Characterization of acetonitrile ice irradiated by X-rays employing the PROCODA code: II. Desorption processes

In this work, we focus on the study of radiation induced desorption processes that occurred in acetonitrile ice irradiated by broadband X-rays (6 eV to 2 keV) monitored by FTIR spectroscopy at different radiation fluences. In a previous work, we used the PROCODA code to derive the chemical evolution of the ice. Here, we have obtained that the acetonitrile desorbed column density is at least two orders of magnitude larger than the desorbed column densities of daughter or granddaughter molecular species at chemical equilibrium stage. This indicates that total desorption column density is mainly governed by the father molecule, as also previously hypothesized in experimental studies. This occurs basically because the acetonitrile column density is larger than the other ones. In particular, at chemical equilibrium acetonitrile desorption column density represents almost 98\% of the total, while it is close to 1\% for H, CN and CH$_2$, the species with larger molecular desorption percentages at chemical equilibrium. Another derived quantity is what we called intrinsic desorption rate, which is a number per second for individual species. Some of the larger intrinsic desorption rates were: CH$_3$CN ($6.2\times 10^{-6}$), CN ($6.2\times 10^{-6}$), H ($5.7\times 10^{-6}$), CH$_2$ ($5.7\times 10^{-6}$) and C$_2$N$_2$ ($4.4\times 10^{-6}$). These results help to put constrain in astrochemical models and can be also useful to clarify some astronomical radio observations.Comment: To appear in MNRA

Virality of medical content in Russian social media

The work objective is to conduct a sociological study aimed at assessing validity (appropriateness) of the traditional characteristics and formation of a pool of specialized characteristics of the viral content, used in the promotion of health services by means of social media marketin

On chemical bonding of Helium with hcp-Beryllium

Chemical inertness is the key property of helium determining its solubility, distribution and accumulation kinetics in metals. Against all expectations, our ab initio calculations show a substantial chemical bonding between He and Be atoms in the hcp-Be matrix when He occupies a non-symmetric position in a basal plane.Comment: Revised version of manuscript, 4 pages, 4 figure

The ion-acoustic instability in the pre-flare plasma near the loop footpoints at solar active regions

The necessary physical conditions for development of the ion-acoustic instability in the chromospheric part of a flaring loop current circuit are investigated. Two possible scenarios have been studied. First, we consider that pre-flare loop plasma with the large-scale sub-Dreicer electric field has a classical Coulomb conductivity and, second, when anomalous resistance appears due to saturation of Bernstein turbulence. The Fontenla-Avrett-Loeser (FAL) model of the solar atmosphere was used to describe the pre-flare plasma. We have shown that investigated instability can grow and develop either in the presence of the Coulomb conductivity or saturated Bernstein turbulence. We demonstrate that in the case of small-scale instability, the threshold value for the degree of nonisothermality is high and, therefore, cannot be reached by inclusion of the ordinary Joule heating. The ion-acoustic instability can develop at the pre-flare loop footpoints provided the electrons are more than 10 times hotter than the ions there. © Author(s) 2013

Sampling of quantum dynamics at long time

The principle of energy conservation leads to a generalized choice of transition probability in a piecewise adiabatic representation of quantum(-classical) dynamics. Significant improvement (almost an order of magnitude, depending on the parameters of the calculation) over previous schemes is achieved. Novel perspectives for theoretical calculations in coherent many-body systems are opened.Comment: Revised versio

Lab-Scale Study of the Calcium Carbonate Dissolution and Deposition by Marine Cyanobacterium Phormidium subcapitatum

Suggestions that calcification in marine organisms changes in response to global variations in seawater chemistry continue to be advanced (Wilkinson, 1979; Degens et al. 1985; Kazmierczak et al. 1986; R. Riding 1992). However, the effect of [Na+] on calcification in marine cyanobacteria has not been discussed in detail although [Na+] fluctuations reflect both temperature and sea-level fluctuations. The goal of these lab-scale studies therefore was to study the effect of environmental pH and [Na+] on CaCO3 deposition and dissolution by marine cyanobacterium Phormidium subcapitatum. Marine cyanobacterium P. subcapitatum has been cultivated in ASN-III medium. [Ca2+] fluctuations were monitored with Ca(2+) probe. Na(+) concentrations were determined by the initial solution chemistry. It was found that the balance between CaCO3 dissolution and precipitation induced by P. subcapitatum grown in neutral ASN III medium is very close to zero. No CaCO3 precipitation induced by cyanobacterial growth occurred. Growth of P. subcapitatum in alkaline ASN III medium, however, was accompanied by significant oscillations in free Ca(2+) concentration within a Na(+) concentration range of 50-400 mM. Calcium carbonate precipitation occurred during the log phase of P. subcapitatum growth while carbonate dissolution was typical for the stationary phase of P. subcapitatum growth. The highest CaCO3 deposition was observed in the range of Na(+) concentrations between 200-400 mM. Alkaline pH also induced the clamping of P. subcapitatum filaments, which appeared to have a strong affinity to envelop particles of chemically deposited CaCO3 followed by enlargement of those particles size. EDS analysis revealed the presence of Mg-rich carbonate (or magnesium calcite) in the solution containing 10-100 mM Na(+); calcite in the solution containing 200 mM Na(+); and aragonite in the solution containing with 400 mM Na(+). Typical present-day seawater contains xxmM Na(+). Early (Archean) seawater was likely less saline. The division of marine cyanobacterium P. subcapitatum is associated with periodic deposition and dissolution of CaCO3, the rhythms and intensity of which are dependent on concentrations of both OH(-) and Na(+). Thus, the role of present-day marine cyanobacteria in the global carbonate cycle might be reduced to aggregation and recrystallization of available CaCO3 particles in marine water rather than long-term precipitation and accumulation of CaCO3 deposits. For lower Na(+) concentrations, precipitation of carbonates by cyanobacteria would be even less significant. These results suggest that the lack of calcified cyanobacteria in stromatalite-bearing Precambrian sequences can be explained not only by high dissolved inorganic carbon concentrations but also by lower salinity, as well as possible lower pH compared to present-day oceans

A New Look at Calcium Digermanide CaGe2_2: A High-Performing Semimetal Transparent Conducting Material for Ge Optoelectronics

Following a recently manifested guide of how to team up infrared transparency and high electrical conductivity within semimetal materials [C. Cui $et$ $al.$ Prog. Mater. Sci. 2023, 136, 101112], we evaluate an applicability of the calcium digermanide (CaGe$_2$) thin film electrodes for the advanced Ge-based optical devices. Rigorous growth experiments were conducted to define the optimal annealing treatment and thickness of the Ca-Ge mixture for producing stable CaGe$_2$ layers with high figure of merit (FOM) as transparent conducting material. Ab-initio electronic band structure calculations and optical modeling confirmed CaGe$_2$ semimetal nature, which is responsible for a demonstrated high FOM. To test CaGe$_2$ electrodes under actual conditions, a planar Ge photodetector (PD) with metal-semiconductor-metal structure was fabricated, where CaGe$_2$/Ge interface acts as Schottky barrier. The resulting Ge PD with semimetal electrodes outperformed commercially available Ge devices in terms of both photoresponse magnitude and operated spectral range. Moreover, by using femtosecond-laser projection lithography, a mesh CaGe$_2$ electrode with the relative broadband transmittance of 90\% and sheet resistance of 20 $\Omega$/sq. was demonstrated, which further enhanced Ge PD photoresponse. Thus, obtained results suggest that CaGe$_2$ thin films have a great potential in numerous applications promoting the era of advanced Ge optoelectronics.Comment: 12 pages, 4 figure