Determination of the Deep Inelastic Contribution to the Generalised Gerasimov-Drell-Hearn Integral for the Proton and Neutron

The virtual photon absorption cross section differences [sigma_1/2-sigma_3/2] for the proton and neutron have been determined from measurements of polarised cross section asymmetries in deep inelastic scattering of 27.5 GeV longitudinally polarised positrons from polarised 1H and 3He internal gas targets. The data were collected in the region above the nucleon resonances in the kinematic range nu < 23.5 GeV and 0.8 GeV**2 < Q**2 < 12 GeV**2. For the proton the contribution to the generalised Gerasimov-Drell-Hearn integral was found to be substantial and must be included for an accurate determination of the full integral. Furthermore the data are consistent with a QCD next-to-leading order fit based on previous deep inelastic scattering data. Therefore higher twist effects do not appear significant.Comment: 6 pages, 3 figures, 1 table, revte

Observation of a Coherence Length Effect in Exclusive Rho^0 Electroproduction

Exclusive incoherent electroproduction of the rho^0(770) meson from 1H, 2H, 3He, and 14N targets has been studied by the HERMES experiment at squared four-momentum transfer Q**2>0.4 GeV**2 and positron energy loss nu from 9 to 20 GeV. The ratio of the 14N to 1H cross sections per nucleon, known as the nuclear transparency, was found to decrease with increasing coherence length of quark-antiquark fluctuations of the virtual photon. The data provide clear evidence of the interaction of the quark- antiquark fluctuations with the nuclear medium.Comment: RevTeX, 5 pages, 3 figure

Distance matters to sperm whales : behavioural disturbance in response to both sonar received level and source distance

Funding: This work was supported by US Naval Facility Engineering Command / Living Marine Resources (LMR) research program (grant no. N39430–17-C-1935); The Netherlands Ministry of Defense; Defense Science and Technology Lab (UK Ministry of Defense; grant no. DSTLX-1000137649); and DGA (French Ministry of Defense; grant no. 1883003901). The Royal Norwegian Navy supported the work by supplying access to the frigate KNM Otto Sverdrup. PW was supported by the RANNÍS Icelandic Research Fund (grant no. 207081).Understanding the main drivers of behavioural disturbance in deep-diving cetaceans would improve predictions of anthropogenic noise effects on individual animals, habitats and populations. To investigate the potential roles of received level and source distance on behavioural disturbance, we tagged 14 sperm whales in northern Norway with multi-sensor data loggers and conducted dose-escalation experiments. Each experiment included 1 to 4 tagged individuals and involved multiple vessel passes (‘exposure sessions’, n = 25 total) by a navy frigate or research vessel towing a naval sonar, at different starting distances and maximum source levels. We analysed behaviour state series and proxies for locomotor activity and foraging success with generalized additive mixed models. The probability of occurrence of non-foraging active behaviour was affected by received level, source distance and session order, with decreased foraging effort at higher received levels and shorter distances, and during subsequent sessions (indicating short-term sensitisation). Prey capture attempts decreased with increasing received level when whales kept foraging. Similar to what has been suggested for some populations of blue whales and beaked whales regularly exposed to navy sonar, but unlike northern bottlenose whales in more pristine waters, source distance affected sperm whale behavioural responses on a high-latitude foraging ground.Peer reviewe

First indications that northern bottlenose whales are sensitive to behavioural disturbance from anthropogenic noise

-Although northern bottlenose whales were the most heavily hunted beaked whale, we have little information about this species in its remote habitat of the North Atlantic Ocean. Underwater anthropogenic noise and disruption of their natural habitat may be major threats, given the sensitivity of other beaked whales to such noise disturbance. We attached dataloggers to 13 northern bottlenose whales and compared their natural sounds and movements to those of one individual exposed to escalating levels of 1–2 kHz upsweep naval sonar signals. At a received sound pressure level (SPL) of 98 dB re 1 μPa, the whale turned to approach the sound source, but at a received SPL of 107 dB re 1 μPa, the whale began moving in an unusually straight course and then made a near 180° turn away from the source, and performed the longest and deepest dive (94 min, 2339 m) recorded for this species. Animal movement parameters differed significantly from baseline for more than 7 h until the tag fell off 33–36 km away. No clicks were emitted during the response period, indicating cessation of normal echolocation-based foraging. A sharp decline in both acoustic and visual detections of conspecifics after exposure suggests other whales in the area responded similarly. Though more data are needed, our results indicate high sensitivity of this species to acoustic disturbance, with consequent risk from marine industrialization and naval activity

Structural Basis for Polyproline-Mediated Ribosome Stalling and Rescue by the Translation Elongation Factor EF-P

Ribosomes synthesizing proteins containing consecutive proline residues become stalled and require rescue via the action of uniquely modified translation elongation factors, EF-P in bacteria, or archaeal/eukaryotic a/eIF5A. To date, no structures exist of EF-P or eIF5A in complex with translating ribosomes stalled at polyproline stretches, and thus structural insight into how EF-P/eIF5A rescue these arrested ribosomes has been lacking. Here we present cryo-EM structures of ribosomes stalled on proline stretches, without and with modified EF-P. The structures suggest that the favored conformation of the polyproline-containing nascent chain is incompatible with the peptide exit tunnel of the ribosome and leads to destabilization of the peptidyltRNA. Binding of EF-P stabilizes the P-site tRNA, particularly via interactions between its modification and the CCA end, thereby enforcing an alternative conformation of the polyproline-containing nascent chain, which allows a favorable substrate geometry for peptide bond formation

Diving apart together : call propagation in diving long-finned pilot whales

This research was funded by Office of Naval Research awards [N00014-08-1-0984, N00014-10-1-0355, N00014-15-1-2341], the Dutch Royal Navy (Koninklijke Nederlandse Marine) and the Norwegian Navy (Forsvarets Forskningsinstitutt – FFI).Group-living animals must communicate to stay in contact. In long-finned pilot whales, there is a trade-off between the benefits of foraging individually at depth and the formation of tight social groups at the surface. Using theoretical modelling and empirical data of tagged pairs within a group, we examined the potential of pilot whale social calls to reach dispersed group members during foraging periods. Both theoretical predictions and empirical data of tag pairs showed a potential for communication between diving and non-diving group members over separation distances up to 385 m (empirical) and 1800 m (theoretical). These distances match or exceed pilot whale dive depths recorded across populations. Call characteristics and environmental characteristics were analysed to investigate determinants of call detectability. Longer calls with a higher sound pressure level (SPL) that were received in a quieter environment were more often detected than their shorter, lower SPL counterparts within a noisier environment. In a noisier environment, calls were louder and had a lower peak frequency, indicating mechanisms for coping with varying conditions. However, the vulnerability of pilot whales to anthropogenic noise is still of concern as the ability to cope with increasing background noise may be limited. Our study shows that combining propagation modelling and actual tag recordings provides new insights into the communicative potential for social calls in orientation and reunion with group members for deep-diving pilot whales.Publisher PDFPeer reviewe

Protease inhibitor homologues of dendrotoxin do not bind to dendrotoxin acceptors on synaptosomal membranes or facilitate neuromuscular transmission

The dendrotoxins are a homologous group of potassium channel-blocking polypeptides found in mamba snake venom. They are similar in sequence and structure to Kunitz-type serine protease inhibitors. Modified and native protease inhibitors were assayed for dendrotoxin-like activity using radioligand-binding and twitch tension-recording methods. Despite the large number and high concentration of compounds tested, no protease inhibitor displayed dendrotoxin-like activity. The results indicate that the protease-inhibiting and potassium channel-blocking activities of these two groups of polypeptides are not linked