330,382 research outputs found
Constraining the cosmic-ray ionization rate and spectrum with NIR spectroscopy of dense clouds. A testbed for JWST
No full textContext. Low-energy cosmic rays (CRs) control the thermo-chemical state and the coupling between gas and magnetic fields in dense molecular clouds. However, current estimates of the low-energy CR spectrum (E-2-1 GeV) and the associated CR ionization rate are highly uncertain. Aims. We apply, for the first time, a new method for constraining the CR ionization rate and the CR spectral shape using H2 rovibrational lines from cold molecular clouds. Methods. Using the MMIRS instrument on the MMT, we obtained deep near-infrared (NIR) spectra in six positions within four dense cores, namely, G150, G157, G163, G198, with column densities of NH2-1022 cm-2. Results. We derived 3ÏA? upper limits on the H2 (1-0)S(0) line (2.22 μm) brightness in the range I-=-5.9-ÃA - -10-8 to 1.2-ÃA - -10-7 erg cm-2 s-1 sr-1 for the different targets. Using both an analytic model and a numerical model of CR propagation, we convert these into upper limits on the CR ionization rate in the clouds-interior, ζ-=-1.5 to 3.6-ÃA - -10-16 s-1, and lower limits on the low-energy spectral slope of interstellar CR protons, α-=-0.97 to -0.79. We show that while MMT was unable to detect the H2 lines due to high atmospheric noise, JWST/NIRSpec will be able to efficiently detect the CR-excited H2 lines, making it the ideal method for constraining the otherwise elusive low-energy CRs and shedding light on the sources and propagation modes of CRs
La Roma del Belli nel Grand Tour
No full textLa Roma del Grand Tour è largamente assente nell'opera del Belli, che dà spazio invece a una Roma "turistica" più autentica e profonda
Star formation quenching in massive galaxies
No full textUnderstanding how and why star formation turns off in massive galaxies is a major challenge for studies of galaxy evolution. Many theoretical explanations have been proposed, but a definitive consensus is yet to be reached
Measure inducing classification and regression trees for functional data
No full textWe propose a tree-based algorithm (μCART) for classification and regression problems in the context of functional data analysis, which allows to leverage measure learning and multiple splitting rules at the node level, with the objective of reducing error while retaining the interpretability of a tree. For each internal node, our main contribution is the idea of learning a weighted functional (Formula presented.) space by means of constrained convex optimization, which is then used to extract multiple weighted integral features from the functional predictors, in order to determine the binary split. The approach is designed to manage multiple functional predictors and/or responses, by defining suitable splitting rules and loss functions that can depend on the specific problem and can also be combined with additional scalar and categorical predictors, as the tree is grown with the original greedy CART algorithm. We focus on the case of scalar-valued functional predictors defined on unidimensional domains and illustrate the effectiveness of our method in both classification and regression tasks, through a simulation study and four real-world applications
The comparative advantage of government : a review
No full textIn theory, market failures are necessary but not sufficient conditions for justifying government intervention in the production of goods and services. Even without market failures, there might be a case for government intervention on the grounds of poverty reduction or merit goods (for example, mandatory elementary education and mandatory use of seatbelts in cars and of helmets on motorbikes). In every case, contends the author, a case for government intervention must first identify the particular market failure that prevents the private sector from producing the socially optimal quantity of the good or service. Second, it must select the intervention that will most improve welfare. Third, it must show that society will be better off as a result of government involvement--must show that the benefits will outweigh the costs. It is impossible to judge a priori whether or what type of government intervention is appropriate to a particular circumstance or even to a class of situations. Such judgments are both country- and situation-specific and must be made on a case-by-case basis. To be sure, it is easier to make such judgments about market failures based on externalities, public goods, and so on, than about the market failures based on imperfect information. Market failures rooted in incomplete markets and imperfect information are pervasive: Markets are almost always incomplete, and information is always imperfect. This does not mean that there is always a case for government intervention and that further analysis is unnecessary. On the contrary, there is a keener need for analysis. The welfare consequences of the"new market failures"are more difficult to measure so government intervention's contribution to welfare is likely to be more difficult to assess and the case for intervention (especially the provision of goods and services) is more difficult to make. One must also keep in mind that government interventions are often poorly designed and overcostly. Poorly designed interventions may create market failures of their own. Governments concerned about low private investment in high-risk projects, for example, may guarantee them against risk but in the process create problems of moral hazard and induce investors to take no actions to mitigate such risks. And some interventions may turn out to be too costly relative to the posited benefits. In seeking to provide extension services, for example, governments may incur costs that are higher than the benefits farmers receive.Decentralization,Environmental Economics&Policies,Economic Theory&Research,Health Economics&Finance,Labor Policies,Health Economics&Finance,Banks&Banking Reform,Knowledge Economy,Environmental Economics&Policies,Economic Theory&Research
Politicarum dissertartionum de statu imperiorum, regnorum, principatuum, et rerumpublicarum, ...
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