Many-body physics of a quantum fluid of exciton-polaritons in a semiconductor microcavity

Some recent results concerning nonlinear optics in semiconductor microcavities are reviewed from the point of view of the many-body physics of an interacting photon gas. Analogies with systems of cold atoms at thermal equilibrium are drawn, and the peculiar behaviours due to the non-equilibrium regime pointed out. The richness of the predicted behaviours shows the potentialities of optical systems for the study of the physics of quantum fluids.Comment: Proceedings of QFS2006 conference to appear on JLT

Collective excitations in the Unitary Correlation Operator Method and relativistic QRPA studies of exotic nuclei

The collective excitation phenomena in atomic nuclei are studied in two different formulations of the Random Phase Approximation (RPA): (i) RPA based on correlated realistic nucleon-nucleon interactions constructed within the Unitary Correlation Operator Method (UCOM), and (ii) relativistic RPA (RRPA) derived from effective Lagrangians with density-dependent meson-exchange interactions. The former includes the dominant interaction-induced short-range central and tensor correlations by means of an unitary transformation. It is shown that UCOM-RPA correlations induced by collective nuclear vibrations recover a part of the residual long-range correlations that are not explicitly included in the UCOM Hartree-Fock ground state. Both RPA models are employed in studies of the isoscalar monopole resonance (ISGMR) in closed-shell nuclei across the nuclide chart, with an emphasis on the sensitivity of its properties on the constraints for the range of the UCOM correlation functions. Within the Relativistic Quasiparticle RPA (RQRPA) based on Relativistic Hartree-Bogoliubov model, the occurrence of pronounced low-lying dipole excitations is predicted in nuclei towards the proton drip-line. From the analysis of the transition densities and the structure of the RQRPA amplitudes, it is shown that these states correspond to the proton pygmy dipole resonance.Comment: 15 pages, 4 figures, submitted to Physics of Atomic Nuclei, conference proceedings, "Frontiers in the Physics of Nucleus", St. Petersburg, 28. June-1. July, 200

Cotinine participation in chronic nicotinic withdrawal syndrome in rats (Preliminary study)

Numerosos datos clínicos y experimentales han demostrado que la nicotina del tabaco (NI) es la razón de la adicción al tabaco en los seres humanos, a través de la inducción de la tolerancia y la dependencia física. El humo del tabaco contiene otros alcaloides que pueden contribuir a la adicción, como la cotinina (COT). En este estudio se evaluaron los posibles efectos de la COT en ratas durante el síndrome de abstinencia nicotínica midiendo la actividad locomotora espontánea (ALE) utilizando el test del campo abierto. El estudio se llevó a cabo con dos grupos de ratas que recibieron NI 10 mg / kg / día en agua potable durante 120 días (grupos A y B). Luego, en el grupo A, se sustituyó NI por agua potable y en el grupo B, sustituido por COT 12 mg / kg, durante 24 horas en ambos grupos. La actividad locomotora espontánea se registró al final del día 120 (nivel basal) y al final del día 121, al final del período de abstinencia. Los resultados obtenidos se compararon con las mediciones basales. El grupo A mostró diferencias significativas en 3 de los 9 movimientos medidos y el grupo B mostró diferencias significativas en 7 de los 9 movimientos medidos. Cuando el grupo A se comparó con el grupo B sólo 1 movimiento mostró diferencia significativa. Estos resultados sugieren que en la administración crónica de nicotina y en estas condiciones experimentales, la cotinina participa en el síndrome de abstinencia nicotínica.A large amount of clinical and experimental data has shown that tobacco nicotine (NI) is the reason for tobacco addiction in humans, through the induction of tolerance and physical dependence. Tobacco smoke contains other alkaloids that may contribute to addiction, such as cotinine (COT). In this study we evaluated the possible effects of COT in rats during NI abstinence syndrome by measuring spontaneous locomotor activity (SLA) with an open field test. The study was carried out with two groups of rats receiving NI 10 mg / kg / day in drinking water for 120 days (groups A and B). Then, in group A, NI was replaced by drinking water and in group B, substituted by COT, 12 mg / kg, for 24 hours in both groups. Spontaneous locomotor activity was recorded at the end of day 120 (baseline) and at the end of day 121, the end of the abstinence period. The results obtained were compared against the baseline measurements and group A showed significant differences in 3 of the 9 movements measured and group B displayed significant differences in 7 of the 9 movements measured. When group A was compared with Group B only 1 movement showed any significant differences. These results suggest that cotinine participates in the nicotine withdrawal syndrome in chronic nicotine administration under these experimental conditions.Fil: Sassone, Adriana Haydée. Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica. Departamento de Sanidad Nutrición Bromatología y Toxicología; ArgentinaFil: Merini, Luciano Jose. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis; Argentina. Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica. Departamento de Sanidad Nutrición Bromatología y Toxicología; ArgentinaFil: Quiroga, Patricia Noemí. Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica. Departamento de Sanidad Nutrición Bromatología y Toxicología; ArgentinaFil: Sarchi, María I.. Universidad de Buenos Aires; ArgentinaFil: Lopez, Clara M.. Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica. Departamento de Sanidad Nutrición Bromatología y Toxicología; ArgentinaFil: Roses, Otmaro Enrique. Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica. Departamento de Sanidad Nutrición Bromatología y Toxicología; ArgentinaFil: Perazzo, Juan C.. Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica. Departamento de Sanidad Nutrición Bromatología y Toxicología; Argentin

Out-of-equilibrium physics in driven dissipative coupled resonator arrays

Coupled resonator arrays have been shown to exhibit interesting many- body physics including Mott and Fractional Hall states of photons. One of the main differences between these photonic quantum simulators and their cold atoms coun- terparts is in the dissipative nature of their photonic excitations. The natural equi- librium state is where there are no photons left in the cavity. Pumping the system with external drives is therefore necessary to compensate for the losses and realise non-trivial states. The external driving here can easily be tuned to be incoherent, coherent or fully quantum, opening the road for exploration of many body regimes beyond the reach of other approaches. In this chapter, we review some of the physics arising in driven dissipative coupled resonator arrays including photon fermionisa- tion, crystallisation, as well as photonic quantum Hall physics out of equilibrium. We start by briefly describing possible experimental candidates to realise coupled resonator arrays along with the two theoretical models that capture their physics, the Jaynes-Cummings-Hubbard and Bose-Hubbard Hamiltonians. A brief review of the analytical and sophisticated numerical methods required to tackle these systems is included.Comment: Chapter that appeared in "Quantum Simulations with Photons and Polaritons: Merging Quantum Optics with Condensed Matter Physics" edited by D.G.Angelakis, Quantum Science and Technology Series, Springer 201

Susceptibility trends of Bacteroides fragilis group isolates from Buenos Aires, Argentina Tendencias en el perfil de sensibilidad de aislamientos del grupo Bacteroides fragilis obtenidos en Buenos Aires, Argentina

The aim of this study was to analyze the susceptibility trends to seven antibiotics of Bacteroides fragilis group isolates based on three survey studies performed by the Committee of Anaerobic Bacteria between 1989 and 2002. Fifty three, 82 and 65 B. fragilis group isolates were collected during each period. The antimicrobial agents included were: ampicillin, ampicillin-sulbactam (2:1), cefoxitin, piperacillin, imipenem, clindamycin, and metronidazole. Minimal inhibitory concentrations (MICs) were determined according to the reference agar dilution method described by the Clinical and Laboratory Standards Institute (CLSI, formerly NCCLS). The most active antibiotics for B. fragilis and non- B. fragilis species throughout the three periods were: imipenem with 99.1 and 100% of activity, respectively, and metronidazole with 100% of activity. The susceptibility to ampicillin-sulbactam showed a decrease, from 100% to 90.3% and to 82.4 % in the last period, for both B. fragilis and non-B. fragilis species, respectively. The overall susceptibility rates for cefoxitin, piperacillin, and clindamycin were significantly different between B. fragilis and non-B. fragilis species (84.2% vs. 56.5%; 85.9% vs. 66.7% and 88.8% vs. 64.7%, respectively, p< 0.05). Cefoxitin was the antibiotic that showed more variations as regards periods and species. The susceptibility rates for clindamycin were low, about 60%, for non-B. fragilis species during the last two periods. The variations observed in the susceptibility patterns of the B. fragilis group isolates emphasize the need to continue monitoring the emergence of resistance in order to guide the election of the most appropriate antibiotic therapy scheme for anaerobic infections.<br>El objetivo de este estudio fue evaluar las variaciones en el perfil de sensibilidad frente a siete antimicrobianos de aislamientos del grupo Bacteroides fragilis, mediante el análisis de tres relevamientos realizados por la Subcomisión de Bacterias Anaerobias de la Asociación Argentina de Microbiología (años 1989-1991, 1996-1998 y 1999-2002). En los citados períodos se recolectaron 53, 82 y 65 aislamientos del grupo B. fragilis. Se evaluó la actividad de: ampicilina, ampicilina-sulbactama (2:1), cefoxitina, piperacilina, imipenem, clindamicina y metronidazol. La concentración inhibitoria mínima (CIM) se determinó utilizando el método de dilución en agar, según las normas del Clinical and Laboratory Standards Institute (CLSI, anteriormente NCCLS). En los tres períodos considerados, los antibióticos más activos frente a aislamientos de la especie B. fragilis como así también frente a aislamientos pertenecientes a otras especies del grupo B. fragilis fueron imipenem, con 99,1 y 100% de actividad, respectivamente, y metronidazol, con 100% de actividad. Con ampicilina-sulbactama se observó a lo largo del tiempo una disminución de la sensibilidad, desde el 100% en el primer período hasta un 90,3 y 82,4% en el último, para B. fragilis y para especies del grupo distintas de B. fragilis, respectivamente. Cuando se consideraron los tres períodos juntos, se observaron diferencias significativas entre la especie B. fragilis y los restantes aislamientos del grupo para cefoxitina, piperacilina y clindamicina (84,2% vs. 56,5%; 85,9% vs. 66,7% and 88,8% vs. 64,7%, respectivamente, p< 0.05). Cefoxitina fue el antibiótico que mostró mayores variaciones a través del tiempo y entre especies. Las tasas de sensibilidad a clindamicina fueron bajas (alrededor del 60%) entre los aislamientos no pertenecientes a la especie B. fragilis durante los últimos dos períodos. Las variaciones observadas en los perfiles de sensibilidad del grupo B. fragilis muestran la necesidad de vigilar periódicamente la emergencia de resistencia a los antimicrobianos, a fin de orientar el tratamiento de las infecciones por bacterias anaerobias