Evidence of several dipolar quasi-invariants in Liquid Crystals

In a closed quantum system of N coupled spins with magnetic quantum number I, there are about (2I + 1)^N constants of motion. However, the possibility of observing such quasi-invariant (QI) states in solid-like spin systems in Nuclear Magnetic Resonance (NMR) is not a strictly exact prediction. The aim of this work is to provide experimental evidence of several QI, in the proton NMR of small spin clusters, besides those already known Zeeman, and dipolar orders (strong and weak). We explore the spin states prepared with the Jeener-Broekaert pulse sequence by analyzing the time-domain signals yielded by this sequence as a function of the preparation times, in a variety of dipolar networks. We observe that the signals can be explained with two dipolar QIs only within a range of short preparation times. At longer times the time-domain signals have an echo-like behaviour. We study their multiple quantum coherence content on a basis orthogonal to the z-basis and see that such states involve a significant number of correlated spins. Then we show that the whole preparation time-scale can only be reconstructed by assuming the occurrence of multiple QI which we isolate experimentally

Quasi-equilibrium states in thermotropic liquid crystals studied by multiple quantum NMR

We study the nature of the quasiinvariants in nematic 5CB and measure their relaxation times by encoding the multiple quantum coherences of the states following the JB pulse pair on two orthogonal bases, Z and X. The experiments were also performed in powder adamantane at 301 K which is used as a reference compound having only one dipolar quasiinvariant. We show that the evolution of the quantum states during the build up of the quasi-equilibrium state in 5CB prepared under the S condition is similar to the case of adamantane and that their quasi-equilibrium density operators have the same tensor structure. In contrast, the second constant of motion, whose explicit operator form is not known, involves a richer composition of multiple quantum coherences on the X basis of even order, in consistency with the truncation inherent in its definition. We exploited the exclusive presence coherences 4, 6, 8, besides 0 and 2 under the W condition to measure the spin-lattice relaxation time T_{W} accurately, so avoiding experimental difficulties that usually impair dipolar order relaxation measurement such as Zeeman contamination at high fields, and also superposition of the different quasiinvariants. This procedure opens the possibility of measuring the spin-lattice relaxation of a quasiinvariant independent of the Zeeman and S reservoirs, so incorporating a new relaxation parameter useful for studying the complex molecular dynamics in mesophases. In fact, we report the first measurement of T_{W} in a liquid crystal at high magnetic fields. The comparison of the obtained value with the one corresponding to a lower field (16 MHz) points out that the relaxation of the W-order strongly depends on the intensity of the external magnetic field, similarly to the case of the S reservoir, indicating that the relaxation of the W-quasiinvariant is also governed by the cooperative molecular motions.Comment: 7 figures. http://www.famaf.unc.edu.ar/series/AFis2005.ht

State-insensitive trapping of Rb atoms: linearly versus circularly polarized lights

We study the cancellation of differential ac Stark shifts in the 5s and 5p states of rubidium atom using the linearly and circularly polarized lights by calculating their dynamic polarizabilities. Matrix elements were calculated using a relativistic coupled-cluster method at the single, double and important valence triple excitations approximation including all possible non-linear correlation terms. Some of the important matrix elements were further optimized using the experimental results available for the lifetimes and static polarizabilities of atomic states. "Magic wavelengths" are determined from the differential Stark shifts and results for the linearly polarized light are compared with the previously available results. Possible scope of facilitating state-insensitive optical trapping schemes using the magic wavelengths for circularly polarized light are discussed. Using the optimized matrix elements, the lifetimes of the 4d and 6s states of this atom are ameliorated.Comment: 13 pages, 13 tables and 4 figure

Reading ecosystem services at the local scale through a territorial approach: The case of peri-urban agriculture in the thau Lagoon, Southern France

© 2015 by the author(s). In recent years, the ecosystem services (ES) concept has become a major paradigm for natural resource management. While policy-makers demand “hard” monetary evidence that nature conservation would be worth investing in, ongoing attempts are being made to formalize the concept as a scientifically robust “one size fits all” analytical framework. These attempts have highlighted several major limitations of the ES concept. First, to date, the concept has paid little attention to the role of humans in the production of ES. Second, the ongoing formalization of the ES concept is turning it into a “technology of globalization,” thereby increasingly ignoring the socio-cultural context and history within which ecosystems emerge. Third, economic valuation has been shown to limit local stakeholders in expressing their daily and immediate ways of interacting with their environment over and beyond extrinsic motivation provided by financial gains. We address these three limitations by analyzing a social evaluation of the roles of peri-urban farmland from a territorial perspective. Our case study is the Thau lagoon in southern France. We conducted in-depth interviews with a broad range of stakeholders and ran two participatory workshops. Using a territorial meta-model that distinguishes three levels— physical, logical, and existential—stakeholder data were analyzed to unravel the interplay of territorial elements at these three levels that gives rise to ES in two broad categories: food production and aesthetic landscape. The coupling of ES and territory concepts opens up several novel analytical perspectives. It allows partitioning of ES in a manner that “re-contextualizes” them and gives insight about both their physical constituents and their meaning at the territorial level. Additional research should incorporate the dynamics of service demand and supply, and further investigate options for implementation

Zentrale Resultate der Gesamtevaluation familienbezogener Leistungen

Mit der von der Bundesregierung in Auftrag gegebenen Gesamtevaluation ehe- und familienbezogener Leistungen wurden erstmals zentrale Instrumente der deutschen Familienpolitik systematisch und umfassend evaluiert. Dabei wurden folgende familienpolitische Ziele vorgegeben: die Sicherung der wirtschaftlichen Stabilität der Familien, die bessere Vereinbarkeit von Familie und Beruf, die frühe Förderung von Kindern, die Erfüllung von Kinderwünschen und der Nachteilsausgleich zwischen den Familien. Die Gesamtschau der Ergebnisse der Evaluationsstudien des DIW Berlin, ifo und ZEW zeigt, dass primär eine Maßnahme heraussticht, mit der keine familienpolitischen Zielkonflikte verbunden sind. Dies ist die öffentliche Finanzierung der Kindertagesbetreuung. In sie sollte weiter investiert werden - die bisherige Elternbeteiligung sollte zunächst beibehalten und für Verbesserungen der Qualität verwandt werden. Auch das Elterngeld verursacht kaum Zielkonflikte und sollte so weiterentwickelt werden, dass es mehr Anreize für eine partnerschaftliche Arbeitsteilung setzt. Finanzieller Spielraum könnte durch eine Reform des Ehegattensplittings hin zu einem gedeckelten Realsplitting gewonnen werden. Aufgrund relativ schwacher Effekte des Kindergeldes auf die analysierten Ziele sollte von einer Erhöhung dieser Leistung abgesehen werden.Commissioned by the Federal Government, the Overall Evaluation of Benefit Payments to Married Couples and Families is the first study to systematically and comprehensively evaluate the key instruments of German family policy. The evaluation focused on the following family-policy goals: securing families' financial stability, better reconciliation of family and career, early support for children, fulfilling the desire to have children, and compensating for inequalities between families. Viewed as a whole, the findings of the evaluation studies conducted by the DIW Berlin, ifo, and ZEW primarily show that one measure stands out as not having any conflicting family-policy objectives - namely public funding of daycare for children. There should be further investment in this measure - current parent participation should be retained initially and used to improve quality. The parental leave benefit (Elterngeld) also cause hardly any goal conflicts and should be developed further in order to provide greater incentives for fair division of labor between the partners. A reform of income splitting within the income tax for married couples toward limited real income splitting (Realsplitting) could help generate more financial scope. Since child benefit has relatively weak effects on the goals analyzed, it should not be increased

Two-Photon Doppler cooling of alkaline-earth-metal and ytterbium atoms

A new possibility of laser cooling of alkaline-earth-metal and Ytterbium atoms using a two-photon transition is analyzed. We consider a $^{1}S_{0}$ - $^{1}S_{0}$ transition, with excitation in near resonance with the $^{1}P_{1}$ level. This greatly increases the two-photon transition rate, allowing an effective transfer of momentum. The experimental implementation of this technique is discussed and we show that for Calcium, for example, two-photon cooling can be used to achieve a Doppler limit of 123 microKelvin. The efficiency of this cooling scheme and the main loss mechanisms are analyzed.Comment: 7 pages, 5 figure

Information sharing and credit : firm-level evidence from transition countries

We investigate whether information sharing among banks has affected credit market performance in the transition countries of Eastern Europe and the former Soviet Union, using a large sample of firm-level data. Our estimates show that information sharing is associated with improved availability and lower cost of credit to firms. This correlation is stronger for opaque firms than transparent ones and stronger in countries with weak legal environments than in those with strong legal environments. In cross-sectional estimates, we control for variation in country-level aggregate variables that may affect credit, by examining the differential impact of information sharing across firm types. In panel estimates, we also control for the presence of unobserved heterogeneity at the firm level, as well as for changes in macroeconomic variables and the legal environment

Projectile Δ\Delta and target-Roper excitation in the p (d, d')X reaction

In this paper we compare a model that contains the mechanisms of $\Delta$ excitation in the projectile and Roper excitation in the target with experimental data from two (d, d') experiments on a proton target. The agreement of the theory with the experiment is fair for the data taken at T_d = 2.3 GeV. The $\Delta$ excitation in the projectile is predicted close to the observed energy with the correct width. The theory, however, underpredicts by about 40% the cross sections measured at T_d = 1.6 GeV at angles where the cross section has fallen by about two orders of magnitude. The analysis done here allows to extract an approximate strength for the excitation of the Roper [N^*(1440)] excitation and a qualitative agreement with the theoretical predictions is also found.Comment: 8 ps figure