Experimental entanglement distribution by separable states

The distribution of entanglement between macroscopically separated parties represents a crucial protocol for future quantum information networks. Surprisingly, it has been theoretically shown that two distant systems can be entangled by sending a third mediating system that is not entangled with either of them. Such a possibility seems to contradict the intuition that to distribute entanglement, the transmitted system always needs to be entangled with the sender. Here, we experimentally distribute entanglement by exchanging a subsystem and successfully prove that this subsystem is not entangled with either of the two parties. Our implementation relies on the preparation of a specific three-mode Gaussian state containing thermal noise that demolishes the entanglement in two of the three bipartite splittings. After transmission of a separable mode this noise can be removed by quantum interference. Our work demonstrates an unexpected variant of entanglement distribution and improves the understanding necessary to engineer multipartite quantum information networks.Comment: 9 pages, 6 figure

Quantitative dopplersonografische Bestimmung der Hirndurchblutung bei Neugeborenen mit angeborenem Herzfehler

Zentrale Frage dieser Arbeit war, ob die bei Neugeborenen durch einen angeborenen Herzfehler veränderte Hämodynamik zu einem verminderten zerebralen Blutflussvolumen führt. Es wurde die Hypothese untersucht, ob ein negativer Zusammenhang zwischen gesamtem zerebralem Blutflussvolumen (CBFV) und Schweregrad eines Windkessellecks (WKL), bedingt durch einen extrakardialen Links-Rechts-Shunt, besteht. Als erster Teil der Arbeit wurde in einer prospektiven Test-Retest-Studie zwischen November 2008 und April 2009 die Reliabilität der quantitativen dopplersonografischen Bestimmung des CBFV an 20 jugendlichen Probanden untersucht und nachgewiesen (Variationskoeffizient 10,0 %, Pearson-Korrelationskoeffizient und Intraklassenkoeffizient jeweils 0,86, absolute und relative Untersucherdifferenz 2,6 ± 80 ml/min bzw. 0,5 ± 9,7 %). Dadurch konnte gezeigt werden, dass die verwendete Methodik auch bei neu eingelernten Untersuchern reliable Ergebnisse liefert. In einer prospektiven Pilot-Studie wurde zwischen März 2009 und März 2011 bei 38 Neugeborenen mit AHF im postmenstruellen Alter (PA) von 33,6 - 44,4 (Median 40,4) Wochen das gesamte CBFV vor dem ersten herzchirurgischen operativen Eingriff dopplersonografisch bestimmt. Die Neugeborenen mit AHF hatten ein gesamtes CBFV von 62 ± 20 (17 - 106) ml/min und eine gesamte Hirnperfusion (CBFVH) von 17 ± 6 (6 - 29) ml/100 g Hirngewicht/min bei einem berechneten Hirngewicht von 368 ± 70 (221 - 552) g. CBFV, CBFVH und Hirngewicht stiegen mit dem PA signifikant an. Ein signifikanter Zusammenhang zwischen gesamtem CBFV und Hirngewicht war nicht nachweisbar. Die Versorgung des Gehirns erfolgte zu 24 ± 8 % über das hintere Stromgebiet und änderte sich nicht mit steigendem PA. Sowohl das Gesamtkollektiv als auch Neugeborene mit schwerem WKL wiesen ein signifikant vermindertes gesamtes CBFV auf (98,34 % - Konfidenzintervall der auf ein altersentsprechendes Normkollektiv bezogenen Z-Werte: -0,938 - (-0,688) bzw. -2,389 - (-0,051)). Neugeborene ohne WKL hatten kein signifikant vermindertes gesamtes CBFV. Deskriptiv zeichnete sich in Abhängigkeit der Schwere des WKL ein Rückgang der diastolischen Perfusion ab, wohingegen die maximalen systolischen Flussgeschwindigkeiten (Vs) gegenüber dem Normkollektiv erhöht waren. Zusammenfassend weisen die Ergebnisse dieser Studie auf ein erhöhtes präoperatives Risiko für zerebrale Schädigungen bei Neugeborenen mit AHF hin, bedingt durch ein signifikant vermindertes zerebrales Blutflussvolumen bei hämodynamisch relevantem Windkesselleck und die erhöhte Inzidenz an Frühgeburten. Die bei Neugeborenen mit AHF überhäufig vorhandenen kleinen Kopfumfänge lassen eine bereits intrauterin beeinträchtigte Hirnentwicklung vermuten

Recognition of Peptidoglycan Fragments by the Transpeptidase PBP4 From Staphylococcus aureus

Peptidoglycan (PG) is an essential component of the cell envelope, maintaining bacterial cell shape and protecting it from bursting due to turgor pressure. The monoderm bacterium Staphylococcus aureus has a highly cross-linked PG, with ~90% of peptide stems participating in DD-cross-links and up to 15 peptide stems connected with each other. These cross-links are formed in transpeptidation reactions catalyzed by penicillin-binding proteins (PBPs) of classes A and B. Most S. aureus strains have three housekeeping PBPs with this function (PBP1, PBP2, and PBP3) but MRSA strains have acquired a third class B PBP, PBP2a, which is encoded by the mecA gene and required for the expression of high-level resistance to β-lactams. Another housekeeping PBP of S. aureus is PBP4, which belongs to the class C PBPs, and hence would be expected to have PG hydrolase (DD-carboxypeptidase or DD-endopeptidase) activity. However, previous works showed that, unexpectedly, PBP4 has transpeptidase activity that significantly contributes to both the high level of cross-linking in the PG of S. aureus and to the low level of β-lactam resistance in the absence of PBP2a. To gain insights into this unusual activity of PBP4, we studied by NMR spectroscopy its interaction in vitro with different substrates, including intact peptidoglycan, synthetic peptide stems, muropeptides, and long glycan chains with uncross-linked peptide stems. PBP4 showed no affinity for the complex, intact peptidoglycan or the smallest isolated peptide stems. Transpeptidase activity of PBP4 was verified with the disaccharide peptide subunits (muropeptides) in vitro, producing cyclic dimer and multimer products; these assays also showed a designed PBP4(S75C) nucleophile mutant to be inactive. Using this inactive but structurally highly similar variant, liquid-state NMR identified two interaction surfaces in close proximity to the central nucleophile position that can accommodate the potential donor and acceptor stems for the transpeptidation reaction. A PBP4:muropeptide model structure was built from these experimental restraints, which provides new mechanistic insights into mecA independent resistance to β-lactams in S. aureus

Database of epidemic trends and control measures during the first wave of COVID-19 in mainland China.

OBJECTIVES: In this data collation study, we aimed to provide a comprehensive database describing the epidemic trends and responses during the first wave of coronavirus disease 2019 (COVID-19) throughout the main provinces in China. METHODS: From mid-January to March 2020, we extracted publicly available data regarding the spread and control of COVID-19 from 31 provincial health authorities and major media outlets in mainland China. Based on these data, we conducted descriptive analyses of the epidemic in the six most-affected provinces. RESULTS: School closures, travel restrictions, community-level lockdown, and contact tracing were introduced concurrently around late January but subsequent epidemic trends differed among provinces. Compared with Hubei, the other five most-affected provinces reported a lower crude case fatality ratio and proportion of critical and severe hospitalised cases. From March 2020, as the local transmission of COVID-19 declined, switching the focus of measures to the testing and quarantine of inbound travellers may have helped to sustain the control of the epidemic. CONCLUSIONS: Aggregated indicators of case notifications and severity distributions are essential for monitoring an epidemic. A publicly available database containing these indicators and information regarding control measures is a useful resource for further research and policy planning in response to the COVID-19 epidemic

The Redundancy of Peptidoglycan Carboxypeptidases Ensures Robust Cell Shape Maintenance in Escherichia coli

Peptidoglycan (PG) is an essential structural component of the bacterial cell wall and maintains the integrity and shape of the cell by forming a continuous layer around the cytoplasmic membrane. The thin PG layer of Escherichia coli resides in the periplasm, a unique compartment whose composition and pH can vary depending on the local environment of the cell. Hence, the growth of the PG layer must be sufficiently robust to allow cell growth and division under different conditions. We have analyzed the PG composition of 28 mutants lacking multiple PG enzymes (penicillin-binding proteins [PBPs]) after growth in acidic or near-neutral-pH media. Statistical analysis of the muropeptide profiles identified dd-carboxypeptidases (DD-CPases) that were more active in cells grown at acidic pH. In particular, the absence of the DD-CPase PBP6b caused a significant increase in the pentapeptide content of PG as well as morphological defects when the cells were grown at acidic pH. Other DD-CPases (PBP4, PBP4b, PBP5, PBP6a, PBP7, and AmpH) and the PG synthase PBP1B made a smaller or null contribution to the pentapeptide-trimming activity at acidic pH. We solved the crystal structure of PBP6b and also demonstrated that the enzyme is more stable and has a lower Km at acidic pH, explaining why PBP6b is more active at low pH. Hence, PBP6b is a specialized DD-CPase that contributes to cell shape maintenance at low pH, and E. coli appears to utilize redundant DD-CPases for normal growth under different conditions