Comet 133P/Elst–Pizarro is the first known and currently best-characterized member of the main-belt comets, a recently identified class of objects that exhibit cometary activity but which are ...dynamically indistinguishable from main-belt asteroids. We report here on the results of a multiyear monitoring campaign from 2003 to 2008, and present observations of the return of activity in 2007. We find a pattern of activity consistent with seasonal activity modulation. Additionally, recomputation of phase function parameters using data in which 133P was inactive yields new IAU parameters of HR= 15.49 ± 0.05 mag and GR= 0.04 ± 0.05, and linear parameters of mR(1, 1, 0) = 15.80 ± 0.05 mag and β= 0.041 ± 0.005 mag deg−1. The comparison between predicted magnitudes using these new parameters and the comet's actual brightnesses during its 2002 and 2007 active periods reveals the presence of unresolved coma during both episodes, of the order of ∼0.20 of the nucleus cross-section in 2002 and ∼0.25 in 2007. Multifilter observations during 133P's 2007 active outburst yield mean nucleus colours of B−V= 0.65 ± 0.03, V−R= 0.36 ± 0.01 and R−I= 0.32 ± 0.01, with no indication of significant rotational variation, and similar colours for the trail. Finally, while 133P's trail appears shorter and weaker in 2007 than in 2002, other measures of activity strength such as dust velocity and coma contamination of nucleus photometry are found to remain approximately constant. We attribute changes in trail strength to the timing of observations and projection effects, thus finding no evidence of any substantial decrease in the activity strength between 2002 and 2007.
This study evaluated clinical features of individuals with long COVID (5-8 months after diagnosis) who reported sleep and memory problems (62 cases) compared to those without (52 controls). Both ...groups had a similar mean age (41
39 years). Around 86% of the participants were non-hospitalized at the time of infection, and none of them were vaccinated at that point. Subsequently, both cases and controls received the vaccine; however, the vaccination rates differed significantly between the groups (30.7%
51.0%). Cases and controls had similar rates of symptoms at acute COVID phase. However, cases were more likely to experience coryza, dyspnea, headache, and nausea/vomiting during long COVID. Regarding new-onset symptoms in long COVID, 12.9% of cases had dyspnea, and 14.5% experienced nausea/vomiting, whereas in the control group there were only 1.9% and 0.0%, respectively. Cases also had a significantly higher prevalence of persistent headache (22.6%
7.7%), and dyspnea (12.9%
0.0). In addition, cases also showed an increased rate of mental health complaints: disability in daily activities (45.2%
9.6%;
< 0.001); concentration/sustained attention difficulties (74.2%
9.6%;
< 0.001); anxiety-Generalized Anxiety Disorder 2-item scale (GAD-2) ≥ 3 (66.1%
34.6%;
= 0.0013); and "post-COVID sadness" (82.3%
40.4%;
< 0.001). We observed a significant correlation between sadness and anxiety in cases, which was not observed in controls (P=0.0212; Spearman correlation test). Furthermore, the frequency of concomitant sadness and anxiety was markedly higher in cases compared to controls (59.7%
19.2%) (
< 0.0001; Mann-Whitney test). These findings highlight a noteworthy association between sadness and anxiety specifically in cases. In conclusion, our data identified concurrent psychological phenotypes in individuals experiencing sleep and memory disturbances during long COVID. This strengthens the existing evidence that SARS-CoV-2 causes widespread brain pathology with interconnected phenotypic clusters. This finding highlights the need for comprehensive medical attention to address these complex issues, as well as major investments in testing strategies capable of preventing the development of long COVID sequelae, such as vaccination.
This study seeks to investigate the local reinforcement of low carbon cast steel specimens with WC–metal matrix composites (WC–MMCs), to obtain a new material effective in competing with hard alloy ...steels. For this purpose, a powder compact of tungsten carbide (WC) and iron (Fe) was prepared and placed in the mold cavity before casting. The reactions that occurred with the molten steel led to the formation of the WC–MMC and, consequently, to the local reinforcement of the steel. The microstructure of the WC–MMC reinforcement was characterized by scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and electron backscatter diffraction (EBSD). The results showed a microstructural variation throughout the depth of the reinforcement. In the surface region, most of the original WC particles retain their polygonal morphology, but towards the base metal, the dissolution of the WC particles increased with the formation of (Fe,W)6C carbides. Closer to the base metal, dendritic eutectic carbides of (Fe,W)6C and fine (Fe,W)23C6 precipitates in a matrix of martensite were formed. The mechanical properties of the reinforcement were evaluated by hardness and ball-cratering abrasion tests. The results revealed a significant increase in hardness, being three times harder than the base metal, and a decrease of 39% in the wear rate.
In this work, austenitic stainless steel specimens were locally reinforced with WC particles. The reinforcements were fabricated via an ex situ technique based on powder technology. Mixtures of WC, ...Fe, and M0101 binder were cold-pressed to obtain powder compacts. After debinding and sintering, the porous WC-Fe inserts were fixed in a mold cavity, where they reacted with liquid metal. Microstructural analysis was conducted for characterization of the phases constituting the produced reinforcement zone and the bonding interface. The results revealed that the reinforcement is a graded material with compositional and microstructural gradients throughout its thickness. The zone nearest to the surface has a ferrous matrix with homogeneously distributed WC particles and (Fe,W,Cr)
C and (Fe,W,Cr)
C carbides, formed from the liquid metal reaction with the insert. This precipitation leads to austenite destabilization, which transforms into martensite during cooling. A vast dissolution of the WC particles occurred in the inner zones, resulting in more intense carbides formation. Cr-rich carbides ((Fe,Cr,W)
C
, and (Fe,Cr,W)
C
) formed in the interdendritic regions of austenite; this zone is characterized by coarse dendrites of austenite and a multi-phase interdendritic network composed of carbides. An interface free of discontinuities and porosities indicates good bonding of the reinforcement zone to stainless steel.
New observations show that the light curve of Kuiper Belt contact binary (139775) 2001 QG298 has changed substantially since the first observations in 2003. The 2010 light curve has a peak-to-peak ...photometric range of Delta *Dm 2010 = 0.7 ? 0.1 mag, significantly lower than in 2003, Delta *Dm 2003 = 1.14 ? 0.04 mag. This change is most simply interpreted if 2001 QG298 has an obliquity near 90?. The observed decrease in Delta *Dm is caused by a change in viewing geometry, from equator-on in 2003 to nearly 16? (the orbital angular distance covered by the object between the observations) off the equator in 2010. The 2003 and 2010 light curves have the same rotation period and appear in phase when shifted by an integer number of full rotations, also consistent with high obliquity. Based on the new 2010 light curve data, we find that 2001 QG298 has an obliquity of Delta *e = 90? ? 30?. Current estimates of the intrinsic fraction of contact binaries in the Kuiper Belt are debiased assuming that these objects have randomly oriented spins. If, as 2001 QG298, Kuiper Belt Object contact binaries tend to have large obliquities, a larger correction is required. As a result, the abundance of contact binaries may be larger than previously believed.
High-chromium white cast-iron specimens locally reinforced with TiC-metal matrix composites were successfully produced via an in situ technique based on combustion synthesis. Powder mixtures of Ti, ...Al, and graphite were prepared and compressed to fabricate green powder compacts that were inserted into the mold cavity before the casting. The heat of the molten iron causes the ignition of the combustion reaction of the reactant powders, resulting in the formation of the TiC by self-propagating high-temperature synthesis. The microstructure of the resultant composites and the bonding interfaces was characterized by scanning electron microscopy and energy dispersive spectroscopy (SEM/EDS), X-ray diffraction (XRD), and transmission electron microscopy (TEM). The microstructural results showed a good adhesion of the composite, suggesting an effective infiltration of the metal into the inserted compact, yet a non-homogeneous distribution of the TiC in the martensite matrix was observed. Based on the results, the in situ synthesis appears to be a great potential technique for industrial applications.
In this study, the effect of microstructural characteristics on the mechanical properties of high-chromium white cast iron-matrix composites reinforced by in situ TiC and ex situ WC was investigated. ...To this end, two different powder mixtures (Ti + Al + graphite and WC + Fe) were compressed to produce green compacts that were inserted into the mold, before casting. The microstructure of the resulting composites and the base metal was characterized using optical microscopy (OM) and scanning electron microscopy with energy dispersive spectroscopy (SEM/EDS). The microstructural analysis revealed a sound bonding between the composite zone and the base metal. The reinforcement with WC particles showed a homogeneous distribution of the carbide particles, unlike the reinforcement with TiC particles. The mechanical properties of the reinforcements were evaluated using hardness and ball-cratering micro-abrasion tests. The results showed that both reinforcements increase the hardness and wear performance of the base material, which was the best performance achieved by the reinforcement with WC particles.
Discovered in 2010 October by the Lincoln Near-Earth Asteroid Research (LINEAR) survey, P/2010 TO20 LINEAR-Grauer (P/LG) was initially classified as an inert Jupiter Trojan. Subsequent observations ...obtained in 2011 October revealed P/LG to be a Jupiter-family comet (JFC). P/LG has one of the largest perihelia (q = 5.1 au) and lowest eccentricities (e = 0.09) of the known JFCs. We report on observations of P/LG taken on 2011 October 29 and numerical simulations of its orbital evolution. Analysis of our data reveals that P/LG has a small nucleus (<3 km in radius) with broad-band colours (B − R = 0.99 ± 0.06 mag, V − R = 0.47 ± 0.06 mag) typical of JFCs. We find a model-dependent mass-loss rate close to 100 kg s−1, most likely powered by water-ice sublimation. Our numerical simulation indicates that the orbit of P/LG is unstable on very short (10-100 yr) time-scales and suggest that this object has recently evolved into its current location from a more distant, Centaur-type orbit. The orbit, dynamics and activity of P/LG share similarities with the well-known case of comet 29P/Schwassmann-Wachmann 1.
New observations show that the light curve of Kuiper Belt contact binary (139775) 2001 QG{sub 298} has changed substantially since the first observations in 2003. The 2010 light curve has a ...peak-to-peak photometric range of {Delta}m{sub 2010} = 0.7 {+-} 0.1 mag, significantly lower than in 2003, {Delta}m{sub 2003} = 1.14 {+-} 0.04 mag. This change is most simply interpreted if 2001 QG{sub 298} has an obliquity near 90{sup 0}. The observed decrease in {Delta}m is caused by a change in viewing geometry, from equator-on in 2003 to nearly 16{sup 0} (the orbital angular distance covered by the object between the observations) off the equator in 2010. The 2003 and 2010 light curves have the same rotation period and appear in phase when shifted by an integer number of full rotations, also consistent with high obliquity. Based on the new 2010 light curve data, we find that 2001 QG{sub 298} has an obliquity of {epsilon} = 90{sup 0} {+-} 30{sup 0}. Current estimates of the intrinsic fraction of contact binaries in the Kuiper Belt are debiased assuming that these objects have randomly oriented spins. If, as 2001 QG2{sub 98}, Kuiper Belt Object contact binaries tend to have large obliquities, a larger correction is required. As a result, the abundance of contact binaries may be larger than previously believed.
We present the results of an optical light-curve survey of 114 Jovian Trojan asteroids conducted to determine the fraction of contact binaries. Sparse sampling was used to assess the photometric ...range of the asteroids, and those showing the largest ranges were targeted for detailed follow-up observations. This survey led to the discovery of two Trojan asteroids, (17365) and (29314), displaying large light-curve ranges (~1 mag) and long rotation periods (<2 rotations day-1) consistent with a contact binary nature. The optical light curves of both asteroids are well matched by Roche binary equilibrium models. Using these binary models, we find low densities of ~600 and 800 kg m-3, suggestive of porous interiors. The fraction of contact binaries is estimated to be between 6% and 10%, comparable to the fraction in the Kuiper Belt. The total binary fraction in the Trojan clouds (including both wide and close pairs) must be higher.
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