VHE gamma-ray observations of the young synchrotron-dominated SNRs G1.9+0.3 and G330.2+1.0 with H.E.S.S

Supernova remnants (SNRs) are widely considered to be accelerators of cosmic rays (CR). They are also expected to produce very-high-energy (VHE; $E > 100$ GeV) gamma rays through interactions of high-energy particles with the surrounding medium and photon fields. They are, therefore, promising targets for observations with ground-based imaging atmospheric Cherenkov telescopes like the H.E.S.S. telescope array. VHE gamma-ray emission has already been discovered from a number of SNRs, establishing them as a prominent source class in the VHE domain. Of particular interest are the handful of SNRs whose X-ray spectra are dominated by non-thermal synchrotron emission, such as the VHE gamma-ray emitters RX J0852.0-4622 (Vela Jr.) and RX J1713-3946. The shell-type SNRs G1.9+0.3 and G330.2+1.0 also belong to this subclass and are further notable for their young ages ($\leq 1$ kyr), especially G1.9+0.3, which was recently determined to be the youngest SNR in the Galaxy ($\sim100$ yr). These unique characteristics motivated investigations with H.E.S.S. to search for VHE gamma rays. The results of the H.E.S.S. observations and analyses are presented, along with implications for potential particle acceleration scenarios.Comment: ICRC 2011 proceedings, 4 pages, 2 figures, 3 table

Simple heuristics for the assembly line worker assignment and balancing problem

We propose simple heuristics for the assembly line worker assignment and balancing problem. This problem typically occurs in assembly lines in sheltered work centers for the disabled. Different from the classical simple assembly line balancing problem, the task execution times vary according to the assigned worker. We develop a constructive heuristic framework based on task and worker priority rules defining the order in which the tasks and workers should be assigned to the workstations. We present a number of such rules and compare their performance across three possible uses: as a stand-alone method, as an initial solution generator for meta-heuristics, and as a decoder for a hybrid genetic algorithm. Our results show that the heuristics are fast, they obtain good results as a stand-alone method and are efficient when used as a initial solution generator or as a solution decoder within more elaborate approaches.Comment: 18 pages, 1 figur

New unidentified H.E.S.S. Galactic sources

H.E.S.S. is one of the most sensitive instruments in the very high energy (VHE; > 100 GeV) gamma-ray domain and has revealed many new sources along the Galactic Plane. After the successful first VHE Galactic Plane Survey of 2004, H.E.S.S. has continued and extended that survey in 2005-2008, discovering a number of new sources, many of which are unidentified. Some of the unidentified H.E.S.S. sources have several positional counterparts and hence several different possible scenarios for the origin of the VHE gamma-ray emission; their identification remains unclear. Others have so far no counterparts at any other wavelength. Particularly, the lack of an X-ray counterpart puts serious constraints on emission models. Several newly discovered and still unidentified VHE sources are reported here.Comment: ICRC 2009 proceeding

Look at that! BERT can be easily distracted from paying attention to morphosyntax

Syntactic knowledge involves not only the ability to combine words and phrases, but also the capacity to relate different and yet truth-preserving structural variations (e.g. passivization, inversion, topicalization, extraposition, clefting, etc.), as well as the ability to infer that these syntactic variations all adhere to common morphosyntactic rules, like subject-verb agreement. Although there is some evidence that BERT has rich syntactic knowledge, our adversarial approach suggests that it is not deployed in a robust and linguistically appropriate way. English BERT can be tricked to miss even quite simple syntactic generalizations, when compared with GPT-2, underscoring the need for stronger priors and for linguistically controlled experiments in evaluatio

Enhanced Optical Dichroism of Graphene Nanoribbons

The optical conductivity of graphene nanoribbons is analytical and exactly derived. It is shown that the absence of translation invariance along the transverse direction allows considerable intra-band absorption in a narrow frequency window that varies with the ribbon width, and lies in the THz range domain for ribbons 10-100nm wide. In this spectral region the absorption anisotropy can be as high as two orders of magnitude, which renders the medium strongly dichroic, and allows for a very high degree of polarization (up to ~85) with just a single layer of graphene. The effect is resilient to level broadening of the ribbon spectrum potentially induced by disorder. Using a cavity for impedance enhancement, or a stack of few layer nanoribbons, these values can reach almost 100%. This opens a potential prospect of employing graphene ribbon structures as efficient polarizers in the far IR and THz frequencies.Comment: Revised version. 10 pages, 7 figure

Quironómidos (Diptera, Chironomidae) de alta montaña de la Sierra de Estrela (Portugal) y adiciones a la fauna de Portugal y la Península Ibérica

A Chironomidae (Diptera) fauna list for headwater streams of high altitude areas in Serra da Estrela (Portugal) is presented, doubling the previously established species richness for the region. The findings include 17 new records for Portugal, which represent an increase to 219 species for the Continental Portugal Chironomidae fauna. Two new records were detected for the Iberian Peninsula: one species (Tvetenia duodenaria), and one subgenus –Psectrocladius (Mesopsectrocladius)–; and the presence of the genus Natarsia is confirmed. The last two occurrences correspond to monoespecific taxa of the Palearctic region. However, as taxonomic identification has been based on larval material, instead of pupae, pupal exuviae or imagoes, species level assignment is still uncertain.Se presenta una lista de especies de Chironomidae (Diptera) recolectadas en los ríos de cabecera de zonas de alta montaña en la Serra da Estrela (Portugal). Con esta aportación se duplica la riqueza de especies regional conocida hasta el momento y se eleva la fauna de quironómidos del Portugal continental a 219 especies. Se incluyen dos nuevas citas para la Península Ibérica, una especie (Tvetenia duodenaria) y un subgénero –Psectrocladius (Mesopsectrocladius)–, y se confirma la presencia del género Natarsia. En los dos últimos casos se trata de larvas de taxones hasta el momento monoespecíficos en la región paleárctica, pero al no haberse recolectado pupas o adultos no se puede asegurar la identificación específica

Mapping of cavitating flow regimes in injectors for medium-/heavy-duty diesel engines

Reducing the sac volume size of medium-/heavy-duty diesel engine injector nozzles can minimise the fuel dripping into the combustion chamber at the end of injection events, which has been linked to reduced engine-out emissions. This study demonstrates the effect of reduction in the sac volume of diesel fuel injectors utilised in medium-/heavy-duty applications on the internal nozzle flow. This is realised by comparison of two heavy-duty diesel nozzles that feature a large difference in sac volume size of almost three times. For visualisation purposes, the nozzles have been enlarged by six times, and replicas were manufactured from a transparent material. High-speed digital imaging was used to capture the instantaneous spatial and temporal characteristics of geometric as well as dynamic vortex cavitation structures. The investigation was conducted in a steady-state flow test rig for three different needle valve lifts. For all tested conditions, the flow behaviour was analysed at three distinct areas of the nozzle, these being the needle seat, the sac volume and the injection hole. Interpretation of experimental observations was supported by parallel computational fluid dynamics simulations of the exact conditions measured during the experiments. Post-processing of the captured images has revealed the ensemble – average cavitation location, its standard deviation and the cavitation structures life – time inside the sac volume. Results showed a significant dependency of the internal nozzle flow on the sac volume size and identified clear differences in the structure of the cavitation pockets inside the sac volume under certain operating conditions