Ukupni (elastični i neelastični) udarni presjeci raspršenja elektrona na molekulama N2O, CF4, NO I F2

Electron impact total (elastic + inelastic) cross sections and total ionization cross sections are calculated for N2O, CF4, NO and F2 molecules from the thresholds to 5 keV. A model complex optical potential is calculated for each collision system from the corresponding molecular wave function at the Hartree-Fock level. The resulting complex optical potential, free from any adjustable parameter, is treated exactly in a variable-phase approach to calculate scattering complex phase shifts and the total cross sections. The present results are found to be consistent with the existing experimental measurements.Izračunali smo ukupne elektronske sudarne (elastične i neelastične) i ukupne ionizacijske udarne presjeke za molekule N2O, CF4, NO i F2 za energije od praga do 5 keV. Modelske kompleksne optičke potencijale smo izračunali za svaki sustav na osnovi odgovarajućih molekulskih Hartree-Fockovih valnih funkcija. Postignute optičke potencijale, bez parametara za podešavanje, primijenili smo egzaktno s promjenljivim fazama u računima kompleksnih faznih pomaka i ukupnih udarnih presjeka. Ishodi računa su u skladu s dostupnim rezultatima mjerenja

Diferencijalni udarni presjeci za rašprsenje elektrona atomima iterbija

Electron scattering by ytterbium atom is studied at energies 10, 20, 40, 60 and 80 eV, by applying a parameter-free complex optical potential. The real part of the complex optical potential includes the static potential Vst(r), the polarization potential Vpol(r) that consists of the short range correlation and long-range polarization effects and Vex(r) term consisting of electron exchange interaction which is modelled by assuming the electron charge cloud as a free electron gas. The loss of flux into the inelastic channels is included via a phenomenological absorption potential. Our results are compared with the recent experimental measurements.Proučavamo raspršenje elektrona na enegijama 10, 20, 40, 60 i 80 eV primjenom bezparametarskog kompleksnog optičkog potencijala. Realni dio optičkog potencijala uključuje statički potencijal Vst(r), polarizacijski potencijal Vpol(r) koji se sastoji od kratko-dosežnih korelacija i dugo-dosežnih polarizacijskih efekata i član Vex(r) koji se sastoji od elektronskog međudjelovanja izmjene, a izražen je pretpostavivši oblak elektronskog naboja kao slobodan elektronski plin. Gubitak toka u neelastične kanale uključuje se preko fenomenološkog apsorpcijskog potencijala. Postignuti ishodi uspoređuju se s nedavnim eksperimentalnim podacima

Ukupni (elastični i neelastični) udarni presjeci raspršenja elektrona na molekulama N2O, CF4, NO I F2

Electron impact total (elastic + inelastic) cross sections and total ionization cross sections are calculated for N2O, CF4, NO and F2 molecules from the thresholds to 5 keV. A model complex optical potential is calculated for each collision system from the corresponding molecular wave function at the Hartree-Fock level. The resulting complex optical potential, free from any adjustable parameter, is treated exactly in a variable-phase approach to calculate scattering complex phase shifts and the total cross sections. The present results are found to be consistent with the existing experimental measurements.Izračunali smo ukupne elektronske sudarne (elastične i neelastične) i ukupne ionizacijske udarne presjeke za molekule N2O, CF4, NO i F2 za energije od praga do 5 keV. Modelske kompleksne optičke potencijale smo izračunali za svaki sustav na osnovi odgovarajućih molekulskih Hartree-Fockovih valnih funkcija. Postignute optičke potencijale, bez parametara za podešavanje, primijenili smo egzaktno s promjenljivim fazama u računima kompleksnih faznih pomaka i ukupnih udarnih presjeka. Ishodi računa su u skladu s dostupnim rezultatima mjerenja

Diferencijalni udarni presjeci za rašprsenje elektrona atomima iterbija

Electron scattering by ytterbium atom is studied at energies 10, 20, 40, 60 and 80 eV, by applying a parameter-free complex optical potential. The real part of the complex optical potential includes the static potential Vst(r), the polarization potential Vpol(r) that consists of the short range correlation and long-range polarization effects and Vex(r) term consisting of electron exchange interaction which is modelled by assuming the electron charge cloud as a free electron gas. The loss of flux into the inelastic channels is included via a phenomenological absorption potential. Our results are compared with the recent experimental measurements.Proučavamo raspršenje elektrona na enegijama 10, 20, 40, 60 i 80 eV primjenom bezparametarskog kompleksnog optičkog potencijala. Realni dio optičkog potencijala uključuje statički potencijal Vst(r), polarizacijski potencijal Vpol(r) koji se sastoji od kratko-dosežnih korelacija i dugo-dosežnih polarizacijskih efekata i član Vex(r) koji se sastoji od elektronskog međudjelovanja izmjene, a izražen je pretpostavivši oblak elektronskog naboja kao slobodan elektronski plin. Gubitak toka u neelastične kanale uključuje se preko fenomenološkog apsorpcijskog potencijala. Postignuti ishodi uspoređuju se s nedavnim eksperimentalnim podacima

Low and intermediate energy electron collisions with the C2−_2^- molecular anion

Calculations are presented which use the molecular R-matrix with pseudo-states (MRMPS) method to treat electron impact electron detachment and electronic excitation of the carbon dimer anion. Resonances are found above the ionisation threshold of C$_2^-$ with $^1\Sigma^+_g$, $^1\Pi_g$ and $^3\Pi_g$ symmetry. These are shape resonances trapped by the effect of an attractive polarisation potential competing with a repulsive Coulomb interaction. The $\Pi_g$ resonances are found to give structure in the detachment cross section similar to that observed experimentally. Both excitation and detachment cross sections are found to be dominated by large impact parameter collisions whose contribution is modelled using the Born approximation.Comment: 18 pages, 5 figures constructed from 8 file

Multiple scattering approach to elastic electron collisions with molecular clusters

We revisit our multiple-scattering method to treat low energy elastic electron collisions with (H2O)2. Calculations are performed for different geometries of the water dimer with different dipole moments. The effect of the dipole moment of the cluster is analysed. The elastic cross sections are compared to R-matrix results. Good agreement is found above 1 eV for all geometries. Results conrm the validity of the technique

Shedding of SARS-CoV-2 in feces and urine and its potential role in person-to-person transmission and the environment-based spread of COVID-19

The recent detection of SARS-CoV-2 RNA in feces has led to speculation that it can be transmitted via the fecal-oral/ocular route. This review aims to critically evaluate the incidence of gastrointestinal (GI) symptoms, the quantity and infectivity of SARS-CoV-2 in feces and urine, and whether these pose an infection risk in sanitary settings, sewage networks, wastewater treatment plants, and the wider environment (e.g. rivers, lakes and marine waters). A review of 48 independent studies revealed that severe GI dysfunction is only evident in a small number of COVID-19 cases, with 11 ± 2% exhibiting diarrhea and 12 ± 3% exhibiting vomiting and nausea. In addition to these cases, SARS-CoV-2 RNA can be detected in feces from some asymptomatic, mildly- and pre-symptomatic individuals. Fecal shedding of the virus peaks in the symptomatic period and can persist for several weeks, but with declining abundances in the post-symptomatic phase. SARS-CoV-2 RNA is occasionally detected in urine, but reports in fecal samples are more frequent. The abundance of the virus genetic material in both urine (ca. 102–105 gc/ml) and feces (ca. 102–107 gc/ml) is much lower than in nasopharyngeal fluids (ca. 105–1011 gc/ml). There is strong evidence of multiplication of SARS-CoV-2 in the gut and infectious virus has occasionally been recovered from both urine and stool samples. The level and infectious capability of SARS-CoV-2 in vomit remain unknown. In comparison to enteric viruses transmitted via the fecal-oral route (e.g. norovirus, adenovirus), the likelihood of SARS-CoV-2 being transmitted via feces or urine appears much lower due to the lower relative amounts of virus present in feces/urine. The biggest risk of transmission will occur in clinical and care home settings where secondary handling of people and urine/fecal matter occurs. In addition, while SARS-CoV-2 RNA genetic material can be detected by in wastewater, this signal is greatly reduced by conventional treatment. Our analysis also suggests the likelihood of infection due to contact with sewage-contaminated water (e.g. swimming, surfing, angling) or food (e.g. salads, shellfish) is extremely low or negligible based on very low predicted abundances and limited environmental survival of SARS-CoV-2. These conclusions are corroborated by the fact that tens of million cases of COVID-19 have occurred globally, but exposure to feces or wastewater has never been implicated as a transmission vector

Spatially-Resolved O II Recombination Line Observations of the Ring Nebula, NGC 6720

We present spatially-resolved spectral of O II permitted lines and [O III] forbidden lines in the Ring Nebula NGC 6720. We find significant differences in the spatial distribution of the O II and [O III] lines. The [O III] emission follows the H-beta emission measure; however, the O II emission peaks closer to the central star. This suggests that radiative recombination may not be the primary mechanism for producing the O II lines. O+2 abundances derived from O II lines are 5-10 times larger than those derived from [O III] in the region within 20" of the central star, but agree to within 0.2-0.3 dex outside this region. The [O III] electron temperature rises smoothly from about 10,000 K in the outer shell to about 12,000 K in the center; we see no evidence for a temperature jump that would be associated with a shock. If temperature fluctuations are responsible for the discrepancy in O+2 abundances, the average temperature would have to be approximately 6,500 K in the He$^{+2}$ zone and about 9,000 K in the outer shell in order to force the [O III]-derived abundance to equal that derived from O II. We therefore argue that temperature fluctuations can not explain the abundance discrepancy. The O II emission does not peak at the locations of dusty knots, creating difficulties for models which explain the O II - [O III] discrepancy by density fluctuations. We examine the possibility high-temperature dielectronic recombination in a central hot bubble enhances the O II line strengths in the central nebula. However, comparison of recombination rates with collisional excitation rates shows that the increase in recombination emission due to dielectronic recombination at T ~ 10^5 K is not sufficient to overcome the increase in [O III] emission. (Abridged)Comment: 33 pages, 11 postscript figures. Scheduled to appear in the 1 Sept 2001 Astrophysical Journa