Insonation of cyclohexanoate electrooxidation at platinum in methanol produces a similar switch in product distribution from one-electron per-molecule dimers towards products from the two-electron ...route via the carbocation, irrespective of whether the ultrasonic bath employs 38 or 850 kHz frequencies. However, 850 kHz produces a cleaner reaction and higher yields, with more than two-fold greater yield of total extracted products over the silent system, and one-and-a-half times yield enhancement over insonation at 38 kHz.
Log-aesthetic spirals are currently being studied as fair curves that can be used in computer aided design. A family of planar log-aesthetic spirals that include a point of zero curvature is used in ...this paper. The two-point G 1 Hermite data that is considered has some restrictions on the angles. This paper proves that for any member of the family, a unique segment of that spiral can be found that matches given two-point G 1 Hermite data.
We present the discovery of eclipses in the X-ray light curves of the X-ray binary Swift J1858.6-0814. From these, we find an orbital period of \(P=76841.3_{-1.4}^{+1.3}\) s (\(\approx21.3\) hours) ...and an eclipse duration of \(t_{\rm ec}=4098_{-18}^{+17}\) s (\(\approx1.14\) hours). We also find several absorption dips during the pre-eclipse phase. From the eclipse duration to orbital period ratio, the inclination of the binary orbit is constrained to \(i>70^\circ\). The most likely range for the companion mass suggests that the inclination is likely to be closer to this value than \(90^\circ\). The eclipses are also consistent with earlier data, in which strong variability ('flares') and the long orbital period prevent clear detection of the period or eclipses. We also find that the bright flares occurred preferentially in the post-eclipse phase of the orbit, likely due to increased thickness at the disc-accretion stream interface preventing flares being visible during the pre-eclipse phase. This supports the notion that variable obscuration is responsible for the unusually strong variability in Swift J1858.6-0814.
NGC 5907 ULX1 is the most luminous ultra-luminous X-ray pulsar (ULXP) known to date, reaching luminosities in excess of 1e41 erg/s. The pulsar is known for its fast spin-up during the on-state. Here, ...we present a long-term monitoring of the X-ray flux and the pulse period between 2003-2022. We find that the source was in an off- or low-state between mid-2017 to mid-2020. During this state, our pulse period monitoring shows that the source had spun down considerably. We interpret this spin-down as likely being due to the propeller effect, whereby accretion onto the neutron star surface is inhibited. Using state-of-the-art accretion and torque models, we use the spin-up and spin-down episodes to constrain the magnetic field. For the spin-up episode, we find solutions for magnetic field strengths of either around 1e12G or 1e13G, however, the strong spin-down during the off-state seems only to be consistent with a very high magnetic field, namely, >1e13G. This is the first time a strong spin-down is seen during a low flux state in a ULXP. Based on the assumption that the source entered the propeller regime, this gives us the best estimate so far for the magnetic field of NGC 5907 ULX1.
We continue the analysis of NuSTAR data from the recent discovery outburst of MAXI J1820+070 (optical counterpart ASASSN-18ey), focussing on an observation including unusual flaring behaviour during ...the hard to soft state transition, which is a short phase of outbursts and so comparatively rarely observed. Two plateaus in flux are separated by a variable interval lasting ~10 ks, which shows dipping then flaring stages. The variability is strongest (with fractional variability up to \(F_{\rm Var}\sim10\%\)) at high energies and reduces as the contribution from disc emission becomes stronger. Flux-resolved spectra show that the variability is primarily due to the power law flux changing. We also find a long soft lag of the thermal behind the power law emission, which is \(20_{-1.2}^{+1.6}\) s during the flaring phase. The lag during the dipping stage has a different lag-energy spectrum, which may be due to a wave passing outwards through the disc. Time resolved spectral fitting suggests that the lag during the flaring stage may be due to the disc re-filling after being disrupted to produce the power law flare, perhaps related to the system settling after the jet ejection which occurred around 1 day before. The timescales of these phenomena imply a low viscosity parameter, \(\alpha\sim10^{-3}\), for the inner region of the disc.
Obscuration events in type I active galactic nuclei (AGN) have been detected more frequently in recent years. The strong flux decrease in the soft X-ray band between observations has been caused by ...clouds with large column densities transiting our line-of-sight (LOS) and covering the central AGN. Another event has been captured in NGC 3227 at the end of 2019. We aim to determine the nature of the observed spectral variability in 2019 obscuration event. We split the two XMM-Newton observations from 2019 into timing bins of length \(\sim\) 10 ks. We used the SPEX code to analyse the 0.35-10 keV EPIC-PN spectra of each timing bin. In the first observation (Obs 1), there is a strong anti-correlation between the column density (\(N_H\)) of the obscurer and the continuum normalisations of the X-ray power-law and soft Comptonisation components (\(N_{pow}\) and \(N_{comt}\), respectively). The powerlaw continuum models the hard X-rays produced by the corona, and the Comptonisation component models the soft X-ray excess and emission from the accretion disk. Through further testing we conclude that the continuum is likely to drive the observed variability, but we cannot rule out a possible contribution from NH of the obscurer if it fully transverses across the ionising source within our LOS during the observation. The ionisation parameter (\(\xi\)) of the obscurer is not easily constrained, and therefore it is not clear whether it varies in response to changes in ionising continuum. The second observation (Obs 2) displays a significantly lower count rate due to the combination of a high NH and covering fraction of the obscurer, and a lower continuum flux. The observed variability seen during the obscuration event of NGC 3227 in 2019 is likely driven by the continuum, but the obscurer varies at the same time, making it difficult to distinguish between the two possibilities with full certainty.
The hard X-ray emission from magnetars and other isolated neutron stars remains under-explored. An instrument with higher sensitivity to hard X-rays is critical to understanding the physics of ...neutron star magnetospheres and also the relationship between magnetars and Fast Radio Bursts (FRBs). High sensitivity to hard X-rays is required to determine the number of magnetars with hard X-ray tails, and to track transient non-thermal emission from these sources for years post-outburst. This sensitivity would also enable previously impossible studies of the faint non-thermal emission from middle-aged rotation-powered pulsars (RPPs), and detailed phase-resolved spectroscopic studies of younger, bright RPPs. The High Energy X-ray Probe (HEX-P) is a probe-class mission concept that will combine high spatial resolution X-ray imaging (\(<5\) arcsec half-power diameter (HPD) at 0.2--25 keV) and broad spectral coverage (0.2--80 keV) with a sensitivity superior to current facilities (including XMM-Newton and NuSTAR). HEX-P has the required timing resolution to perform follow-up observations of sources identified by other facilities and positively identify candidate pulsating neutron stars. Here we discuss how HEX-P is ideally suited to address important questions about the physics of magnetars and other isolated neutron stars.
We treated 19 patients with advanced breast cancer resistant to tamoxifen with a new specific antioestrogen (ICI 182780) which, in animal studies, has no agonist activity. 13 (69%) patients responded ...(7 had partial responses and 6 showed no change) to monthly intramuscular injections of ICI 182780 after progression on tamoxifen, for a median duration of 18 months with minimum side effects. Preliminary evidence suggests that the agent is without effects on the liver or the hypothalamic-pituitary axis. ICI 182780 appears to be a promising new agent for treatment of advanced and early breast cancer.
We report on a NuSTAR and XMM-Newton program that has observed a sample of three extremely luminous, heavily obscured WISE-selected active galactic nuclei (AGNs) at z ~ 2 across a broad X-ray band ...(0.1-79 keV). The parent sample, selected to be faint or undetected in the WISE 3.4 mu m (W1) and 4.6 mu m (W2) bands but bright at 12 mu m (W3) and 22 mu m (W4), are extremely rare, with only ~1000 so-called "W1 W2-dropouts" across the extragalactic sky. These are among the most AGNs known, though the optical spectra rarely show evidence of a broad-line region and the selection criteria imply heavy obscuration even at rest-frame 1.5 mu m. The discovery of a significant population of heavily obscured, extremely luminous AGNs would not conform to the standard paradigm of a receding torus, in which more luminous quasars are less likely to be obscured, and instead suggests that an additional source of obscuration is present in these extreme sources.
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