Structures in circumbinary disks: Prospects for observability

During the past decade circumbinary disks have been discovered around various young binary stars. Hydrodynamical calculations indicate that the gravitational interaction between the central binary star and the surrounding disk results in global perturbations of the disk density profile. We study the observability of characteristic large-scale disk structures resulting from the binary-disk interaction in the case of close binary systems. We derived the structure of circumbinary disks from smoothed-particle hydrodynamic simulations. Subsequently, we performed radiative transfer simulations to obtain scattered light and thermal reemission maps. We investigated the influence of the binary mass ratio, the inclination of the binary orbit relative to the disk midplane, and the eccentricity of the binary orbit on observational quantities. We find that ALMA will allow tracing asymmetries of the inner edge of the disk and potentially resolving spiral arms if the disk is seen face-on. For an edge-on orientation, ALMA will allow detecting perturbations in the disk density distribution through asymmetries in the radial brightness profile. Through the asymmetric structure of the disks, areas are formed with a temperature $2.6$ times higher than at the same location in equivalent unperturbed disks. The time-dependent appearance of the density waves and spiral arms in the disk affects the total re-emission flux of the object by a few percent.Comment: 8 pages, 9 figures, to appear in A&

Tracing large-scale structures in circumstellar disks with ALMA

Planets are supposed to form in circumstellar disks. The gravitational potential of a planet perturbs the disk and leads to characteristic structures, i.e. spiral waves and gaps, in the disk's density profile. We perform a large-scale parameter study of the observability of these planet-induced structures in circumstellar disks with ALMA. On the basis of HD and MHD simulations, we calculated the disk temperature structure and (sub)mm images of these systems. These were used to derive simulated ALMA images. Because appropriate objects are frequent in Taurus, we focused on a distance of 140pc and a declination of 20{\deg}. The explored range of star-disk-planet configurations consists of 6 HD simulations (including magnetic fields and different planet masses), 9 disk sizes, 15 total disk masses, 6 different central stars, and two different grain size distributions. On almost all scales and in particular down to a scale of a few AU, ALMA is able to trace disk structures induced by planet-disk interaction or by the influence of magnetic fields on the wavelength range between 0.4 and 2.0mm. In most cases, the optimum angular resolution is limited by the sensitivity. However, within the range of typical masses of protoplanetary disks (0.1-0.001Msun) the disk mass has a minor impact on the observability. It is possible to resolve disks down to 2.67e-6Msun and trace gaps induced by a planet with M_p/M_s = 0.001 in disks with 2.67e-4Msun with a signal-to-noise ratio greater than three. The central star has a major impact on the observability of gaps, as well as the considered maximum grainsize of the dust in the disk. In general, it is more likely to trace planet-induced gaps in our MHD models, because gaps are wider in the presence of magnetic fields. We also find that zonal flows resulting from MRI create gap-like structures in the disk's re-emission radiation, which are observable with ALMA.Comment: 17 pages, 21 figure

Observability of large-scale structures in circumstellar disks and analysis of their origin

Zirkumstellare Scheiben sind die Geburtsstätte von Planetensystemen. Sie bestehen zu einem überwiegenden Teil aus Gas und etwa 1% Staub und bilden sich im Zuge der Sternentstehung. Gerade die seit Kurzem möglichen Beobachtungen dieser Objekte mit ALMA bringen immer mehr ans Licht, dass es sich bei zirkumstellaren Scheiben um hoch dynamische Objekte mit großskaligen Strukturen in der Materialverteilung handelt. Inzwischen sind viele Wechselwirkungsmechanismen vorgeschlagen worden, die solche Strukturen erklären können. Allerdings ist es auch notwendig, die Beobachtbarkeit dieser theoretischen Mechanismen im Detail zu untersuchen, um ein Werkzeug zur Interpretation realer Messungen zur Hand zu haben. Besonders eignet sich hierfür ein dreiteiliges Vorgehen, bei dem zunächst die Störung der Scheibendichtestruktur in Hydrodynamiksimulationen beschrieben wird. Im nächsten Schritt werden dann Strahlungstransport-Simulationen auf der Grundlage dieser Dichteverteilungen durchgeführt und hierauf aufbauend Beobachtungen mit ausgewählten Instrumenten simuliert. Im Rahmen dieser Arbeit werden die charakteristischen Strukturen, die durch Planet-Scheibe-, Binärsystem-Scheibe- und Magnetfeld-Scheibe-Wechselwirkung in der Dichteverteilung der zirkumplanetaren, beziehungsweise zirkumbinären Scheibe entstehen, auf diese Weise untersucht. Dabei liegt ein besonderes Augenmerk auf simulierten ALMA-Beobachtungen im (sub)mm-Wellenlängenbereich. Dennoch werden auch andere Bereiche des elektromagnetischen Spektrums in die Analyse mit einbezogen, da erst durch die Kombination von Multiwellenlängen-Beobachtungen wirklich Ursachen für Scheibenstrukturen erkannt werden können. Dies ist vor allem deshalb wichtig, da es ein Ergebnis der Arbeit ist, dass ALMA für alle berücksichtigten Wechselwirkungsmechanismen tatsächlich charakteristische Strukturen beobachten kann, diese sich aber trotz unterschiedlicher Ursache derart ähneln können, dass eine Unterscheidung nicht möglich ist. So ist im Rahmen der durchgeführten Untersuchungen eine Unterscheidung der Auswirkung von Magnetfeld-Scheibe- und Planet-Scheibe-Wechselwirkung erst durch die Detektion der direkten Abstrahlung des Planeten möglich. Es werden die Bedingungen erforscht und angegeben, unter denen die planetare Abstrahlung detektiert werden kann und welche Rückschlüsse aus einer solchen Messung auf die Eigenschaften des Planeten möglich sind. Zudem zeigt sich, dass der Staub in einer zirkumstellaren Scheibe in Abhängigkeit seiner Größe eine Verteilung besitzt, die große Unterschiede zur Verteilung der Gasmoleküle besitzt. Da dieser aber für die Kontinuumsabstrahlung im (sub)mm-Wellenlängenbereich verantwortlich ist, können gerade die durch ihn erzeugten Strukturen besonders gut beobachtet werden. Das entworfene Modell zeigt hierbei große, augenscheinliche Ähnlichkeit zu einer ALMA-Beobachtung von HL Tau. Insgesamt zeigt die Arbeit allerdings, dass die Vielfalt der Ursachen für Strukturen in zirkumstellaren Scheiben so groß ist, dass ein Rückschluss von der Beobachtung einer Struktur auf die tatsächliche Ursache nicht eindeutig ist.Circumstellar disks are expected to be the birthplace of planetary systems. They predominantly consist of gas, with about 1% dust, and they are a byproduct of star formation. Since its inauguration, ALMA has revealed, that these objects are highly dynamical and show large scale structures in their distribution of matter. Meanwhile, several interactions have been proposed to create these structures. However, it is necessary to explore the observability of the theoretical models in detail to provide a means to interpret real measurements. In particular, a three step method is appropriate for this purpose. First, the interaction processes have to be investigated in hydrodynamical simulations of the disk density profiles. Second, on the basis of these density profiles, follow-up radiative transport calculations must be performed and finally the observability for selected instruments must be predicted from the radiative transfer outcome. This thesis investigates characteristic large scale disk structures resulting from planet-disk, binary-disk and magnetic-field-disk interactions. It focuses on predicting ALMA observations in the (sub)mm wavelength range. However, the rest parts of the electro-magnetic spectrum will also be included in the investigation, because only with a combination of multi-wavelength observations it is feasible to determine the origin of a disk structure. In particular, one key result of the thesis is that ALMA is able to observe the characteristic structures of each considered interaction process, but these could appear very similar although the origin is different. Within the parameter space considered, magnetic-field-disk and planet-disk interaction can only be distinguished on the basis of the direct radiation of the planetary source. The conditions under which it is possible to detect the planetary radiation are investigated, along with what one can learn from a measurement of this radiation about the properties of the planet. In addition, the decoupling of the motion of sufficiently large dust particles from that of the gas is explored, which leads to a distribution of these particles totally different from the distribution of the gas molecules in the disk. These large dust particles dominate the thermal continuum emission of a circumstellar disk in the (sub)mm range. Thus, structures in the distribution of large particles are particularly easy to observe with ALMA. Our model shows a qualitative similarity to the recent ALMA observation of HL Tau. In general, this thesis shows that there is a large variety of disk structures and origins. Therefore, tracing from observed disk structures back to their origins is ambiguous

Frankenstein: Advanced Wireless Fuzzing to Exploit New Bluetooth Escalation Targets

Wireless communication standards and implementations have a troubled history regarding security. Since most implementations and firmwares are closed-source, fuzzing remains one of the main methods to uncover Remote Code Execution (RCE) vulnerabilities in deployed systems. Generic over-the-air fuzzing suffers from several shortcomings, such as constrained speed, limited repeatability, and restricted ability to debug. In this paper, we present Frankenstein, a fuzzing framework based on advanced firmware emulation, which addresses these shortcomings. Frankenstein brings firmware dumps "back to life", and provides fuzzed input to the chip's virtual modem. The speed-up of our new fuzzing method is sufficient to maintain interoperability with the attached operating system, hence triggering realistic full-stack behavior. We demonstrate the potential of Frankenstein by finding three zero-click vulnerabilities in the Broadcom and Cypress Bluetooth stack, which is used in most Apple devices, many Samsung smartphones, the Raspberry Pis, and many others. Given RCE on a Bluetooth chip, attackers may escalate their privileges beyond the chip's boundary. We uncover a Wi-Fi/Bluetooth coexistence issue that crashes multiple operating system kernels and a design flaw in the Bluetooth 5.2 specification that allows link key extraction from the host. Turning off Bluetooth will not fully disable the chip, making it hard to defend against RCE attacks. Moreover, when testing our chip-based vulnerabilities on those devices, we find BlueFrag, a chip-independent Android RCE.Comment: To be published at USENIX Securit

Planet-induced disk structures: A comparison between (sub)mm and infrared radiation

Young giant planets, which are embedded in a circumstellar disk, will significantly perturb the disk density distribution. This effect can potentially be used as an indirect tracer for planets. We investigate the feasibility of observing planet-induced gaps in circumstellar disks in scattered light. We perform 3D hydrodynamical disk simulations combined with subsequent radiative transfer calculations in scattered light for different star, disk, and planet configurations. The results are compared to those of a corresponding study for the (sub)mm thermal re-emission. The feasibility of detecting planet-induced gaps in scattered light is mainly influenced by the optical depth of the disk and therefore by the disk size and mass. Planet-induced gaps are in general only detectable if the photosphere of the disks is sufficiently disturbed. Within the limitations given by the parameter space here considered, we find that gap detection is possible in the case of disks with masses below $\sim 10^{-4\dots-3} \, \rm M_\odot$. Compared to the disk mass that marks the lower Atacama Large (Sub)Millimeter Array (ALMA) detection limit for the thermal radiation re-emitted by the disk, it is possible to detect the same gap both in re-emission and scattered light only in a narrow range of disk masses around $\sim 10^{-4} \, \rm M_\odot$, corresponding to $16\%$ of cases considered in our study.Comment: 4 pages, 6 figure

Correlated percolation and the correlated resistor network

We present some exact results on percolation properties of the Ising model, when the range of the percolating bonds is larger than nearest-neighbors. We show that for a percolation range to next-nearest neighbors the percolation threshold Tp is still equal to the Ising critical temperature Tc, and present the phase diagram for this type of percolation. In addition, we present Monte Carlo calculations of the finite size behavior of the correlated resistor network defined on the Ising model. The thermal exponent t of the conductivity that follows from it is found to be t = 0.2000 +- 0.0007. We observe no corrections to scaling in its finite size behavior.Comment: 16 pages, REVTeX, 6 figures include

Interobserver reliability and diagnostic performance of Chiari II malformation measures in MR imaging—part 2

PURPOSE: Brain MR imaging is essential in the assessment of Chiari II malformation in clinical and research settings concerning spina bifida. However, the interpretation of MR images of the malformation is not always straightforward. Morphometric analyses of the extent of Chiari II malformation may improve the assessment. In an attempt to select appropriate morphometric measures for this purpose, we investigated the interobserver reliability and diagnostic performance of several morphometric measures of Chiari II malformation on MR images. METHODS: Brain MR images of 79 children [26 with open spinal dysraphism, 17 with closed spinal dysraphism, and 36 without spinal dysraphism; mean age 10.6 (SD 3.2; range, 6-16) years] were evaluated. All children had been assessed for Chiari II malformation (defined as cerebellar herniation in combination with open spinal dysraphism; n = 23). Three observers blindly and independently reviewed the MR images for 21 measures of the cerebellum, brainstem, and posterior fossa in three planes. The interobserver reliability was assessed by an agreement index (AI = 1 - RRE) and the diagnostic performance by receiver operating characteristic analyses. RESULTS: Reliability was good for most measures, except for the degree of herniation of the vermis and tonsil. Most values differed statistically significantly between children with and without Chiari II malformation. The measures mamillopontine distance and cerebellar width showed excellent diagnostic performance. CONCLUSIONS: Morphometric measures may reliably quantify the morphological distortions of Chiari II malformation on MR images and provide additional tools to assess the severity of Chiari II malformation in clinical and research settings

Psychological intervention with working memory training increases basal ganglia volume: A VBM study of inpatient treatment for methamphetamine use

Background: Protracted methamphetamine (MA) use is associated with decreased control over drug craving and altered brain volume in the frontostriatal network. However, the nature of volumetric changes following a course of psychological intervention for MA use is not yet known. Methods: 66 males (41 MA patients, 25 healthy controls, HC) between the ages of 18–50 were recruited, the MA patients from new admissions to an in-patient drug rehabilitation centre and the HC via public advertisement, both in Cape Town, South Africa. 17 MA patients received 4 weeks of treatment as usual (TAU), and 24 MA patients completed TAU plus daily 30-minute cognitive training (CT) using an N-back working memory task. Magnetic resonance imaging (MRI) at baseline and 4-week follow-up was acquired and voxel-based morphometry (VBM) was used for analysis. Results: TAU was associated with larger bilateral striatum (caudate/putamen) volume, whereas CT was associated with more widespread increases of the bilateral basal ganglia (incorporating the amygdala and hippocampus) and reduced bilateral cerebellum volume coinciding with improvements in impulsivity scores. Conclusions: While psychological intervention is associated with larger volume in mesolimbic reward regions, the utilisation of additional working memory training as an adjunct to treatment may further normalize frontostriatal structure and function