A new experimental procedure for characterizing quantum effects in small magnetic particle systems

A new experimental procedure is discussed, which aims at separating thermal from quantum behavior independently of the energy barrier distribution in small particle systems. Magnetization relaxation data measured between 60 mK and 5 K on a sample of nanoparticles is presented. The comparison between experimental data and numerical calculations shows a clear departure from thermal dynamics for our sample, which was not obvious without using the new procedure presented here.Comment: LaTeX source, 6 pages, 5 PostScript figure

Quantum cohomology of minuscule homogeneous spaces

Abstract. We prove that the quantum cohomology ring of any minuscule or cominuscule homogeneous space, specialized at q = 1, is semisimple. This implies that complex conjugation defines an algebra automorphism of the quantum cohomology ring localized at the quantum parameter. We check that this involution coincides with the strange duality defined in our previous article. We deduce Vafa-Intriligator type formulas for the Gromov-Witten invariants

Non-monotonic field-dependence of the ZFC magnetization peak in some systems of magnetic nanoparticles

We have performed magnetic measurements on a diluted system of gamma-Fe2O3 nanoparticles (~7nm), and on a ferritin sample. In both cases, the ZFC-peak presents a non-monotonic field dependence, as has already been reported in some experiments,and discussed as a possible evidence of resonant tunneling. Within simple assumptions, we derive expressions for the magnetization obtained in the usual ZFC, FC, TRM procedures. We point out that the ZFC-peak position is extremely sensitive to the width of the particle size distribution, and give some numerical estimates of this effect. We propose to combine the FC magnetization with a modified TRM measurement, a procedure which allows a more direct access to the barrier distribution in a field. The typical barrier values which are obtained with this method show a monotonic decrease for increasing fields, as expected from the simple effect of anisotropy barrier lowering, in contrast with the ZFC results. From our measurements on gamma-Fe2O3 particles, we show that the width of the effective barrier distribution is slightly increasing with the field, an effect which is sufficient for causing the observed initial increase of the ZFC-peak temperatures.Comment: LaTeX file 19 pages, 9 postscript figures. To appear in Phys. Rev. B (tentative schedule: Dec.97

Triangulations and Severi varieties

We consider the problem of constructing triangulations of projective planes over Hurwitz algebras with minimal numbers of vertices. We observe that the numbers of faces of each dimension must be equal to the dimensions of certain representations of the automorphism groups of the corresponding Severi varieties. We construct a complex involving these representations, which should be considered as a geometric version of the (putative) triangulations

The Use of Pedicled Perforator Flaps in Chest Reconstruction: A Systematic Review of Outcomes and Reliability

BACKGROUND: In recent years, pedicled perforator flaps have revolutionized plastic surgery by reducing donor site morbidity and ensuring larger and deeper reconstructions with local pedicled cutaneous flaps. The aim of the study was to make a systematic review of perforator pedicled propeller flaps (PPPFs) in chest reconstruction. METHODS: Pubmed and Cochrane databases were searched from 1989 to October 2016 for articles describing the use of PPPFs in chest reconstruction. The preferred reporting items for systematic reviews and meta analyses statement was used in the selection process. The review was registered on international prospective register of systematic reviews. Furthermore, operative technique, indications and complications were searched. RESULTS: Twenty-four articles were selected (174 patients and 182 flaps). Oncological surgery was the first etiology (34.5%), followed by infections (11.5%), chest keloid scars (6.23%), malformations (4.6%), burns (3.4%), chronic ulcers (2.3%), Verneuil disease (1.8%), and acute wounds (1.8%). The arc of rotation was between 90° and 120° in 24.2%. The mean surface of flaps was 127.45 ± 123.11 cm. Dissection was subfascial in 78.5% of the cases. Complications were found in 9.9% of patients and included mainly wound dehiscence (4.4%) and hematoma/seroma (2.2%). One case of total necrosis (0.5%) and 2 cases of partial necrosis (1.1%) were found. CONCLUSIONS: The possibility of numerous pedicles makes it possible for PPPFs to offset most areas of wall chest defects. Furthermore, this surgical technique is reliable and reproducible, with lower donor site morbidity than that in the case of muscular flaps, which are classically used in this location

The Energy Spectra and Relative Abundances of Electrons and Positrons in the Galactic Cosmic Radiation

Observations of cosmic-ray electrons and positrons have been made with a new balloon-borne detector, HEAT (the "High-Energy Antimatter Telescope"), first flown in 1994 May from Fort Sumner, NM. We describe the instrumental approach and the data analysis procedures, and we present results from this flight. The measurement has provided a new determination of the individual energy spectra of electrons and positrons from 5 GeV to about 50 GeV, and of the combined "all-electron" intensity (e+ + e-) up to about 100 GeV. The single power-law spectral indices for electrons and positrons are alpha = 3.09 +/- 0.08 and 3.3 +/- 0.2, respectively. We find that a contribution from primary sources to the positron intensity in this energy region, if it exists, must be quite small.Comment: latex2e file, 30 pages, 15 figures, aas2pp4.sty and epsf.tex needed. To appear in May 10, 1998 issue of Ap.

Small-scale spatial variability of soil CO2 flux: Implication for monitoring strategy

In recent decades, soil CO2 flux measurements have been often used in both volcanic and seismically active areas to investigate the interconnections between temporal and spatial anomalies in degassing and telluric activities. In this study, we focus on a narrow degassing area of the Piton de la Fournaise volcano, that has been chosen for its proximity and link with the frequently active volcanic area. Our aim is to constrain the degassing in this narrow area and identify the potential processes involved in both spatial and temporal soil CO2 variations in order to provide an enhanced monitoring strategy for soil CO2 flux. We performed a geophysical survey (self-potential measurements: SP; electrical resistivity tomography: ERT) to provide a high-resolution description of the subsurface. We identified one main SP negative anomaly dividing the area in two zones. Based on these results, we set ten control points, from the site of the main SP negative anomaly up to 230 m away, where soil CO2 fluxes were weekly measured during one year of intense eruptive activity at Piton de la Fournaise. Our findings show that lateral and vertical soil heterogeneities and structures exert a strong control on the degassing pattern. We find that temporal soil CO2 flux series at control points close to the main SP negative anomaly better record variations linked to the volcanic activity. We also show that the synchronicity between the increase of soil CO2 flux and deep seismicity can be best explained by a pulsed process pushing out the CO2 already stored and fractionated in the system. Importantly, our findings show that low soil CO2 fluxes and low carbon isotopic signature are able to track variations of volcanic activity in the same way as high fluxes and high carbon isotopic signature do. This result gives important insights in terms of monitoring strategy of volcanic and seismotectonic areas in geodynamics contexts characterized by difficult environmental operational conditions as commonly met in tropical areaPublished13-264A. Oceanografia e climaJCR Journa

Near-surface environmentally forced changes in the Ross Ice Shelf observed with ambient seismic noise

Author Posting. © American Geophysical Union, 2018. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 45 (2018): 11,187-11,196, doi:10.1029/2018GL079665.Continuous seismic observations across the Ross Ice Shelf reveal ubiquitous ambient resonances at frequencies >5 Hz. These firn‐trapped surface wave signals arise through wind and snow bedform interactions coupled with very low velocity structures. Progressive and long‐term spectral changes are associated with surface snow redistribution by wind and with a January 2016 regional melt event. Modeling demonstrates high spectral sensitivity to near‐surface (top several meters) elastic parameters. We propose that spectral peak changes arise from surface snow redistribution in wind events and to velocity drops reflecting snow lattice weakening near 0°C for the melt event. Percolation‐related refrozen layers and layer thinning may also contribute to long‐term spectral changes after the melt event. Single‐station observations are inverted for elastic structure for multiple stations across the ice shelf. High‐frequency ambient noise seismology presents opportunities for continuous assessment of near‐surface ice shelf or other firn environments.NSF Office of Polar Programs Grant Number: PLR-11425182019-04-1