Multi-messenger observations of a binary neutron star merger

On 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 170817A) with a time delay of ~1.7 s with respect to the merger time. From the gravitational-wave signal, the source was initially localized to a sky region of 31 deg2 at a luminosity distance of 40+8-8 Mpc and with component masses consistent with neutron stars. The component masses were later measured to be in the range 0.86 to 2.26 Mo. An extensive observing campaign was launched across the electromagnetic spectrum leading to the discovery of a bright optical transient (SSS17a, now with the IAU identification of AT 2017gfo) in NGC 4993 (at ~40 Mpc) less than 11 hours after the merger by the One- Meter, Two Hemisphere (1M2H) team using the 1 m Swope Telescope. The optical transient was independently detected by multiple teams within an hour. Subsequent observations targeted the object and its environment. Early ultraviolet observations revealed a blue transient that faded within 48 hours. Optical and infrared observations showed a redward evolution over ~10 days. Following early non-detections, X-ray and radio emission were discovered at the transient’s position ~9 and ~16 days, respectively, after the merger. Both the X-ray and radio emission likely arise from a physical process that is distinct from the one that generates the UV/optical/near-infrared emission. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches. These observations support the hypothesis that GW170817 was produced by the merger of two neutron stars in NGC4993 followed by a short gamma-ray burst (GRB 170817A) and a kilonova/macronova powered by the radioactive decay of r-process nuclei synthesized in the ejecta

Why Should We Preserve Fishless High Mountain Lakes?

High mountain lakes are originally fishless, although many have had introductions of non-native fish species, predominantly trout, and recently also minnows introduced by fishermen that use them as live bait. The extent of these introductions is general and substantial often involving many lakes over mountain ranges. Predation on native fauna by introduced fish involves profound ecological changes since fish occupy a higher trophic level that was previously inexistent. Fish predation produces a drastic reduction or elimination of autochthonous animal groups, such as amphibians and large macroinvertebrates in the littoral, and crustaceans in the plankton. These strong effects raise concerns for the conservation of high mountain lakes. In terms of individual species, those adapted to live in larger lakes have suffered a higher decrease in the size of their metapopulation. This ecological problem is discussed from a European perspective providing examples from two study areas: the Pyrenees and the Western Italian Alps. Species-specific studies are urgently needed to evaluate the conservation status of the more impacted species, together with conservation measures at continental and regional scales, through regulation, and at local scale, through restoration actions, aimed to stop further invasive species expansions and to restore the present situation. At different high mountain areas of the world, there have been restoration projects aiming to return lakes to their native fish-free status. In these areas autochthonous species that disappeared with the introduction of fish are progressively recovering their initial distribution when nearby fish-free lakes and ponds are available

Cerebral hemodynamic and metabolic changes in patients with fulminant hepatic failure during liver transplantation

Background. Cerebral autoregulation and metabolism may be seriously compromised in patients with fulminant hepatic failure (FHF). The mechanism responsible for the alteration in cerebral blood flow (CBF) has not been yet clearly defined; however, it is known that it does correlate with liver function. Orthotopic liver transplant (OLT) rapidly restores normal liver function, but little is known about the restoration of cerebral metabolism and hemodynamics. To investigate the relationship between liver function and CBF, we evaluated autoregulation and metabolic changes during OLT in six patients comatose due to FHF. Methods. We evaluated autoregulation based on a linear regression analysis between mean arterial blood pressure and parallel CBF velocity (CBFV) changes using transcranial Doppler ultrasound. Cerebral metabolism rate was estimated by the arterial-jugular venous oxygen content difference (a-jDO(2)), while the percentile variation in cerebral metabolic rate for oxygen (CMRO2) was estimated using CBFV percentile variation rather than CBF percentile variation (eCMRO(2)). Results. Prior to transplant autoregulation was impaired in all patients. However it markedly improved at the end of surgery (P <.05). The eCMRO(2) improved as well, particularly among subjects who displayed prompt neurological recovery. In all patients the a-jDO(2) was low before transplantation increasing to normal values at the end of surgery. Conclusions. A hallmark of FHF seems to be failure of autoregulation, which is linked to uncoupling between CBF and CMRO2 as attested by an a-jDO(2) lower than normal in all patients (luxury perfusion). The recovery of liver function rapidly improves cerebral hemodynamics and metabolic stability. The study of autoregulation and eCMRO(2) recovery using Doppler monitoring proffers the possibility to predict early graft function after liver reperfusion. In our patients eCMRO(2) seemed to be associated with improved neurological outcomes