Large‐diameter visible and buried impact basins, seen as “quasi‐circular depressions” (QCDs) in MOLA gridded data, provide a self‐consistent chronology for major events on early Mars in terms of ...N(200) crater retention ages. On the basis of a conversion to model absolute ages, this chronology extends back hundreds of millions of years into a previously unknown “pre‐Noachian” epoch during which a now buried highlands surface was established, in which several very large impact basins formed while the global magnetic field was still present. A cluster of very large “lowland‐making” basins occurred at a model age of about 4.13 GY (or earlier), forming the fundamental topography of the Mars crustal dichotomy at a time prior to the age of the oldest visible highland crust. This early event in Martian history marks the transition from the “pre‐Noachian” to the Early Noachian when the well‐preserved Hellas, Argyre, and Isidis basins formed, all after the global magnetic field died.
Essential to the functionality of qubit-based sensors are control protocols, which shape their response in frequency space. However, in common control routines out-of-band spectral leakage ...complicates interpretation of the sensor's signal. In this work, we leverage discrete prolate spheroidal sequences (a.k.a. Slepian sequences) to synthesize provably optimal narrowband controls ideally suited to spectral estimation of a qubit's noisy environment. Experiments with trapped ions demonstrate how spectral leakage may be reduced by orders of magnitude over conventional controls when a near resonant driving field is modulated by Slepians, and how the desired narrowband sensitivity may be tuned using concepts from RF engineering. We demonstrate that classical multitaper techniques for spectral analysis can be ported to the quantum domain and combined with Bayesian estimation tools to experimentally reconstruct complex noise spectra. We then deploy these techniques to identify previously immeasurable frequency-resolved amplitude noise in our qubit's microwave synthesis chain.
Large impacts simultaneously reset both the surface age and the magnetization of the entire depth of crust over areas comparable to the final size of the resulting craters. These properties make ...large impact craters (>300 km in diameter) ideal “magnetic markers” for constraining the history of the Martian core dynamo. However, the relationship between crustal magnetization and magnetic field measured in orbit is nonunique, making the measured magnetic field signature of an impact crater only a proxy for the magnetization (or lack thereof) below. Using Monte Carlo Fourier domain modeling of subsurface magnetization, we calculate probability distributions of the magnetic field signatures of partially and completely demagnetized craters. We compare these distributions to measured magnetic field signatures of 41 old impact craters on Mars larger than 300 km in diameter and calculate probabilities of their magnetization state. We compare these probabilities to cratering densities and absolute model ages and in this manner arrive at a robust time history of Martian large‐crater magnetization and hence of the Martian dynamo. We conclude that the most likely scenario was a Mars dynamo active when the oldest detectable basins formed, ceasing before the Hellas and Utopia impacts, between 4.0 and 4.1 Ga (in model age) and not thereafter restarting. The Mars atmosphere was thereafter exposed directly to erosion by the solar wind, significantly altering the path of climate evolution. Further improvements to the history of the Martian dynamo will require better crater age estimates and lower altitude magnetic field data.
Key Points
Magnetization probability distributions are calculated with statistical methods.
The Martian dynamo ceased before the Prometheus impact at a model age of ~4 Ga.
The dynamo was still inactive after the Antoniadi impact (model age of 3.8 Ga).
The magnetic signatures and crater retention ages of the 19 largest (>1000 km diameter) impact basins on Mars are examined to constrain the history of the acquisition of crustal magnetization during ...the Noachian era. The 5 most clearly impact‐demagnetized basins are younger than the 14 basins within which lies substantially re‐magnetized crust. Poisson analysis shows that the most likely time of this magnetization cessation was 4.115–4.13 Ga (model age) and that it occurred quickly, taking less than 20 Ma. A global decrease in effective crustal magnetic susceptibility due, e.g., to a decrease in the rate of hydrothermal alteration, is one possible explanation. Alternatively, the cessation of post‐impact magnetization reflects the rapid death of the Martian dynamo.
In October 2021, brexucabtagene autoleucel became the first anti-CD19 chimeric antigen receptor T cell product to receive approval from the US Food and Drug Administration to treat adults with ...relapsed and refractory B cell acute lymphoblastic leukemia (r/r ALL). The approval is based on results from the Zuma-3 trial and significantly widens treatment options for this patient population. In this article we will review outcomes from this study and its implications.
Blocking lymphocyte chemotaxis with an oral inhibitor of the CCR5 receptor was associated with reduced incidence of visceral graft-versus-host disease (GVHD) in patients undergoing reduced-intensity ...conditioned allogeneic hematopoietic stem-cell transplantation.
Acute graft-versus-host disease (GVHD) is a major cause of death and complications after allogeneic hematopoietic stem-cell transplantation (HSCT). The condition occurs in 30 to 50% of patients receiving HLA-matched transplants from a related donor and in 50 to 70% of those receiving transplants from an unrelated donor.
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The pathogenesis of GVHD is multifactorial, but ultimately, donor-derived T cells recognize recipient antigens as foreign, resulting in activation, expansion, and cytokine release and leading to destruction of host tissues.
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Current therapies for GVHD target T cells and cytokines, often antagonize T-cell–mediated graft-versus-tumor responses, and delay immune reconstitution.
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Preventing GVHD without intensive immune . . .
Steroid-refractory (SR) acute gastrointestinal (GI) graft-versus-host disease (GVHD) is associated with significant mortality in allogeneic hematopoietic cell transplantation recipients. We ...retrospectively evaluated the efficacy of tocilizumab for the treatment of SR biopsy-proven acute lower GI GVHD in 16 consecutive adult transplant recipients between October 2015 and July 2016. Tocilizumab 8 mg/kg was administered every 2 weeks until achievement of complete response, defined as resolution of all manifestations of GI GVHD, or until patients had progression or initiation of other therapy. Ten of 16 patients (62.5%; 95% CI, 0.39-82) achieved a complete response after a median time of 11 days (range, 2-28 days) from tocilizumab initiation. The median time to response onset (improvement in stage by at least 1) was 1 day (range, 1-4 days). Tocilizumab was administered at a median of 9 days (range, 3-75 days) from GVHD diagnosis and 10 days (range, 3-75 days) from initiation of high-dose steroids. At a median follow-up of 7.6 months (range, 0.8-27.7 months) from initiation of tocilizumab, 6/16 (37.5%) patients are alive and free of their underlying hematologic malignancy. Tocilizumab appears to be a highly active agent for the treatment of severe SR lower GI acute GVHD.
Ancient lowlands on Mars Frey, Herbert V.; Roark, James H.; Shockey, Kelly M. ...
Geophysical research letters,
15 May 2002, Letnik:
29, Številka:
10
Journal Article
Recenzirano
Mars Orbiter Laser Altimeter (MOLA) data provide compelling evidence that the martian lowlands, below the smooth and sparsely cratered northern plains, are extremely old, far older than the plains ...which cover them. The evidence is in the form of a very large population of “Quasi‐Circular Depressions” (QCDs), many of which are very evident in the MOLA elevation data but generally not visible in available imagery. We interpret these “invisible” QCDs to be buried impact basins. Cumulative number versus diameter curves for lowland QCDs suggests the buried lowland surface is older than the visible highland surface and that the lowland plains are a relatively thin (1–2 km) veneer overlying this much older surface. We conclude that the martian lowlands have been low and stable for nearly all of martian history.
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