-19

The new coronavirus SARS-Cov-2, which was discovered in Wuhan in December 2019, caused the COVID-19 pandemic. Anti-epidemic protection in different affected countries differs in the scope of regime-restrictive measures and response regulations. The most effective was a set of quarantine measures in combination with early detection of epidemic outbreaks and their blocking. The massive impact of the population in most countries of the world has led to the inefficiency of all three major medical units of the biological threats response system: clinical, epidemiological and laboratory – which are crucial in eliminating of pandemic. The lack of specific means of treatment and prevention requires constant monitoring of the epidemic situation and timely correction of measures to curb the negative trends in the epidemic situation. Medical facilities are at high risk of infecting both medical staff and all those seeking medical care, which requires the total introduction of specific infection control measures for COVID-19 at all levels of medical care, including the evacuation and sorting of patients. The rapid progression of the COVID-19 epidemic process on the planet at the background of data on low reproductive numbers indicates a lack of knowledge about the main manifestations and patterns of the epidemic process of this extremely dangerous infectious disease. It may be the main reason for ineffective countermeasures. The evolution of SARS-Cov-2 with the formation of three subtypes and five genotypes of the pathogen, especially the emergence of a variant of the D614G virus with increased contagiousness and virulence, requires effective virological monitoring to create of valid diagnostic test systems and assess the prospects for specific active immunoprevention against COVID-19. Lack of data on the infectious dose of SARS-Cov-2, taking into account the mechanisms of transmission of the pathogen, the presence of a high proportion of asymptomatic forms of the disease, limited data on “super source of infection” of the pathogen, large losses among medical personnel, differences in response systems to biological hazards and other circumstances complicate the possibility of an effective anti-epidemic response to COVID-19. Lack of control over compliance with the recommended number of countermeasures intensifies the development of the epidemic process during the introduction of adaptive quarantine.Новий коронавірус SARS-Cov-2, який виявили в м. Ухань у грудні 2019 р., спричинив пандемію COVID-19. Протиепідемічний захист у різних уражених країнах відрізняється за обсягами режимно-обмежувальних заходів і регламентами реагування. Найефективнішим виявився комплекс карантинних заходів у поєднанні з раннім виявленням епідемічних осередків та їх блокуванням. Масовість ураження населення в більшості країнах світу зумовила неефективність діяльності усіх трьох основних медичних ланок системи реагування на біологічні загрози: клінічної, епідеміологічної та лабораторної, – які є визначальними у ліквідації пандемії. Відсутність засобів лікування і профілактики вимагає постійного моніторингу епідемічної ситуації та своєчасної корекції заходів стримання її негативних тенденцій розвитку. Медичні заклади стали об’єктами високого ризику зараження як медичного персоналу, так і усіх, хто звертається за медичною допомогою, що вимагає тотального запровадження специфічних заходів інфекційного контролю щодо COVID-19 на всіх рівнях надання медичної допомоги, включно на етапах евакуації та сортування хворих. Швидке прогресування розвитку епідемічного процесу COVID-19 на планеті на фоні даних про низьке репродуктивне число свідчить про недостатність знань з основних проявів і закономірностей епідемічного процесу цього особливо небезпечного інфекційного захворювання, що може бути основною причиною неефективності протиепідемічних заходів. Еволюція SARS-Cov-2 з формуванням трьох підтипів і п’яти генотипів збудника, особливо поява варіанту вірусу D614G з підвищеною контагіозністю і вірулентністю, вимагає ефективного вірусологічного моніторингу для створення валідних діагностичних тест-систем і оцінювання перспективності застосування специфічної активної імунопрофілактики на момент появи вакцин проти COVID-19. Відсутність даних про інфікувальну дозу SARS-Cov-2 із врахуванням механізмів передачі збудника інфекції, наявність високої частки асимптомних форм хвороби, обмежені дані щодо «суперрозповсюджувачів» патогена, великі втрати серед медичного персоналу, відмінності в системах реагування на біологічні небезпеки на уражених територіях та низка інших обставин ускладнюють можливості ефективного протиепідемічного реагування на COVID-19. Відсутність контролю дотримання рекомендованого обсягу протиепідемічних заходів інтенсифікує розвиток епідемічного процесу в період запровадження адаптивного карантину

Algebraic-matrix calculation of vibrational levels of triatomic molecules

We introduce an accurate and efficient algebraic technique for the computation of the vibrational spectra of triatomic molecules, of both linear and bent equilibrium geometry. The full three-dimensional potential energy surface (PES), which can be based on entirely {\it ab initio} data, is parameterized as a product Morse-cosine expansion, expressed in bond-angle internal coordinates, and includes explicit interactions among the local modes. We describe the stretching degrees of freedom in the framework of a Morse-type expansion on a suitable algebraic basis, which provides exact analytical expressions for the elements of a sparse Hamiltonian matrix. Likewise, we use a cosine power expansion on a spherical harmonics basis for the bending degree of freedom. The resulting matrix representation in the product space is very sparse and vibrational levels and eigenfunctions can be obtained by efficient diagonalization techniques. We apply this method to carbonyl sulfide OCS, hydrogen cyanide HCN, water H$_2$O, and nitrogen dioxide NO$_2$. When we base our calculations on high-quality PESs tuned to the experimental data, the computed spectra are in very good agreement with the observed band origins.Comment: 11 pages, 2 figures, containg additional supporting information in epaps.ps (results in tables, which are useful but not too important for the paper

Methane in the atmosphere of the transiting hot Neptune GJ436b?

We present an analysis of seven primary transit observations of the hot Neptune GJ436b at 3.6, 4.5 and $8~\mu$m obtained with the Infrared Array Camera (IRAC) on the Spitzer Space Telescope. After correcting for systematic effects, we fitted the light curves using the Markov Chain Monte Carlo technique. Combining these new data with the EPOXI, HST and ground-based $V, I, H$ and $K_s$ published observations, the range $0.5-10~\mu$m can be covered. Due to the low level of activity of GJ436, the effect of starspots on the combination of transits at different epochs is negligible at the accuracy of the dataset. Representative climate models were calculated by using a three-dimensional, pseudo-spectral general circulation model with idealised thermal forcing. Simulated transit spectra of GJ436b were generated using line-by-line radiative transfer models including the opacities of the molecular species expected to be present in such a planetary atmosphere. A new, ab-initio calculated, linelist for hot ammonia has been used for the first time. The photometric data observed at multiple wavelengths can be interpreted with methane being the dominant absorption after molecular hydrogen, possibly with minor contributions from ammonia, water and other molecules. No clear evidence of carbon monoxide and dioxide is found from transit photometry. We discuss this result in the light of a recent paper where photochemical disequilibrium is hypothesised to interpret secondary transit photometric data. We show that the emission photometric data are not incompatible with the presence of abundant methane, but further spectroscopic data are desirable to confirm this scenario.Comment: 19 pages, 10 figures, 1 table, Astrophysical Journal in pres

Laboratory investigation of shock-induced dissociation of buckminsterfullerene and astrophysical insights

Fullerene C60 is one of the most iconic forms of carbon found in the interstellar medium (ISM). The interstellar chemistry of carbon-rich components, including fullerenes, is driven by a variety of energetic processes including UV and X-ray irradiation, cosmic-ray (CR) bombardment, electron impact, and shock waves. These violent events strongly alter the particle phase and lead to the release of new molecular species in the gas phase. Only a few experimental studies on the shock processing of cosmic analogs have been conducted so far. We explored in the laboratory the destruction of buckminsterfullerene C60 using a pressure-driven shock tube coupled with optical diagnostics. Our efforts were first devoted to probing in situ the shock-induced processing of C60 at high temperatures (≤4500 K) by optical emission spectroscopy. The analysis of the spectra points to the massive production of C2 units. A broad underlying continuum was observed as well and was attributed to the collective visible emission of carbon clusters, generated similarly in large amounts. This proposed assignment was performed with the help of calculated emission spectra of various carbon clusters. The competition between dissociation and radiative relaxation, determined by statistical analysis, alludes to a predominance of clusters with less than 40 carbon atoms. Our laboratory experiments, supported by molecular dynamics simulations performed in the canonical ensemble, suggest that C60 is very stable, and that high-energy input is required to process it under interstellar low-density conditions and to produce C2 units and an abundance of intermediate-sized carbon clusters. These results provide some insights into the life cycle of carbon in space. Our findings hint that only J-type shocks with velocities above ∼100 km s−1 or C-type shocks with velocities above 9 km s−1 can lead to the destruction of fullerenes. Observational tracers of this process remain elusive, however. Our work confirms the potential of shock tubes for laboratory astrophysics

Identifiable Acetylene Features Predicted for Young Earth-like Exoplanets with Reducing Atmospheres Undergoing Heavy Bombardment

The chemical environments of young planets are assumed to be largely influenced by the impacts of bodies lingering on unstable trajectories after the dissolution of the protoplanetary disk. We explore the chemical consequences of impacts within the context of reducing planetary atmospheres dominated by carbon monoxide, methane, and molecular nitrogen. A terawatt high-power laser was selected in order to simulate the airglow plasma and blast wave surrounding the impactor. The chemical results of these experiments are then applied to a theoretical atmospheric model. The impact simulation results in substantial volume mixing ratios within the reactor of 5% hydrogen cyanide (HCN), 8% acetylene (C2H2), 5% cyanoacetylene (HC3N), and 1% ammonia (NH3). These yields are combined with estimated impact rates for the early Earth to predict surface boundary conditions for an atmospheric model. We show that impacts might have served as sources of energy that would have led to steady-state surface quantities of 0.4% C2H2, 400 ppm HCN, and 40 ppm NH3. We provide simulated transit spectra for an Earth-like exoplanet with this reducing atmosphere during and shortly after eras of intense impacts. We predict that acetylene is as observable as other molecular features on exoplanets with reducing atmospheres that have recently gone through their own "heavy bombardments," with prominent features at 3.05 and 10.5 μm

Ground-state ammonia and water in absorption towards Sgr B2

We have used the Odin submillimetre-wave satellite telescope to observe the ground state transitions of ortho-ammonia and ortho-water, including their 15N, 18O, and 17O isotopologues, towards Sgr B2. The extensive simultaneous velocity coverage of the observations, >500 km/s, ensures that we can probe the conditions of both the warm, dense gas of the molecular cloud Sgr B2 near the Galactic centre, and the more diffuse gas in the Galactic disk clouds along the line-of-sight. We present ground-state NH3 absorption in seven distinct velocity features along the line-of-sight towards Sgr B2. We find a nearly linear correlation between the column densities of NH3 and CS, and a square-root relation to N2H+. The ammonia abundance in these diffuse Galactic disk clouds is estimated to be about (0.5-1)e-8, similar to that observed for diffuse clouds in the outer Galaxy. On the basis of the detection of H218O absorption in the 3 kpc arm, and the absence of such a feature in the H217O spectrum, we conclude that the water abundance is around 1e-7, compared to ~1e-8 for NH3. The Sgr B2 molecular cloud itself is seen in absorption in NH3, 15NH3, H2O, H218O, and H217O, with emission superimposed on the absorption in the main isotopologues. The non-LTE excitation of NH3 in the environment of Sgr B2 can be explained without invoking an unusually hot (500 K) molecular layer. A hot layer is similarly not required to explain the line profiles of the 1_{1,0}-1_{0,1} transition from H2O and its isotopologues. The relatively weak 15NH3 absorption in the Sgr B2 molecular cloud indicates a high [14N/15N] isotopic ratio >600. The abundance ratio of H218O and H217O is found to be relatively low, 2.5--3. These results together indicate that the dominant nucleosynthesis process in the Galactic centre is CNO hydrogen burning.Comment: 10 pages, 5 figure