Modelling the ArH+^+ emission from the Crab Nebula

We have performed combined photoionization and photodissociation region (PDR) modelling of a Crab Nebula filament subjected to the synchrotron radiation from the central pulsar wind nebula, and to a high flux of charged particles; a greatly enhanced cosmic ray ionization rate over the standard interstellar value, $\zeta_0$, is required to account for the lack of detected [C I] emission in published Herschel SPIRE FTS observations of the Crab Nebula. The observed line surface brightness ratios of the OH$^+$ and ArH$^+$ transitions seen in the SPIRE FTS frequency range can only be explained with both a high cosmic ray ionization rate and a reduced ArH$^+$ dissociative recombination rate compared to that used by previous authors, although consistent with experimental upper limits. We find that the ArH$^+$/OH$^+$ line strengths and the observed H$_2$ vibration-rotation emission can be reproduced by model filaments with $n_{\rm{H}} = 2 \times 10^4$ cm$^{-3}$, $\zeta = 10^7 \zeta_0$ and visual extinctions within the range found for dusty globules in the Crab Nebula, although far-infrared emission from [O I] and [C II] is higher than the observational constraints. Models with $n_{\rm{H}} = 1900$ cm$^{-3}$ underpredict the H$_2$ surface brightness, but agree with the ArH$^+$ and OH$^+$ surface brightnesses and predict [O I] and [C II] line ratios consistent with observations. These models predict HeH$^+$ rotational emission above detection thresholds, but consideration of the formation timescale suggests that the abundance of this molecule in the Crab Nebula should be lower than the equilibrium values obtained in our analysis.Comment: Accepted by MNRAS. Author accepted manuscript. Accepted on 05/09/2017. Deposited on 05/09/1

Desorption From Interstellar Ices

The desorption of molecular species from ice mantles back into the gas phase in molecular clouds results from a variety of very poorly understood processes. We have investigated three mechanisms; desorption resulting from H_2 formation on grains, direct cosmic ray heating and cosmic ray induced photodesorption. Whilst qualitative differences exist between these processes (essentially deriving from the assumptions concerning the species-selectivity of the desorption and the assumed threshold adsorption energies, E_t) all three processes are found to be potentially very significant in dark cloud conditions. It is therefore important that all three mechanisms should be considered in studies of molecular clouds in which freeze-out and desorption are believed to be important. Employing a chemical model of a typical static molecular core and using likely estimates for the quantum yields of the three processes we find that desorption by H_2 formation probably dominates over the other two mechanisms. However, the physics of the desorption processes and the nature of the dust grains and ice mantles are very poorly constrained. We therefore conclude that the best approach is to set empirical constraints on the desorption, based on observed molecular depletions - rather than try to establish the desorption efficiencies from purely theoretical considerations. Applying this method to one such object (L1689B) yields upper limits to the desorption efficiencies that are consistent with our understanding of these mechanisms.Comment: 11 pages, 5 figures, accepted by MNRAS subject to minor revision which has been carried ou

The L1157-B1 astrochemical laboratory: testing the origin of DCN

L1157-B1 is the brightest shocked region of the large-scale molecular outflow, considered the prototype of chemically rich outflows, being the ideal laboratory to study how shocks affect the molecular gas. Several deuterated molecules have been previously detected with the IRAM 30m, most of them formed on grain mantles and then released into the gas phase due to the shock. We aim to observationally investigate the role of the different chemical processes at work that lead to formation the of DCN and test the predictions of the chemical models for its formation. We performed high-angular resolution observations with NOEMA of the DCN(2-1) and H13CN(2-1) lines to compute the deuterated fraction, Dfrac(HCN). We detected emission of DCN(2-1) and H13CN(2-1) arising from L1157-B1 shock. Dfrac(HCN) is ~4x10$^{-3}$ and given the uncertainties, we did not find significant variations across the bow-shock. Contrary to HDCO, whose emission delineates the region of impact between the jet and the ambient material, DCN is more widespread and not limited to the impact region. This is consistent with the idea that gas-phase chemistry is playing a major role in the deuteration of HCN in the head of the bow-shock, where HDCO is undetected as it is a product of grain-surface chemistry. The spectra of DCN and H13CN match the spectral signature of the outflow cavity walls, suggesting that their emission result from shocked gas. The analysis of the time dependent gas-grain chemical model UCL-CHEM coupled with a C-type shock model shows that the observed Dfrac(HCN) is reached during the post-shock phase, matching the dynamical timescale of the shock. Our results indicate that the presence of DCN in L1157-B1 is a combination of gas-phase chemistry that produces the widespread DCN emission, dominating in the head of the bow-shock, and sputtering from grain mantles toward the jet impact region.Comment: Accepted for publication in A&A. 7 pages, 5 Figures, 1 Tabl

First ALMA maps of HCO, an important precursor of complex organic molecules, towards IRAS 16293-2422

The formyl radical HCO has been proposed as the basic precursor of many complex organic molecules such as methanol (CH$_3$OH) or glycolaldehyde (CH$_2$OHCHO). Using ALMA, we have mapped, for the first time at high angular resolution ($\sim$1$^{\prime\prime}$, $\sim$140 au), HCO towards the Solar-type protostellar binary IRAS 16293$-$2422, where numerous complex organic molecules have been previously detected. We also detected several lines of the chemically related species H$_2$CO, CH$_3$OH and CH$_2$OHCHO. The observations revealed compact HCO emission arising from the two protostars. The line profiles also show redshifted absorption produced by foreground material of the circumbinary envelope that is infalling towards the protostars. Additionally, IRAM 30m single-dish data revealed a more extended HCO component arising from the common circumbinary envelope. The comparison between the observed molecular abundances and our chemical model suggests that whereas the extended HCO from the envelope can be formed via gas-phase reactions during the cold collapse of the natal core, the HCO in the hot corinos surrounding the protostars is predominantly formed by the hydrogenation of CO on the surface of dust grains and subsequent thermal desorption during the protostellar phase. The derived abundance of HCO in the dust grains is high enough to produce efficiently more complex species such as H$_2$CO, CH$_3$OH, and CH$_2$OHCHO by surface chemistry. We found that the main formation route of CH$_2$OHCHO is the reaction between HCO and CH$_2$OH.Comment: Accepted in Monthly Notices of the Royal Astronomical Society; 19 pages, 12 figures, 7 table

EKSPLORASI SPLUNK UNTUK MEMBANGUN DASHBOARD DAN ALERT BERDASARKAN DATA SYSLOG (STUDI KASUS : DATA CENTER PT. TELEKOMUNIKASI INDONESIA)

Menghubungkan sistem dan mengotomatisasi proses bisnis adalah hal yang penting untuk menghemat biaya, meningkatkan efisiensi operasional, dan memperoleh peluang bisnis baru. Untuk alasan ini, teknologi yang memanage syslog merupakan prioritas tinggi sehingga splunk menjadi salah satu jawaban dari teknologi management syslog. Konsep splunk digunakan untuk pengolahan syslog dalam lingkungan jaringan dengan berbagai cara. Dashboard dan alert merupakan inti dari arsitektur splunk. Dashboard dan alert yang dimaksud merupakan fitur utama splunk, yang merupakan bagian penting dalam arsitektur splunk karena menyediakan dasar-dasar proses monitoring sebuah jaringan yang digunakan oleh splunk untuk melakukan searching syslog. Contoh proses searching syslog menggunakan splunk ialah integrasi syslog pada jaringan di PT. Telekomunikasi Indonesia. Jaringan yang akan diintegrasikan ialah jaringan broadband yang bertujuan untuk mengotomatisasi syslog pada setiap perangkat jaringan dengan menggunakan dashboard dan alert akan digunakan sebagai solusi dengan menggunakan Splunk. Kata kunci: Splunk, Dashboard, Alert, Syslog, Broadban

Polyphenols and organic acids as alternatives to antimicrobials in poultry rearing: a review.

For decades antibiotics have been used in poultry rearing to support high levels of production. Nevertheless, several problems have arisen because of the misuse of antibiotics (i.e., antibiotic resistance, residues in animal products, environmental pollution). Thus, the European Union (EU) as well as the European Food Safety Authority (EFSA) promote action plans to diminish the use of antibiotics in animal production. Alternatives to antibiotics have been studied. Polyphenols (PPs) or organic acids (OAs) seem to be two accredited solutions. Phenolic compounds, such as phenols, flavonoids, and tannins exert their antimicrobial effect with specific mechanisms. In contrast, short chain fatty acids (SCFAs) and medium chain fatty acids (MCFAs), the OAs mainly used as antibiotics alternative, act on the pathogens depending on the pKa value. This review aims to collect the literature reporting the effects of these substances applied as antimicrobial molecules or growth promoter in poultry feeding (both for broilers and laying hens). Organic acids and PPs can be used individually or in blends, exploiting the properties of each component. Collected data highlighted that further research needs to focus on OAs in laying hens’ feeding and also determine the right combination in blends with PPs

An efficient method for determining the chemical evolution of gravitationally collapsing prestellar cores

We develop analytic approximations to the density evolution of prestellar cores, based on the results of hydrodynamical simulations. We use these approximations as input for a time-dependent gas-grain chemical code to investigate the effects of differing modes of collapse on the molecular abundances in the core. We confirm that our method can provide reasonable agreement with an exact numerical solution of both the hydrodynamics and chemistry while being significantly less computationally expensive, allowing a large grid of models varying multiple input parameters to be run. We present results using this method to illustrate how the chemistry is affected not only by the collapse model adopted, but also by the large number of unknown physical and chemical parameters. Models which are initially gravitationally unstable predict similar abundances despite differing densities and collapse timescales, while ambipolar diffusion produces more extended inner depleted regions which are not seen in observations of prestellar cores. Molecular observations are capable of discriminating between modes of collapse despite the unknown values of various input parameters. We also investigate the evolution of the ambipolar diffusion timescale for a range of collapse modes, metallicities and cosmic ray ionization rates, finding that it remains comparable to or larger than the collapse timescale during the initial stages for all models we consider, but becomes smaller at later evolutionary stages. This confirms that ambipolar diffusion is an important process for diffuse gas, but becomes less significant as cores collapse to higher densities.Comment: Accepted by AJ. Author accepted manuscript. Accepted 29/05/2018, deposited 05/06/201

Collisional excitation of interstellar PO(X-2 Pi) by He: new ab initio potential energy surfaces and scattering calculations

We acknowledge the financial support from the COST Action CM1401 “Our Astrochemical History”. This research utilized Queen Mary's Mid-Plus computational facilities, supported by QMUL Research-IT and funded by EPSRC grant EP/K000128/1. S. M. acknowledges Indigo Dean for very useful discussions. I. J.-S. acknowledges the financial support received from the STFC through an Ernest Rutherford Fellowship (proposal number ST/L004801)