Dominik Gronkieicz (NCAC, Warsaw)
Stefan Dziembowski (Faculty of Mathematics, Informatics, and Mechanics, Warsaw University)
The cryptographic currencies (also dubbed the cryptocurrencies) are a fascinating recent concept whose popularity exploded in the last 6-7 years. The most prominent of them is Bitcoin, introduced in 2008 by an anonymous developer using a pseudonym "Satoshi Nakamoto". These currencies quickly gained noticeable attention among the general public, and their economic importance is rapidly growing - the current capitalization of Bitcoin is over 250 billion USD, and the average number of transactions per day is well above 200,000. The goal of this talk is to provide a research-oriented introduction to the technological aspects of cryptocurrencies. We will start with a description of Bitcoin and its main design principles. We will then discuss some of the weaknesses of Bitcoin, and ideas for alternative cryptocurrencies. Note: this talk will not contain any advice on investing in cryptocurrencies.
Rodolfo Smiljanic (NCAC, Warsaw)
Aleksander Kaminker ( Ioffe Physical-Technical Institute, Saint Petersburg)
Thermal evolution of neutron stars (NSs) with variable internal heaters distributed over NS crust is discussed with special emphasis on the effects of crustal supefluidity. Superfluidity can significantly shorten and intensify the thermal surface emission from a star in response to an internal heater's outburst. This can be important for interpretation of observed outbursts of transiently accreting NSs in low-mass X-ray binaries (LMXBs) as well as of long outbursts of magnetars. Particular attention is paid to the so called quasi-persistent LMXBs where intense accretion overheats NS crusts. An analysis of the IGR J17480-2446 source shows a reasonable agreement between observations of long-term afterburst relaxation and theoretical models of relaxation in NSs with strong superfluidity and partly accreted (hybrid) crusts.
Nathan Leigh (Museum of Natural History, New York)
In this talk, we briefly review the concept of chaos in highly collisional gravitationally-bound systems of interacting particles. These concepts are then applied to the classic three- and four-body problems in Newtonian gravity. A statistical mechanics methodology is applied in order to derive analytic expressions for the properties of the outcomes of these interactions. This includes the orbital parameter distributions expected for populations of binary and triple star systems produced as a result of three- and four-body interactions. Such small-number collisional interactions occur regularly in star clusters throughout the Universe, across all mass scales. At higher cluster masses, such as globular and nuclear star clusters, stellar-mass black holes (BHs) are thought to be regular participants in these interactions. This is a key step that influences directly the interpretation of observations of BH-BH mergers using gravitational wave (GW) detectors, such as aLIGO. We discuss how the ever-growing number of observed BH-BH mergers can be used to constrain the astrophysical environments from which the detected GWs originate.
Bogumił Pilecki (NCAC, Warsaw)
Cepheids are radially pulsating giants and supergiants, and form one of the most important classes of variable stars. They have proved to be very useful in many different areas of astrophysics. Cepheids are important distance indicators in the local Universe and key objects for testing the predictions of stellar evolution and stellar pulsation theories. A presence of Cepheids in eclipsing binary systems give us an opportunity to measure and study their physical parameters, including the mass, which we can hardly determine for single stars. The analysis of such systems is very challenging and new methods had to be developed to take full advantage of this configuration. These objects are also very rare and hard to find. In total, we have studied seven Cepheids in six eclipsing binary systems and found firm relations between such observed parameters as period mass and radius. The results based on evolution and pulsation models can be now compared with observations and challenged. The study resulted in finding evidence for binary interactions during the evolution and a non-pulsating object inside the instability strip. Our measurements provide strong constraints for solving the famous Cepheid mass discrepancy problem.
Samuel Lander (CAMK, Warsaw)
Neutron stars host the strongest known magnetic fields in the Universe. These fields play several key roles in the evolution and dynamics of neutron stars, as well as powering the emission which allows us to observe them. Unlike normal stars, like the Sun, neutron stars have no mechanism for continuously regenerating their magnetic fields, so the fields which exist must be in a dynamically stable equilibrium in order to survive. Since we have no direct probe of the interior magnetic field of neutron stars, we must resort to theoretical models. Realistic models need, however, to incorporate a challenging piece of neutron-star physics: the fact that the star’s core forms a superconducting fluid. We describe how to account for the microscopic physics of superconductivity in large-scale models of the whole neutron star, and present some of the first equilibrium models for magnetic fields in the star's superconducting core. We conclude by looking at the interplay between rotation and magnetic fields in neutron stars, and show how the star’s rotation and magnetic axes can evolve to become either aligned or orthogonal.
Michela Mapelli (University of Padova)
On September 14 2015, the LIGO interferometers captured a gravitational wave (GW) signal from two merging black holes (BHs), opening the era of GW astrophysics. Five BH mergers have been reported so far, three of them involving massive BHs (>30 solar masses). According to stellar evolution models, such massive BHs can originate from massive relatively metal-poor stars. Understanding the formation of binary BH systems (BHBs) is a major challenge for astrophysics: it involves a plethora of dynamical and stellar-evolution processes, which can be studied only via advanced numerical codes. In this talk, I will discuss the main formation pathways of merging BHs with particular attention to the main open questions and to the next frontiers of population synthesis and dynamical models.
Rainer Spurzem (National Astronomical Observatories of China)
Black Holes are difficult to detect through electromagnetic radiation alone. Indirect evidence for their existence in our universe has been accumulated on a large range of black hole mass scales (supermassive in galactic nuclei, stellar in X-ray binaries and most notably recently by direct gravitational wave detection through LIGO/Virgo). Intermediate mass black holes may exist too, but remain the most speculative variety of their kind. Recently, gravitational waves from coalescing stellar mass black holes have been detected by the LIGO instruments. This is considered a first direct evidence of the existence of black holes and their binaries. In our team we have been working on the interaction of black holes on all mass scales with stellar clusters surrounding them - globular and nuclear star clusters with stellar mass black holes and galactic nuclei with supermassive ones. We study with computer simulations based on direct N-body simulations with Post-Newtonian general relativity (if needed) how black holes form, build binaries, evolve, disrupt stars, and emit gravitational waves. Recently in collaboration with CAMK we are exploring ways to form intermediate mass black holes. The talk will give an overview of simulations, methods used and results obtained. Astrophysical topics are for example the ``detection'' of black hole mergers like observed by LIGO in our N-body models, and the merger of supermassive binary black holes in galactic nuclei, with prediction of expected low-frequency gravitational wave emission.
Nicolas Chamel (Université Libre de Bruxelles)
Formed in the aftermath of gravitational core-collapse supernova explosions, neutron stars are the most compact observed stars. Their average density exceeds than that found inside the heaviest atomic nuclei. Neutron stars are also endowed with the strongest magnetic fields known, which can reach millions of billions times that of the Earth. According to our current understanding, a neutron star is stratified into distinct layers. The surface is probably covered by a metallic ocean. The solid layers beneath consist of a crystal lattice of pressure-ionized atoms embedded in a highly degenerate electron gas. With increasing density, nuclei become progressively more neutron rich until neutrons start to drip out of nuclei thus delimiting the boundary between the outer and inner regions of the crust, where neutron-proton clusters are immersed in a neutron liquid. At about half the density of heavy nuclei, the crust dissolves into an homogeneous liquid mixture of nucleons and leptons. The composition of the innermost part of the core remains highly uncertain. During this talk, our developments of unified and thermodynamically consistent equations of state of dense matter in neutron stars will be reviewed.
Tomaso Belloni (INAF - Osservatorio Astronomico di Brera)
I will review the current standpoint of fast variability from black-hole binary systems. The large amount of data obtained in the past two decades has led to a significant advancement in our knowledge, although it still needs to be consolidated through new observations. I will present the more recent evidences of General Relativistic effects obtained from RossiXTE data and will present new data from the Astrosat mission.
Krzysztof Czart (ESO)
Polish Astronomical Society is an organization of professional astronomers with about 250 members. It's activities can be divided into two categories: science related activities and science communication activities. During the presentation there will be an opportunity to get information about all major projects run by the organization, some of it's future plans and also how to become a member of the organization and some useful information for members.
Ariadna Murguia-Bertheir (University of California)
LIGO discovered gravitational waves from a binary black hole merger, marking the beginning of a new era in astrophysics. This revolutionary discovery challenged our understanding of compact objects, especially the formation of these massive binaries. In my talk I will describe how a common envelope phase aids in understanding the assembly of this merger. A common envelope phase occurs when, in a binary, one of the stars evolves and engulfs its companion (in this case a black hole). I will talk about how the flow around the embedded companion affects the inspiral and the fate of the binary. I will discuss the necessary conditions for disk assembly around the companion, and the possible implications for the LIGO binary black hole.
Dipanjan Mukherjee (University of Torino, Italy)
Relativistic jets from AGNs are an important driver of feedback in galaxies. Although primarily considered in the context of energy deposition at scales of ~100 kpc to regulate mass inflow, the jets first interact with the host galaxy's ISM before breaking out to larger scales. Our recent 3D relativistic hydrodynamic simulations, performed on scales of several kpc, investigates the interaction of such jets with an inhomogeneous turbulent ISM within the potential of a galaxy. These simulations address the local gas physics, which is often missed in large scale cosmological simulations due to lack of sufficient resolution. The jets are found to couple strongly with the turbulent ISM, driving fast moving lateral outflows of multi-phase gas. The resultant outflows though strong, do not escape the galaxy, supporting a galactic fountain scenario of feedback, rather than a blow out phase as envisaged previously. We compare the effect of jet power and ISM density on the feedback efficiency. We show that low power jets remain confined within the host for a longer time driving shocks through the ISM, potentially quenching star formation on a large scale. We have performed simulations with two different ISM morphologies: spherical and disk. Jet-ISM coupling is stronger in spherically distributed gas. In gas disks, although the jet breaks out easily, the ensuing high pressure bubble compresses the disk driving shocks. Jets inclined to the disk behave differently, launching sub-relativistic vertical outflows while strongly perturbing the disk, as observed in galaxies like NGC 1052, IC 5063 etc. I will discuss the implications of these results on the evolution of the ISM of the host galaxy, and the effects on observable diagnostics.
Naosad Alam (Saha Institute of Nuclear Physics)
The bulk properties of neutron stars are predominantly governed by the equation of state (EoS) of asymmetric nuclear matter. The nuclear matter EoS for an arbitrary isospin asymmetry is characterized by the nuclear matter parameters, like, incompressibility coefficient, symmetry energy coefficient and their density derivatives. However, the knowledge of these nuclear parameters is limited. One can access the information about these nuclear parameters through their correlations with various observational properties of neutron stars. In this presentation, I will focus on the correlation of neutron star properties with various key parameters of nuclear matter equation of state. I will show a strong and almost model-independent correlation of neutron star radii with the linear combination of the slopes of the nuclear matter incompressibility coefficient and symmetry energy coefficient. I will also discuss the influence of the density dependence of symmetry energy on the critical parameters of asymmetric nuclear matter which are important for core-collapse simulations and the crustal properties of neutron stars.
Andrew Hamilton (JILA, Boulder)
This seminar will tell three stories about what happens inside astronomical black holes. The first story is about the simplest kind of black hole, a non-rotating Schwarzschild black hole. I show that the singularity is a surface, not a point, and I show that Hawking radiation diverges near the singular surface. There is no firewall paradox. The second story is about rotating black holes. A rotating black hole has an inner horizon where there is a (Poisson-Israel) instability, which I call the black hole particle accelerator, which is the most violent instability in the Universe, including the Big Bang. I show that the instability gives way to complicated oscillatory (Belinskii-Khalatnikov-Lifshitz) collapse. The third story is the most fantastic. You will have to attend the seminar to hear it.
Attention: the talk will start at 1:30 pm.
Dipanjan Mukherjee (Dipartimento di Fisica, Universit`a degli Studi di Torino)
Relativistic jets from AGNs are an important driver of feedback in galaxies. Although primarily considered in the context of energy deposition at scales of ~100 kpc to regulate mass inflow, the jets first interact with the host galaxy's ISM before breaking out to larger scales. Our recent 3D relativistic hydrodynamic simulations, performed on scales of several kpc, investigates the interaction of such jets with an inhomogeneous turbulent ISM within the potential of a galaxy. These simulations address the local gas physics, which is often missed in large scale cosmological simulations due to lack of sufficient resolution. The jets are found to couple strongly with the turbulent ISM, driving fast moving lateral outflows of multi-phase gas. The resultant outflows though strong, do not escape the galaxy, supporting a galactic fountain scenario of feedback, rather than a blow out phase as envisaged previously. We compare the effect of jet power and ISM density on the feedback efficiency. We show that low power jets remain confined within the host for a longer time driving shocks through the ISM, potentially quenching star formation on a large scale. We have performed simulations with two different ISM morphologies: spherical and disk. Jet-ISM coupling is stronger in spherically distributed gas. In gas disks, although the jet breaks out easily, the ensuing high pressure bubble compresses the disk driving shocks. Jets inclined to the disk behave differently, launching sub-relativistic vertical outflows while strongly perturbing the disk, as observed in galaxies like NGC 1052, IC 5063 etc. I will discuss the implications of these results on the evolution of the ISM of the host galaxy, and the effects on observable diagnostics.
Alessandro Papitto (Osservatorio Astronomico di Roma)
Millisecond pulsars are the quickest spinning compact objects known and hence the best probes to measure the state of ultradense matter and test the theory of General Relativity. They attain their very fast rotation during a Gyr-long phase of accretion of matter from a low mass companion star, which drives a bright X-ray emission. When the mass transfer stops magnetospheric pulsed emission powered by the star rotation - and observed preferentially in the radio and gamma-ray bands - sets in. This complex evolution has been recently demonstrated by the discovery of transitional millisecond pulsars (Papitto et al. 2013, Nature) that swing between an accretion-powered X-ray pulsar regime and a rotationally-powered radio pulsar state on a time scale of a few weeks, or even shorter. These pulsars show an incredibly rich phenomenology that reflects all the possible outcomes of the interaction between the pulsar wind of particles and radiation and matter in an accretion disk. This has been confirmed by the discovery of optical pulsations from a transitional pulsar (Ambrosino, Papitto et al., 2017, Nature Astronomy), the first ever from a millisecond spinning neutron star. The pulsations were observed by using the fast photometer SiFAP at the INAF Galileo Telescope. Optical pulses were detected when the pulsar was surrounded by an accretion disk, but they are most likely originated by a rotation-powered magnetospheric process. The profound implications for our understanding of the pulsar disk/magnetosphere interaction will be discussed.
Marcin Semczuk (NCAC, Warsaw)
Milky Way, M31 and M33 are the three largest galaxies in the Local Group. M31 and M33 create a somewhat separated pair, with their relative distance being ~4 times smaller than the distance to the Milky Way. Except for their proximity, there are several other traits suggesting that the two galaxies interacted in the past. M33 has a warped gaseous and stellar disks that might have a tidal origin and both galaxies exhibited a rapid increase in their star formation rates at around 2 Gyr ago. During the seminar, I will discuss arguments for and against the possible past interaction between M33 and M31 and I will present our recent results on our attempt to simulate the recent history of the system.
Fabian Welc (Institute of Archaeology, UKSW, Warszawa)
Just two decades ago, Holocne was considered as relatively climatically stable period, but recent, reseach revealed extremely dynamic climate fluctuations which took place during last 10,000 years. These sudden and catastrophic climate fluctuations are referred to as Rapid Climatic Changes (RCC) or Bond events. They represented eight cold oscillations that took place every 1500 years. Bond or RCC events contributed to significant environmental changes in various parts of the world (especially on the northern hemisphere) and exerted an overwhelming influence on the development and disappearance of the past ancient cultures and civilisations. Until now, it is not known what triggers RCC events. One of the most acceptable concepts is the impact of astronomical factors such as changes in earth's orbit parameters and value of insolation. Today there is no doubt that past cultures have developed in accordance with the rhythm of climate change, but this issue has only been subject to insightful multidisciplinary research for last several years. The main subject of the presentation will focus on rapid climate oscillations related to the Bond events no. 5 (8.2 ka BP), 3 (4,2 ka BP) and 1 (1.5 ka BP), because they have had a significant, even catastrophic impact on ancient civilizations.
Mary Loli Martinez Aldama (Center for Theoretical Physics, PAN, Warsaw)
The study of the AGN accreting close to the Eddington limit (L/LEdd~1)
has taken an important role, due to their potential use as standard
candles for cosmological applications. With the purpose to understand
the physics of extreme quasar, we perform a spectroscopic analysis of a
sample of highly accreting quasars at high redshift (z~2–3). Our sample
were observed with the OSIRIS spectrograph on the GTC 10.4 m telescope
located at the Observatorio del Roque de los Muchachos in La Palma. The
highly accreting quasars were identified using the 4D
Eigenvector 1 formalism, which is able to organize type 1 quasars over a
broad range of redshift and luminosity. The kinematic and physical
properties of the broad line region have been derived by fitting the
profiles of strong UV emission lines such as AlIII λ1860, SiIII]λ1892
and CIII]λ1909. We find that AlIIIλ1860 can be associated with a
low-ionization virialized sub-system. xA sources show strong blueshifts
in the high-ionization lines like in CIVλ1549, indicating a relation
between the high Eddington ratios and the productions of outflows. The
extreme radiative properties of highly accreting quasar make them prime
candidates for maximum feedback effects on the host galaxy. The
characterization of extreme quasar allow to assemble large samples of
extreme quasars from the latest data releases of the SDSS, especially
useful for deriving independent estimates of ΩM in the redshift range
1
Phil Uttley (Astronomical Institute Anton Pannekoek Universiteit van Amsterdam)
X-ray spectral-timing is an approach to studying the X-ray variability of accreting compact objects, which combines photon energies and arrival-times to determine the causal relationship between the emission components. With this approach, we are starting to ‘map’ the innermost regions of accreting black hole systems. In this talk I will review this growing field in X-ray astronomy and show how it is being further revolutionised by remarkable results from the the Neutron star Interior Composition Explorer (NICER), which was installed on the International Space Station last year. NICER has an unprecedented capability to study the brightest X-ray sources in the sky - X-ray binaries - with no instrumental distortion or telemetry losses, even for count rates above 1e4 counts per second.
Nicolas Peschken (CAMK, Warsaw)
Galactic bars are a central elongated stellar structure found in the center of many disc galaxies, such as the Milky Way. Those bars are central for the study of disc galaxies, as they impact the whole disc structure and morphology, for both the gas and stars. Their formation mechanisms are diverse, as they can form in secular evolution, or be triggered by external perturbers. I will present my work about the study of galactic bars in Illustris, a large hydrodynamical cosmological simulation with hundred thousands of galaxies. After presenting the general properties of bars and the bar frequency in Illustris disc galaxies, I will focus on bars tidally induced, i.e. when the bar forms from an interaction with another galaxy.
Petri Vaisanen (SAAO)
I will summarise the current status of SALT, the 10m optical telescope in South Africa, including its instruments and some recent science results. I will in particular highlight the new science strategy adopted recently to focus the future work and collaborations. I will talk about the instrumentation development plans for the next years supporting those science goals, and how these could benefit the Polish astronomical community.
Tsvi Piran (The Hebrew University of Jerusalem)
The observed GRB (170817A) that followed GW170817 confirmed the longstanding prediction of association of short GRBs with neutron star mergers. The unique large scale observational campaign that followed confirmed further predictions, and in particular that mergers are the dominant sites of r-process nucleosynthesis. They also provided numerous surprising observations, teaching us a lot about these events. . I discuss past predictions, current observations and their implications and future prospects of joint detection of GRBs and GW signals. Among the latter, most exciting is the possibility that the gravitational waves observations will teach us about the inner working of GRBs central engine and the acceleration process of relativistic jets.
Attention: Tsvi Piran's Colloquium will start at 2:15 pm
Alok Chandra Gupta (Aryabhatta Research Institute of Observational Sciences, Manora Peak, Nainital, India)
Bhupendra Mishra (JILA, Boulder, CO)
The physics of accretion around compact objects has been widely studied in last few decades. However, it has been only recently possible to perform fully global magnetohydrodynamical simulations using supercomputing models. I shall be talking about the role of strong large scale seed magnetic fields in the time evolution of geometrically thin accretion disks around black holes. Geometrically thin disks are challenging to simulate due to requirement of exceptionally high resolution (about 24 cells per disk scale height). I used cutting edge static mesh refinement (SMR) to resolve such disks with an effective resolution of 2048x256x1024 and maintain a reasonable time step close to polar regions. In this numerical model, I initialized thin disks with purely vertical magnetic field in spherical polar coordinates. Due to differential rotation, the model builds up strong toroidal magnetic field over the dynamical time scale. The toroidal field causes disk 'levitation' and accretion at higher altitudes (z ~ 0.3 in cylindrical coordinates) and outflows in the disk midplane. Such disks are called magnetically 'elevated' disks. There are various astrophysical problems where such strong magnetic field can play an essential role in shaping the accretion flow in the vicinity of black holes. I shall mainly talk about following relevant astrophysical aspects: 1. Angular momentum transportation in accretion disks ? 2. Spectral state transitions in black hole X-ray binaries 3. Magnetically elevated accretion in AGNs and their evolution
Anna Jacyszyn-Dobrzeniecka (Astronomical Observatory, Warsaw University)
I will present a three-dimensional structure of the Magellanic System using over 9000 Classical Cepheids (CCs) and almost 23000 RR Lyrae (RRL) stars from the OGLE Collection of Variable Stars. Given the vast coverage of the OGLE-IV data and very high completeness of the sample we were able to study the Magellanic System in great details. Our analysis of CCs distribution shows that contrary to previous results the LMC bar shows no offset from the galaxy plane. Moreover, we found that the northern arm, along with its smaller component, is located closer to us than the entire sample. The CCs in the SMC have a non-planar distribution that can be described as an ellipsoid extended almost along the line of sight. RRL stars revealed a very regular distribution in both Magellanic Clouds. Lately, we have very carefully studied once again the distribution of both types of pulsators in the Magellanic Bridge area. We showed that there is no evidence of an actual physical connection between the Clouds in RRL stars distribution. We only see the two halos overlapping. Moreover, our study showed that there are several CCs in the Magellanic Bridge area that seem to form a genuine connection between the Clouds. Their on-sky locations match very well young stars and neutral hydrogen distribution.
Andrzej Zdziarski (NCAC, Warsaw)
Cyg X-3 is the only known X-ray binary in the Galaxy with a Wolf-Rayet donor. The compact object is probably a black hole. It is a very bright and variable multiwavelength source, but its emission shows features substantially different from those in accreting black-hole binaries. I will review the properties of this system and present new results on its radio, X-ray and gamma-ray emission.
Bei You (School of Physics and Technology, Wuhan University, Wuhan, China)
One interesting observational appearance in X-ray binaries is the broadband X-ray variability, covering timescales from 0.01 s to thousands of seconds. Fast Fourier analysis of variability reveals Quasi-Periodic Oscillations (QPOs) in some X-ray binaries. However, the physical origin of QPOs is still under debate. As for low-frequency (1∼10 Hz) QPO (LFQPOs), the possible mechanism involves the so-called Lense–Thirring precession, which is due to the frame-dragging effect in the strong gravity field. We developed a Monte Carlo code to compute the Compton-scattered X-ray flux arising from a hot inner flow that undergoes Lense–Thirring precession. In this talk, I will review our modeling results on X-ray variability of LFQPO, and discuss its application on understanding the observed variability, including recent results from the Hard X-ray Modulation Telescope (HXMT, also named "Insight") which is China’s first X-ray astronomy satellite.
Camilo Posada (Institute of Physics Faculty of Philosophy and Science Silesian University in Opava)
The Schwarzschild interior solution, or ‘Schwarzschild star’, for a spherically symmetric mass with constant energy density, shows a divergence in pressure when the radius of the star R = (9/4)M. Recently, Mazur and Mottola showed that this divergence is integrable, inducing non-isotropic transverse stresses on a surface of some radius R0. When this radius approaches the Schwarzschild radius, the interior solution becomes one with negative pressure and no event horizon, which resembles a gravastar. Using Hartle’s structure equations, for equilibrium configurations in slow rotation, we report results of surface and integral properties for a slowly rotating Schwarzschild star beyond the Buchdahl limit, RS < R < (9/8)RS, where RS is the Schwarzschild radius. We found that quantities like the moment of inertia I, and the mass quadrupole moment Q approach to the corresponding values for the Kerr metric to second order in the angular velocity. These results provide a solution to the problem of the source of a slowly rotating Kerr black hole.
Krzysztof Łazowski (Mass Laboratory, Central Office of Measures, Warsaw)
In the speech we will discuss issues with the present definition of the kg and efforts to overcome them. We become acquainted with recommendations for the redefinition of the kg, revised SI system based on fundamental constants of nature and realization of a definition of the kg. Finally we will talk about dissemination of the mass unit, air–vacuum transfer and establishing traceability to the new kilogram.
Czesław Radzewicz (Department of Physics, Warsaw University)
