A search for energy-dependence of the Kes 73/1E 1841-045 morphology in GeV

While the Kes 73/1E 1841-045 system had been confirmed as an extended GeV source, whether its morphology depends on the photon energy or not deserves our further investigation. Adopting data collected by Fermi Large Area Telescope (LAT) again, we look into the extensions of this source in three energy bands individually: 0.3-1 GeV, 1-3 GeV and 3-200 GeV. We find that the 0.3-1 GeV morphology is point-like and is quite different from those in the other two bands, although we cannot robustly reject a unified morphology for the whole LAT band.Comment: Approved for publication in PoS as a proceeding of the 7th International Fermi Symposium (IFS2017

Fermi Large Area Telescope Observations of the Fast-dimming Crab Nebula in 60-600 MeV

Context: The Crab pulsar and its nebula are the origin of relativistic electrons which can be observed through their synchrotron and inverse Compton emission. The transition between synchrotron-dominated and inverse-Compton-dominated emissions takes place at $\approx 10^9$ eV. Aims: The short-term (weeks to months) flux variability of the synchrotron emission from the most energetic electrons is investigated with data from ten years of observations with the Fermi Large Area Telescope (LAT) in the energy range from 60 MeV to 600 MeV. Methods: The off-pulse light-curve has been reconstructed from phase-resolved data. The corresponding histogram of flux measurements is used to identify distributions of flux-states and the statistical significance of a lower-flux component is estimated with dedicated simulations of mock light-curves. The energy spectra for different flux states are reconstructed. Results: We confirm the presence of flaring-states which follow a log-normal flux distribution. Additionally, we discover a low-flux state where the flux drops to as low as 18.4% of the intermediate-state average flux and stays there for several weeks. The transition time is observed to be as short as 2 days. The energy spectrum during the low-flux state resembles the extrapolation of the inverse-Compton spectrum measured at energies beyond several GeV energy, implying that the high-energy part of the synchrotron emission is dramatically depressed. Conclusions: The low-flux state found here and the transition time of at most 10 days indicate that the bulk ($>75$%) of the synchrotron emission above $10^8$ eV originates in a compact volume with apparent angular size of $\theta\approx0.4" t_\mathrm{var}/(5 \mathrm{d})$. We tentatively infer that the so-called inner knot feature is the origin of the bulk of the $\gamma$-ray emission.Comment: Accepted by A&A on 05.05.2020; Original version submitted on 19.09.201

Inferring the origins of the pulsed gamma-ray emission from the Crab pulsar with 10-year Fermi LAT data

Context: The Crab pulsar is a bright $\gamma$-ray source detected at photon energies up to $\sim$1 TeV. Its phase-averaged and phase-resolved $\gamma$-ray spectra below 10 GeV exhibit exponential cutoffs while those above 10 GeV apparently follow simple power-laws. Aims: We re-visit the $\gamma$-ray properties of the Crab pulsar with 10-year \emph{Fermi} Large Area Telescope (LAT) data in the range of 60 MeV--500 GeV. With the phase-resolved spectra, we investigate the origins and mechanisms responsible for the emissions. Methods: The phaseograms are reconstructed for different energy bands and further analysed using a wavelet decomposition. The phase-resolved energy spectra are combined with the observations of ground-based instruments like MAGIC and VERITAS to achieve a larger energy converage. We fit power-law models to the overlapping energy spectra from 10 GeV to $\sim$1 TeV. We include in the fit a relative cross-calibration of energy scales between air-shower based gamma-ray telescopes with the orbital pair-production telescope of the Fermi mission. Results: We confirm the energy-dependence of the $\gamma$-ray pulse shape, and equivalently, the phase-dependence of the spectral shape for the Crab pulsar. A relatively sharp cutoff at a relatively high energy of $\sim$8 GeV is observed for the bridge-phase emission. The $E>$10 GeV spectrum observed for the second pulse peak is harder than those for other phases. Conclusions: In view of the diversity of phase-resolved spectral shapes of the Crab pulsar, we tentatively propose a multi-origin scenario where the polar-cap, outer-gap and relativistic-wind regions are involved.Comment: Original article published in A&A on 10.08.2020; Data values available at CDS via http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/640/A43 ; Erratum (at the back) accepted by A&A on 10.03.2021; Sincere gratitude is given to D. Horns for his encouragement regarding my submission as a single autho

Understanding the continued usage of business e-learning courses in HK corporations

Other research has investigated different aspects of e-learning, e.g. comparing the effectiveness of e-learning with traditional classroom training and on the success of IT or computer skills training. This study focused on how to ensure that individuals continue their usage of business and management e-learning courses for self-development in Hong Kong Corporations. A theoretical framework was developed based on Venkatesh’s model of System Usage, Bhattacherjee’s Expectation-Confirmation Model and Seddon’s re-specification of DeLone and McLean’s Information System Success Model. The proposed model was calibrated with 212 valid samples from five corporations in Hong Kong and was validated with 15 questionnaires from a small e-commerce company of 50 staff at a different time. The data supported the model and the model had a moderate explanatory power (R2=37%) for continued usage. The structural model was not affected by different collection periods (first collection batch vs last collection batch), sample (calibration vs validation), gender (male vs female), position (manager vs non-manager), and computer usage experience (10 years or more vs less than 10 years). However, the model was different for groups of different ages (age 36 and above vs below 36) and educational levels (university graduates vs non-university graduates). Further research and the business implications for improving the continued usage of business e-learning courses are discussed.Education for the 21 st century - impact of ICT and Digital Resources ConferenceRed de Universidades con Carreras en Informática (RedUNCI

The mixing of powders in the horizontal rotating drum mixers

The literature published on powder mixing is reviewed and the conclusion drawn that the operation is misunderstood and the situation confused because insufficient attention has been paid to the properties of particles being mixed. As an aid to simplification, powders are classified as free-flowing powders where the particle motion is individual, and non-free-flowing powders where the mixing is more concerned with the shuffling and subsequent breaking down of large agglomerates. This thesis considers the mixing of free-flowing powders only. [Continues.

Rotationally-Driven Fragmentation for the Formation of the Binary Protostellar System L1551 IRS 5

Either bulk rotation or local turbulence is widely invoked to drive fragmentation in collapsing cores so as to produce multiple star systems. Even when the two mechanisms predict different manners in which the stellar spins and orbits are aligned, subsequent internal or external interactions can drive multiple systems towards or away from alignment thus masking their formation process. Here, we demonstrate that the geometrical and dynamical relationship between the binary system and its surrounding bulk envelope provide the crucial distinction between fragmentation models. We find that the circumstellar disks of the binary protostellar system L1551 IRS 5 are closely parallel not just with each other but also with their surrounding flattened envelope. Measurements of the relative proper motion of the binary components spanning nearly 30 yr indicate an orbital motion in the same sense as the envelope rotation. Eliminating orbital solutions whereby the circumstellar disks would be tidally truncated to sizes smaller than are observed, the remaining solutions favor a circular or low-eccentricity orbit tilted by up to $\sim$25$^\circ$ from the circumstellar disks. Turbulence-driven fragmentation can generate local angular momentum to produce a coplanar binary system, but which bears no particular relationship with its surrounding envelope. Instead, the observed properties conform with predictions for rotationally-driven fragmentation. If the fragments were produced at different heights or on opposite sides of the midplane in the flattened central region of a rotating core, the resulting protostars would then exhibit circumstellar disks parallel with the surrounding envelope but tilted from the orbital plane as is observed.Comment: Accepted for publication in Ap

Biopolymer Networks and Cellular Mechanosensing

Cells and tissues are mechanical as well as biochemical machines, and cellular response to mechanical cues can have as large an influence on structure and function as chemical signals. The mechanical properties of cells are largely determined by networks of semiflexible polymers forming the cytoskeleton, which has viscoelastic properties that differ in important ways from the viscoelasticity of common synthetic materials. Two such features are the high resistance to deformation achieved by a remarkably low volume fraction of protein, and the increase in stiffness that occurs when the cytoskeletal network is deformed. The actin filaments, microtubules and intermediate filaments that comprise the cytoskeleton of most cell types are linear polymers with some important similarities but also some fundamental differences. The stiffness of the individual polymer types is vastly different, with persistence lengths ranging from 1 mm for the 24 nm diameter microtubules to a few 100 nm for the 10-14 nm diameter intermediate filaments. The material properties of these biopolymer networks are proposed to function as part of the mechanosensing mechanism in cells, and the stiffness of cytoskeletal networks is similar to that of common extracellular protein networks such as those formed by collagen and fibrin in which many cell types function. Examples of the morphologic differences in fibroblasts and astrocytes grown on chemically identical surfaces overlying gels with elastic moduli spanning the range from 50 to 12,000 Pa illustrate the large effect of stiffness differences on cell structure and function

Multiwavelength studies of G298.6−-0.0: An old GeV supernova remnant interacting with molecular clouds

Hadronic $\gamma$-ray sources associated with supernova remnants (SNRs) can serve as stopwatches for the escape of cosmic rays from SNRs, which gradually develops from highest-energy particles to lowest-energy particles with time. In this work, we analyze the 13.7~yr \emph{Fermi}-LAT data to investigate the $\gamma$-ray feature in/around the SNR G298.6$-$0.0 region. With $\gamma$-ray spatial analyses, we detect three point-like components. Among them, Src-NE is at the eastern SNR shell, and Src-NW is adjacent to the western edge of this SNR. Src-NE and Src-NW demonstrate spectral breaks at energies around/below 1.8~GeV, suggesting an old SNR age of $>$10~kyr. We also look into the X-ray emission from the G298.6$-$0.0 region, with the Chandra-ACIS data. We detected an extended keV source having a centrally filled structure inside the radio shell. The X-ray spectra are well fit by a model which assumes a collisional ionisation equilibrium of the thermal plasma, further supporting an old SNR age. Based on our analyses of the NANTEN CO- and ATCA-Parkes HI-line data, we determined a kinematic distance of $\sim$10.1~kpc from us to G298.6$-$0.0. This distance entails a large physical radius of the SNR of $\sim$15.5~pc, which is an additional evidence for an old age of $>$10~kyr. Besides, the CO data cube enables us to three-dimensionally locate the molecular clouds (MCs) which are potentially interacting with SNR G298.6$-$0.0 and could account for the hadronic $\gamma$-rays detected at Src-NE or Src-NW. Furthermore, the multiwavelength observational properties unanimously imply that the SNR--MC interaction occurs mainly in the northeast direction.Comment: Accepted by Publications of the Astronomical Society of Japan (PASJ) on 16-Jan-202

Would adults with autism be less likely to bury the survivors? An eye movement study of anomalous text reading

In a single eye movement experiment we investigated the effects of context on the time course of local and global anomaly processing during reading in adults with Autism Spectrum Disorder (ASD). In one condition short paragraph texts contained anomalous target words. Detection of the anomaly was only possible through evaluation of word meaning in relation to the global context of the whole paragraph (Passage Level Anomalies). In another condition the anomaly could be detected via computation of a local thematic violation within a single sentence embedded in the paragraph (Sentence Level Anomalies).For the sentence level anomalies the ASD group, in contrast with the typically developing (TD) group, showed early detection of the anomaly as indexed by regressive eye movements from the critical target word upon fixation. Conversely, for the passage level anomalies, and in contrast with the ASD group, the TD group showed early detection of the anomaly, with increased regressive eye movements once the critical word had been fixated.The reversal of the pattern of regression path data for the two groups, for the sentence and passage level anomalies, is discussed in relation to cognitive accounts of ASD