Globally, soil organic matter (SOM) contains more than three times as much carbon as either the atmosphere or terrestrial vegetation. Yet it remains largely unknown why some SOM persists for ...millennia whereas other SOM decomposes readily--and this limits our ability to predict how soils will respond to climate change. Recent analytical and experimental advances have demonstrated that molecular structure alone does not control SOM stability: in fact, environmental and biological controls predominate. Here we propose ways to include this understanding in a new generation of experiments and soil carbon models, thereby improving predictions of the SOM response to global warming.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
We show that, up to plausible uncertainties in BR(Bc→τν), the R2 leptoquark can simultaneously explain the observation of anomalies in RK(*) and RD(*) without requiring large couplings. The former is ...achieved via a small coupling to first generation leptons, which boosts the decay rate Γ(B¯→K¯(*)e+e−). Finally we motivate a neutrino mass model that includes the S3 leptoquark, which can alleviate a mild tension with the most conservative limits on BR(Bc→τν).
Using a simple two step fabrication process substrates with a large and uniform Raman enhancement, based on flexible free standing nanopillars can be manufactured over large areas using readily ...available silicon processing equipment.
For centuries, scientists have attempted to identify and document analytical laws that underlie physical phenomena in nature. Despite the prevalence of computing power, the process of finding natural ...laws and their corresponding equations has resisted automation. A key challenge to finding analytic relations automatically is defining algorithmically what makes a correlation in observed data important and insightful. We propose a principle for the identification of nontriviality. We demonstrated this approach by automatically searching motion-tracking data captured from various physical systems, ranging from simple harmonic oscillators to chaotic double-pendula. Without any prior knowledge about physics, kinematics, or geometry, the algorithm discovered Hamiltonians, Lagrangians, and other laws of geometric and momentum conservation. The discovery rate accelerated as laws found for simpler systems were used to bootstrap explanations for more complex systems, gradually uncovering the "alphabet" used to describe those systems.
A
bstract
We reconsider a model introducing a scalar leptoquark
ϕ
∼ (
3
,
1
,
−1
/
3) to explain recent deviations from the standard model in semileptonic
B
decays. The leptoquark can accommodate the ...persistent tension in the decays
B
¯
→
D
∗
τ
ν
¯
as long as its mass is lower than approximately 10 TeV, and we show that a sizeable Yukawa coupling to the right-chiral tau lepton is necessary for an acceptable explanation. A characteristic prediction of this scenario is a value of
R
D
*
slightly smaller than the current world average. Agreement with the measured
B
¯
→
D
∗
τ
ν
¯
rates is mildly compromised for parameter choices addressing the tensions in
b
→
sμμ
, where the model can significantly reduce the discrepancies in angular observables, branching ratios and the lepton-flavor-universality observables
R
K
and
R
K
*
. The leptoquark can also reconcile the predicted and measured value of the anomalous magnetic moment of the muon and appears naturally in models of radiative neutrino mass derived from lepton-number violating effective operators. As a representative example, we incorporate the particle into an existing two-loop neutrino mass scenario derived from a dimension-nine operator. In this specific model, the structure of the neutrino mass matrix provides enough freedom to explain the small masses of the neutrinos in the region of parameter space dictated by agreement with the anomalies in
B
¯
→
D
∗
τ
ν
¯
, but not the
b
→
s
transition. This is achieved without excessive fine-tuning in the parameters important for neutrino mass.
CP and discrete flavour symmetries Holthausen, Martin; Lindner, Manfred; Schmidt, Michael A.
The journal of high energy physics,
04/2013, Letnik:
2013, Številka:
4
Journal Article
Recenzirano
Odprti dostop
A
bstract
We give a consistent definition of generalised CP transformations in the context of discrete flavour symmetries. Non-trivial consistency conditions imply that every generalised CP ...transformation can be interpreted as a representation of an automorphism of the discrete group. This allows us to give consistent generalised CP transformations of popular flavour groups. We are able to clear up issues concerning recent claims about geometrical CP violation in models based on
T
′
, clarify the origin of ”calculable phases” in Δ(27) and explain why apparently CP violating scalar potentials of
A
4
result in a CP conserving ground state.
Soil organic carbon (SOC) dynamics represent a persisting uncertainty in our understanding of the global carbon cycle. SOC storage is strongly linked to plant inputs via the formation of soil organic ...matter, but soil geochemistry also plays a critical role. In tropical soils with rapid SOC turnover, the association of organic matter with soil minerals is particularly important for stabilising SOC but projected increases in tropical forest productivity could trigger feedbacks that stimulate the release of stored SOC. Here, we demonstrate limited additional SOC storage after 13-15 years of experimentally doubled aboveground litter inputs in a lowland tropical forest. We combined biological, physical, and chemical methods to characterise SOC along a gradient of bioavailability. After 13 years of monthly litter addition treatments, most of the additional SOC was readily bioavailable and we observed no increase in mineral-associated SOC. Importantly, SOC with weak association to soil minerals declined in response to long-term litter addition, suggesting that increased plant inputs could modify the formation of organo-mineral complexes in tropical soils. Hence, we demonstrate the limited capacity of tropical soils to sequester additional C inputs and provide insights into potential underlying mechanisms.
The effect of alkylation on the terminal position of aryl and heteroaryl hydrazines in the Fischer indole synthesis was examined. Compared to their unalkylated counterparts, reactions using alkylated ...hydrazines provided indole products with higher yields and faster rates. The reactions can be conducted at lower temperatures and are compatible with acid-sensitive functionality. The terminally alkylated hydrazines were readily prepared by a new two-step sequence and held as stable hydrazinium salts. The mild formation of the salts along with the favorable Fischer indole reaction conditions highlights the potential of this approach in later-stage synthetic use.
Pyrogenic organic matter (PyOM) decomposes on centennial timescale in soils, but the processes regulating its decay are poorly understood. We conducted one of the first studies of PyOM and wood ...decomposition in a temperate forest using isotopically labeled organic substrate, and quantified microbial incorporation and physico‐chemical transformations of PyOM in situ. Stable‐isotope (13C and 15N) enriched PyOM and its precursor wood were added to the soil at 2 cm depth at ambient (N0) and increased (N+) levels of nitrogen fertilization. The carbon (C) and nitrogen (N) of added PyOM or wood were tracked through soil to 15 cm depth, in physically separated soil density fractions and in benzene polycarboxylic acids (BPCA) molecular markers. After 10 months in situ, more PyOM‐derived C (>99% of initial 13C‐PyOM) and N (90% of initial 15N‐PyOM) was recovered than wood derived C (48% of 13C‐wood) and N (89% under N0 and 48% under N+). PyOM‐C and wood‐C migrated at the rate of 126 mm yr−1 with 3–4% of PyOM‐C and 4–8% of wood‐C recovered below the application depth. Most PyOM C was recovered in the free light fraction (fLF) (74%), with 20% in aggregate‐occluded and 6% in mineral associated fractions – fractions that typically have much slower turnover times. In contrast, wood C was recovered mainly in occluded (33%) or dense fraction (27%). PyOM addition induced loss of native C from soil (priming effect), particularly in fLF (13%). The total BPCA‐C content did not change but after 10 months the degree of aromatic condensation of PyOM decreased, as determined by relative contribution of benzene hexa‐carboxylic acid (B6CA) to the total BPCA C. Soil microbial biomass assimilated 6–10% of C from the wood, while PyOM contributions was negligible (0.14–0.18%). The addition of N had no effect on the dynamics of PyOM while limited effect on wood.
We propose a variant of the Pati-Salam model, with gauge group SU(4)C × SU(2)L × U(1)Y′, in which the chiral left-handed quarks and leptons are unified into a 4_ of SU(4)C, while the right-handed ...quarks and leptons have quite a distinct treatment. The SU(4)C leptoquark gauge bosons can explain the measured deviation of lepton flavor universality in the rare decays: ¯B → ¯K(*)¯ℓℓ,ℓ = μ, e (taken as a hint of new physics). The model satisfies the relevant experimental constraints and makes predictions for the important B and τ decays and results in a correlation between leptonic Bs decays and RK. These predictions will be tested at the LHCb and Belle II experiments when increased statistics become available.
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