Group velocity and causality in standard relativistic resistive magnetohydrodynamics

Group velocity of electromagnetic waves in plasmas derived by standard relativistic resistive MHD (resistive RMHD) equations is superluminal. If we assume that the group velocity represents the propagation velocity of a signal, we have to worry about the causality problem. That is, some acausal phenomena may be induced, such that information transportation to the absolute past and spontaneous decrease in the entropy. Here, we tried to find the acausal phenomena using standard resistive RMHD numerical simulations in the suggested situation of the acausal phenomena. The calculation results showed that even in such situations no acausal effect happens. The numerical result with respect to the velocity limit of the information transportation is consistent with a linear theory of wave train propagation. Our results assure that we can use these equations without problems of acausal phenomena.Comment: 28 pages, 10 figure

J/psi production at RHIC-PHENIX

The J/psi is considered to be among the most important probes for the deconfined quark gluon plasma (QGP) created by relativistic heavy ion collisions. While the J/psi is thought to dissociate in the QGP by Debye color screening, there are competing effects from cold nuclear matter (CNM), feed-downs from excited charmonia (chi_c and psi') and bottom quarks, and regeneration from uncorrelated charm quarks. Measurements that can provide information to disentangle these effects are presented in this paper.Comment: 4 pages, 3 figures, conference proceedings: the 20th International Conference on Ultra-Relativistic Nucleus-Nucleus Collisions, Quark Matter 2008, Jaipur (India), 4-10 February 2008, submitted to J. Phys. G: Nuclear and Particle Physic

Low density molecular gas in the galaxy

The distributions and physical conditions in molecular gas in the interstellar medium have been investigated in both the Galaxy and towards external galaxies. For example, Galactic plane surveys in the CO J =1-0 line with the Columbia 1.2-m telescope and with the Five College Radio Astronomy Observatory (FCRAO) 14-m telescopes have been able to trace spiral arms more clearly than HI surveys have been able to reveal, and indicate that most of molecular mass is contained in Giant Molecular Clouds (GMCs). Extensive maps of the whole Milky Way showed two prominent features, the 4-kpc molecular ring and the Galactic center. The physical conditions in the Galaxy have been studied by comparing the intensity of CO J =1-0 line with those of other lines, e.g., 13CO J =1-0, higher J transitions of CO, and dense gas tracers such as HCO+, CS, and HCN. Previous studies were however strongly biased towards regions where CO emission was known to be intense. The radial distribution of molecular hydrogen shows that most of the H2 gas which is indirectly traced by observations of its associated CO emission, originates from the inner Galaxy (Dame 1993). Extending outwards from a galacto-centric distance of ~7 kpc, the H2 mass surface density decreases dramatically, and HI dominates over H2 in the outer Galaxy. What are physical conditions of molecular gas where the CO emission is relatively weak, and can we really trace all of the molecular gas through obervations of CO? These kinds of problems have not been solved yet, but are addressed in our study

Conversion of laparoscopic colorectal resection for cancer: What is the impact on short-term outcomes and survival?

Laparoscopic resection for colon and rectal cancer is associated with quicker return of bowel function, reduced postoperative morbidity rates and shorter length of hospital stay compared to open surgery, with no differences in long-term survival. Conversion to open surgery is reported in up to 30% of patients enrolled in randomized control trials comparing open and laparoscopic colorectal resection for cancer. In this review, reasons for conversion are anatomical-related factors, disease-related-factors and surgeon-related factors. Body mass index, local tumour extension and co-morbidities are independent predictors of conversion. The current evidence has shown that patients with converted resection for colon cancer have similar outcomes compared to patients undergoing a laparoscopic completed or open resection. The few studies that have assessed the outcomes after conversion of laparoscopic rectal resection reported significantly higher rates of complications and longer length of hospital stay in converted patients compared to laparoscopically treated patients. No definitive conclusions can be drawn when converted and open rectal resections are compared. Early and pre-emptive conversion appears to have more favourable outcomes than reactive conversion; however, further large studies are needed to better define the optimal timing of conversion. With regard to long-term oncologic outcome, overall and disease-free survival in the case of conversion in laparoscopic colorectal cancer surgery seems to be worse than those achieved in patients in whom resection was successfully completed by laparoscopy. Although a worse long-term oncologic outcome has been suggested, it remains difficult to draw a proper conclusion due to the heterogeneity of the long-term outcomes as well as the inclusion of both colon and rectal cancer patients in most of the studies. Therefore, we discuss the currently available evidence of the impact of conversion in laparoscopic resection for colon and rectal cancer on both short-term outcomes and long-term survival

Crystallographic disorder and electron scattering on structural two-level systems in ZrAs1.4Se0.5

Single crystals of ZrAs1.4Se0.5 (PbFCl type structure) were grown by chemical vapour transport. While their thermodynamic and transport properties are typical for ordinary metals, the electrical resistivity exhibits a shallow minimum at low temperatures. Application of strong magnetic fields does not influence this anomaly. The minimum of the resistivity in ZrAs1.4Se0.5 apparently originates from interaction between the conduction electrons and structural two-level systems. Significant disorder in the As-Se substructure is inferred from X-ray diffraction and electron microprobe studies

Modification of Caloris ejecta blocks by long-lived mass-wasting: A volatile-driven process?

The Caloris basin is the largest well-preserved impact basin on Mercury. As such, Caloris ejecta afford us an opportunity to study material from Mercury’s deep interior with remote sensing. We have made observations of the geomorphology, colour, distribution, and flank slopes of the circum-Caloris knobs. Our observations suggest that these circum-Caloris knobs are modified ejecta blocks from the Caloris impact. High-resolution MESSENGER images show that knobs are conical and relatively uncratered compared with the surrounding plains, which implies the knobs have undergone resurfacing. We have observed material that has sloughed off knobs superposing impact craters that demonstrably postdate the Caloris impact, which requires some knob modification to have been more recent. We have observed hollows, depressions in Mercury’s surface generally believed to have been caused by volatile-loss, on and closely associated with several knobs, which indicates that many knobs contain volatile material and that knob modification could extend into Mercury’s recent past. Our measurements show that knob flanks typically have slopes of ∼21°, which is steep for a mound of unconsolidated material that was originally emplaced ∼3.8 Ga. The conical shape of knobs, their steep slopes, the dearth of superposed craters on knobs, and knob superposition relationships with other landforms suggest that Caloris ejecta blocks of arbitrary original shape were modified into their present shapes by long-lived mass-wasting. Mass-wasting must have dominated over impact gardening, which would have produced domal morphologies only. We suggest that mass-wasting was probably driven by volatile-loss, in a manner analogous to terrestrial landforms called ‘molards’. If the circum-Caloris knobs are analogous to molards, then they represent a landform and a process hitherto undocumented on Mercury, with implications for the volatile content of the planet’s interior. These knobs therefore are prime targets for BepiColombo, which could search for fresh failures and volatile exposures in the knobs

Debris-flow release processes investigated through the analysis of multi-temporal LiDAR datasets in north-western Iceland

Debris flows are fast‐moving gravity flows of poorly sorted rock and soil, mixed and saturated with water. Debris‐flow initiation has been studied using empirical and experimental modelling, but the geomorphic changes, indicative of different triggering processes, are difficult to constrain with field observations only. We identify signatures to distinguish two different debris‐flow release styles by integrating high‐resolution multi‐temporal remote sensing datasets and morphometric analysis. We analyse debris flows sourced above the town of Ísafjörður (Iceland). Two debris‐flow triggering processes were previously hypothesized for this site: (i) slope failure, characterised by landslides evolving into debris flows, and (ii) the fire‐hose effect, in which debris accumulated in pre‐existing, steep‐sided bedrock passages is transported by a surge of water. It is unknown which process dominates and determines the local risk. To investigate this question, we compare airborne LiDAR elevation models and aerial photographs collected in 2007 with similar data from 2013. We find that two new debris‐flow tracks were created by slope failures. These are characterised by steep sliding surfaces and lateral leveed channels. Slope failure also occurred in two large, recently active tracks, creating the preparatory conditions for the fire‐hose effect to mobilise existing debris. These tracks show alternating zones of fill and scour along their length, and debris stored below the source‐area at rest angles >35°. Our approach allows us to identify and quantify the morphological changes produced by slope failure release process, which generated the preparatory conditions for the fire‐hose effect. As debris flows are rarely observed in action and morphological changes induced by them are difficult to detect and monitor, the same approach could be applied to other landscapes to understand debris‐flow initiation in absence of other monitoring information, and can improve the identification of zones at risk in inhabited areas near hillslopes with potential for debris flows

The Subaru Coronagraphic Extreme Adaptive Optics system: enabling high-contrast imaging on solar-system scales

The Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) instrument is a multipurpose high-contrast imaging platform designed for the discovery and detailed characterization of exoplanetary systems and serves as a testbed for high-contrast imaging technologies for ELTs. It is a multi-band instrument which makes use of light from 600 to 2500nm allowing for coronagraphic direct exoplanet imaging of the inner 3 lambda/D from the stellar host. Wavefront sensing and control are key to the operation of SCExAO. A partial correction of low-order modes is provided by Subaru's facility adaptive optics system with the final correction, including high-order modes, implemented downstream by a combination of a visible pyramid wavefront sensor and a 2000-element deformable mirror. The well corrected NIR (y-K bands) wavefronts can then be injected into any of the available coronagraphs, including but not limited to the phase induced amplitude apodization and the vector vortex coronagraphs, both of which offer an inner working angle as low as 1 lambda/D. Non-common path, low-order aberrations are sensed with a coronagraphic low-order wavefront sensor in the infrared (IR). Low noise, high frame rate, NIR detectors allow for active speckle nulling and coherent differential imaging, while the HAWAII 2RG detector in the HiCIAO imager and/or the CHARIS integral field spectrograph (from mid 2016) can take deeper exposures and/or perform angular, spectral and polarimetric differential imaging. Science in the visible is provided by two interferometric modules: VAMPIRES and FIRST, which enable sub-diffraction limited imaging in the visible region with polarimetric and spectroscopic capabilities respectively. We describe the instrument in detail and present preliminary results both on-sky and in the laboratory.Comment: Accepted for publication, 20 pages, 10 figure

The near-infrared reflected spectrum of source I in Orion-KL

Source I in the Orion-KL nebula is believed to be the nearest example of a massive star still in the main accretion phase. It is thus one of the best cases for studying the properties of massive protostars to constrain high-mass star formation theories. Near-infrared radiation from source I escapes through the cavity opened by the OMC1 outflow and is scattered by dust towards our line of sight. The reflected spectrum offers a unique possibility of observing the emission from the innermost regions of the system and probing the nature of source I and its immediate surroundings. We obtained moderately high spectral-resolution (R~9000) observations of the near-infrared diffuse emission in several locations around source I/Orion-KL. We observed a widespread rich absorption line spectrum that we compare with cool stellar photospheres and protostellar accretion disk models. The spectrum is broadly similar to strongly veiled, cool, low-gravity stellar photospheres in the range Teff~3500-4500 K, luminosity class I-III. An exact match explaining all features has not been found, and a plausible explanation is that a range of different temperatures contribute to the observed absorption spectrum. The 1D velocity dispersions implied by the absorption spectra, sigma~30 km/s, can be explained by the emission from a disk around a massive, mstar~10 Msun, protostar that is accreting at a high rate, mdot~3x10^{-3} Msun/yr. Our observations suggest that the near-infrared reflection spectrum observed in the Orion-KL region is produced close to source I and scattered to our line of sight in the OMC1 outflow cavity. The spectrum allows us to exclude source I being a very large, massive protostar rotating at breakup speed. We suggest that the absorption spectrum is produced in a disk surrounding a ~10 Msun protostar, accreting from its disk at a high rate of a few 10^{-3} Msun/yr.Comment: Accepted for publication on A&

Discovery of the Coldest Imaged Companion of a Sun-Like Star

We present the discovery of a brown dwarf or possible planet at a projected separation of 1.9" = 29 AU around the star GJ 758, placing it between the separations at which substellar companions are expected to form by core accretion (~5 AU) or direct gravitational collapse (typically >100 AU). The object was detected by direct imaging of its thermal glow with Subaru/HiCIAO. At 10-40 times the mass of Jupiter and a temperature of 550-640 K, GJ 758 B constitutes one of the few known T-type companions, and the coldest ever to be imaged in thermal light around a Sun-like star. Its orbit is likely eccentric and of a size comparable to Pluto's orbit, possibly as a result of gravitational scattering or outward migration. A candidate second companion is detected at 1.2" at one epoch.Comment: 5 pages, 3 figures, 2 tables. Accepted for publication in ApJ Letter