404 research outputs found
Big Bang Nucleosynthesis Constraints on Hadronically and Electromagnetically Decaying Relic Neutral Particles
Big Bang nucleosynthesis in the presence of decaying relic neutral particles
is examined in detail. All non-thermal processes important for the
determination of light-element abundance yields of 2H, 3H, 3He, 4He, 6Li, and
7Li are coupled to the thermonuclear fusion reactions to obtain comparatively
accurate results. Predicted light-element yields are compared to
observationally inferred limits on primordial light-element abundances to infer
constraints on the abundances and properties of relic decaying particles with
decay times in the interval 0.01 sec < tau < 10^(12) sec. Decaying particles
are typically constrained at early times by 4He or 2H, at intermediate times by
6Li, and at large times by the 3He/2H ratio. Constraints are shown for a large
number of hadronic branching ratios and decaying particle masses and may be
applied to constrain the evolution of the early Universe.Comment: 24 pages (revtex), 11 figures, title changed, matches published
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Diffractive point sets with entropy
After a brief historical survey, the paper introduces the notion of entropic
model sets (cut and project sets), and, more generally, the notion of
diffractive point sets with entropy. Such sets may be thought of as
generalizations of lattice gases. We show that taking the site occupation of a
model set stochastically results, with probabilistic certainty, in well-defined
diffractive properties augmented by a constant diffuse background. We discuss
both the case of independent, but identically distributed (i.i.d.) random
variables and that of independent, but different (i.e., site dependent) random
variables. Several examples are shown.Comment: 25 pages; dedicated to Hans-Ude Nissen on the occasion of his 65th
birthday; final version, some minor addition
Elevated NET, Calprotectin, and Neopterin Levels Discriminate between Disease Activity in COVID-19, as Evidenced by Need for Hospitalization among Patients in Northern Italy
Coronavirus disease 2019 (COVID-19) displays clinical heterogeneity, but little information is available for patients with mild or very early disease. We aimed to characterize biomarkers that are useful for discriminating the hospitalization risk in a COVID-19 cohort from Northern Italy during the first pandemic wave. We enrolled and followed for four weeks 76 symptomatic SARS-CoV-2 positive patients and age/sex-matched healthy controls. Patients with mild disease were discharged (n.42), and the remaining patients were hospitalized (n.34). Blood was collected before any anti-inflammatory/immunosuppressive therapy and assessed for soluble C5b-9/C5a, H3-neutrophil extracellular traps (NETs), calprotectin, and DNase plasma levels via ELISA and a panel of proinflammatory cytokines via ELLA. Calprotectin and NET levels discriminate between hospitalized and non-hospitalized patients, while DNase negatively correlates with NET levels; there are positive correlations between calprotectin and both NET and neopterin levels. Neopterin levels increase in patients at the beginning of the disease and do so more in hospitalized than non-hospitalized patients. C5a and sC5b-9, and other acute phase proteins, correlate with neopterin, calprotectin, and DNase. Both NET and neopterin levels negatively correlate with platelet count. We show that calprotectin, NETs, and neopterin are important proinflammatory parameters potentially useful for discriminating between COVID-19 patients at risk of hospitalization
Structure and Mode-of-Action of the Two-Peptide (Class-IIb) Bacteriocins
This review focuses on the structure and mode-of-action of the two-peptide (class-IIb) bacteriocins that consist of two different peptides whose genes are next to each other in the same operon. Optimal antibacterial activity requires the presence of both peptides in about equal amounts. The two peptides are synthesized as preforms that contain a 15–30 residue double-glycine-type N-terminal leader sequence that is cleaved off at the C-terminal side of two glycine residues by a dedicated ABC-transporter that concomitantly transfers the bacteriocin peptides across cell membranes. Two-peptide bacteriocins render the membrane of sensitive bacteria permeable to a selected group of ions, indicating that the bacteriocins form or induce the formation of pores that display specificity with respect to the transport of molecules. Based on structure–function studies, it has been proposed that the two peptides of two-peptide bacteriocins form a membrane-penetrating helix–helix structure involving helix–helix-interacting GxxxG-motifs that are present in all characterized two-peptide bacteriocins. It has also been suggested that the membrane-penetrating helix–helix structure interacts with an integrated membrane protein, thereby triggering a conformational alteration in the protein, which in turn causes membrane-leakage. This proposed mode-of-action is similar to the mode-of-action of the pediocin-like (class-IIa) bacteriocins and lactococcin A (a class-IId bacteriocin), which bind to a membrane-embedded part of the mannose phosphotransferase permease in a manner that causes membrane-leakage and cell death
Insights into the 1968–1997 Dasht-e-Bayaz and Zirkuh earthquake sequences, eastern Iran, from calibrated relocations, InSAR and high-resolution satellite imagery
The sequence of seismicity in the Dasht-e-Bayaz and Zirkuh region of northeastern Iran, which includes 11 destructive earthquakes within a period of only 30 years, forms one of the most outstanding examples of clustered large and intermediate-magnitude seismic activity in the world.We perform a multiple-event relocation analysis, with procedures to remove systematic location bias, of 169 earthquakes, most of which occurred in the period 1968–2008, to better image the distribution of seismicity within this highly active part of Iran. The geographic locations of the clustered earthquakes were calibrated by the inclusion of phase arrivals from seismic stations at short epicentral distances, and also by matching the relative locations of the three largest events in the study to their mapped surface ruptures. The two independent calibration methods provide similar results that increase our confidence in the accuracy of the distribution of relocated epicentres. These calibrated epicentres, combined with the mapping of faults from high-resolution satellite imagery, and from an InSAR-derived constraint on fault location in one case, allow us to associate individual events with specific faults, and even with specific segments of faults, to better understand the nature of the active tectonics in this region during the past four decades. Several previous assumptions about the seismicity in this region are confirmed: (1) that the 1968 August 30 Mw 7.1 Dasht-e-Bayaz earthquake nucleated at a prominent segment boundary and left-step in the fault trace, (2) that the 1968 September 11 Mw 5.6 aftershock occurred on the Dasht-e-Bayaz fault at the eastern end of the 1968 rupture and (3) that the 1976 November 7 Mw 6.0 Qayen earthquake probably occurred on the E–W left-lateral Avash Fault. We show, in addition, that several significant events, including the 1968 September 1 and 4 (Mw 6.3 and 5.5) Ferdows earthquakes, the 1979 January 16 (Mw 6.5) and 1997 June 25 (Mw 5.9) Boznabad events and the 1979 December 7 (Mw 5.9) Kalat-e-Shur earthquake are likely to have ruptured previously unknown faults. Our improved description of the faulting involved in the 1968–1997 earthquake sequence highlights the importance of rupturing of conjugate left- and right-lateral faults in closely spaced events, or potentially even within a single earthquake, as was likely the case at the eastern end of the 1979 November 27 (Mw 7.1) Khuli-Buniabad main shock. The high level of clustered seismic activity probably results from the simultaneous activity on left- and right-lateral faults, an inherently unstable arrangement that must evolve rapidly. The combination of high-resolution satellite imagery and calibrated earthquake locations is a useful tool for investigating active tectonics, even in the absence of detailed field observations
Seismic constraints from a Mars impact experiment using InSight and Perseverance
NASA’s InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) mission has operated a sophisticated suite of seismology and geophysics instruments on the surface of Mars since its arrival in 2018. On 18 February 2021, we attempted to detect the seismic and acoustic waves produced by the entry, descent and landing of the Perseverance rover using the sensors onboard the InSight lander. Similar observations have been made on Earth using data from both crewed1,2 and uncrewed3,4 spacecraft, and on the Moon during the Apollo era5, but never before on Mars or another planet. This was the only seismic event to occur on Mars since InSight began operations that had an a priori known and independently constrained timing and location. It therefore had the potential to be used as a calibration for other marsquakes recorded by InSight. Here we report that no signal from Perseverance’s entry, descent and landing is identifiable in the InSight data. Nonetheless, measurements made during the landing window enable us to place constraints on the distance–amplitude relationships used to predict the amplitude of seismic waves produced by planetary impacts and place in situ constraints on Martian impact seismic efficiency (the fraction of the impactor kinetic energy converted into seismic energy)
Listening for the landing: seismic detections of perseverance's arrival at Mars with InSight
The entry, descent, and landing (EDL) sequence of NASA's Mars 2020 Perseverance Rover will act as a seismic source of known temporal and spatial localization. We evaluate whether the signals produced by this event will be detectable by the InSight lander (3,452 km away), comparing expected signal amplitudes to noise levels at the instrument. Modeling is undertaken to predict the propagation of the acoustic signal (purely in the atmosphere), the seismoacoustic signal (atmosphere-to-ground coupled), and the elastodynamic seismic signal (in the ground only). Our results suggest that the acoustic and seismoacoustic signals, produced by the atmospheric shock wave from the EDL, are unlikely to be detectable due to the pattern of winds in the martian atmosphere and the weak air-to-ground coupling, respectively. However, the elastodynamic seismic signal produced by the impact of the spacecraft's cruise balance masses on the surface may be detected by InSight. The upper and lower bounds on predicted ground velocity at InSight are 2.0 × 10−14 and 1.3 × 10−10 m s−1. The upper value is above the noise floor at the time of landing 40% of the time on average. The large range of possible values reflects uncertainties in the current understanding of impact-generated seismic waves and their subsequent propagation and attenuation through Mars. Uncertainty in the detectability also stems from the indeterminate instrument noise level at the time of this future event. A positive detection would be of enormous value in constraining the seismic properties of Mars, and in improving our understanding of impact-generated seismic waves
Monocyte-mediated Tumoricidal Activity via the Tumor Necrosis Factor–related Cytokine, TRAIL
Global Transcriptional Analysis of Spontaneous Sakacin P-Resistant Mutant Strains of Listeria monocytogenes during Growth on Different Sugars
Subclass IIa bacteriocins have strong antilisterial activity and can control the growth of Listeria monocytogenes in food. However, L. monocytogenes may develop resistance towards such bacteriocins. In this follow-up study, the transcriptomes of a high level (L502-1) and a low level (L502-6) spontaneous sakacin P-resistant mutant strain of L. monocytogenes were compared to the wild-type (L502). The growth of the resistant strains was reduced on mannose but not affected on cellobiose and the transcriptomics was performed during growth on these sugars. The mannose phosphotransferase system (PTS) encoded by the mptACD operon (mpt) is known for transporting mannose and also act as a receptor to class IIa bacteriocins. The mpt was repressed in L502-1 and this is in accordance with abolition of the bacteriocin receptor with resistance to class IIa bacteriocins. In contrast, the mpt was induced in L502-6. Despite the induction of the mpt, L502-6 showed 1,000 times more resistance phenotype and reduced growth on mannose suggesting the mannose-PTS may not be functional in L502-6. The microarray data suggests the presence of other transcriptional responses that may be linked to the sakacin P resistance phenotype particularly in L502-6. Most of commonly regulated genes encode proteins involved in transport and energy metabolism. The resistant strains displayed shift in general carbon catabolite control possibly mediated by the mpt. Our data suggest that the resistant strains may have a reduced virulence potential. Growth sugar- and mutant-specific responses were also revealed. The two resistant strains also displayed difference in stability of the sakacin P resistance phenotype, growth in the presence of both the lytic bacteriophage P100 and activated charcoal. Taken together, the present study showed that a single time exposure to the class IIa bacteriocin sakacin P may elicit contrasting phenotypic and transcriptome responses in L. monocytogenes possibly through regulation of the mpt
The extreme r-element rich, iron-poor halo giant CS31082-001: Implications for the r-process site(s) and radioactive cosmochronology
We present a high-resolution spectroscopic analysis of the bright (V=11.7), extreme halo giant CS31082-001 ([Fe/H] = -2.9), obtained in an ESO-VLT Large Programme dedicated to very metal-poor stars. We find CS31082-001 to be extremely rich in r-process elements, comparable in this respect only to the similarly metal-poor, but carbon-enriched, giant CS22892-052. As a result of the extreme overabundance of the heaviest r-process elements, and negligible blending from CH and CN molecular lines, a reliable measurement is obtained of the U II line at 386 nm, for the first time in a halo star, along with numerous lines of Th II, as well as lines of 25 other r-process elements. Abundance estimates for a total of 43 elements are reported in CS31082-001, almost half of the entire periodic table. All elements with 56 \leq Z \leq 72 follow the Solar r-element pattern, reduced by about 1.25 dex ([r/Fe]=+1.7 dex, a factor 50). Pb, in contrast, seems to be below the shifted Solar r-process distribution, possibly indicating an error in the latter, while thorium is more enhanced than the lighter nuclides. Thus, while a universal production ratio for the r-process elements seems to hold in the interval 56 \leq Z \leq 72, it breaks down in the actinide region. When available, the U/Th is thus preferable to Th/Eu for radioactive dating: (i) because of its faster decay rate and smaller sensitivity to observational errors, and (ii) because the inital production ratio of the neighboring nuclides 238U and 232Th is more robustly predicted than the 151Eu/232Th ratio. Our current best estimate for the age of CS31082-001 is 14.0+/-2.4 Gyr
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