2,093 research outputs found
Numerical modelling of heat generation in porous planetesimal collisions
An important unanswered question in planetary science is how planetesimals,
the ~1–100 km solid precursors to asteroids and planets, were heated
in the early Solar System. This thesis quantifies one possible heat source:
planetesimal collisions. Recent work has predicted that collision velocities
and planetesimal porosities were likely to have been higher than previously
thought; this is likely to have significant implications on collision heating.
The approach adopted in this research was to numerically model shock
heating during planetesimal collisions. Simulations showed that an increase
in porosity can significantly increase heating: in a 5 km s-1 collision between
equal sized, non-porous planetesimals, no material was heated to the solidus,
compared to two thirds of the mass of 50% porous planetesimals. Velocity
also strongly influences heating: at 4 km s-1, an eighth of the mass of 50%
porous planetesimals was heated to the solidus, compared to the entire mass
at 6 km s-1. Further simulations quantified the influence on heating of the
impactor-to-target mass ratio, the initial planetesimal temperature and the
impact angle.
A Monte Carlo model was developed to examine the cumulative heating
caused by a population of impactors striking a parent body. In the majority
of collisions the impactor was much smaller than the parent body, and only
minor heating was possible. However, some larger or faster impactors were
capable of causing significant heating without disrupting the parent body;
these collisions could have heated up to 10% of the parent body to the solidus.
To cause global heating, the collision must have catastrophically disrupted
the parent body.
The increase in specific internal energy from collisions was compared with
the decay of short-lived radionuclides. In the first ~6 Ma, radioactive decay
was the most important heat source. After ~10 Ma, the energy caused
by collisions was likely to have overtaken radioactive decay as the dominant
source
Genome sequence of an alphaherpesvirus from a beluga whale (Delphinapterus leucas)
Beluga whale alphaherpesvirus 1 was isolated from a blowhole swab taken from a juvenile beluga whale. The genome is 144,144 bp in size and contains 86 putative genes. The virus groups phylogenetically with members of the genus Varicellovirus in subfamily Alphaherpesvirinae and is the first alphaherpesvirus sequenced from a marine mammal
Genome sequence of a gammaherpesvirus from a common bottlenose dolphin (Tursiops truncatus)
A herpesvirus genome was sequenced directly from a biopsy specimen of a rectal lesion from a female common bottlenose dolphin. This genome sequence comprises a unique region (161,235 bp) flanked by multiple copies of a terminal repeat (4,431 bp) and contains 72 putative genes. The virus was named common bottlenose dolphin gammaherpesvirus 1
Scientific mindfulness: a foundation for future themes in international business
We conceptualize new ways to qualify what themes should dominate the future IB
research agenda by examining three questions: Whom should we ask? What should we ask and which selection criteria should we apply? What are the contextual forces? We propose scientific mindfulness as the way forward for generating themes in IB research
Cohomological Donaldson-Thomas theory of a quiver with potential and quantum enveloping algebras
This paper concerns the cohomological aspects of Donaldson-Thomas theory for
Jacobi algebras and the associated cohomological Hall algebra, introduced by
Kontsevich and Soibelman. We prove the Hodge-theoretic categorification of the
integrality conjecture and the wall crossing formula, and furthermore realise
the isomorphism in both of these theorems as Poincar\'e-Birkhoff-Witt
isomorphisms for the associated cohomological Hall algebra. We do this by
defining a perverse filtration on the cohomological Hall algebra, a result of
the "hidden properness" of the semisimplification map from the moduli stack of
semistable representations of the Jacobi algebra to the coarse moduli space of
polystable representations. This enables us to construct a degeneration of the
cohomological Hall algebra, for generic stability condition and fixed slope, to
a free supercommutative algebra generated by a mixed Hodge structure
categorifying the BPS invariants. As a corollary of this construction we
furthermore obtain a Lie algebra structure on this mixed Hodge structure - the
Lie algebra of BPS invariants - for which the entire cohomological Hall algebra
can be seen as the positive part of a Yangian-type quantum group.Comment: v5 final version, 64 pages, to appear in Invent. Math. Many thanks to
the anonymous referee for helpful suggestion
Discovery and validation of cell cycle arrest biomarkers in human acute kidney injury
Introduction
Acute kidney injury (AKI) can evolve quickly and clinical measures of function often fail to detect AKI at a time when interventions are likely to provide benefit. Identifying early markers of kidney damage has been difficult due to the complex nature of human AKI, in which multiple etiologies exist. The objective of this study was to identify and validate novel biomarkers of AKI. Methods
We performed two multicenter observational studies in critically ill patients at risk for AKI - discovery and validation. The top two markers from discovery were validated in a second study (Sapphire) and compared to a number of previously described biomarkers. In the discovery phase, we enrolled 522 adults in three distinct cohorts including patients with sepsis, shock, major surgery, and trauma and examined over 300 markers. In the Sapphire validation study, we enrolled 744 adult subjects with critical illness and without evidence of AKI at enrollment; the final analysis cohort was a heterogeneous sample of 728 critically ill patients. The primary endpoint was moderate to severe AKI (KDIGO stage 2 to 3) within 12 hours of sample collection. Results
Moderate to severe AKI occurred in 14% of Sapphire subjects. The two top biomarkers from discovery were validated. Urine insulin-like growth factor-binding protein 7 (IGFBP7) and tissue inhibitor of metalloproteinases-2 (TIMP-2), both inducers of G1 cell cycle arrest, a key mechanism implicated in AKI, together demonstrated an AUC of 0.80 (0.76 and 0.79 alone). Urine [TIMP-2]·[IGFBP7] was significantly superior to all previously described markers of AKI (P \u3c0.002), none of which achieved an AUC \u3e0.72. Furthermore, [TIMP-2]·[IGFBP7] significantly improved risk stratification when added to a nine-variable clinical model when analyzed using Cox proportional hazards model, generalized estimating equation, integrated discrimination improvement or net reclassification improvement. Finally, in sensitivity analyses [TIMP-2]·[IGFBP7] remained significant and superior to all other markers regardless of changes in reference creatinine method. Conclusions
Two novel markers for AKI have been identified and validated in independent multicenter cohorts. Both markers are superior to existing markers, provide additional information over clinical variables and add mechanistic insight into AKI. Trial registration
ClinicalTrials.gov number NCT01209169
Momentum Enhancement during Kinetic Impacts in the Low-intermediate-strength Regime: Benchmarking and Validation of Impact Shock Physics Codes
In 2022 September, the DART spacecraft (NASA’s contribution to the Asteroid Impact & Deflection Assessment (AIDA) collaboration) will impact the asteroid Dimorphos, the secondary in the Didymos system. The crater formation and material ejection will affect the orbital period. In 2027, Hera (ESA’s contribution to AIDA) will investigate the system, observe the crater caused by DART, and characterize Dimorphos. Before Hera’s arrival, the target properties will not be well-constrained. The relationships between observed orbital change and specific target properties are not unique, but Hera’s observations will add additional constraints for the analysis of the impact event, which will narrow the range of feasible target properties. In this study, we use three different shock physics codes to simulate momentum transfer from impactor to target and investigate the agreement between the results from the codes for well-defined target materials. In contrast to previous studies, care is taken to use consistent crushing behavior (e.g., distension as a function of pressure) for a given porosity for all codes. First, we validate the codes against impact experiments into a regolith simulant. Second, we benchmark the codes at the DART impact scale for a range of target material parameters (10%–50% porosity, 1.4–100 kPa cohesion). Aligning the crushing behavior improves the consistency of the derived momentum enhancement between the three codes to within +/−5% for most materials used. Based on the derived mass–velocity distributions from all three codes, we derive scaling parameters that can be used for studies of the ejecta curtain
Oxidative dearomatisation: the key step of sorbicillinoid biosynthesis
An FAD-dependent monooxygenase encoding gene (SorbC) was cloned from Penicillium chrysogenum E01-10/3 and expressed as a soluble protein in Escherichia coli. The enzyme efficiently performed the oxidative dearomatisation of sorbicillin and dihydrosorbicillin to give sorbicillinol and dihydrosorbicillinol respectively. Bioinformatic examination of the gene cluster surrounding SorbC indicated the presence of two polyketide synthase (PKS) encoding genes designated sorbA and sorbB. The gene sorbA-encodes a highly reducing iterative PKS while SorbB encodes a non-reducing iterative PKS which features a reductive release domain usually involved in the production of polyketide aldehydes. Using these observations and previously reported results from isotopic feeding experiments a new and simpler biosynthetic route to the sorbicillin class of secondary metabolites is proposed which is consistent with all reported experimental results.Al Baha University, Saudi ArabiaEP/F066104/1BB/I003355/1BMBFERASMUS programm
Genome sequence of white sturgeon herpesvirus 1 isolated from farmed white sturgeon (Acipenser transmontanus)
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