518 research outputs found
Quantum Interactions Between Non-Perturbative Vacuum Fields
We develop an approach to investigate the non-perturbative dynamics of
quantum field theories, in which specific vacuum field fluctuations are treated
as the low-energy dynamical degrees of freedom, while all other vacuum field
configurations are explicitly integrated out from the path integral. We show
how to compute the effective interaction between the vacuum field degrees of
freedom both perturbatively (using stochastic perturbation theory) and fully
non-perturbatively (using lattice field theory simulations). The present
approach holds to all orders in the couplings and does not rely on the
semi-classical approximation.Comment: 15 pages, 4 figure
Strong CP Violation in External Magnetic Fields
We study the response of the QCD vacuum to an external magnetic field, in the
presence of strong CP violation. Using chiral perturbation theory and large N_c
expansion, we show that the external field would polarize quantum fluctuations
and induce an electric dipole moment of the vacuum, along the direction of the
magnetic field. We estimate the magnitude of this effect in different physical
scenarios. In particular, we find that the polarization induced by the magnetic
field of a magnetar could accelerate electric charges up to energies of the
order \theta 10^3 TeV. We also suggest a connection with the possible existence
of "hot-spots" on the surface of neutron stars.Comment: 4 pages, 1 figure. Major revision. Phenomenological analysis extende
Ultra-Low Noise Microwave Extraction from Fiber-Based Optical Frequency Comb
In this letter, we report on all-optical fiber approach to the generation of
ultra-low noise microwave signals. We make use of two erbium fiber mode-locked
lasers phase locked to a common ultra-stable laser source to generate an 11.55
GHz signal with an unprecedented relative phase noise of -111 dBc/Hz at 1 Hz
from the carrier.The residual frequency instability of the microwave signals
derived from the two optical frequency combs is below 2.3 10^(-16) at 1s and
about 4 10^(-19) at 6.5 10^(4)s (in 5 Hz bandwidth, three days continuous
operation).Comment: 12 pages, 3 figure
Laparoscopic Roux-en-Y Gastric Bypass After Failed Vertical Banded Gastroplasty: a Multicenter Experience with 203 Patients
Background: Vertical banded gastroplasty (VBG) has long been the main restrictive procedure for morbid obesity but has many long-term complications for which conversion to Roux-en-Y gastric bypass (RYGBP) is often considered the best option. Methods: This series regroups patients operated on by three different surgeons in four different centers. All data were collected prospectively, then pooled and analyzed retrospectively. Results: Out of 2,522 RYGBP performed between 1998 and 2010, 538 were reoperations, including 203 laparoscopic RYGBP after VBG. There were 175 women and 28 men. The mean BMI before VBG was 43.2â±â6.3, and the mean BMI before reoperation was 37.4â±â8.3. Most patients had more than one indication for reoperation and/or had regained significant weight. There was no conversion to open surgery. A total of 24 patients (11.8%) developed complications, including nine (4.5%) who required reoperation and one death. With a follow-up of 88.9% after 8years, the mean BMI after 1, 3, 5, 7, and 9years was 29.1, 28.8, 28.7, 29.9, and 28.8, respectively. Conclusions: On the basis of this experience, the largest with laparoscopic reoperative RYGBP after failed VBG, we conclude that this procedure can safely be performed in experienced hands, with weight loss results similar to those observed after primary RYGBP. In patients with too difficult an anatomy below the cardia, dividing the esophagus just above the esophago-gastric junction and performing an esophagojejunostomy may be a safe alternative to converting to a Scopinaro-type BPD, obviating the additional long-term risks associated with malabsorptio
Computing the Effective Hamiltonian of Low-Energy Vacuum Gauge Fields
A standard approach to investigate the non-perturbative QCD dynamics is
through vacuum models which emphasize the role played by specific gauge field
fluctuations, such as instantons, monopoles or vortexes. The effective
Hamiltonian describing the dynamics of the low-energy degrees of freedom in
such approaches is usually postulated phenomenologically, or obtained through
uncontrolled approximations. In a recent paper, we have shown how lattice field
theory simulations can be used to rigorously compute the effective Hamiltonian
of arbitrary vacuum models by stochastically performing the path integral over
all the vacuum field fluctuations which are not explicitly taken into account.
In this work, we present the first illustrative application of such an approach
to a gauge theory and we use it to compute the instanton size distribution in
SU(2) gluon-dynamics in a fully model independent and parameter-free way.Comment: 10 pages, 4 figure
Ultrastable lasers based on vibration insensitive cavities
We present two ultra-stable lasers based on two vibration insensitive cavity
designs, one with vertical optical axis geometry, the other horizontal.
Ultra-stable cavities are constructed with fused silica mirror substrates,
shown to decrease the thermal noise limit, in order to improve the frequency
stability over previous designs. Vibration sensitivity components measured are
equal to or better than 1.5e-11 per m.s^-2 for each spatial direction, which
shows significant improvement over previous studies. We have tested the very
low dependence on the position of the cavity support points, in order to
establish that our designs eliminate the need for fine tuning to achieve
extremely low vibration sensitivity. Relative frequency measurements show that
at least one of the stabilized lasers has a stability better than 5.6e-16 at 1
second, which is the best result obtained for this length of cavity.Comment: 8 pages 12 figure
Robot-assisted gastrojejunal anastomosis does not improve the results of the laparoscopic Roux-en-Y gastric bypass
Creatine salts provide neuroprotection even after partial impairment of the creatine transporter
open6Creatine, a compound that is critical for energy metabolism of nervous cells, crosses the blood-brain barrier (BBB) and the neuronal plasma membrane with difficulty, and only using its specific transporter. In the hereditary condition where the creatine transporter is defective (creatine transporter deficiency) there is no creatine in the brain, and administration of creatine is useless lacking the transporter. The disease is severe and incurable. Creatine-derived molecules that could cross BBB and plasma membrane independently of the transporter might be useful to cure this condition. Moreover, such molecules could be useful also in stroke and other brain ischemic conditions. In this paper, we investigated three creatine salts, creatine ascorbate, creatine gluconate and creatine glucose. Of these, creatine glucose was ineffective after transporter block with guanidine acetic acid (GPA) administration. Creatine ascorbate was not superior to creatine in increasing tissue creatine and phosphocreatine content after transporter impairment, however even after such impairment it delayed synaptic failure during anoxia. Finally, creatine gluconate was superior to creatine in increasing tissue content of creatine after transporter block and slowed down PS disappearance during anoxia, an effect that creatine did not have. These findings suggest that coupling creatine to molecules having a specific transporter may be a useful strategy in creatine transporter deficiency. In particular, creatine ascorbate has effects comparable to those of creatine in normal conditions, while being superior to it under conditions of missing or impaired creatine transporter.openAdriano, E; Garbati, P; Salis, A; Damonte, G; Millo, E; Balestrino, MAdriano, ENRICO GIOVANNI; Garbati, Patrizia; Salis, Annalisa; Damonte, Gianluca; Millo, Enrico; Balestrino, Maurizi
Dynamique de l'or et d'autres minĂ©raux lourds dans un profil d'altĂ©ration cuirassĂ© du Burkina Faso, Afrique de l'Ouest : intĂ©rĂȘt pour l'interprĂ©tation de la mise en place des matĂ©riaux constituant les cuirasses de haut glacis
Le profil d'altération cuirassé de haut glacis, développé dans l'environnement du site aurifÚre de Gangaol, a subi des phases d'altération suffisamment intenses pour que des minéraux résistants, comme le zircon et l'or, présentent des traces de dissolution importantes. Dans l'horizon supérieur de la cuirasse, ces minéraux altérés coexistent avec des particules d'or conservant des formes primaires intactes et avec des sulfures sains. Au sein de cet horizon, les teneurs en particules d'or sont plus élevées dans la matrice que dans les nodules fortement indurés. Cela implique qu'à ce niveau, le cuirassement a affecté un matériau contenant des éléments de nature et de degré d'altération variés. L'absence d'or dans la partie médiane du profil confirme un certain degré d'allochtonie des matériaux parentaux de l'horizon supérieur de la cuirasse. (Résumé d'auteur
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