284 research outputs found
Analyse du CeCoIn5 sous implantion dâatomes dâhĂ©liums afin de conduire le systĂšme supraconducteur vers lâordre antiferromagnĂ©tique par pression nĂ©gative
La supraconductivitĂ© dans la famille des composĂ©s de type fermions lourds tel le CeCoIn5 se dĂ©veloppe Ă proximitĂ© dâune instabilitĂ© antiferromagnĂ©tique. La proximitĂ© de cette instabi- litĂ© indique un point quantique critique (anglais pour âquantum critical pointâ QCP) entre la phase antiferromagnĂ©tique et un liquide de Fermi. Ă ce point, les deux Ă©tats fondamentaux du systĂšme sont en compĂ©tition et peuvent ĂȘtre perturbĂ©s par une variation de la pression ou de la composition chimique. Dans cette proposition, nous Ă©tudions la rĂ©ciprocitĂ© entre les deux mĂ©thodes de perturbation du point quantique critique. Pour ce faire, on change la composition chimique du CeCoIn5 en dopant le cristal avec des atomes dâytterbium qui prennent la place du cĂ©rium dans la structure.
La substitution de certains atomes de cĂ©rium par de lâytterbium est Ă©quivalent Ă©lectroniquement Ă enlever un Ă©lectron de la couche 4f car lâytterbium est bivalent dans la structure CeCoIn5 . Ainsi, on dĂ©truit des moments magnĂ©- tiques dans le rĂ©seau fortement corrĂ©lĂ© de centres de Kondo et pousse le matĂ©riau vers la phase antiferromagnĂ©tique. Dans la mĂȘme optique, on utilise un accĂ©lĂ©rateur de particules pour implanter des atomes dâhĂ©lium dans la maille du cristal. Les atomes dâhĂ©lium agissent comme une source de pression nĂ©gative qui dilatent le rĂ©seau et rĂ©duisent la cohĂ©rence entre certaines quasi-particules de Kondo. On propose alors que cette implantation pourrait induire lâordre antiferromagnĂ©tique puisquâelle favorise lâinteraction magnĂ©tique longue portĂ©e. Dans un premier ordre, on a dopĂ© les Ă©chantillons de CeCoIn5 dopĂ© Ă l'Yb avec une concentration de 5%, 10% et 15%.
Tel quâattendu, suite aux mesures de la chaleur spĂ©cifique en fonction de la tempĂ©rature, on sâaperçoit que la valeur de la tempĂ©rature de transition de phase supraconductrice diminue lorsquâon augmente le dopage dans le monocristal. On montre ainsi la dĂ©pendance entre la concentration de dopant dans le cristal et la destruction inhomogĂšne de lâĂ©tat corrĂ©lĂ©. Lorsquâon remplace des Ă©lectrons de lâorbitale 4f par des trous de cette bande, on dĂ©truit la cohĂ©rence entre les centres de Kondo qui induit la supraconductivitĂ©. Cette variation chimique peut ĂȘtre utilisĂ©e comme un paramĂštre de rĂ©glage qui favorise le rĂ©gime de lâinteraction magnĂ©tique prĂšs du QCP. Similairement, suite Ă une implantation dâatomes dâhĂ©lium de 0.1%, 0.5% et 1% des mailles dans les premiers 15 micromĂštre de CeCoIn5 , on constate que la dilatation du rĂ©seau rĂ©duit linĂ©airement lâintĂ©raction globale du rĂ©gime fortement corrĂ©lĂ© entre les singulets de Kondo. Cependant, la cohĂ©rence entre les centres de Kondo est plus difficile Ă obtenir, ce qui diminue la tempĂ©rature critique (Tc) de la transition de phase supraconductrice. On associe cette diminution de Tc proche dâun QCP Ă la suppression inhomogĂšne du rĂ©gime liquide de Fermi. Alors, lâapplication dâune pression nĂ©gative par implantation dâhĂ©lium est considĂ©rĂ©e comme un paramĂštre de rĂ©glage qui avantage lâinteraction magnĂ©tique longue portĂ©e et conduit le cristal vers lâordre AFM.Superconductivity in the family of heavy fermion compounds such as CeCoIn5 develops near an antiferromagnetic instability. The proximity of this instability indicates a quantum critical point (QCP) between the antiferromagnetic phase and a Fermi liquid ground state. At such a point, the two ground states of the system are in competition and applying pressure or changeing the chemical composition moves the system away from the QCP. In this work, we study the reciprocity between the two methods of perturbation of the QCP. In this sense, the chemical composition of the CeCoIn5 is changed by doping the system with ytterbium atoms, which replace the cerium. The substitution of cerium which is trivalent and carries a magnetic moment atoms by the bivalent ytterbium is electronically and non-magnetic electron of the shell 4f by a hole of the same orbital and removing a magnetic moment. Thus, we destroy magnetic moments causing the Kondo coherence and push the material towards the antiferromagnetic phase. In the same vein, an accelerator is used to implant helium atoms in the lattice of the crystal. Helium atoms act as a source of negative pressure which expands the lattice and which destroys the coherence between certain Kondo singlets. It is then proposed that this implantation should eventually induce antiferromagnetic order since this is favoring the long-range magnetic interaction.
First, Ce1âxYbxCoIn5 samples were doped with an Yb concentration of x = 5%, 10% and 15%. As expected, following the measurements of the specific heat as a function of temperature, it is found that the value of the temperature of the superconducting phase transition (Tc) decreases when the level of doping increases in the single crystal. Thus, we conclude that the more electrons in the 4f orbital are replaced by holes of this band, the more we destroy the coherence between the Kondo center which induces superconductivity We also show that this inhomogeneous destruction of the correlated state is linear with the concentration of induced holes in the crystal. we conclude that the more electrons in the 4f orbital are replaced by holes of this band, the more we destroy the coherence between the Kondo center which induces superconductivity. In this sense, this chemical variation used as a tunning parameter favors the magnetic state near the QCP.
Similarly, following a helium atom implantation of 0.1%, 0.5% and 1% of the lattices in the first 15 ÎŒm of CeCoIn5 , we find that lattice expansion linearly decreases the correlation between Kondo singlets. Thus, the coherence between Kondo centers is more difficult to achieve, which decreases the critical temperature (Tc) towards the superconducting phase transition. This linear decrease of Tc close to a QCP is associated to the suppression of the Fermi liquid regime and thus is expected to lea the crystal to the AFM order. Then, the application of a negative pressure by helium implantation can be considered as a tunning parameter which benefits the long-range magnetic interactio
Evidence for 3d bosonization from monopole operators
We give evidence for 3d bosonization in Conformal Field Theories (CFTs) by
computing monopole operator scaling dimensions in 2+1 dimensional quantum
electrodynamics (QED3) with Chern-Simons level and complex bosons in a
large expansion. We first consider the case, where we show that
scaling dimensions previously computed to subleading order in can be
extrapolated to and matched to Wilson-Fisher CFT scaling
dimensions with around 5\% error, which is evidence for particle-vortex
duality. We then generalize the subleading calculation to large and fixed
, extrapolate to , and consider monopole operators that are
conjectured to be dual to non-degenerate scalar operators in a theory of a
single Dirac fermion. We find matches typically with 1\% error or less, which
is strong evidence of this so-called `seed' duality that implies a web of 3d
bosonization dualities among CFTs.Comment: 4 pages plus appendices, no figures. v2 minor typos corrected,
submitted for publicatio
Flexible silicon photonic transmitter with segmented modulator and 32 nm CMOS driver IC
ConferenciaWe present a novel silicon photonic transmitter including 90nm CMOS segmented
modulator co-packaged with low power 32nm CMOS driver IC. Optical equalization is
demonstrated for the first time with the multi-segment Mach-Zehnder modulator at 22Gb/s.
OCIS codes: (130.4110) Modulator; (250.3140) Integrated optoelectronic circuits
Flexible transmitter employing Silicon-segmented Machâzehnder modulator with 32-nm CMOS distributed driver
ArtĂculo cientĂficoWe propose a flexible optical transmitter for shortreach optical interconnects that includes a silicon photonic segmented Mach-Zehnder modulator (MZM) driven by a distributed six-channel 32nm SOI CMOS driver integrated circuit. Optical equalization is demonstrated to extend the bandwidth limitation of the transmitter with NRZ signaling at 25Gb/s. We also generate four-level pulse amplitude modulation (PAM-4) signaling using the same transmitter architecture. Transmission of 46Gb/s PAM-4 signal with bit error rate (BER) well below hard-decision forward error correction limit (BER=3.8Ă10-3) is experimentally demonstrated. Low driver power consumption of 130 mW at 46Gb/s PAM-4, corresponding to 2.8 pJ/bit power efficiency, is also achieved
Pharaonic necrostratigraphy : a review of geological and archaeological studies in the Theban Necropolis, Luxor, West Bank, Egypt
Author Posting. © The Author(s), 2009. This is the author's version of the work. It is posted here by permission of John Wiley & Sons for personal use, not for redistribution. The definitive version was published in Terra Nova 21 (2009): 237-256, doi:10.1111/j.1365-3121.2009.00872.x.We present a review of archeological and geological studies on the West Bank as a basis
for discussing the geological setting of the tombs and geologically related problems with a view
to providing archeologists with a framework in which to conduct their investigations on the
restoration, preservation and management of the antique monuments. Whereas the geology of
the Upper Nile Valley appears to be deceptively simple, the lithologic succession is vertically
variable, and we have recognized and defined several new lithologic units within the upper Esna
Shale Formation. We have been able to delineate lithologic (shale/limestone) contacts in several
tombs and observed that the main chambers in some were excavated below the Esna Shale in the
Tarawan Chalk Formation. We have been able to document changing dip in the strata (warping)
in several tombs, and to delineate two major orientations of fractures in the field. Investigations
behind the Temple of Hatshepsut, in the Valley of the Kings and around Deir El Medina, have
revealed four broad regional structures. We confirm that the hills located near the Nile Valley,
such as Sheik Abel Qurna, do not belong to the tabular structure of the Theban Mountain, but
are discrete displaced blocks of the Thebes Limestone and overlying El Miniya, as supported by
Google Earth photographs
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The Paleocene/Eocene boundary Global Standard Stratotype-section and Point (GSSP): Criteria for Characterisation and Correlation
The choice of a Paleocene/Eocene (P/E) Global Standard Stratotype-section and Point (GSSP) is complicated by the fact that there exists confusion on the exact denotation of the Paleocene and Eocene Series and their constituent lower rank (stage) units. While we can now resolve this problem by recourse to rigorous historical analysis, actual placement of the GSSP is further exacerbated by an embarrassment of riches (in regards to 7 criteria suitable for characterising and correlating a PIE GSSP but which span a temporal interval of greater than 2 my).
Following the precept that the boundaries between higher level chronostratigraphic units are to be founded upon the boundaries of their lowest constituent stages in a nested hierarchy, we note that one of the criteria providing global correlation potential (a stable isotope excursion in marine and terrestrial stratigraphies) lies at a stratigraphic level more than !my older than the base of the stratotypic Ypresian Stage to which the base of the Eocene Series has been subordinated until now. Lowering a chronostratigraphic unit by this extent risks a significant modification to the original geohistorical denotation of the Ypresian Stage and the Eocene Series.
We discuss here four options that are open to Voting Members of the Paleogene Subcommission. One solution consists in adjusting slightly the base of the Ypresian Stage (and, thus, the Eocene Series) so as to be correlatable on the basis of the lowest occurrence/First Appearance Datum (LO/FAD) of the calcareous nannofossil species Tribrachiatus.digitalis. Another solution would be to decouple series and stages so that the Ypresian Stage remains essentially unaltered but the base of tbe Eocene is relocated so as to be correlated on the basis of the Carbon Isotope Excursion (CIE).
Two (compromise) solutions consist in erecting a new stage for the upper/terminal Paleocene (between the Thanetian [sensu Dollfus] and Ypresian Stages) characterised at its base by the global stable isotope excursion. The P/E GSSP may then be placed at the base of the stratotypic Ypresian Stage (thus preserving historical continuity and conceptual denotation and stability) or at the base of the newly erected stage (facilitating correlation of the base of the Eocene series, at least in principle). Both GSSPs should be placed in suitable marine stratigraphic sections yet to be determined but upon which there is considerable current investigative activity
The Dababiya corehole, Upper Nile Valley, Egypt : preliminary results
Author Posting. © Austrian Geological Society, 2012. This article is posted here by permission of Austrian Geological Society for personal use, not for redistribution. The definitive version was published in Austrian Journal of Earth Sciences 105, no. 1 (2012): 161-168.The Dababiya corehole was drilled in the Dababiya Quarry (Upper Nile Valley, Egypt), adjacent to the GSSP for the Paleocene/
Eocene boundary, to a total depth of 140 m and bottomed in the lower Maastrichtian Globotruncana aegyptiaca Zone of the Dakhla
Shale Formation. Preliminary integrated studies on calcareous plankton (foraminifera, nannoplankton), benthic foraminifera, dinoflagellates,
ammonites, geochemistry, clay mineralogy and geophysical logging indicate that: 1) The K/P boundary lies between
80.4 and 80.2 m, the Danian/Selandian boundary between ~ 41 and 43 m, the Selandian/Thanetian boundary at ~ 30 m (within the
mid-part of the Tarawan Chalk) and the Paleocene/Eocene boundary at 11.75 m (base [planktonic foraminifera] Zone E1 and [calcareous
nannoplankton] Zone NP9b); 2) the Dababiya Quarry Member (=Paleocene/Eocene Thermal Maximum interval) extends
from 11.75 to 9.5 m, which is ~1 m less than in the adjacent GSSP outcrop.; 3) the Late Cretaceous (Maastrichtian) depositional
environment was nearshore, tropical-sub tropical and nutrient rich; the latest Maastrichtian somewhat more restricted (coastal); and
the early Danian cooler, low(er) salinity with increasing warmth and depth of water (i.e., more open water); 4) the Paleocene is further
characterized by outer shelf (~ 200 m), warm water environments as supported by foraminifera P/B ratios > 85% (~79-28 m),
whereas benthic foraminifera dominate (>70%) from ~27-12 m (Tarawan Chalk and Hanadi Member) due, perhaps, in part to increased
dissolution (as observed in nearby outcrop samples over this interval); 5) during the PETM, enhanced hydrodynamic conditions
are inferred to have occurred on the sea-floor with increased river discharge (in agreement with sedimentologic evidence),
itself a likely cause for very high enhanced biological productivity on the epicontinental shelf of Egypt; 6) correlation of in situ measured
geophysical logs of Natural Gamma Ray (GR), Single-Point Resistance (PR), Self-Potential (SP), magnetic susceptibility
(MS), and Resistivity, and Short Normal (SN) and Long Normal (LN) showed correspondence to the lithologic units. The Dababiya
Quarry Member, in particular, is characterized by very high Gamma Ray and Resistivity Short Normal values.The Dababiya corehole was made possible by the
financial support of the National Geographic Society
Clinical Practice Guideline for Systemic Antifungal Prophylaxis in Pediatric Patients With Cancer and Hematopoietic Stem-Cell Transplantation Recipients
PURPOSE: To develop a clinical practice guideline for systemic antifungal prophylaxis in pediatric patients with cancer and hematopoietic stem-cell transplantation (HSCT) recipients. METHODS: Recommendations were developed by an international multidisciplinary panel that included a patient advocate. We conducted a systematic review of systemic antifungal prophylaxis in children and adults with cancer and HSCT recipients. The Grading of Recommendations Assessment, Development, and Evaluation approach was used to make strong or weak recommendations and to classify level of evidence as high, moderate, low, or very low. The panel considered directness of the data to pediatric patients. RESULTS: There were 68 randomized trials included in the systematic review, of which 6 (9%) were conducted in a solely pediatric population. Strong recommendations were made to administer systemic antifungal prophylaxis to children and adolescents receiving treatment of acute myeloid leukemia, to those undergoing allogeneic HSCT pre-engraftment, and to those receiving systemic immunosuppression for graft-versus-host disease treatment. A strong recommendation was made to administer a mold-active agent with an echinocandin or a mold-active azole when systemic antifungal prophylaxis is warranted. For children younger than 13 years of age, an echinocandin, voriconazole, or itraconazole is suggested. Posaconazole may also be used in those age 13 years or older. A strong recommendation against routine administration of amphotericin as systemic antifungal prophylaxis was made. CONCLUSION: We developed a clinical practice guideline for systemic antifungal prophylaxis administration in pediatric patients with cancer and HSCT recipients. Implementation and assessment of guideline-concordant rates and impacts are important future steps
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