281 research outputs found
Planets orbiting Quark Nova compact remnants
We explore planet formation in the Quark Nova scenario. If a millisecond pulsar explodes as a Quark Nova, a protoplanetary disk can be formed out of the metal rich fall-back material. The propeller mechanism transfers angular momentum from the born quark star to the disk that will go through viscous evolution with later plausible grain condensation and planet formation. As a result, earth-size planets on circular orbits may form within short radii from the central quark star. The planets in the PSR1257+12 system can be explained by our model if the Quark Nova compact remnant is born with a period of ms following the explosion. We suggest that a good portion of the Quark Nova remnants may harbour planetary systems
The canonical effect in statistical models for relativistic heavy ion collisions
Enforcing exact conservation laws instead of average ones in statistical
thermal models for relativistic heavy ion reactions gives raise to so called
canonical effect, which can be used to explain some enhancement effects when
going from elementary (e.g. pp) or small (pA) systems towards large AA systems.
We review the recently developed method for computation of canonical
statistical thermodynamics, and give an insight when this is needed in analysis
of experimental data.Comment: 4 pages, 3 figures. Talk given in Strangeness in Quark Matter,
Frankfurt am Main 2001. Submitted to J. Phys. G: Nucl. Part. Phy
Novel cruzain inhibitors for the treatment of Chagas' disease.
The protozoan parasite Trypanosoma cruzi, the etiological agent of Chagas' disease, affects millions of individuals and continues to be an important global health concern. The poor efficacy and unfavorable side effects of current treatments necessitate novel therapeutics. Cruzain, the major cysteine protease of T. cruzi, is one potential novel target. Recent advances in a class of vinyl sulfone inhibitors are encouraging; however, as most potential therapeutics fail in clinical trials and both disease progression and resistance call for combination therapy with several drugs, the identification of additional classes of inhibitory molecules is essential. Using an exhaustive virtual-screening and experimental validation approach, we identify several additional small-molecule cruzain inhibitors. Further optimization of these chemical scaffolds could lead to the development of novel drugs useful in the treatment of Chagas' disease
Quark-nova remnants IV: Application to radio emitting AXP transients
(Abridged) XTE J1810-197 and 1E 1547.0-5408 are two transient AXPs exhibiting
radio emission with unusual properties. In addition, their spin down rates
during outburst show opposite trends, which so far has no explanation. Here, we
extend our quark-nova model for AXPs to include transient AXPs, in which the
outbursts are caused by transient accretion events from a Keplerian (iron-rich)
degenerate ring. For a ring with inner and outer radii of 23.5 km and 26.5 km,
respectively, our model gives a good fit to the observed X-ray outburst from
XTE J1810-197 and the behavior of temperature, luminosity, and area of the two
X-ray blackbodies with time. The two blackbodies in our model are related to a
heat front (i.e. Bohm diffusion front) propagating along the ring's surface and
an accretion hot spot on the quark star surface. Radio pulsations in our model
are caused by dissipation at the light cylinder of magnetic bubbles, produced
near the ring during the X-ray outburst. The delay between X-ray peak emission
and radio emission in our model is related to the propagation time of these
bubbles to the light cylinder. We predict a ~1 year and ~1 month delay for XTE
J1810-197 and 1E 1547.0-5408, respectively. The observed flat spectrum, erratic
pulse profile, and the pulse duration are all explained in our model as a
result of X-point reconnection events induced by the dissipation of the bubbles
at the light cylinder. The spin down rate of the central quark star can either
increase or decrease depending on how the radial drift velocity of the magnetic
islands changes with distance from the central star. We suggest an evolutionary
connection between transient AXPs and typical AXPs in our model.Comment: 16 journal pages, 4 figures and 1 table [Version accepted for
publication in A&A
SGRs and AXPs proposed as ancestors of the Magnificent seven
The recently suggested correlation between the surface temperature and the
magnetic field in isolated neutron stars does not seem to work well for SGRs,
AXPs and X-ray dim isolated neutron stars (XDINs; specifically the Magnificent
Seven or M7). Instead by appealing to a Color-Flavor Locked Quark Star (CFLQS)
we find a more natural explanation. In this picture, the heating is provided by
magnetic flux expulsion from a crust-less superconducting quark star. Combined
with our previous studies concerning the possibility of SGRs, AXPs, and XDINs
as CFLQSs, this provides another piece of evidence that these objects are all
related. Specifically, we propose that XDINs are the descendants of SGRs and
AXPs.Comment: submitted to A&A letters to the edito
Fall-back crust around a quark-nova compact remnant I: The degenerate shell case with applications to SGRs, AXPs and XDINs
We explore the formation and evolution of debris ejected around quark stars
in the Quark Nova scenario, and the application to Soft Gamma-ray Repeaters
(SGRs) and Anomolous X-ray Pulsars (AXPs). If an isolated neutron star explodes
as a Quark Nova, an Iron-rich shell of degenerate matter forms out of the
fall-back (crust) material. Our model can account for many of the observed
features of SGRs and AXPs such as: (i) the two types of bursts (giant and
regular); (ii) the spin-up and spin-down episodes during and following the
bursts with associated persistant increases in ; (iii) the energetics
of the boxing day burst, SGR180620; (iv) the presence of an Iron line as
observed in SGR190014; (v) the correlation between the far-Infrared and the
X-ray fluxes during the bursting episode and the quiescent phase; (vi) the hard
X-ray component observed in SGRs during the giant bursts, and (vii) the
discrepancy between the ages of SGRs/AXPs and their supernova remnants. We also
find a natural evolutionary relationship between SGRs and AXPs in our model
which predicts that only the youngest SGRs/AXPs are most likely to exhibit
strong bursting. Many features of X-ray Dim Isolated Neutron stars (XDINs) are
also accounted for in our model such as, (i) the two-component blackbody
spectra; (ii) the absorption lines around 300 eV; and (iii) the excess optical
emission.Comment: submitted to Ap
Continuous Mental Effort Evaluation during 3D Object Manipulation Tasks based on Brain and Physiological Signals
Designing 3D User Interfaces (UI) requires adequate evaluation tools to
ensure good usability and user experience. While many evaluation tools are
already available and widely used, existing approaches generally cannot provide
continuous and objective measures of usa-bility qualities during interaction
without interrupting the user. In this paper, we propose to use brain (with
ElectroEncephaloGraphy) and physiological (ElectroCardioGraphy, Galvanic Skin
Response) signals to continuously assess the mental effort made by the user to
perform 3D object manipulation tasks. We first show how this mental effort
(a.k.a., mental workload) can be estimated from such signals, and then measure
it on 8 participants during an actual 3D object manipulation task with an input
device known as the CubTile. Our results suggest that monitoring workload
enables us to continuously assess the 3DUI and/or interaction technique
ease-of-use. Overall, this suggests that this new measure could become a useful
addition to the repertoire of available evaluation tools, enabling a finer
grain assessment of the ergonomic qualities of a given 3D user interface.Comment: Published in INTERACT, Sep 2015, Bamberg, German
On the exact conservation laws in thermal models and the analysis of AGS and SIS experimental results
The production of hadrons in relativistic heavy ion collisions is studied
using a statistical ensemble with thermal and chemical equilibrium. Special
attention is given to exact conservation laws, i.e. certain charges are treated
canonically instead of using the usual grand canonical approach. For small
systems, the exact conservation of baryon number, strangeness and electric
charge is to be taken into account. We have derived compact, analytical
expressions for particle abundances in such ensemble. As an application, the
change in ratios in AGS experiments with different interaction system
sizes is well reproduced. The canonical treatment of three charges becomes
impractical very quickly with increasing system size. Thus, we draw our
attention to exact conservation of strangeness, and treat baryon number and
electric charge grand canonically. We present expressions for particle
abundances in such ensemble as well, and apply them to reproduce the large
variety of particle ratios in GSI SIS 2 A GeV Ni-Ni experiments. At the
energies considered here, the exact strangeness conservation fully accounts for
strange particle suppression, and no extra chemical factor is needed.Comment: Talk given at Strangeness in Quark Matter '98, Padova, Italy (1998).
Submitted to J.Phys. G. 5 pages, 2 figure
Quark nova imprint in the extreme supernova explosion SN 2006gy
The extremely luminous supernova 2006gy (SN 2006gy) is among the most
energetic ever observed. The peak brightness was 100 times that of a typical
supernova and it spent an unheard of 250 days at magnitude -19 or brighter.
Efforts to describe SN 2006gy have pushed the boundaries of current supernova
theory. In this work we aspire to simultaneously reproduce the photometric and
spectroscopic observations of SN 2006gy using a quark nova model. This analysis
considers the supernova explosion of a massive star followed days later by the
quark nova detonation of a neutron star. We lay out a detailed model of the
interaction between the supernova envelope and the quark nova ejecta paying
special attention to a mixing region which forms at the inner edge of the
supernova envelope. This model is then fit to photometric and spectroscopic
observations of SN 2006gy. This QN model naturally describes several features
of SN 2006gy including the late stage light curve plateau, the broad H{\alpha}
line and the peculiar blue H{\alpha} absorption. We find that a progenitor mass
between 20Msun and 40Msun provides ample energy to power SN 2006gy in the
context of a QN.Comment: 15 pages, 9 figure
Exact Baryon, Strangeness and Charge Conservation in Hadronic Gas Models
Relativistic heavy ion collisions are studied assuming that particles can be
described by a hadron gas in thermal and chemical equilibrium. The exact
conservation of baryon number, strangeness and charge are explicitly taken into
account. For heavy ions the effect arising from the neutron surplus becomes
important and leads to a substantial increase in e.g. the ratio.
A method is developed which is very well suited for the study of small systems.Comment: 5 pages, 5 Postscript figure
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