Neutrino emission from a GRB afterglow shock during an inner supernova shock breakout

The observations of a nearby low-luminosity gamma-ray burst (GRB) 060218 associated with supernova SN 2006aj may imply an interesting astronomical picture where a supernova shock breakout locates behind a relativistic GRB jet. Based on this picture, we study neutrino emission for early afterglows of GRB 060218-like GRBs, where neutrinos are expected to be produced from photopion interactions in a GRB blast wave that propagates into a dense wind. Relativistic protons for the interactions are accelerated by an external shock, while target photons are basically provided by the incoming thermal emission from the shock breakout and its inverse-Compton scattered component. Because of a high estimated event rate of low-luminosity GRBs, we would have more opportunities to detect afterglow neutrinos from a single nearby GRB event of this type by IceCube. Such a possible detection could provide evidence for the picture described above.Comment: 6 pages, 2 figures, accepted for publication in MNRA

Processing of immiscible alloys by a twin-screw rheomixing process

Immiscible alloys with a microstructure in which a soft phase dispersed homogeneously in a hard matrix have great potential applications in advanced bearing systems, especially for automotive industry. Though the melt of an immiscible alloy is miscible at the temperature above the miscibility gap, it decomposes into two liquids when it passes through the liquid miscibility gap. Despite great efforts made worldwide, including extensive space experiments, no casting techniques so far can produce the desirable microstructure. Based on the extensive experience in mixing the immiscible organic liquids offered by the polymer processing community, a rheomixing process for immiscible alloys has been successfully developed at Brunel University using a twin-crew extruder. This paper presents the twin-screw rheomixing process and the experimental results on rheomixing of the immiscible Zn-Pb alloys

Probing the large-scale structure of the universe through gravitational-wave observations

The improvements in the sensitivity of the gravitational wave (GW) network enable the detection of several large redshift GW sources by third-generation GW detectors. These advancements provide an independent method to probe the large-scale structure of the universe by using the clustering of the binary black holes. The black hole catalogs are complementary to the galaxy catalogs because of large redshifts of GW events, which may imply that binary black holes (BBHs) are a better choice than galaxies to probe the large-scale structure of the universe and cosmic evolution over a large redshift range. To probe the large-scale structure, we used the sky position of the binary black holes observed by third-generation GW detectors to calculate the angular correlation function (ACF) and the bias factor of the population of binary black holes. This method is also statistically significant as 5000 BBHs are simulated. Moreover, for the third-generation GW detectors, we found that the bias factor can be recovered to within 33$\%$ with an observational time of ten years. This method only depends on the GW source-location posteriors; hence, it can be an independent method to reveal the formation mechanisms and origin of the BBH mergers compared to the electromagnetic method

Twin-screw rheomoulding of AZ91D Mg-alloys

Twin-screw rheomoulding is a new semisolid process for the near net shape production of metal’s components. It includes the advantage combination in both die-casting and injection moulding. In this unique process, a liquid alloy is fed into a twin-screw extruder, where the alloy is intensively sheared and cooled into the interval of liquidus and solidus to produce semisolid slurry with fine primary particles of pre-determined volume fraction. The well-sheared semisolid slurry is then discharged into a shot cylinder and subsequently injected into a mould cavity for component shaping. This paper introduces the development of the prototype machine and the experimental work carried out with industrial AZ91D magnesium alloy. The operating characteristics of the newly developed machine, microstructures and mechanical properties of rheomoulded AZ91D magnesium alloy will be reported

Interaction of Feature Guided Waves with Defects in Composite Structural Bends

Complex-shaped composite structures such as bends, stiffeners, and ribs are increasingly incorporated in aerospace applications because of their attractive mechanical properties and good moldability. However, damages like matrix cracking and delamination can be caused in these structures by stress concentration and out-of-plane impacts during the in-service use, consequently degrading the system integrity and reliability. Ultrasonic feature guided waves (FGW) can serve as promising candidates for their inspection as they can propagate along the feature long distances and potentially detect the possible defects. In this study, potential FGW modes have been identified in 90° carbon fiber/epoxy (CF/EP) quasi-isotropic bent plates by applying the Semi-Analytical Finite Element (SAFE) method. These modes show strong energy confinement in the bend region and have limited radiation to the adjacent plates, which are promising for the long-range inspection. The interaction of identified bend-guided waves with different types of defects is studied by the 3D Finite Element (FE) simulation. Their reflection coefficient spectra are calculated and the sensitivity to different defects is discussed. Preliminary experiments are also performed to validate the modeling results

An energetic blast wave from the December 27 giant flare of the soft gamma-ray repeater 1806-20

Recent follow-up observations of the December 27 giant flare of SGR 1806-20 have detected a multiple-frequency radio afterglow from 240 MHz to 8.46 GHz, extending in time from a week to about a month after the flare. The angular size of the source was also measured for the first time. Here we show that this radio afterglow gives the first piece of clear evidence that an energetic blast wave sweeps up its surrounding medium and produces a synchrotron afterglow, the same mechanism as established for gamma-ray burst afterglows. The optical afterglow is expected to be intrinsically as bright as $m_R\simeq13$ at t\la 0.1 days after the flare, but very heavy extinction makes the detection difficult because of the low galactic latitude of the source. Rapid infrared follow-up observations to giant flares are therefore crucial for the low-latitude SGRs, while for high-latitude SGRs (e.g. SGR 0526-66), rapid follow-ups should result in identification of their possible optical afterglows. Rapid multi-wavelength follow-ups will also provide more detailed information of the early evolution of a fireball as well as its composition.Comment: Updated version, accepted for publication in ApJ Letter

Large magnetothermal conductivity of HoMnO_3 single crystals and its relation to the magnetic-field induced transitions of magnetic structure

We study the low-temperature heat transport of HoMnO_3 single crystals to probe the magnetic structures and their transitions induced by magnetic field. It is found that the low-T thermal conductivity (\kappa) shows very strong magnetic-field dependence, with the strongest suppression of nearly 90% and the biggest increase of 20 times of \kappa compared to its zero-field value. In particular, some ``dip"-like features show up in \kappa(H) isotherms for field along both the ab plane and the c axis. These behaviors are found to shed new light on the complex H-T phase diagram and the field-induced re-orientations of Mn^{3+} and Ho^{3+} spin structures. The results also demonstrate a significant spin-phonon coupling in this multiferroic compound.Comment: 5 pages, 4 figures, accepted for publication in Phys. Rev.