61 research outputs found
Diversity of new Martian crater clusters informs meteoroid atmospheric interactions
We investigated 634 crater clusters on Mars detected between 2007 and 2021,
which represent more than half of all impacts discovered in this period. Crater
clusters form when meteoroids in the 10 kg to 10 ton mass range break-up in
Mars' atmosphere to produce a few to a few hundred fragments that hit the
ground. The properties of the clusters can inform our understanding of
meteoroid properties and the processes that govern their fragmentation. We
mapped individual craters 1 m within each cluster and defined a range of
cluster properties based on the spatial and size distributions of the craters.
The large data set, with over eight times more cluster observations than
previous work, provides a more robust statistical investigation of crater
cluster parameters and their correlations. Trends in size, dispersion and large
crater fraction with elevation support weak atmospheric filtering of material.
The diversity in the number of individual craters within a cluster, and their
size-frequency distributions, may reflect either a diversity in fragmentation
style, fragility or internal particle sizes.Comment: 12 pages, 12 figures at the en
Exploring the vicinity of the Bogomol'nyi-Prasad-Sommerfield bound
We investigate systems of real scalar fields in bidimensional spacetime,
dealing with potentials that are small modifications of potentials that admit
supersymmetric extensions. The modifications are controlled by a real
parameter, which allows implementing a perturbation procedure when such
parameter is small. The approach allows obtaining the energy and topological
charge in closed forms, up to first order in the parameter. We illustrate the
procedure with some examples. In particular, we show how to remove the
degeneracy in energy for the one-field and the two-field solutions that appear
in a model of two real scalar fields.Comment: Revtex, 9 pages, To be published in J. Phys.
Tiling the plane without supersymmetry
We present a way of tiling the plane with a regular hexagonal network of
defects. The network is stable and follows in consequence of the
three-junctions that appear in a model of two real scalar fields that presents
symmetry. The symmetry is effective in both the vacuum and defect
sectors, and no supersymmetry is required to build the network.Comment: Revtex, 4 pages, 1 ps figure; version to appear in Phys. Rev. Let
Low molecular weight heparin (reviparin) in percutaneous transluminal coronary angioplasty. Results of a randomized, double-blind, unfractionated heparin and placebo-controlled, multicenter trial (REDUCE trial)
Objectives. The specific objective of the REDUCE trial was to evaluate the effect of low molecular weight heparin on the incidence and occurrence of restenosis in patients undergoing percutaneous transluminal coronary angioplasty (PTCA). Background. Unfractionated heparin and its low molecular weight fragments possess antiproliferative effects and have been shown to reduce neointimal smooth muscle cell migration and proliferation in response to vascular injury in experimental studies. Methods. The REDUCE trial is an international prospective, randomized, double-blind, multicenter study. Twenty-six centers in Europe and Canada enrolled 625 patients with single-lesion coronary artery obstructions suitable for PTCA. Three hundred six patients received reviparin as a 7,000-U bolus before PTCA, followed by 10,500 U as an infusion over 24 h and then twice-daily 3,500-U subcutaneous application for 28 days. The 306 patients in the control group received a bolus of 10,000 U o
Bags, junctions, and networks of BPS and non-BPS defects
We investigate several models of coupled scalar fields that present discrete
Z_2, Z_2 x Z_2, Z_3 and other symmetries. These models support topological
domain wall solutions of the BPS and non-BPS type. The BPS solutions are
stable, but the stability of the non-BPS solutions may depend on the parameters
that specify the models. The BPS and non-BPS states give rise to bags, and also
to three-junctions that may allow the presence of networks of topological
defects. In particular, we show that the non-BPS defects of a specific model
that engenders the Z_3 symmetry give rise to a stable regular hexagonal network
of domain walls.Comment: Revtex, 16 pages, 6 ps figures; Shorter version to be published in
Phys. Rev.
Intravenous alteplase for stroke with unknown time of onset guided by advanced imaging: systematic review and meta-analysis of individual patient data
Background: Patients who have had a stroke with unknown time of onset have been previously excluded from thrombolysis. We aimed to establish whether intravenous alteplase is safe and effective in such patients when salvageable tissue has been identified with imaging biomarkers. Methods: We did a systematic review and meta-analysis of individual patient data for trials published before Sept 21, 2020. Randomised trials of intravenous alteplase versus standard of care or placebo in adults with stroke with unknown time of onset with perfusion-diffusion MRI, perfusion CT, or MRI with diffusion weighted imaging-fluid attenuated inversion recovery (DWI-FLAIR) mismatch were eligible. The primary outcome was favourable functional outcome (score of 0–1 on the modified Rankin Scale [mRS]) at 90 days indicating no disability using an unconditional mixed-effect logistic-regression model fitted to estimate the treatment effect. Secondary outcomes were mRS shift towards a better functional outcome and independent outcome (mRS 0–2) at 90 days. Safety outcomes included death, severe disability or death (mRS score 4–6), and symptomatic intracranial haemorrhage. This study is registered with PROSPERO, CRD42020166903. Findings: Of 249 identified abstracts, four trials met our eligibility criteria for inclusion: WAKE-UP, EXTEND, THAWS, and ECASS-4. The four trials provided individual patient data for 843 individuals, of whom 429 (51%) were assigned to alteplase and 414 (49%) to placebo or standard care. A favourable outcome occurred in 199 (47%) of 420 patients with alteplase and in 160 (39%) of 409 patients among controls (adjusted odds ratio [OR] 1·49 [95% CI 1·10–2·03]; p=0·011), with low heterogeneity across studies (I2=27%). Alteplase was associated with a significant shift towards better functional outcome (adjusted common OR 1·38 [95% CI 1·05–1·80]; p=0·019), and a higher odds of independent outcome (adjusted OR 1·50 [1·06–2·12]; p=0·022). In the alteplase group, 90 (21%) patients were severely disabled or died (mRS score 4–6), compared with 102 (25%) patients in the control group (adjusted OR 0·76 [0·52–1·11]; p=0·15). 27 (6%) patients died in the alteplase group and 14 (3%) patients died among controls (adjusted OR 2·06 [1·03–4·09]; p=0·040). The prevalence of symptomatic intracranial haemorrhage was higher in the alteplase group than among controls (11 [3%] vs two [<1%], adjusted OR 5·58 [1·22–25·50]; p=0·024). Interpretation: In patients who have had a stroke with unknown time of onset with a DWI-FLAIR or perfusion mismatch, intravenous alteplase resulted in better functional outcome at 90 days than placebo or standard care. A net benefit was observed for all functional outcomes despite an increased risk of symptomatic intracranial haemorrhage. Although there were more deaths with alteplase than placebo, there were fewer cases of severe disability or death. Funding: None
Using Log Files to Assess Web-Enabled Information System Usage
This article presents a beginning point for understanding log file assessment techniques. This paper identifies and discusses measurement techniques and issues for the analysis of webserver and CGI interface logfiles, describes the lessons learned from two projects which assessed use of a web-enabled tool at a large federal agencies, and postulates about other types of research which might benefit from the employment of log file analysis technique
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