1,297 research outputs found
Topological Insulators
Topological insulators are electronic materials that have a bulk band gap
like an ordinary insulator, but have protected conducting states on their edge
or surface. The 2D topological insulator is a quantum spin Hall insulator,
which is a close cousin of the integer quantum Hall state. A 3D topological
insulator supports novel spin polarized 2D Dirac fermions on its surface. In
this Colloquium article we will review the theoretical foundation for these
electronic states and describe recent experiments in which their signatures
have been observed. We will describe transport experiments on HgCdTe quantum
wells that demonstrate the existence of the edge states predicted for the
quantum spin Hall insulator. We will then discuss experiments on Bi_{1-x}Sb_x,
Bi_2 Se_3, Bi_2 Te_3 and Sb_2 Te_3 that establish these materials as 3D
topological insulators and directly probe the topology of their surface states.
We will then describe exotic states that can occur at the surface of a 3D
topological insulator due to an induced energy gap. A magnetic gap leads to a
novel quantum Hall state that gives rise to a topological magnetoelectric
effect. A superconducting energy gap leads to a state that supports Majorana
fermions, and may provide a new venue for realizing proposals for topological
quantum computation. We will close by discussing prospects for observing these
exotic states, a well as other potential device applications of topological
insulators.Comment: 23 pages, 20 figures, Published versio
Radio Astronomy
Contains reports on five research projects.National Aeronautics and Space Administration (Grant NsG-419)Joint Services Electronics Program (Contract DA36-039-AMC-03200(E)
Influence de la teneur en ciment sur les propriĂ©tĂ©s thermomĂ©caniques des blocs dâargile comprimĂ©e et stabilisĂ©e
Ce travail vise Ă dĂ©terminer la rĂ©sistance Ă la compression et la conductivitĂ© thermique des blocs Ă base dâargile comprimĂ©e et stabilisĂ©e au ciment dâune part et Ă Ă©tudier la variation de ces propriĂ©tĂ©s en fonction de la teneur en ciment dâautre part. Les mesures rĂ©alisĂ©es indiquent que la rĂ©sistance des blocs sans ciment est de 3,7 MPa par « voie sĂšche » pour une conductivitĂ© thermique de 0,91 Wm-1K-1 (dĂ©terminĂ©e Ă lâaide dâun fluxmĂštre). Lâincorporation de ciment entraine une variation de ces deux propriĂ©tĂ©s. Ainsi on note dâabord une baisse de la rĂ©sistance suivie dâune augmentation au delĂ de 4% de ciment. Toutefois la conductivitĂ© thermique des blocs ayant les teneurs en ciment les plus importantes reste proche de celle des blocs sans ciment.Mots-clĂ©s: bloc dâargile, ciment portland, stabilisation, rĂ©sistance en compression, conductivitĂ© thermique. Influence of cement content on the thermomechanical properties of compressed and stabilized clay blocks This work aims to determine the compressive strength and the thermal conductivity of clay compressed blocks and stabilized with cement and to study the influence of the cement ratio on these characteristics of the blocks. The resistance of blocks without cement is (determined at dry state) is 3.7 MPa and measurements made with a fluxmeter show that the thermal conductivity of these blocks is 0,91 Wm-1 K-1. The results show also that the thermal conductivity and the compressive strength of the blocks vary according to the cement ratio. However the thermal conductivity of the blocks with high cement ratio is close to that of the blocks without cement.Keywords: clay blocks, Portland cement, stabilization, compressive strength, thermal conductivity
A new host for a new Rossomyrmex minuchae population
Social parasites usually rely on chemical cues (cuticular hydrocarbons) to successfully invade and coexist with their hosts. Most ants that are obligate social parasites (slave-makers) can parasitize several related host species with different levels of chemical similarity although there are few exceptions where there is only a single host species. An example of the latter is Rossomyrmex minuchae, which was known to be only associated with Proformica longiseta. However, a recent discovery of a new R. minuchae population revealed that it can parasitize P. nasuta, a species with a separate distribution to P. longiseta. Chemical analyses of cuticular hydrocarbons show local adaptation of the parasite to its host in this new population, being more similar to P. nasuta than to other R. minuchae populations. In addition, genetic analyses evidence differences from the other known populations, from which it split 1.21 Mya during glacial and interglacial periods of the Pleistocene and remained separated to the present day. This historical genetic isolation and the chemical differences found between parasite populations may evidence a speciation process and support the local hostâparasite coevolutionM Silvestre and FM AzcĂĄrate received administrative and fnancial support from the Spanish Ministry of Economy and Competitiveness (Project CGL2014-53789-R). Sierra de Guadarrama National Park provided the permits for the sampling (ref 10/101642.9/16). This work was also partially funded by the University of JaĂ©n through the âPlan Operativo de Apoyo a la InvestigaciĂłn 2021-2022
Drosophila Condensin II subunit Chromosome-associated protein D3 regulates cell fate determination through non-cell-autonomous signaling
Citation: Klebanow, L. R., Peshel, E. C., Schuster, A. T., De, K., Sarvepalli, K., Lemieux, M. E., . . . Longworth, M. S. (2016). Drosophila Condensin II subunit Chromosome-associated protein D3 regulates cell fate determination through non-cell-autonomous signaling. Development, 143(15), 2791-2802. doi:10.1242/dev.133686The pattern of the Drosophila melanogaster adult wing is heavily influenced by the expression of proteins that dictate cell fate decisions between intervein and vein during development. dSRF (Blistered) expression in specific regions of the larval wing disc promotes intervein cell fate, whereas EGFR activity promotes vein cell fate. Here, we report that the chromatin-organizing protein CAP-D3 acts to dampen dSRF levels at the anterior/posterior boundary in the larval wing disc, promoting differentiation of cells into the anterior crossvein. CAP-D3 represses KNOT expression in cells immediately adjacent to the anterior/posterior boundary, thus blocking KNOT-mediated repression of EGFR activity and preventing cell death. Maintenance of EGFR activity in these cells depresses dSRF levels in the neighboring anterior crossvein progenitor cells, allowing them to differentiate into vein cells. These findings uncover a novel transcriptional regulatory network influencing Drosophila wing vein development, and are the first to identify a Condensin II subunit as an important regulator of EGFR activity and cell fate determination in vivo
Radio Astronomy
Contains reports on five research projects.National Aeronautics and Space Administration (Grant NsG-419)National Aeronautics and Space Administration (Contract NSR-22-009-120)Lincoln Laboratory Purchase Order No. 74
Radio Astronomy
Contains research objectives and reports on six research projects.National Aeronautics and Space Administration (Contract NSR-22-009-120)National Aeronautics and Space Administration (Grant NsG-419)Joint Services Electronics Programs (U. S. Army, U.S. Navy, and U.S. Air Force) under Contract DA 36-039-AMC-03200(E
The Chemistry of the Postpharyngeal Gland of Female European Beewolves
Females of the European beewolf, Philanthus triangulum, possess a large glove-shaped gland in the head, the postpharyngeal gland (PPG). They apply the content of the PPG to their prey, paralyzed honeybees, where it delays fungal infestation. Here, we describe the chemical composition of the gland by using combined GC-MS, GC-FTIR, and derivatization. The PPG of beewolves contains mainly long-chain unsaturated hydrocarbons (C23âC33), lower amounts of saturated hydrocarbons (C14âC33), and minor amounts of methyl-branched hydrocarbons (C17âC31). Additionally, the hexane-soluble gland content is comprised of small amounts of an unsaturated C25 alcohol, an unknown sesquiterpene, an octadecenylmethylester, and several long-chain saturated (C25, C27) and unsaturated (C23âC27) ketones, some of which have not yet been reported as natural products. Surprisingly, we found a dimorphism with regard to the major component of the PPG with some females having (Z)-9-pentacosene, whereas others have (Z)-9-heptacosene as their predominant component. The biological relevance of the compounds for the prevention of fungal growth on the prey and the significance of the chemical dimorphism are discussed
Online Monitoring of the Osiris Reactor with the Nucifer Neutrino Detector
Originally designed as a new nuclear reactor monitoring device, the Nucifer
detector has successfully detected its first neutrinos. We provide the second
shortest baseline measurement of the reactor neutrino flux. The detection of
electron antineutrinos emitted in the decay chains of the fission products,
combined with reactor core simulations, provides an new tool to assess both the
thermal power and the fissile content of the whole nuclear core and could be
used by the Inter- national Agency for Atomic Energy (IAEA) to enhance the
Safeguards of civil nuclear reactors. Deployed at only 7.2m away from the
compact Osiris research reactor core (70MW) operating at the Saclay research
centre of the French Alternative Energies and Atomic Energy Commission (CEA),
the experiment also exhibits a well-suited configuration to search for a new
short baseline oscillation. We report the first results of the Nucifer
experiment, describing the performances of the 0.85m3 detector remotely
operating at a shallow depth equivalent to 12m of water and under intense
background radiation conditions. Based on 145 (106) days of data with reactor
ON (OFF), leading to the detection of an estimated 40760 electron
antineutrinos, the mean number of detected antineutrinos is 281 +- 7(stat) +-
18(syst) electron antineutrinos/day, in agreement with the prediction 277(23)
electron antineutrinos/day. Due the the large background no conclusive results
on the existence of light sterile neutrinos could be derived, however. As a
first societal application we quantify how antineutrinos could be used for the
Plutonium Management and Disposition Agreement.Comment: 22 pages, 16 figures - Version
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