9 research outputs found
FACT - Highlights from more than Five Years of Unbiased Monitoring at TeV Energies
No full textThe First G-APD Cherenkov Telescope (FACT) is monitoring blazars at TeV energies. Thanks to the observing strategy, the automatic operation and the usage of solid state photosensors (SiPM, aka G-APDs), the duty cycle of the instrument has been maximized and the observational gaps minimized. This provides a unprecedented, unbiased data sample of almost 9000~hours of data of which 2375 hours were taken in 2016. An automatic quick look analysis provides results with low latency on a public website. More than 40 alerts have been sent in the last three years based on this. To study the origin of the very high energy emission from blazars simultaneous multi-wavelength and multi-messenger observations are crucial to draw conclusions on the underlying emission mechanisms, e.g. to distinguish between leptonic and hadronic models. FACT not only participates in multi-wavelength studies, correlation studies with other instruments and multi-messenger studies, but also collects time-resolved spectral energy distributions using a target-of-opportunity program with X-ray satellites. At TeV energies, FACT provides an unprecedented, unbiased data sample. Using up to 1850 hours per source, the duty cycle of the sources and the characteristics of flares at TeV energies are studied. In the presentation, the highlights from more than five years of monitoring will be summarized including several flaring activities of Mrk 421, Mrk 501 and 1ES 1959+650.D. Dorner, J. Adam, M.L. Ahnen, D. Baack, M. Balbo, A. Biland, M. Blank, T. Bretz, a, K. Bruegge, M. Bulinski, J. Buss, A. Dmytriiev, S. Einecke, D. Elsaesser, C. Hempfling, T. Herbst, D. Hildebrand, L. Kortmann, L. Linhoff, M. Mahlke, a, K. Mannheim, S.A. Mueller, D. Neise, A. Neronov, M. Noethe, J. Oberkirch, A. Paravac, F. Pauss, W. Rhode, B. Schleicher, F. Schulz, A. Shukla, V. Sliusar, F. Temme, J. Thaele, R. Walte
FACT - Time-resolved blazar SEDs
No full textBlazars are highly variable objects and their spectral energy distribution (SED) features two peaks. The emission at low energies is understood, however, the origin of the emission at TeV energies is strongly debated. While snapshots of SEDs usually can be explained with simple models, the evolution of SEDs challenges many models and allows for conclusions on the emission mechanisms. Leptonic models expect a correlation between the two peaks, while hadronic models can accommodate more complex correlations. To study time-resolved SEDs, we set up a target-of-opportunity program triggering high-resolution X-ray observations based on the monitoring at TeV energies by the First G-APD Cherenkov Telescope (FACT). To search for time lags and identify orphan flares, this is accompanied by X-ray monitoring with the Swift satellite. These observations provide an excellent multi-wavelength (MWL) data sample showing the temporal behaviour of the blazar emission along the electromagnetic spectrum. To constrain the origin of the TeV emission, we extract the temporal evolution of the low energy peak from Swift data and calculate the expected flux at TeV energies using a theoretical model. Comparing this to the flux measured by FACT, we want to conclude on the underlying physics. Results from more than five years of monitoring will be discussed.D. Dorner, J. Adam, M.L. Ahnen, D. Baack, M. Balbo, A. Biland, M. Blank, T. Bretz, a, K. Bruegge, M. Bulinski, J. Buss, A. Dmytriiev, S. Einecke, D. Elsaesser, C. Hempfling, T. Herbst, D. Hildebrand, L. Kortmann, L. Linhoff, M. Mahlke, a, K. Mannheim, S.A. Mueller, D. Neise, A. Neronov, M. Noethe, J. Oberkirch, A. Paravac, F. Pauss, W. Rhode, B. Schleicher, F. Schulz, A. Shukla, V. Sliusar, F. Temme, J. Thaele, R. Walter, FACT Collaboration, A. Kreikenbohm, K. Leite
Dielectric properties and spatial distribution of polarization in polyethylene aged under ac voltage in a humid atmosphere
No full textNRC publication: Ye
MAPping out distribution routes for kinesin couriers
No full textIn the crowded environment of eukaryotic cells, diffusion is an inefficient distribution mechanism for cellular components. Long-distance active transport is required and is performed by molecular motors including kinesins. Furthermore, in highly polarized, compartmentalized and plastic cells such as neurons, regulatory mechanisms are required to ensure appropriate spatio-temporal delivery of neuronal components. The kinesin machinery has diversified into a large number of kinesin motor proteins as well as adaptor proteins that are associated with subsets of cargo. However, many mechanisms contribute to the correct delivery of these cargos to their target domains. One mechanism is through motor recognition of subdomain-specific microtubule (MT) tracks, sign-posted by different tubulin isoforms, tubulin post-translational modifications (PTMs), tubulin GTPase activity and MT associated proteins (MAPs). With neurons as a model system, a critical review of these regulatory mechanisms is presented here, with particular focus on the emerging contribution of compartmentalised MAPs. Overall, we conclude that – especially for axonal cargo – alterations to the MT track can influence transport, although in vivo, it is likely that multiple track-based effects act synergistically to ensure accurate cargo distribution
Electrostatic manipulation of piezoelectric fibres using a sharp probe electrode in a dielectric liquid: Analysis of the electrohydrodynamic phenomena
No full textMicro-assembly techniques have been identified as a major technology ‘pillar’ that
will underpin further advancements in integrated micro-and nano-systems. In practice,
there is a generic requirement for component parts that are often fragile, or that have
been prepared by mutually incompatible processes, to be brought together to make a
complete working system. This thesis discusses an electrostatic positioning technique
for micro-scale elements that could form the basis of an industrial process.
A highly non-uniform field generated between a needle-like upper electrode and a
bottom flat electrode can be used to electrostatically capture, displace, and relocate
elements into a predefined spatial configuration. The very intense field at the needle
tip can facilitate the collection of the material at a precise point. However charge
injection and local dielectric breakdown must also be considered as they can induce
instability near the tip, and consequently interfere with any picking up action.
The principal physical phenomena and potential benefits are analysed and discussed,
considering three different configurations to achieve the pick and place operation for a
micro-fibre in the needle-plane configuration. The first two are operated on an
isolated single fibre lying on a flat bottom electrode, applying respectively a DC or an
AC voltage. The third case is that of a group of fibres, and it exploits a
dielectrophoretic chain structuring effect to assist in the micro-manipulation
technique. Experimentation has focussed on the importance of the charge transfer
mechanisms, leading to a model which provides good agreement with the observed
behaviour. Moreover, an analysis of the forces exerted on the fibres showed that they
arise not only from a polarisation effect, but that there is also an electrophoretic
contribution.
The viability of the proposed technique has been demonstrated using lead zirconate
titanate (PZT rods and carbon fibres)
Encroachment of sandplain heathland (kwongan) by Allocasuarina huegeliana in the Western Australian wheatbelt: the role of herbivores, fire and other factors
No full textKwongan, also known as sandplain heathland, occurs in remnant vegetation throughout the fragmented landscape of the Western Australian wheatbelt. This vegetation community has high levels of species richness and endemism, and is of high conservation value. In many vegetation remnants in the wheatbelt the native tree species Allocasuarina huegeliana (rock sheoak) is expanding out from its normal range and encroaching into kwongan. A. huegeliana may ultimately dominate the kwongan, causing a decline in floristic diversity. Altered disturbance regimes, particularly the absence of fire and reduced or absent browsing mammal herbivores, are likely to be responsible for causing A. huegeliana encroachment.
This study used experimental and observational data from patches of kwongan in three Nature Reserves in the central and southern wheatbelt to investigate the role of fire, native mammal activities and interactions between these two factors in shaping A. huegeliana woodland kwongan community boundaries. Investigations were carried out into the characteristics of encroaching A. huegeliana populations; the environmental factors affecting the extent of encroachment, naturally recruited juveniles, and seedling emergence and establishment; historical and current abundances of native mammals; and the effects of mammal herbivores on seedling establishment during inter-fire and post-fire periods.
Results from this study confirm that A. huegeliana has encroached into kwongan throughout the wheatbelt region and recruitment appears likely to continue in most areas. Few of the environmental factors measured in this study affected the extent of encroachment, the locations of naturally recruited A. huegeliana juveniles, and seedling germination and establishment. Western grey kangaroos (Macropus fuliginosus) browsed extensively on seedlings, which largely prevented them from establishing in open areas of kwongan. However, numerous A. huegeliana seedlings escaped browsing herbivores by establishing in perennial shrubs, where they appeared to be tolerant of increased levels of inter-specific competition.
There was no native mammal common to all three Reserves that declined around the time that A. huegeliana encroachment most likely began in the 1970s. In addition, tammar wallabies (Macropus eugenii) had little effect even where their densities were high. It is therefore unlikely that the decline of an individual mammal species initiated encroachment. A. huegeliana encroachment appears to be driven by increased propagule pressure, which is in turn caused by increased inter-fire intervals. Long periods of time without fire have enabled fire-sensitive A. huegeliana trees to produce increasing quantities of seed that are continuously released into kwongan. A range of other factors may interact synergistically with this process to affect encroachment and these are also discussed. This study considered the implications of these findings for management of remnant vegetation in fragmented landscapes, particularly kwongan in the Western Australian wheatbelt, and areas for further research are suggested
Ventilation and outcomes following robotic-assisted abdominal surgery : an international, multicentre observational study
No full textBackground: International data on the epidemiology, ventilation practice, and outcomes in patients undergoing abdominal robotic-assisted surgery (RAS) are lacking. The aim of the study was to assess the incidence of postoperative pulmonary complications (PPCs), and to describe ventilator management after abdominal RAS.
Methods: This was an international, multicentre, prospective study in 34 centres in nine countries. Patients >= 18 yr of age undergoing abdominal RAS were enrolled between April 2017 and March 2019. The Assess Respiratory Risk in Surgical Patients in Catalonia (ARISCAT) score was used to stratify for higher risk of PPCs (>= 26). The primary outcome was the incidence of PPCs. Secondary endpoints included the preoperative risk for PPCs and ventilator management.
Results: Of 1167 subjects screened, 905 abdominal RAS patients were included. Overall, 590 (65.2%) patients were at increased risk for PPCs. Meanwhile, 172 (19%) patients sustained PPCs, which occurred more frequently in 132 (22.4%) patients at increased risk, compared with 40 (12.7%) patients at lower risk of PPCs (absolute risk difference: 12.2% [95% confidence intervals (CI), 6.8-17.6%]; P<0.001). Plateau and driving pressures were higher in patients at increased risk, compared with patients at low risk of PPCs, but no ventilatory variables were independently associated with increased occurrence of PPCs. Development of PPCs was associated with a longer hospital stay.
Conclusions: One in five patients developed one or more PPCs (chiefly unplanned oxygen requirement), which was associated with a longer hospital stay. No ventilatory variables were independently associated with PPCs
Postoperative Pulmonary Complications in Conventional Laparoscopic vs Robot-Assisted Abdominal Surgery
No full textImportance: Robot-assisted surgery (RAS) is increasingly used for abdominal procedures; however, postoperative pulmonary complications (PPCs) are more frequent in patients undergoing RAS compared with patients undergoing conventional laparoscopic surgery (CLS). Objective: To compare the incidence of PPCs after CLS and RAS and to determine which patient-, surgery-, and anesthesia-related factors are associated with PPCs. Design, Setting, and Participants: This cohort study used the Laparoscopic and Robot-Assisted Surgery (LapRAS) database, a pooled dataset containing individual patient data of 2 worldwide prospective cohort studies: the Local Assessment of Ventilatory Management During General Anaesthesia for Surgery (LAS VEGAS) study and the Assessment of Ventilatory Management During General Anesthesia for Robotic Surgery and Its Effects on Postoperative Pulmonary Complications (AVATaR) study. Data were collected from adult patients requiring intraoperative ventilation during general anesthesia for CLS or RAS surgical procedures from 163 centers and 31 countries in the Americas, Europe, the Middle East, and North Africa from January 2013 to March 2019. Data were analyzed from December 2023 to October 2024. Exposures: Type of surgical approach (CLS vs RAS), duration of intraoperative ventilation, and intensity of mechanical ventilation, assessed using the 4 times the driving pressure (DP) plus respiratory rate (RR) estimator (4DP + RR). Main Outcome and Measures: The primary outcome was occurrence of 1 or more PPCs in the first 5 postoperative days. Mixed-effects logistic regression assessed associations with PPCs; mediation and matched cohort analyses served as sensitivity analyses. Results: A total of 2738 patients (median [IQR] age, 56 [41-66] years; 1456 female [53.1%]) were included. PPCs occurred in 172 of 903 patients (19.0%) in the RAS group and 174 of 1835 patients (9.5%) in the CLS group (P <.001). Duration of intraoperative ventilation was longer in RAS compared with CLS (median [IQR] duration, 219 [180-270] vs 95 [68-145] minutes; P <.001) and the intensity of mechanical ventilation was higher (median [IQR] intensity, 84 [69-100] vs 72 [60-87] 4DP + RR; P <.001). PPCs were independently associated only with duration of ventilation (adjusted odds ratio [aOR], 1.49; 95% CI, 1.33-1.66; P <.001), not with the surgical approach (ie, RAS vs CLS; aOR, 1.35; 95% CI, 0.72-2.54; P =.35) nor the intensity of ventilation as measured by 4DP + RR (aOR, 1.01; 95% CI, 1.01-1.01; P =.21). A post hoc analysis showed a more pronounced association of intensity of ventilation in surgical procedures of shorter duration. Conclusions and Relevance: In this cohort study, patients who received RAS vs CLS had a higher incidence of PPCs and received longer and more intense mechanical ventilation; however, only the duration of ventilation rather than intensity of ventilation or type of surgical approach (ie, RAS vs CLS) was independently associated with the occurrence of PPCs, indicating that the longer duration of ventilation in RAS underlies the higher incidence of PPCs observed in those who undergo this type of surgery
