505 research outputs found
Kondo effect and channel mixing in oscillating molecules
We investigate the electronic transport through a molecule in the Kondo
regime. The tunneling between the electrode and the molecule is asymmetrically
modulated by the oscillations of the molecule, i.e., if the molecule gets
closer to one of the electrodes the tunneling to that electrode will increase
while for the other electrode it will decrease. The system is described by a
two-channel Anderson model with phonon-assisted hybridization, which is solved
with the Wilson numerical renormalization group method. The results for several
functional forms of tunneling modulation are presented. For a linearized
modulation the Kondo screening of the molecular spin is caused by the even or
odd conduction channel. At the critical value of the electron-phonon coupling
an unstable two-channel Kondo fixed point is found. For a realistic modulation
the spin at the molecular orbital is Kondo screened by the even conduction
channel even in the regime of strong coupling. A universal consequence of the
electron-phonon coupling is the softening of the phonon mode and the related
instability to perturbations that break the left-right symmetry. When the
frequency of oscillations decreases below the magnitude of such perturbation,
the molecule is abruptly attracted to one of the electrodes. In this regime,
the Kondo temperature is enhanced and, simultaneously, the conductance through
the molecule is suppressed.Comment: published versio
Southern Extension to the Breeding Range of the Gyrfalcon, Falco Rusticolus, in Eastern North America
We report the observation of four gyrfalcon (Falco rusticolus) nests and several adults south of the previously recognized southern limit of the species' breeding distribution in eastern North America. Our southernmost observations extends the known breeding range approximately 400 km to the south. The northern forest tundra biome could delineate the southern limit to the breeding range of the gyrfalcon.Nous rapportons la découverte de quatre nids de faucon gerfaut et la mention de quelques adultes au sud de la limite connue de l'aire de reproduction de l'espèce dans l'est de l'Amérique du Nord. Notre observation la plus méridionale étend l'aire de répartition quelques 400 km plus au sud. Les limites sud de la toundra forestière septentrionale pourraient coincider avec celle de l'aire de reproduction du faucon gerfaut.Mots clés: faucon gerfaut, nicheur, répartition, Baie d’Hudson, Québec
New Bacteriological Patterns in Primary Infected Aorto-iliac Aneurysms: A Single-centre Experience
AbstractObjectivesTo assess causative pathogens and surgical outcomes in patients with primary infected aorto-iliac aneurysms at our institution.DesignRetrospective study of patients treated at a university hospital between 1992 and 2009.ResultsWe identified 26 patients (median age, 63 years) with primary infected aneurysms on the aorta (descending thoracic, n = 2; thoraco-abdominal, n = 3; suprarenal, n = 2; infrarenal, n = 15) or iliac arteries (n = 4). Among them, 22 were symptomatic, including 13 with ruptured aneurysms. The causative organisms, identified in 25/26 patients, were Campylobacter fetus, n = 6; Streptococcus pneumoniae, n = 4; Listeria, n = 3; Salmonella, n = 2; Mycobacterium tuberculosis, n = 2; Staphylococcus aureus, n = 1; and other, n = 7. Immune suppression was a feature in 10 (38.4%) patients. Revascularisation was performed in situ in 23 patients (10 allografts, eight grafts, three superficial femoral veins, and 2 stentgrafts) and by extra-anatomic bypass in three patients.Hospital mortality was 23% (in situ group, 17.4%; extra-anatomic group, 66.7%; χ2 Yates, P = 0.24). During follow-up in the 20 survivors (median, 48.5 months), there were two non-infection-related deaths (five and 24 months) and six (30%) vascular complications.ConclusionsThe bacteriological spectrum of primary infected aorto-iliac aneurysms was wider than previously reported. The availability of new diagnostic tests and increased prevalence of immunosuppression may explain this finding
Quantum Criticality in doped CePd_1-xRh_x Ferromagnet
CePd_1-xRh_x alloys exhibit a continuous evolution from ferromagnetism (T_C=
6.5 K) at x = 0 to a mixed valence (MV) state at x = 1. We have performed a
detailed investigation on the suppression of the ferromagnetic (F) phase in
this alloy using dc-(\chi_dc) and ac-susceptibility (\chi_ac), specific heat
(C_m), resistivity (\rho) and thermal expansion (\beta) techniques. Our results
show a continuous decrease of T_C (x) with negative curvature down to T_C = 3K
at x*= 0.65, where a positive curvature takes over. Beyond x*, a cusp in cac is
traced down to T_C* = 25 mK at x = 0.87, locating the critical concentration
between x = 0.87 and 0.90. The quantum criticality of this region is recognized
by the -log(T/T_0) dependence of C_m/T, which transforms into a T^-q (~0.5) one
at x = 0.87. At high temperature, this system shows the onset of valence
instability revealed by a deviation from Vegard's law (at x_V~0.75) and
increasing hybridization effects on high temperature \chi_dc and \rho.
Coincidentally, a Fermi liquid contribution to the specific heat arises from
the MV component, which becomes dominant at the CeRh limit. In contrast to
antiferromagnetic systems, no C_m/T flattening is observed for x > x_cr rather
the mentioned power law divergence, which coincides with a change of sign of
\beta. The coexistence of F and MV components and the sudden changes in the T
dependencies are discussed in the context of randomly distributed magnetic and
Kondo couplings.Comment: 11 pages, 11 figure
Low temperature magnetic phase diagram of the cubic non-Fermi liquid system CeIn_(3-x)Sn_x
In this paper we report a comprehensive study of the magnetic susceptibility
(\chi), resistivity (\rho), and specific heat (C_P), down to 0.5 K of the cubic
CeIn_(3-x)Sn_x alloy. The ground state of this system evolves from
antiferromagnetic (AF) in CeIn_3(T_N=10.2 K) to intermediate-valent in CeSn_3,
and represents the first example of a Ce-lattice cubic non-Fermi liquid (NFL)
system where T_N(x) can be traced down to T=0 over more than a decade of
temperature. Our results indicate that the disappearance of the AF state occurs
near x_c ~ 0.7, although already at x ~ 0.4 significant modifications of the
magnetic ground state are observed. Between these concentrations, clear NFL
signatures are observed, such as \rho(T)\approx \rho_0 + A T^n (with n<1.5) and
C_P(T)\propto -T ln(T) dependencies. Within the ordered phase a first order
phase transition occurs for 0.25 < x < 0.5. With larger Sn doping, different
weak \rho(T) dependencies are observed at low temperatures between x=1 and x=3
while C_P/T shows only a weak temperature dependence.Comment: 7 pages, 7 figures. Accepted in Eur. J. Phys.
Crystal-field effects in the mixed-valence compounds Yb2M3Ga9 (M= Rh, Ir)
Magnetic susceptibility, heat capacity, and electrical resistivity
measurements have been carried out on single crystals of the intermediate
valence compounds Yb2Rh3Ga9 and Yb2Ir3Ga9. These measurements reveal a large
anisotropy due apparently to an interplay between crystalline electric field
(CEF) and Kondo effects. The temperature dependence of magnetic susceptibility
can be modelled using the Anderson impurity model including CEF within an
approach based on the Non-Crossing Approximation.Comment: Accepted to Phys. Rev.
Early-stage development of novel cyclodextrin-siRNA nanocomplexes allows for successful postnebulization transfection of bronchial epithelial cells.
BACKGROUND: Successful delivery of small interfering RNA (siRNA) to the lungs remains hampered by poor intracellular delivery, vector-mediated cytotoxicity, and an inability to withstand nebulization. Recently, a novel cyclodextrin (CD), SC12CDClickpropylamine, consisting of distinct lipophilic and cationic subunits, has been shown to transfect a number of cell types. However, the suitability of this vector for pulmonary siRNA delivery has not been assessed to date. To address this, a series of high-content analysis (HCA) and postnebulization assays were devised to determine the potential for CD-siRNA delivery to the lungs.
METHODS: SC12CDClickpropylamine-siRNA mass ratios (MRs) were examined for size and zeta potential. In-depth analysis of nanocomplex uptake and toxicity in Calu-3 bronchial epithelial cells was examined using IN Cell(®) HCA assays. Nebulized SC12CDClickpropylamine nanocomplexes were assessed for volumetric median diameter (VMD) and fine particle fraction (FPF) and compared with saline controls. Finally, postnebulization stability was determined by comparing luciferase knockdown elicited by SC12CDClickpropylamine nanocomplexes before and after nebulization.
RESULTS: SC12CDClickpropylamine-siRNA complexation formed cationic nanocomplexes of ≤200 nm in size depending on the medium and led to significantly higher levels of siRNA associated with Calu-3 cells compared with RNAiFect-siRNA-treated cells at all MRs (p
CONCLUSIONS: SC12CDClickpropylamine nanocomplexes can be effectively nebulized for pulmonary delivery of siRNA using Aeroneb technology to mediate knockdown in airway cells. To the best of our knowledge, this is the first study examining the suitability of SC12CDClickpropylamine-siRNA nanocomplexes for pulmonary delivery. Furthermore, this work provides an integrated nanomedicine-device combination for future in vitro and in vivo preclinical and clinical studies of inhaled siRNA therapeutics
Tungsten divertor sources in WEST related to impurity inventory and local plasma conditions
A dedicated series of L-mode deuterium discharges were performed in WEST in which a broad parameter space in terms of divertor plasma temperature (inner divertor at <10 eV, outer divertor up to 50 eV) and impurity flux density was achieved by variation of X point elevation, upstream plasma density and fuelling position and rate. Density steps provided stable reference plasma conditions whilst density scans up to the point of detachment revealed the sputtering threshold behaviour of the dominant sputtering species. Tungsten gross erosion was quantified via the common WI 400.9 nm line and correlated with the residual gas content.</p
Transport in Quantum Dots from the Integrability of the Anderson Model
In this work we exploit the integrability of the two-lead Anderson model to
compute transport properties of a quantum dot, in and out of equilibrium. Our
method combines the properties of integrable scattering together with a
Landauer-Buttiker formalism. Although we use integrability, the nature of the
problem is such that our results are not generically exact, but must only be
considered as excellent approximations which nonetheless are valid all the way
through crossover regimes.
The key to our approach is to identify the excitations that correspond to
scattering states and then to compute their associated scattering amplitudes.
We are able to do so both in and out of equilibrium. In equilibrium and at zero
temperature, we reproduce the Friedel sum rule for an arbitrary magnetic field.
At finite temperature, we study the linear response conductance at the
symmetric point of the Anderson model, and reproduce Costi et al.'s numerical
renormalization group computation of this quantity. We then explore the
out-of-equilibrium conductance for a near-symmetric Anderson model, and arrive
at quantitative expressions for the differential conductance, both in and out
of a magnetic field. We find the expected splitting of the differential
conductance peak into two in a finite magnetic field, . We determine the
width, height, and position of these peaks. In particular we find for H >> T_k,
the Kondo temperature, the differential conductance has maxima of e^2/h
occuring for a bias V close to but smaller than H. The nature of our
construction of scattering states suggests that our results for the
differential magneto-conductance are not merely approximate but become exact in
the large field limit.Comment: 88 pages, 16 figures, uses harvmac.te
Mass-Enhanced Fermi Liquid Ground State in NaCoO
Magnetic, transport, and specific heat measurements have been performed on
layered metallic oxide NaCoO as a function of temperature .
Below a characteristic temperature =3040 K, electrical resistivity
shows a metallic conductivity with a behavior and magnetic susceptibility
deviates from the Curie-Weiss behavior showing a broad peak at 14 K. The
electronic specific heat coefficient is 60 mJ/molK at 2 K.
No evidence for magnetic ordering is found. These behaviors suggest the
formation of mass-enhanced Fermi liquid ground state analogous to that in
-electron heavy fermion compound LiVO.Comment: 4 pages, 4 figures, to be published in Phys. Rev. B 69 (2004
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