78 research outputs found
The Fermion Monte Carlo revisited
In this work we present a detailed study of the Fermion Monte Carlo algorithm
(FMC), a recently proposed stochastic method for calculating fermionic
ground-state energies [M.H. Kalos and F. Pederiva, Phys. Rev. Lett. vol. 85,
3547 (2000)]. A proof that the FMC method is an exact method is given. In this
work the stability of the method is related to the difference between the
lowest (bosonic-type) eigenvalue of the FMC diffusion operator and the exact
fermi energy. It is shown that within a FMC framework the lowest eigenvalue of
the new diffusion operator is no longer the bosonic ground-state eigenvalue as
in standard exact Diffusion Monte Carlo (DMC) schemes but a modified value
which is strictly greater. Accordingly, FMC can be viewed as an exact DMC
method built from a correlated diffusion process having a reduced Bose-Fermi
gap. As a consequence, the FMC method is more stable than any transient method
(or nodal release-type approaches). We illustrate the various ideas presented
in this work with calculations performed on a very simple model having only
nine states but a full sign problem. Already for this toy model it is clearly
seen that FMC calculations are inherently uncontrolled.Comment: 49 pages with 4 postscript figure
Coherent coupling between radio frequency, optical, and acoustic waves in piezo-optomechanical circuits
The interaction of optical and mechanical modes in nanoscale optomechanical
systems has been widely studied for applications ranging from sensing to
quantum information science. Here, we develop a platform for cavity
optomechanical circuits in which localized and interacting 1550 nm photons and
2.4 GHz phonons are combined with photonic and phononic waveguides. Working in
GaAs facilitates manipulation of the localized mechanical mode either with a
radio frequency field through the piezo-electric effect, or optically through
the strong photoelastic effect. We use this to demonstrate a novel acoustic
wave interference effect, analogous to coherent population trapping in atomic
systems, in which the coherent mechanical motion induced by the electrical
drive can be completely cancelled out by the optically-driven motion. The
ability to manipulate cavity optomechanical systems with equal facility through
either photonic or phononic channels enables new device and system
architectures for signal transduction between the optical, electrical, and
mechanical domains
Optomechanical Crystals
Structured, periodic optical materials can be used to form photonic crystals
capable of dispersing, routing, and trapping light. A similar phenomena in
periodic elastic structures can be used to manipulate mechanical vibrations.
Here we present the design and experimental realization of strongly coupled
optical and mechanical modes in a planar, periodic nanostructure on a silicon
chip. 200-Terahertz photons are co-localized with mechanical modes of Gigahertz
frequency and 100-femtogram mass. The effective coupling length, which
describes the strength of the photon-phonon interaction, is as small as 2.9
microns, which, together with minute oscillator mass, allows all-optical
actuation and transduction of nanomechanical motion with near quantum-limited
sensitivity. Optomechanical crystals have many potential applications, from
RF-over-optical communication to the study of quantum effects in mesoscopic
mechanical systems.Comment: 16 pages, 7 figure
A Phase 3 Trial of Luspatercept in Patients with Transfusion-Dependent ÎČ-Thalassemia
BACKGROUND: Patients with transfusion-dependent ÎČ-thalassemia need regular red-cell transfusions. Luspatercept, a recombinant fusion protein that binds to select transforming growth factor ÎČ superfamily ligands, may enhance erythroid maturation and reduce the transfusion burden (the total number of red-cell units transfused) in such patients. METHODS: In this randomized, double-blind, phase 3 trial, we assigned, in a 2:1 ratio, adults with transfusion-dependent ÎČ-thalassemia to receive best supportive care plus luspatercept (at a dose of 1.00 to 1.25 mg per kilogram of body weight) or placebo for at least 48 weeks. The primary end point was the percentage of patients who had a reduction in the transfusion burden of at least 33% from baseline during weeks 13 through 24 plus a reduction of at least 2 red-cell units over this 12-week interval. Other efficacy end points included reductions in the transfusion burden during any 12-week interval and results of iron studies. RESULTS: A total of 224 patients were assigned to the luspatercept group and 112 to the placebo group. Luspatercept or placebo was administered for a median of approximately 64 weeks in both groups. The percentage of patients who had a reduction in the transfusion burden of at least 33% from baseline during weeks 13 through 24 plus a reduction of at least 2 red-cell units over this 12-week interval was significantly greater in the luspatercept group than in the placebo group (21.4% vs. 4.5%, P<0.001). During any 12-week interval, the percentage of patients who had a reduction in transfusion burden of at least 33% was greater in the luspatercept group than in the placebo group (70.5% vs. 29.5%), as was the percentage of those who had a reduction of at least 50% (40.2% vs. 6.3%). The least-squares mean difference between the groups in serum ferritin levels at week 48 was -348 ÎŒg per liter (95% confidence interval, -517 to -179) in favor of luspatercept. Adverse events of transient bone pain, arthralgia, dizziness, hypertension, and hyperuricemia were more common with luspatercept than placebo. CONCLUSIONS: The percentage of patients with transfusion-dependent ÎČ-thalassemia who had a reduction in transfusion burden was significantly greater in the luspatercept group than in the placebo group, and few adverse events led to the discontinuation of treatment. (Funded by Celgene and Acceleron Pharma; BELIEVE ClinicalTrials.gov number, NCT02604433; EudraCT number, 2015-003224-31.)
Locally Resonant Structures for Low Frequency Surface Acoustic Band Gap Applications
International audienc
Experimental observation of resonant filtering in a two-dimensional phononic crystal waveguide
Focusing and Imaging of Flexural Lamb Waves by Pillared Metasurfaces
International audienc
PB1807: OUTCOME OF CORE BINDING FACTOR ACUTE MYELOID LEUKEMIA IN CHILDREN AND ADOLESCENTS: A SINGLE CENTER EXPERIENCE
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