Non-reactive scattering of rotational quantum state selected molecular beams

Non-reactive scattering of rotational quantum state selected molecular beams of symmetric top molecules has been investigated using electrostatic methods. Cross-sections for the defocusing of upper Stark-state molecules in a hexapole electric field have been measured for neat and seeded beams of CH3F with a range of polar and non-polar quencher gases. Calculations of the hexapole focusing voltages for specific rotational states facilitated the assignment of the defocusing cross-sections to individual rotational states in the beam. The technique of Molecular Beam Electric Resonance (MBER) spectrometry has been employed to detect and study individual rotational states, resulting in a dramatic improvement in quantum state resolution over the use of a single hexapole filter. Cross-sections have been measured for the relaxation of selected upper Stark states in beams of methyl halides with a range of polar and non-polar scattering gases. The application of MBER spectrometry to rotational state identification in beams of symmetric to molecules has been explored in this study. Information on the velocity, temperature, and rotational state distribution of the beam can be easily obtained from experimentation using this arrangement. It has also provided insight into the focusing properties of hexapole electric filters. Individual rotational quantum states in a beam of symmetric top molecules could be tagged using an MBER spectrometer for studies of rotational state dependent properties, such as the effect of rotational states in scattering studies. The collisional relaxation of upper Stark-state molecules in a beam could occur through several mechanisms. Cross-sections measured using the technique of MBER have been largely attributed to an Mᴊ changing process. The effects of the long-range attractive van der Waals interaction potential, the relative velocity dependence of the collision partners and the electric field dependence of the Stark energy have been considered in order to account for the magnitude of the relaxation cross-sections measured in this study

Pooled RT-qPCR testing for SARS-CoV-2 surveillance in schools - a cluster randomised trial

Background: The extent to which children and adolescents contribute to SARS-CoV-2 transmission remains not fully understood. Novel high-capacity testing methods may provide real-time epidemiological data in educational settings helping to establish a rational approach to prevent and minimize SARS-CoV-2 transmission. We investigated whether pooling of samples for SARS-CoV-2 detection by RT-qPCR is a sensitive and feasible high-capacity diagnostic strategy for surveillance of SARS-CoV-2 infections in schools. Methods: In this study, students and school staff of 14 educational facilities in Germany were tested sequentially between November 9 and December 23, 2020, two or three times per week for at least three consecutive weeks. Participants were randomized for evaluation of two different age adjusted swab sampling methods (oropharyngeal swabs or buccal swabs compared to saliva swabs using a ‘lolli method’). Swabs were collected and pooled for SARS-CoV-2 RT-qPCR. Individuals of positive pooled tests were retested by RT-qPCR the same or the following day. Positive individuals were quarantined while the SARS-CoV-2 negative individuals remained in class with continued pooled RT-qPCR surveillance. The study is registered with the German Clinical Trials register (registration number: DRKS00023911). Findings: 5,537 individuals were eligible and 3970 participants were enroled and included in the analysis. In students, a total of 21,978 swabs were taken and combined in 2218 pooled RT-qPCR tests. We detected 41 positive pooled tests (1·8%) leading to 36 SARS-CoV-2 cases among students which could be identified by individual re-testing. The cumulative 3-week incidence for primary schools was 564/100,000 (6/1064, additionally 1 infection detected in week 4) and 1249/100,000 (29/2322) for secondary schools. In secondary schools, there was no difference in the number of SARS-CoV-2 positive students identified from pooled oropharyngeal swabs compared to those identified from pooled saliva samples (lolli method) (14 vs. 15 cases; 1·3% vs. 1·3%; OR 1.1; 95%-CI 0·5–2·5). A single secondary school accounted for 17 of 36 cases (47%) indicating a high burden of asymptomatic prevalent SARS-CoV-2 cases in the respective school and community. Interpretation: In educational settings, SARS-CoV-2 screening by RT-qPCR-based pooled testing with easily obtainable saliva samples is a feasible method to detect incident cases and observe transmission dynamics. Funding: Federal Ministry of education and research (BMBF; Project B-FAST in “NaFoUniMedCovid19”; registration number: 01KX2021)