Environment Studies of Pulsar Wind Nebulae and Their Interactions with the Interstellar Medium

Pulsars, rapidly rotating neutron star born from the core-collapse of massive stars, convert a fraction of their rotational energy to accelerate electrons up to high energies. The generated pulsar wind eventually reaches the termination shock and creates a pulsar wind nebula (PWN). There, the particles’ trajectories become randomized, and they produce radio to X-ray emission via synchrotron radiation; and TeV γ-ray emission from the interaction of high energy electrons with the Cosmic Microwave Background; and the infra-red emission from Galactic dust. Although progress has been made towards the understanding of the structure of the pulsar environment, several issues, such as the composition of the pulsar winds, still need to be addressed. Indeed, no direct evidence of hadronic components have yet been discovered inside the PWN. However, nearby dense molecular clouds could provide sufficient target particles for the potential hadrons from the PWN and its progenitor supernova remnant (SNR) to produce significant TeV emission via proton-proton (p-p) interaction. My work thus first consists of conducting interstellar matter (ISM) studies towards several PWNe using the 22-metre Mopra and the 4-metre Nanten radio telescopes. Among the studied PWNe, I particularly focus on HESS J1825−137 and its plausible association with the nearby unidentified TeV source HESS J1826−130. I have mapped the HESS J1826−130 region with Mopra in the 7 and 12 mm bands which, combined with the Nanten CO(1–0) survey and the GRS ¹³CO(1–0), enable an accurate analysis of the morphological and physical properties of several dense molecular clouds found in the line of sight. Interestingly, I have found a massive molecular cloud adjacent to the PWN HESS J1825−137 and overlapping the HESS J1826−130 TeV emission. From our mass estimates, I suggest that the cosmic-rays originating from the progenitor SNR of the pulsar PSRJ1826−1334 can significantly contribute to the TeV emission. We then attempt to model and predict spectral and morphological properties of the TeV emission from the propagation of high energy CRs and electrons, originating from the progenitor SNR and potentially from the PWN.We find that the resulting spectral shape of the TeV γ-ray emission is very sensitive to the diffusion coefficient of high energy particles inside molecular clouds. I also find that only a ‘slow’ diffusion’ of CRs (diffusion coefficient D(E) ∼ 10²⁶ √E/10GeV cm² s⁻¹) results in a significant contribution of the gamma-ray emission towards HESS J1826−130 at all energies. We finally notice that the contribution from hypothetical CRs escaping the PWN HESS J1825−137 is expected to be overshadowed by the contribution of CRs escaping the progenitor SNR. As one expects the latter’s contribution to decrease as time evolves while the former’s contribution to remain somewhat constant, I thus argue that older PWNe may be more suitable candidates to obtain direct evidence of CRs inside PWNe. Among the studied PWNe, I find that, based on simplistic diffusion studies, the ISM surrounding HESS J1809−193 may be a good laboratory to detect CRs escaping the pulsar PSRJ1809−1917.Thesis (Ph.D.) -- University of Adelaide, School of Physical Sciences, 201

Unifying the low-temperature photoluminescence spectra of carbon nanotubes: the role of acoustic phonon confinement

At low temperature the photoluminescence of single-wall carbon nanotubes show a large variety of spectral profiles ranging from ultra narrow lines in suspended nanotubes to broad and asymmetrical line-shapes that puzzle the current interpretation in terms of exciton-phonon coupling. Here, we present a complete set of photoluminescence profiles in matrix embedded nanotubes including unprecedented narrow emission lines. We demonstrate that the diversity of the low-temperature luminescence profiles in nanotubes originates in tiny modifications of their low-energy acoustic phonon modes. When low energy modes are locally suppressed, a sharp photoluminescence line as narrow as 0.7 meV is restored. Furthermore, multi-peak luminescence profiles with specific temperature dependence show the presence of confined phonon modes

Chirality dependence of the absorption cross-section of carbon nanotubes

The variation of the optical absorption of carbon nanotubes with their geometry has been a long standing question at the heart of both metrological and applicative issues, in particular because optical spectroscopy is one of the primary tools for the assessment of the chiral species abundance of samples. Here, we tackle the chirality dependence of the optical absorption with an original method involving ultra-efficient energy transfer in porphyrin/nanotube compounds that allows uniform photo-excitation of all chiral species. We measure the absolute absorption cross-section of a wide range of semiconducting nanotubes at their S22 transition and show that it varies by up to a factor of 2.2 with the chiral angle, with type I nanotubes showing a larger absorption. In contrast, the luminescence quantum yield remains almost constant

Homogeneous linewidth of the intraband transition at 1.55µm in GaN/AlN quantum dots.

PosterWe present homogeneous linewidth measurements of the intraband transition at 1.55 m in GaN/AlN quantum dots by means of non-linear spectral hole-burning experiments. The square-root dependence of the differential transmission signal with the incident pump power reveals the importance of electron-electron scattering in the population relaxation dynamics. We find on the contrary that this scattering process plays a minor role in the coherence relaxation dynamics since the homogeneous linewidth of 15 meV at 5K does not depend on the incident pump power. This suggests the predominance of other dephasing mechanisms such as spectral diffusion, and temperature-dependent measurements support this hypothesi

Intraband and intersubband many-body effects in the nonlinear optical response of single-wall carbon nanotubes

International audienceWe report on the nonlinear optical response of a mono-chiral sample of (6,5) single-wall carbon nanotubes by means of broad-band two-color pump-probe spectroscopy with selective excitation of the S11 excitons. By using a moment analysis of the transient spectra, we show that all the nonlinear features can be accurately accounted for by elementary deformations of the linear absorption spectrum. The photo-generation of S11 excitons induces a broadening and a blue shift of both the S11 and S22 excitonic transitions. In contrast, only the S11 transition shows a reduction of oscillator strength, ruling out population up-conversion. These nonlinear signatures result from many-body effects, including phase-space filling, wave-function renormalization and exciton collisions. This framework is sufficient to interpret the magnitude of the observed nonlinearities and stress the importance of intersubband exciton interactions. Remarkably, we show that these intersubband interactions have the same magnitude as the intraband ones and bring the major contribution to the photo-bleaching of the S22 excitonic transition upon S11 excitation through energy shift and broadening

On pedestrian traffic management in railways station: simulation needs and model assessment

EWGT2018, 21st EURO Working Group on Transportation Meeting, Braunschweig, Allemagne, 17-/09/2018 - 19/09/2018Mass transit rail stations make up complex systems in which passenger flows have significant influence on operations and traffic conditions. Are there pedestrian simulators that can effectively contribute to the management of crowd flows? To answer this question, an assessment grid is built to address scientific principles as well as operational and organizational needs. The scientific principles encompass real-world features to be described, especially causalities to reproduce. The grid is applied to several commercially-available software (including PTVVisWalk, Legion, Anylogic, MassMotion and SimWalk) as well as to research-sourced pedestrian simulators

Testing landscape as cultural expression

Traditional archaeological location modelling, whilst very informative about spatial patterns across a 2D spectrum, can be limited in its contribution to understanding human choice about location. On the other hand, projects combining statistical tests with models influenced by individual immersion techniques have a far better chance of understanding the choices people made in regards to place and confirming the likelihood of these apparent choices. In the past we have statistically tested and confirmed the likelihood that the points on the horizon as indicated by monument alignments as a regional group, were statistically different in terms of direction, altitude and distance from the monuments, compared to any other place on the surrounding visible horizon for monuments within particular regions. That is, the chosen points on the horizon indicated by the alignments do not appear to be random. We then tested the likelihood that monuments were erected with astronomy in mind in different locations across Scotland, using simpler standing stone monuments by region, and some complex monuments individually, like stone circles. We have also used 3D panoramas to view how things were seen at each site from the viewpoint of an individual. We have now created new statistical approaches to test different questions we might have of these panoramas. Most pertinently, we now have a test that can assess whether the two dominant horizon shapes found, which affect which astronomical bodies can be seen at these monuments, were likely chosen by their builders or if their shapes are likely determined by chance factors.The authors are also grateful to the University of Adelaide and the George Southgate Travel and Research grant which allowed one of the authors to attend SEAC 2017 in Santiago D’Compostela.Peer reviewe

Grille d'évaluation des simulations piétons dans le cas des gares ferroviaires

International audienceThis assessment grid is dedicated to evaluating pedestrian models in the context of railway stations, including massive passenger flows and train arrivals and departures’ influence on the pedestrian demand. The evaluation is done for both scientific and industrial goals, and thus includes criteria about the possible use of such models in operations. For example, is the model capable of running simulations fast enough to help a global station management system take decisions in real time. Global methodology is explained in the main article, “On pedestrian traffic management in railway stations: simulation needs and model assessment”, submitted for review for 21st EURO Working Group on Transportation Meeting (EWGT 2018) on April 20th, 2018. The evaluation addresses four aspects of pedestrian models: (1) access conditions (2) application conditions (3) crowd dynamics issues and (4) modeling and simulation. These questions are derived from a literature review (Duives, Daamen, &Hoogendoorn, 2013; Nelson, 1995; Caramuta et al., 2017), empirical knowledge of pedestrian behavior, and previous research (Kabalan, Leurent, Christoforou, & Dubroca-Voisin, 2017). This evaluation grid has been designed to provide a quick overview of a model's capabilities. We consider that giving a global score is irrelevant since the motives of the users can vary widel

One-step grown suspended single walled carbon nanotubes (SWNTS) by plasma enhanced chemical vapor deposition

Communication oraleInternational audienceSuspended single-walled carbon nanotubes were grown only on predefined place of three dimensional structures for future nanotechnology applications . We demonstrated the in situ one-step growth of SWNTs by an electron cyclotron resonance (ECR) CVD method at low temperature (650°C) and low ethylene pressure ( 2x10-3 mbar)[1]. Catalytic Fe or Fe2O3 nanoparticles were directly deposited on Si pillars using a reactive sputtering ECR plasma. SWNTs were originally grown from catalysts on top of the pillars and finished on another silicon pillar or TiN electrode (Fig. 1). Raman scattering in a confocal microscopy setup has been used to measure the RBMs of SWNTs (Fig.2) therefore allowing the diameter distribution identification. We found that very narrow tubes (d<0.8nm) represent a significant amount of the suspended nanotubes. The G and D bands were also observed leading information on respectively, the metallic or semi-conducting nature of the individual nanotubes and their excellent crystallographic quality. Photo-luminescence microscopy will be used to identify individual SWNTs and to determine their chiral indices and study the excitonic diffusion dynamics in this very specific as grown suspended geometry. References [1] M. Delaunay, A. Senillou and M.N. Semeria, U.S. Patent n° US 7,160,585 B2-Jan. 9,200