Intermediate-energy Coulomb excitation of 58,60,62Cr: The onset of collectivity toward N=40

Intermediate-energy Coulomb excitation measurements were performed on the neutron-rich isotopes 58,60,62Cr. The electric quadrupole excitation strengths, B(E2; 01+→21+), of 60,62Cr are determined for the first time. The results quantify the trend of increasing quadrupole collectivity in the Cr isotopes approaching neutron number N=40. The results are confronted with large-scale shell-model calculations in the fpgd shell using the state-of-the-art LNPS effective interaction. Different sets of effective charges are discussed that provide an improved and robust description of the B(E2) values of the neutron-rich Fe and Cr isotopes in this region of rapid shell evolution. The ratio of the neutron and proton transition matrix elements, |Mn/Mp|, is proposed as an effective tool to discriminate between the various choices of effective charges

In-beam γ -ray spectroscopy of Mn 63

Background: Neutron-rich, even-mass chromium and iron isotopes approaching neutron number N=40 have been important benchmarks in the development of shell-model effective interactions incorporating the effects of shell evolution in the exotic regime. Odd-mass manganese nuclei have received less attention, but provide important and complementary sensitivity to these interactions. Purpose: We report the observation of two new γ-ray transitions in Mn63, which establish the (9/2-) and (11/2-) levels on top of the previously known (7/2-) first-excited state. The lifetime for the (7/2-) and (9/2-) excited states were determined for the first time, while an upper limit could be established for the (11/2-) level. Method: Excited states in Mn63 have been populated in inelastic scattering from a Be9 target and in the fragmentation of Fe65. γγ coincidence relationships were used to establish the decay level scheme. A Doppler line-shape analysis for the Doppler-broadened (7/2-)→5/2-, (9/2-)→(7/2-), and (11/2-)→(9/2-) transitions was used to determine (limits for) the corresponding excited-state lifetimes. Results: The low-lying level scheme and the excited-state lifetimes were compared with large-scale shell-model calculations using different model spaces and effective interactions in order to isolate important aspects of shell evolution in this region of structural change. Conclusions: While the theoretical (7/2-) and (9/2-) excitation energies show little dependence on the model space, the calculated lifetime of the (7/2-) level and calculated energy of the (11/2-) level reveal the importance of including the neutron g9/2 and d5/2 orbitals in the model space. The LNPS effective shell-model interaction provides the best overall agreement with the new data

Linking soil microbial community structure to potential carbon mineralization: A continental scale assessment of reduced tillage

Potential carbon mineralization (Cmin) is a commonly used indicator of soil health, with greater Cmin values interpreted as healthier soil. While Cmin values are typically greater in agricultural soils managed with minimal physical disturbance, the mechanisms driving the increases remain poorly understood. This study assessed bacterial and archaeal community structure and potential microbial drivers of Cmin in soils maintained under various degrees of physical disturbance. Potential carbon mineralization, 16S rRNA sequences, and soil characterization data were collected as part of the North American Project to Evaluate Soil Health Measurements (NAPESHM). Results showed that type of cropping system, intensity of physical disturbance, and soil pH influenced microbial sensitivity to physical disturbance. Furthermore, 28% of amplicon sequence variants (ASVs), which were important in modeling Cmin, were enriched under soils managed with minimal physical disturbance. Sequences identified as enriched under minimal disturbance and important for modeling Cmin, were linked to organisms which could produce extracellular polymeric substances and contained metabolic strategies suited for tolerating environmental stressors. Understanding how physical disturbance shapes microbial communities across climates and inherent soil properties and drives changes in Cmin provides the context necessary to evaluate management impacts on standardized measures of soil microbial activity

Reading tea leaves worldwide: decoupled drivers of initial litter decomposition mass-loss rate and stabilisation

The breakdown of plant material fuels soil functioning and biodiversity. Currently, process understanding of global decomposition patterns and the drivers of such patterns are hampered by the lack of coherent large-scale datasets. We buried 36,000 individual litterbags (tea bags) worldwide and found an overall negative correlation between initial mass-loss rates and stabilization factors of plant-derived carbon, using the Tea Bag Index (TBI). The stabilization factor quantifies the degree to which easy-to-degrade components accumulate during early-stage decomposition (e.g. by environmental limitations). However, agriculture and an interaction between moisture and temperature led to a decoupling between initial mass-loss rates and stabilization, notably in colder locations. Using TBI improved mass-loss estimates of natural litter compared to models that ignored stabilization. Ignoring the transformation of dead plant material to more recalcitrant substances during early-stage decomposition, and the environmental control of this transformation, could overestimate carbon losses during early decomposition in carbon cycle models

GW190814: gravitational waves from the coalescence of a 23 solar mass black hole with a 2.6 solar mass compact object

We report the observation of a compact binary coalescence involving a 22.2–24.3 Me black hole and a compact object with a mass of 2.50–2.67 Me (all measurements quoted at the 90% credible level). The gravitational-wave signal, GW190814, was observed during LIGO’s and Virgo’s third observing run on 2019 August 14 at 21:10:39 UTC and has a signal-to-noise ratio of 25 in the three-detector network. The source was localized to 18.5 deg2 at a distance of - + 241 45 41 Mpc; no electromagnetic counterpart has been confirmed to date. The source has the most unequal mass ratio yet measured with gravitational waves, - + 0.112 0.009 0.008, and its secondary component is either the lightest black hole or the heaviest neutron star ever discovered in a double compact-object system. The dimensionless spin of the primary black hole is tightly constrained to �0.07. Tests of general relativity reveal no measurable deviations from the theory, and its prediction of higher-multipole emission is confirmed at high confidence. We estimate a merger rate density of 1–23 Gpc−3 yr−1 for the new class of binary coalescence sources that GW190814 represents. Astrophysical models predict that binaries with mass ratios similar to this event can form through several channels, but are unlikely to have formed in globular clusters. However, the combination of mass ratio, component masses, and the inferred merger rate for this event challenges all current models of the formation and mass distribution of compact-object binaries

Heat standards calibration in the DOE complex

As part of the Department of Energy (DOE) Non-nuclear Reconfiguration Program, the Office of Safeguards and Security Calorimetry Development Program has transferred from EG and G Mound Applied Technologies to the Los Alamos National Laboratory. An important function of this program is the calibration and certification of {sup 238}Pu heat standards, which are used to assure accountability of plutonium and tritium throughout the complex. To facilitate relatively uninterrupted calibration service, two calorimeters have been installed in the Los Alamos Plutonium Facility (TA-55). These calorimeters are capable of highly accurate measurements of heat standards with power ranging from 0.01 to 20 W. In addition, two new EG and G Mound Applied Technologies calibration calorimeters with a robot handling system have been installed in the Nuclear Safeguards Laboratories at Los Alamos National Laboratory. These calorimeters are located in a specially constructed laboratory that is controlled for temperature and humidity to achieve low uncertainty in the measurements. Because transportation of aging heat standards between sites within the DOE complex has become increasingly difficult, the authors are looking into several approaches to this problem. Repackaging of all heat standards to comply with Department of Transportation and American Nuclear Standards Institute requirements is a long-term goal

Designing the interface to encourage more cognitive processing

Cognitive engineering aims to provide operators with immediate access to as much relevant information as possible. However, this can encourage display-based strategies that do not involve committing information to memory. To overcome this problem, a somewhat counterintuitive method is discussed, based upon the theory of soft constraints [1], that involves delaying access to some critical information by one or two seconds. This design technique induces a more planful and memory-based strategy that can improve recall, develop more planning behavior, improve problem solving, and protect against the negative effects of interruption. Furthermore, we provide some preliminary results that this more memory-intensive strategy can be trained through past experience with high access cost and then used in situations where access cost is minimal. This was the case when only half of the training trials involved a higher access cost. Further research is needed to ascertain how long training effects last and what are the ideal training regimes for different types of task