High-sensitivity tool for studying phonon related mechanical losses in low loss materials

Fundamental mechanical loss mechanisms exist even in very pure materials, for instance, due to the interactions of excited acoustic waves with thermal phonons. A reduction of these losses in a certain frequency range is desired in high precision instruments like gravitational wave detectors. Systematic analyses of the mechanical losses in those low loss materials are essential for this aim, performed in a highly sensitive experimental set-up. Our novel method of mechanical spectroscopy, cryogenic resonant acoustic spectroscopy of bulk materials (CRA spectroscopy), is well suited to systematically determine losses at the resonant frequencies of the samples of less than 10^(-9) in the wide temperature range from 5 to 300 K. A high precision set-up in a specially built cryostat allows contactless excitation and readout of the oscillations of the sample. The experimental set-up and measuring procedure are described. Limitations to our experiment due to external loss mechanisms are analysed. The influence of the suspension system as well as the sample preparation is explained.Comment: 4 pages, 3 figures, proceedings of PHONONS07, submitted to Journal of Physics: Conference Serie

Jahn-Teller effect versus Hund's rule coupling in C60N-

We propose variational states for the ground state and the low-energy collective rotator excitations in negatively charged C60N- ions (N=1...5). The approach includes the linear electron-phonon coupling and the Coulomb interaction on the same level. The electron-phonon coupling is treated within the effective mode approximation (EMA) which yields the linear t_{1u} x H_g Jahn-Teller problem whereas the Coulomb interaction gives rise to Hund's rule coupling for N=2,3,4. The Hamiltonian has accidental SO(3) symmetry which allows an elegant formulation in terms of angular momenta. Trial states are constructed from coherent states and using projection operators onto angular momentum subspaces which results in good variational states for the complete parameter range. The evaluation of the corresponding energies is to a large extent analytical. We use the approach for a detailed analysis of the competition between Jahn-Teller effect and Hund's rule coupling, which determines the spin state for N=2,3,4. We calculate the low-spin/high-spin gap for N=2,3,4 as a function of the Hund's rule coupling constant J. We find that the experimentally measured gaps suggest a coupling constant in the range J=60-80meV. Using a finite value for J, we recalculate the ground state energies of the C60N- ions and find that the Jahn-Teller energy gain is partly counterbalanced by the Hund's rule coupling. In particular, the ground state energies for N=2,3,4 are almost equal

Foraging movements of emperor penguins at Pointe Géologie, Antarctica.

International audienceThe foraging distributions of 20 breeding emperor penguins were investigated at Pointe Ge´ologie, Terre Ade´lie, Antarctica by using satellite telemetry in 2005 and 2006 during early and late winter, as well as during late spring and summer, corresponding to incubation, early chick-brooding, late chick-rearing and the adult pre-moult period, respectively. Dive depth records of three post-egg-laying females, two post-incubating males and four late chick-rearing adults were examined, as well as the horizontal space use by these birds. Foraging ranges of chick-provisioning penguins extended over the Antarctic shelf and were constricted by winter pack-ice. During spring ice break-up, the foraging ranges rarely exceeded the shelf slope, although seawater access was apparently almost unlimited. Winter females appeared constrained in their access to open water but used fissures in the sea ice and expanded their prey search effort by expanding the horizontal search component underwater. Birds in spring however, showed higher area-restricted-search than did birds in winter. Despite different seasonal foraging strategies, chick-rearing penguins exploited similar areas as indicated by both a high ‘Area-Restricted-Search Index' and high ‘Catch Per Unit Effort'. During pre-moult trips, emperor penguins ranged much farther offshore than breeding birds, which argues for particularly profitable oceanic feeding areas which can be exploited when the time constraints imposed by having to return to a central place to provision the chick no longer apply

Composition and distribution of the peracarid crustacean fauna along a latitudinal transect off Victoria Land (Ross Sea, Antarctica) with special emphasis on the Cumacea

The following study was the first to describe composition and structure of the peracarid fauna systematically along a latitudinal transect off Victoria Land (Ross Sea, Antarctica). During the 19th Antarctic expedition of the Italian research vessel “Italica” in February 2004, macrobenthic samples were collected by means of a Rauschert dredge with a mesh size of 500 m at depths between 85 and 515 m. The composition of peracarid crustaceans, especially Cumacea was investigated. Peracarida contributed 63% to the total abundance of the fauna. The peracarid samples were dominated by amphipods (66%), whereas cumaceans were represented with 7%. Previously, only 13 cumacean species were known, now the number of species recorded from the Ross Sea increased to 34. Thus, the cumacean fauna of the Ross Sea, which was regarded as the poorest in terms of species richness, has to be considered as equivalent to that of other high Antarctic areas. Most important cumacean families concerning abundance and species richness were Leuconidae, Nannastacidae, and Diastylidae. Cumacean diversity was lowest at the northernmost area (Cape Adare). At the area off Coulman Island, which is characterized by muddy sediment, diversity was highest. Diversity and species number were higher at the deeper stations and abundance increased with latitude. A review of the bathymetric distribution of the Cumacea from the Ross Sea reveals that most species distribute across the Antarctic continental shelf and slope. So far, only few deep-sea records justify the assumption of a shallow-water–deep-sea relationship in some species of Ross Sea Cumacea, which is discussed from an evolutionary point of view

Quantum sensitivity limit of a Sagnac hybrid interferometer based on slow-light propagation in ultra-cold gases

The light--matter-wave Sagnac interferometer based on ultra-slow light proposed recently in (Phys. Rev. Lett. 92, 253201 (2004)) is analyzed in detail. In particular the effect of confining potentials is examined and it is shown that the ultra-slow light attains a rotational phase shift equivalent to that of a matter wave, if and only if the coherence transfer from light to atoms associated with slow light is associated with a momentum transfer and if an ultra-cold gas in a ring trap is used. The quantum sensitivity limit of the Sagnac interferometer is determined and the minimum detectable rotation rate calculated. It is shown that the slow-light interferometer allows for a significantly higher signal-to-noise ratio as possible in current matter-wave gyroscopes.Comment: 12 pages, 6 figure

Efeito da época de semeadura sobre o estabelecimento dos capins Jaraguá (Hyparrhenia rufa (Ness) Stapf e Green Panic (Panicum maximum Jacq. var. Trichoglume).

Com o objetivo de determinar o período mais favorável ao plantio dos capins jaraguá e green panic, visando gerar informações básicas para um eficiente estabelecimento de pastagens dessas forrageiras, em áreas de cerrado, esta sendo conduzido um estudo de sucessivas épocas de semeaduras no CNPGC, Campo Grande, MS. As semeaduras são feitas de 14 em 14 dias, de setembro a fins de fevereiro. O trabalho foi inicIado em 1978 e devera ser concluido em 1981. A area experimental, que apresenta um solo do tipo Latossolo Roxo Alico textura argilosa, de baixa fertilidade natural e bastante infestado por ervas daninhas, foi preparada em fins de agosto de 1978 com aração e gradagem. Naquela ocasião, foram aplicadas 4 t/ha de calcário dolomitico (com 63% de PRNT) e 1 t/ha de superfosfato simples. A cada época de plantio, e efetuado um novo preparo do solo para uniformização da área de eliminação de invasoras. As taxas de semeaduras utilizadas, em sementes viáveis, são de 6 kg/ha para o green panic e 15 kg/ha para o jaraguá.bitstream/item/137409/1/PESQ-EM-ANDAMENTO-11.pd

Efeito da época de semeadura sobre o estabelecimento do capim Marangá (Setaria anceps Stapf cv. Kazungula) em três consorciações com as leguminosas Centrosema (Centrosema pubescens Benth.), Siratro (Macroptilium atropurpureum (D.C.) Urb.) e Estilosantes (Stylosanthes capitata Vog.

A fim de se determinar o período mais favorável ao plantio de consorciação do capim marangá com as leguminosas centrosema, siratro e estilosantes, visando-se gerar informações básicas para um eficiente estabelecimento de pastagens consorciadas em áreas de Cerrado, está sendo conduzido um estudo de sucessivas épocas de semeaduras no CNPGC, Campo Grande,MS. As semeaduras são efetuadas com intervalos de 14 em 14 dias, de setembro a fins de fevereiro. O estudo foi iniciado em 1978 e devera ser concluído em 1981. A área experimental, que apresenta um solo do tipo Latossolo Roxo Alico textura argilosa, de baixa fertilidade natural e bastante infestado por ervas invasoras, foi preparado em fins de agosto de 1978 com aração e gradagem. Naquela ocasião, foram aplicadas 4 t/ha de superfosfato simples. A cada época de plantio, foi efetuado um novo preparo do solo para uniformização da área e eliminação de invasoras. As taxas de semeadura utilizadas, em sementes viáveis, foram de 3 kg/ha para o capim maranga, 4 kg/ha para centrosema, 3 kg/ha para siratro e 1 kg/ha para estilosantes, sendo as sementes das leguminosas escarificadas e inoculadas com rhizobium especifico a cada plantio

Arbitrarily large families of spaces of the same volume

In any connected non-compact semi-simple Lie group without factors locally isomorphic to SL_2(R), there can be only finitely many lattices (up to isomorphism) of a given covolume. We show that there exist arbitrarily large families of pairwise non-isomorphic arithmetic lattices of the same covolume. We construct these lattices with the help of Bruhat-Tits theory, using Prasad's volume formula to control their covolumes.Comment: 9 pages. Syntax corrected; one reference adde

Benefit-cost methodology study with example application of the use of wind generators

An example application for cost-benefit methodology is presented for the use of wind generators. The approach adopted for the example application consisted of the following activities: (1) surveying of the available wind data and wind power system information, (2) developing models which quantitatively described wind distributions, wind power systems, and cost-benefit differences between conventional systems and wind power systems, and (3) applying the cost-benefit methodology to compare a conventional electrical energy generation system with systems which included wind power generators. Wind speed distribution data were obtained from sites throughout the contiguous United States and were used to compute plant factor contours shown on an annual and seasonal basis. Plant factor values (ratio of average output power to rated power) are found to be as high as 0.6 (on an annual average basis) in portions of the central U. S. and in sections of the New England coastal area. Two types of wind power systems were selected for the application of the cost-benefit methodology. A cost-benefit model was designed and implemented on a computer to establish a practical tool for studying the relative costs and benefits of wind power systems under a variety of conditions and to efficiently and effectively perform associated sensitivity analyses

Consorciação de pastagem de Brachiaria decumbens Stapf v. Australiana, com leguminosas plantadas em faixas e sob condições de pastejo.

As pastagens de Brachiaria decumbens apos alguns anos de utilização podem apresentar um decréscimo na produção de matéria seca (MS) resultando em menor capacidade de suporte. Visando solucionar esse problema foi estabelecido um experimento com o objetivo de se manter ou elevar a produtividade de pastagens de B. decumbens pela introdução de leguminosas. As leguminosas foram estabelecidas em faixas onde estão sendo feitas avaliações de persistência das mesmas.bitstream/item/137377/1/PESQ-EM-ANDAMENTO-07.pd