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Detailed analysis on the reflection component for the black hole candidate MAXI J1348-630
No full textThe black hole candidate MAXI J1348-630 was discovered in 2019 January 26, with the Gas Slit Camera (GSC) on-board MAXI. We report a detailed spectral analysis of this source by using the archived data of NuSTAR. A total of nine observations covered the complete outburst evolution of MAXI J1348-630 from the hard state to the soft state and finally back to the hard state. Additionally, the intermediate state is found in the transition from the hard state to the soft state. We use the state-of-the-art reflection model relxill family to fit all the nine spectra, and the spectra from two focal plane module detectors of NuSTAR are jointly fitted for each observation. In particular, we concentrate on the results of the black hole spin parameter and the inclination of the accretion disc. Based on the analysis of the inner radius of the accretion disc, we obtain the spin parameter a∗ = 0.78^(+0.04)_(−0.04), and the inclination angle of the inner disc i = 29.2^(+0.3)_(−0.5)°. Furthermore, we also find that when the black hole is in the hard state, the accretion disc would show a significant truncation. The high iron abundance and ionization of the accretion disc obtained in the fitting results can be possibly explained by the high density of the accretion disc
Mechanism of the alteration in domain-domain communications in human p97/VCP atpase
No full textHuman p97/VCP, an AAA+ ATPase, regulates various cellular activities by interacting with cofactor proteins, including ubiquitin-dependent protein quality control, Golgi-biogenesis, and endoplasmic reticulum-associated degradation (ERAD). Single amino-acid mutation of R155H on the N-domain is the most prevalent, leading to a rare degenerative disease MSP1. The p97 R155H mutant exhibits abnormal ATPase activity and cofactor dysregulation. We pursued biochemical characterization in combination with single-particle cryo-electron microscopy (cryo-EM) to study the interaction of p97^(R155H) mutant with its cofactor p47 and determined the structures of the p97^(R155H)-p47 complex in full length for the first time. In contrast to the wild type, p97^(R155H) occupies approximately 40% in the dodecameric form without nucleotide binding. The p97^(R155H) dodecamer does not bind to p47 or nucleotides and bears close resemblance to the inhibitor bound CB-5083:p97 structure, implying that this may be an inactive form. In the full-length p97^(R155H)-p47 complex structure, the p47 interacts through its UBX domain in an asymmetric manner to bind the p97^(R155H) N-domain with a preference for the N-up at the highest position. The structures also established that the arginine fingers might contribute to the elevated p97^(R155H) ATPase activity. Because the N-terminal domain is spatially far away from the nucleotide-binding site, the intermediate linkers may play a key role in these functional modulations. We went further to study functions of the conserved L464 residue on the D1-D2 linker using mutagenesis and single-particle cryo-EM. The results showed the torsional constraint of the D1-D2 linker likely modulates the D2 ATPase activity, regulating the domain-domain communication in p97 ATPase
Using channel theory to model biochemical networks with feedback
No full textBiochemical signaling networks constantly detect and transmit cell signals to adapt to environmental stimuli. In certain contexts, these responses depend not only on instantaneous signal values but also on their histories. The reliability of information transmission down such noisy network “channels” depends crucially on how well the detection process maps input to output trajectories. Typical analysis describes this mapping using a multivariate Gaussian channel that treats detection of each signal in parallel and with inherent channel noise correlated from one time instant to the next. In relying on “memory” of previously detected signals, however, these now-standard models do not explicitly incorporate feedback from output at previous and more distant timepoints into the assessment of subsequent input processing. I address this feature by proposing a parallel Gaussian channel model with cross-channel feedback where a given parallel channel input may be altered by feedback regulation from outputs at multiple previous timepoints and with variable strengths of correlation. This alternative model is physically distinct from others in that its interpretation of memory implies that a system remembers not only signal detection at previous timepoints, but also specific information about that signal, which has consequences for the subsequent reliability of signal transmission. I present this interpretation using various detection motifs to highlight the effect of feedback on key network reaction properties such as the rate of information transmission
QUBIC VI: Cryogenic half wave plate rotator, design and performance
No full textSetting an upper limit or detection of B-mode polarization imprinted by gravitational waves from Inflation is one goal of modern large angular scale cosmic microwave background (CMB) experiments around the world. A great effort is being made in the deployment of many ground-based, balloon-borne and satellite experiments, using different methods to separate this faint polarized component from the incoming radiation. QUBIC exploits one of the most widely-used techniques to extract the input Stokes parameters, consisting in a rotating half-wave plate (HWP) and a linear polarizer to separate and modulate polarization components. QUBIC uses a step-by-step rotating HWP, with 15° steps, combined with a 0.4°s⁻¹ azimuth sky scan speed. The rotation is driven by a stepper motor mounted on the cryostat outer shell to avoid heat load at internal cryogenic stages. The design of this optical element is an engineering challenge due to its large 370 mm diameter and the 8 K operation temperature that are unique features of the QUBIC experiment. We present the design for a modulator mechanism for up to 370 mm, and the first optical tests by using the prototype of QUBIC HWP (180 mm diameter). The tests and results presented in this work show that the QUBIC HWP rotator can achieve a precision of 0.15° in position by using the stepper motor and custom-made optical encoder. The rotation induces 99% (68% C.L.) and a median cross-polarization χ_(Pol) of 0.12%, with 71% of detectors showing a χ_(Pol)+ 2σ upper limit <1%, measured using selected detectors that had the best signal-to-noise ratio
Spitzer Publication Statistics
No full textWe present statistics on the number of refereed astronomy journal articles that used data from NASA's Spitzer Space Telescope through the end of the calendar year 2020. We discuss the various types of science programs and science categories that were used to collect data during the mission and discuss how operational changes brought on by the depletion of cryogen in 2009 May, including the resulting budget cuts, impacted the publication rate. The post-cryogenic (warm) mission produced fewer papers than the cryogenic mission, but the percentage of the exposure time published did not appreciably change between the warm and cryogenic missions. This was mostly because in the warm mission the length of observations increased, so that each warm paper on average uses more data than the cryogenic papers. We also discuss the speed of publication, archival usage, and the tremendous efficacy of the Legacy and Exploration Science programs (large, coherent investigations), including the value of having well-advertised enhanced data products hosted in centralized archives. We also identify the observations that have been published the largest number of times, and sort them by a variety of metrics (including program type, instrument used, and observation length). Data that have the highest reuse rates in publications were taken early in the Spitzer mission, or belong to one of the large surveys (large either in number of objects, in number of hours observed, or in area covered on the sky). We also assess how often authors have cited the Spitzer fundamental papers or have correctly referenced the Spitzer data they used, finding that as many as 40% of papers have failed to cite the papers, and 15% have made it impossible to identify the data they used
Compact-to-Dendritic Transition in the Reactive Deposition of Brownian Particles
No full textWhen Brownian particles (such as ions, colloids, or misfolded proteins) deposit onto a reactive cluster, the cluster undergoes a transition from a compact to a dendritic morphology. Continuum modeling reveals that the critical radius for this compact-to-dendritic (CTD) transition should be proportional to the particle diffusivity divided by the surface reaction rate. However, previous studies have had limited success verifying that the same scaling arises in the continuum limit of a particle-based deposition model. This discrepancy suggests that the continuum model may be missing part of the microscopic dendrite formation mechanism, a concerning hypothesis given that similar models are commonly used to study dendritic growth in electrodeposition and lithium metal batteries. To clarify the accuracy of such models, we reexamine the particle-based CTD transition using larger system sizes, up to hundreds of millions of particles in some cases, and an improved paradigm for the surface reaction. Specifically, this paradigm allows us to converge our simulations and to work in terms of experimentally accessible parameters. With these methods, we show that in both two and three dimensions, the behavior of the critical radius is consistent with the scaling of the continuum model. Our results help unify the particle-based and continuum views of the CTD transition. In each of these cases, dendrites emerge when particles can no longer diffuse around the cluster within the characteristic reaction timescale. Consequently, this work implies that continuum methods can effectively capture the microscopic physics of dendritic deposition
Non-Nuclear Exploration of the Solar System Study
No full textAdvances in solar array, electric propulsion (EP), and power beaming technologies will very likely enable future missions to the ice giants (Uranus and Neptune) by spacecraft that are completely solar powered. Between 1959 and 2001 the power from solar arrays on missions in Earth orbit have increased by five orders of magnitude (from 1 W to >100,000 W). Simultaneously, the use of solar power has been extended to ever larger distances from the Sun. Three solar powered missions out to solar ranges of just beyond 5 au have now been developed and flown (Rosetta, Juno, and Lucy). At these distances, the solar insolation is roughly 25 times lower than that at 1 au. Solar-powered spacecraft to Saturn, where the solar insolation is 100 times lower than that at 1 au have recently been proposed to NASA. A solar-powered mission to Uranus would have to function where solar insolation is only 4 times lower than it is at Saturn. For Neptune, it would be 9 times lower than at Saturn.
Three improvements in solar array technology are required to make this feasible. First, solar cells have to be able to function in the low-intensity, low-temperature (LILT) environment at Uranus and Neptune. Specially designed triple-junction solar cells have been tested at JPL under LILT conditions equivalent to the environment at 30 au have shown excellent performance (high efficiency and high fill factor). Second, the size of deployable solar arrays has to increase by one to two orders of magnitude relative to the current state of the art. Third, the areal density of solar arrays has to be reduced by an order of magnitude. This will most likely be accomplished through a combination of new thin-film solar cell technology like the Perovskite cells under development worldwide and the development of new deployable solar array structures such as those under investigation for solar-powered satellites.
The solar insolation at Uranus and Neptune is 400 to 900 times lower, respectively, than it is at 1 au. To provide sufficient power for a spacecraft at these destinations requires very large solar arrays. To be practical, such arrays will necessarily need to be very lightweight with a minimum structure mass. The gentle, low-thrust nature of electric propulsion is a good match for such solar arrays since the continuous acceleration of order 10⁻⁵ g will not drive increases in structure mass. In addition, the availability of large amounts of power provided by these arrays between 1 au and 5 to 10 au enables the design of low-thrust trajectories to the ice giants with attractive flight times. Existing ion propulsion technologies, such as NASA’s NEXT ion propulsion system enable flight times of conventionally sized spacecraft (≥1000 kg, not including the solar array) to Uranus of less than 10 years with reasonable propellant masses. For example, a conventionally sized spacecraft with a 150-kg complement of instruments could be delivered to Uranus orbit with a vehicle that has two 60-m x 60-m solar array wings and an areal density of 100 g/m² in a flight time of less than 10 years. The same-sized vehicle could be delivered to orbit around Neptune in a flight time of less than 18 years if the solar array areal density is reduced to 50 g/m². In both cases, larger payload masses can be delivered in similar flight times by increasing the size of the solar array wings. A 440-kg payload mass could be delivered to Neptune orbit in less than 17 years by increasing the solar array size to 70 m x 70 m.
Smaller spacecraft may offer nearer-term opportunities. For example, coupling large, lightweight solar arrays with low-power ion propulsion systems (maximum input power of ~3 kW) can deliver net spacecraft masses to Uranus orbit of several hundred kilograms in flight times of less than 10 years. The only new development for such missions would be solar array wings with dimensions of 30 m x 30 m to 60 m x 60 m with an areal density of 100 g/m². The same EP system could deliver net spacecraft masses of 300 to 500 kg (inclusive of the
payload, but not including the solar array, xenon tank, and xenon mass margin, which are tracked separately) to Neptune orbit with flight times of around 15 years with a 60-m x 60-m solar array that has an areal density of 50 g/m2. Such an array would provide roughly 2.4 kW at Neptune.
The development of directed energy (DE) systems could potentially provide hundreds of watts of power continuously to landed assets from solar-powered orbiting spacecraft. Using a DE system to convert electrical power to light on the orbiting spacecraft and a photo-converter system on the landed asset to convert the DE light back to electricity is effectively a "photonic extension cord." For the DE side, a series of lasers in an array is used to beam power to distant landed assets over distances of hundreds to thousands of kilometers. The landed assets use high efficiency photovoltaics tuned to the laser frequency to convert the laser power back to electrical power. Thermal power from the photon power not converted to electricity may, in some applications, also be useful to the landed asset. State-of-the-art directed-energy systems are solid state, efficient (~50%), low mass (~1 kg/kW_(optical)), and long lifetime (~10⁵ hrs). This technology is improving rapidly, driven by the photonic revolution along with consumer and industrial demand. It is likely even possible to beam power to multiple stationary and even moving targets using unique optical beacons from each target.
The technologies required for non-nuclear exploration of the solar system would also enable or enhance a wide variety of other missions of national interest. The large, ultra-light solar arrays combined with a state-of-the-art electric propulsion system would make possible the orbital exploration of Pluto, as well as a tour of its large moon Charon and smaller moons, with a reasonable mass margin and could potentially eliminate the need for RTGs for this mission. Large, ultra-light solar arrays and state-of-the-art electric propulsion systems could enable missions to chase down and encounter long-period comets and potentially even interstellar objects. This combination of technologies could enable solar electric propulsion (SEP) mission architectures farther out in the solar system, including: a Kuiper belt tour, centaur tour, or maybe even a ‘Grand Tour’ of the gas and ice giants without need for the most optimal planetary alignment, as with the Voyager missions. Sample returns are the next frontier in planetary exploration. The SEP and solar array technologies discussed here would facilitate sample return from a wide range of bodies, including possibly Ceres, Mars, Enceladus, Titan, Triton, and maybe even Mercury. Beaming power from a large, ultra-light solar array in orbit to a landed asset could enable non-nuclear surface exploration of the ice giant’s moons. In the nearer term, directed energy systems could deliver power to the surface of the Moon or Mars. Large, lighter solar arrays could facilitate lower-risk human missions to Mars using very high-power solar electric propulsion systems in mission architectures that don’t require rendezvousing with pre-deployed assets for the return trip. Finally, large, ultra-light solar arrays could power an Arecibo-like radar in space, to enhance characterization of potentially hazardous objects. Such high-power solar arrays combined with ion-beam deflection would be greatly enhance the nations’s planetary defense capabilities
Measurement of W±γ differential cross sections in proton-proton collisions at √s = 13 TeV and effective field theory constraints
No full textDifferential cross section measurements of W±γ production in proton-proton collisions at √s = 13 TeV are presented. The data set used in this study was collected with the CMS detector at the CERN LHC in 2016–2018 with an integrated luminosity of 138 fb⁻¹. Candidate events containing an electron or muon, a photon, and missing transverse momentum are selected. The measurements are compared with standard model predictions computed at next-to-leading and next-to-next-to-leading orders in perturbative quantum chromodynamics. Constraints on the presence of TeV-scale new physics affecting the WWγ vertex are determined within an effective field theory framework, focusing on the O_(3W) operator. A simultaneous measurement of the photon transverse momentum and the azimuthal angle of the charged lepton in a special reference frame is performed. This two-dimensional approach provides up to a factor of ten more sensitivity to the interference between the standard model and the O_(3W) contribution than using the transverse momentum alone
Using Z Boson Events to Study Parton-Medium Interactions in Pb-Pb Collisions
No full textThe spectra measurements of charged hadrons produced in the shower of a parton originating in the same hard scattering with a leptonically decaying Z boson are reported in lead-lead nuclei (Pb-Pb) and proton-proton (pp) collisions at a nucleon-nucleon center-of-mass energy of 5.02 TeV. Both Pb-Pb and pp data sets are recorded by the CMS experiment at the LHC and correspond to an integrated luminosity of 1.7 nb⁻¹ and 320 pb⁻¹, respectively. Hadronic collision data with one reconstructed Z boson candidate with the transverse momentum p_T > 30 GeV/c are analyzed. The Z boson constrains the initial energy and direction of the associated parton. In heavy ion events, azimuthal angular distributions of charged hadrons with respect to the direction of a Z boson are sensitive to modifications of the in-medium parton shower and medium response. compared to reference data from pp interactions, the results for central Pb-Pb collisions indicate a modification of the angular correlations. The measurements of the fragmentation functions and p_T spectra of charged particles in Z boson events, which are sensitive to medium modifications of the parton shower longitudinal structure, are also reported. Significant modifications in central Pb-Pb events compared to the pp reference data are also found for these observables
Five thousand exoplanets at the NASA Exoplanet Archive
No full textThe past three decades have seen the number of known exoplanets grow by over three orders of magnitude. To mark the milestone, the Lead Scientist of the NASA Exoplanet Archive, Jessie Christiansen, looks at the history, the contents and the future of this community resource