The Inheritance of Black Poverty: Technical Paper

This report confirms the stark differences in upward earnings mobility for black men compared to both black women and whites. It also confirms that black women, despite their solid earnings mobility, have very low family income mobility. The report then estimates the impact of racial differences in marriage rates by simulating higher marriage rates among black women: like Race and Economic Opportunity in the United States: An Intergenerational Perspective" by Raj Chetty, Nathaniel Hendren, Maggie Jones, and Sonya Porter, we find no significant effects

Growth rates of amenable groups

Let Fm be a free group with m generators and let R be a normal subgroup such that Fm /R projects onto ℤ. We give a lower bound for the growth rate of the group Fm / R′(where R′ is the derived subgroup of R) in terms of the length ρ= ρ(R) of the shortest non-trivial relation in R. It follows that the growth rate of Fm / R′ approaches 2m-1 as ρ approaches infinity. This implies that the growth rate of an m-generated amenable group can be arbitrarily close to the maximum value 2m- 1. This answers an open question of P. de la Harpe. We prove that such groups can be found in the class of abelian-by-nilpotent groups as well as in the class of virtually metabelian group

Modelling food sourcing decisions under climate change: A data-driven approach

Changes in climate conditions are expected to pose signi cant challenges to the food industry, as it is very likely that they will a ect the production of various crops. As a consequence, decisions associated with the sourcing of food items will need to be reconsidered in the years to come. In this paper, we investigate how environmental changes are likely to a ect the suitability and risk of di erent regions |in terms of growing certain food items| and whether companies should adapt their sourcing decisions due to these changes. In particular, we propose a three-stage approach that guides food sourcing decisions by incorporating climate change data. The methodology utilises environmental data from several publicly available databases and models weather uncertainties to calculate the suitability and risk indices associated with growing a crop in a particular geographical area. The estimated suitability and risk parameters are used in a mean-variance analysis to calculate the optimal sourcing decision. Results from a case example indicate that sourcing decisions of popular food items are likely to require signi cant adaptations due to changes to the suitability of certain regions

Nouveautés sur les débits monstrueux de l'Amazone...

Après une première étude sur les variations saisonnières de l'Amazone, Maurice Pardé proposait en 1954 à la communauté hydrologique la valeur de 100000 à 110000 m3/s comme module de ce fleuve géant qui draine un bassin de plus de 6000000 km2. Ce résultat, que certains jugeaient alors excessif, était basé sur les observations de son compatriote Paul Le Cointe, et sur le calcul d'un bilan hydrique rudimentaire, du fait du très petit nombre de données hydroclimatiques disponibles à cette époque. Après les premiers jaugeages de l'Amazone à Obidos par l'USGS en 1963-64, le module de plus puissant fleuve du monde était alors estimé à 170000-190000 m3/s, attestant ainsi que la première estimation de Pardé n'était absolument pas surestimée... Les résultats obtenus dans le cadre du programme HIBAM (Hidrologia de Bacia Amazonica, DNAEE/CNPq-ORSTOM) ont permis de préciser le régime de l'Amazone et de ses principaux tributaires. Les apports des différents sous-bassins et le module de l'Amazone à son embouchure ont pu être estimés avec une assez bonne précision, ce qui a rendu possible la régionalisation des débits annuels. (Résumé d'auteur

Multiexcitons confined within a sub-excitonic volume: Spectroscopic and dynamical signatures of neutral and charged biexcitons in ultrasmall semiconductor nanocrystals

The use of ultrafast gating techniques allows us to resolve both spectrally and temporally the emission from short-lived neutral and negatively charged biexcitons in ultrasmall (sub-10 nm) CdSe nanocrystals (nanocrystal quantum dots). Because of forced overlap of electronic wave functions and reduced dielectric screening, these states are characterized by giant interaction energies of tens (neutral biexcitons) to hundreds (charged biexcitons) of meV. Both types of biexcitons show extremely short lifetimes (from sub-100 picoseconds to sub-picosecond time scales) that rapidly shorten with decreasing nanocrystal size. These ultrafast relaxation dynamics are explained in terms of highly efficient nonradiative Auger recombination.Comment: 5 pages, 4 figures, to be published in Phys. Rev.

Multiple plasmon resonances in naturally-occurring multiwall nanotubes: infrared spectra of chrysotile asbestos

Chrysotile asbestos is formed by densely packed bundles of multiwall hollow nanotubes. Each wall in the nanotubes is a cylindrically wrapped layer of $Mg_3 Si_2 O_5 (OH)_4$. We show by experiment and theory that the infrared spectrum of chrysotile presents multiple plasmon resonances in the Si-O stretching bands. These collective charge excitations are universal features of the nanotubes that are obtained by cylindrically wrapping an anisotropic material. The multiple plasmons can be observed if the width of the resonances is sufficiently small as in chrysotile.Comment: 4 pages, 5 figures. Revtex4 compuscript. Misprint in Eq.(6) correcte

Projected increases in the annual flood pulse of the Western Amazon

The impact of a changing climate on the Amazon basin is a subject of intensive research because of its rich biodiversity and the significant role of rainforests in carbon cycling. Climate change has also a direct hydrological impact, and increasing efforts have focused on understanding the hydrological dynamics at continental and subregional scales, such as the Western Amazon. New projections from the Coupled Model Inter-comparison Project Phase 5 ensemble indicate consistent climatic warming and increasing seasonality of precipitation in the Peruvian Amazon basin. Here we use a distributed land surface model to quantify the potential impact of this change in the climate on the hydrological regime of the upper Amazon river. Using extreme value analysis, historical and future projections of the annual minimum, mean, and maximum river flows are produced for a range of return periods between 1 and 100 yr. We show that the RCP 4.5 and 8.5 scenarios of climate change project an increased severity of the wet season flood pulse (7.5% and 12% increases respectively for the 100 yr return floods). These findings agree with previously projected increases in high extremes under the Special Report on Emissions Scenarios climate projections, and are important to highlight due to the potential consequences on reproductive processes of in-stream species, swamp forest ecology, and socio-economy in the floodplain, amidst a growing literature that more strongly emphasises future droughts and their impact on the viability of the rainforest system over greater Amazonia

Interest of colchicine for the treatment of cystic fibrosis patients. Preliminary report.

Cystic fibrosis (CF) lung disease is characterized by persistent inflammation. Antiinflammatory drugs, such as corticosteroids and ibuprofen, have proved to slow the decline of pulmonary function although their use is limited because of frequent adverse events. We hypothesized that colchicine could be an alternative treatment because of its antiinflammatory properties and upregulatory effect on cystic fibrosis transmembrane regulator (CFTR) closely related proteins. We herein present results obtained in an open study of eight CF children treated with colchicine for at least 6 months. Clinical status was better in all patients and respiratory function tests significantly improved in five. Median duration of antibiotherapy decreased significantly. These preliminary results support our hypothesis of a beneficial effect of colchicine in CF patients and stress the need for a controlled therapeutic trial

Two-vibron bound states in alpha-helix proteins : the interplay between the intramolecular anharmonicity and the strong vibron-phonon coupling

The influence of the intramolecular anharmonicity and the strong vibron-phonon coupling on the two-vibron dynamics in an $\alpha$-helix protein is studied within a modified Davydov model. The intramolecular anharmonicity of each amide-I vibration is considered and the vibron dynamics is described according to the small polaron approach. A unitary transformation is performed to remove the intramolecular anharmonicity and a modified Lang-Firsov transformation is applied to renormalize the vibron-phonon interaction. Then, a mean field procedure is realized to obtain the dressed anharmonic vibron Hamiltonian. It is shown that the anharmonicity modifies the vibron-phonon interaction which results in an enhancement of the dressing effect. In addition, both the anharmonicity and the dressing favor the occurrence of two different bound states which the properties strongly depend on the interplay between the anharmonicity and the dressing. Such a dependence was summarized in a phase diagram which characterizes the number and the nature of the bound states as a function of the relevant parameters of the problem. For a significant anharmonicity, the low frequency bound states describe two vibrons trapped onto the same amide-I vibration whereas the high frequency bound states refer to the trapping of the two vibrons onto nearest neighbor amide-I vibrations.Comment: may 2003 submitted to Phys. Rev.

Magnetoresistance of high mobility HgTe quantum dot films with controlled charging

Funding: We thank Christopher Melnychuk for very useful discussions. This work was supported by the National Natural Science Foundation of China under grant number 62105022, the University of Chicago Materials Research Science and Engineering Center, which was funded by the National Science Foundation under award number DMR1420709, and by the Department of Defense (DOD) Air Force Office of Scientific Research under grant number FA9550-18-1-0099.The magnetoresistance of HgTe quantum dot films, exhibiting a well-defined 1Se state charging and a relatively high mobility (1-10 cm2 V−1 s−1), is measured as a function of temperature down to 10 K and controlled occupation of the first electronic state. There is a positive-quadratic magnetoresistance which can be several 100% at low temperature and scales like x(1 − x) where x is the filling fraction of the lowest quantum dot state in the conduction band, 1Se. This positive magnetoresistance is orders of magnitude larger than the effect estimated from mobile carriers and it is attributed to the increased confinement induced by the magnetic field. There is also a negative magnetoresistance of 1-20% from 300 K to 10 K which is rather independent of the fractional occupation, and which follows a negative exponential dependence with the magnetic field. It can be empirically fit with an effective g-factor of ∼55 and it is tentatively attributed to the reduction of barrier heights by the Zeeman splitting of the 1Se state.Peer reviewe