Up on the Jaynes-Cummings ladder of a quantum-dot/microcavity system.

In spite of their different natures, light and matter can be unified under the strong-coupling regime, yielding superpositions of the two, referred to as dressed states or polaritons. After initially being demonstrated in bulk semiconductors and atomic systems, strong-coupling phenomena have been recently realized in solid-state optical microcavities. Strong coupling is an essential ingredient in the physics spanning from many-body quantum coherence phenomena, such as Bose-Einstein condensation and superfluidity, to cavity quantum electrodynamics. Within cavity quantum electrodynamics, the Jaynes-Cummings model describes the interaction of a single fermionic two-level system with a single bosonic photon mode. For a photon number larger than one, known as quantum strong coupling, a significant anharmonicity is predicted for the ladder-like spectrum of dressed states. For optical transitions in semiconductor nanostructures, first signatures of the quantum strong coupling were recently reported. Here we use advanced coherent nonlinear spectroscopy to explore a strongly coupled exciton-cavity system. We measure and simulate its four-wave mixing response, granting direct access to the coherent dynamics of the first and second rungs of the Jaynes-Cummings ladder. The agreement of the rich experimental evidence with the predictions of the Jaynes-Cummings model is proof of the quantum strong-coupling regime in the investigated solid-state system.

Soluble cell adhesion molecules and parameters of lipoprotein metabolism in patients with severe burns / Moléculas de adhesión celular soluble y parámetros del metabolismo de la lipoproteína en pacientes con quemaduras severas

BACKGROUND: The role of leukocyte adhesion molecules in patients with burns and their relationship to other parameters of inflammation and lipid metabolism is only recently beginning to be explored. Therefore, we investigated the temporal changes in the levels of soluble cell adhesion molecules and other parameters of inflammation and lipoprotein metabolism in patients with thermal injury. MATERIALS AND METHODS: The serum levels of soluble adhesion molecules, intercellular cell adhesion molecule-1 (sICAM-1), vascular cell adhesion molecule-1 (sVCAM-1), and sE-selectin, C-reactive protein (CRP) and fibrinogen in seven patients with severe burns over a 30- day period were measured to determine the involvement of these factors in the pathophysiology of severe burns. Serum levels of sICAM-1, sVCAM-1 and sE-selectin were determined by ELISA. Furthermore, total cholesterol, high-density lipoprotein cholesterol (HDL chol), low-density lipoprotein cholesterol (LDL chol) and triglycerides (TG) were measured. RESULTS: Blood levels of sICAM-1, sVCAM-1, CRP and fibrinogen increased with maximum values six days after thermal injury. In contrast, serum levels of sE-selectin were elevated two days after thermal injury. The sICAM-1, sVCAM-1 and sE-selectin levels correlated significantly with both the CRP and the fibrinogen levels. Plasma total cholesterol, HDL cholesterol and LDL cholesterol decreased with minimum values four days after thermal injury. Furthermore, an increase of triglyceride levels was observed. CONCLUSION: The observed inflammatory response of soluble cell adhesion molecules could be useful in monitoring endothelial activation immediately following thermal injury. Further studies involving a larger number of patients with burns should help to clarify the extent to which measured parameters, especially the temporal changes of sCAMs, could be relevant in assessing the morbidity of patients with thermal injury.

ANTECEDENTES: El papel de las moléculas de adhesión leucocitaria en pacientes con quemaduras y su relación con otros parámetros de inflamación y metabolismo de lípidos ha comenzado a ser explorados sólo recientemente. Por lo tanto, investigamos los cambios temporales en los niveles de las moléculas de adhesión celular solubles y otros parámetros de inflamación y metabolismo de las lipoproteínas en pacientes con daños térmicos. MATERIALES Y MÉTODOS: Los niveles de suero de las moléculas de adhesión solubles, las moléculas 1 de adhesión intracelular (sICAM-1), las moléculas 1 de adhesión celular vascular (sVCAM-1) y sE-selectina, la proteína reactiva C (CRP), y el fibrinógeno en siete pacientes con quemaduras severas en un período de 30 días, fueron medidas a fin de determinar la participación de estos factores en la patofisiología de las quemaduras severas. Los niveles séricos de sICAM-1, sVCAM-1 y sE-selectina fueron determinados mediante ELISA. Además, se midieron el colesterol total, el colesterol de lipoproteína de alta densidad (HDL col), el colesterol de lipoproteína de baja densidad (LDL col), y los triglicéridos. RESULTADOS: Los niveles de sangre de sICAM-1, sVCAM-1, CRP y fibrinógeno aumentaron a valores máximos, seis días después del daño térmico. Los niveles de sICAM-1, sVCAM-1 y sE-selectina tuvieron una correlación significativa tanto con la CRP como con los niveles de fibrinógeno. El colesterol total de plasma, el colesterol HDL y el colesterol LDL disminuyeron a valores mínimos cuatro días después del daño térmico. Además, se observó un aumento en los niveles de triglicéridos. CONCLUSIÓN: La respuesta inflamatoria observada de las moléculas de adhesión celular soluble puede ser útil para monitorear la activación endotelial inmediatamente luego del daño térmico. Estudios ulteriores que comprendan un gran número de pacientes con quemaduras deben ayudar a aclarar hasta que punto los parámetros medidos, especialmente los cambios temporales de sCAMs, pudieran ser relevantes a la hora de evaluar la morbilidad de los pacientes con heridas térmicas.

Direct observation of correlations between individual photon emission events of a microcavity laser.

Lasers are recognized for coherent light emission, the onset of which is reflected in a change in the photon statistics. For many years, attempts have been made to directly measure correlations in the individual photon emission events of semiconductor lasers. Previously, the temporal decay of these correlations below or at the lasing threshold was considerably faster than could be measured with the time resolution provided by the Hanbury Brown/Twiss measurement set-up used. Here we demonstrate a measurement technique using a streak camera that overcomes this limitation and provides a record of the arrival times of individual photons. This allows us to investigate the dynamical evolution of correlations between the individual photon emission events. We apply our studies to micropillar lasers with semiconductor quantum dots as the active material, operating in the regime of cavity quantum electrodynamics. For laser resonators with a low cavity quality factor, Q, a smooth transition from photon bunching to uncorrelated emission with increasing pumping is observed; for high-Q resonators, we see a non-monotonic dependence around the threshold where quantum light emission can occur. We identify regimes of dynamical anti-bunching of photons in agreement with the predictions of a microscopic theory that includes semiconductor-specific effects.

Soluble cell adhesion molecules and parameters of lipoprotein metabolism in patients with severe burns.

BACKGROUND: The role of leukocyte adhesion molecules in patients with burns and their relationship to other parameters of inflammation and lipid metabolism is only recently beginning to be explored. Therefore, we investigated the temporal changes in the levels of soluble cell adhesion molecules and other parameters of inflammation and lipoprotein metabolism in patients with thermal injury. MATERIALS AND METHODS: The serum levels of soluble adhesion molecules, intercellular cell adhesion molecule-1 (sICAM-1), vascular cell adhesion molecule-1 (sVCAM-1), and sE-selectin, C-reactive protein (CRP) and fibrinogen in seven patients with severe burns over a 30- day period were measured to determine the involvement of these factors in the pathophysiology of severe burns. Serum levels of slCAM-1, sVCAM-1 and sE-selectin were determined by ELISA. Furthermore, total cholesterol, high-density lipoprotein cholesterol (HDL chol), low-density lipoprotein cholesterol (LDL chol) and triglycerides (TG) were measured. RESULTS: Blood levels of sICAM-1, sVCAM-1, CRP and fibrinogen increased with maximum values six days after thermal injury. In contrast, serum levels of sE-selectin were elevated two days after thermal injury. The sICAM-1, sVCAM-1 and sE-selectin levels correlated significantly with both the CRP and the fibrinogen levels. Plasma total cholesterol, HDL cholesterol and LDL cholesterol decreased with minimum values four days after thermal injury. Furthermore, an increase of triglyceride levels was observed. CONCLUSION: The observed inflammatory response of soluble cell adhesion molecules could be useful in monitoring endothelial activation immediately following thermal injury. Further studies involving a larger number of patients with burns should help to clarify the extent to which measured parameters, especially the temporal changes ofsCAMs, could be relevant in assessing the morbidity ofpatients with thermal injury.

Demonstration of strong coupling via electro-optical tuning in high-quality QD-micropillar systems.

We demonstrate electro-optical tuning of single quantum dots (QDs) embedded in high-quality (high-Q) micropillar cavities by exploiting the quantum confined Stark effect (QCSE). Combining electrically contacted high-Q micropillars and large In(0.3) Ga(0.7)As QDs with high oscillator strength facilitates the realization of strong coupling. In our experiments a single QD exciton was electrically tuned on resonance with a cavity mode of a micropillar with 1.9 microm diameter and a quality-factor (Q-factor) of 14,000 enabling the observation of strong coupling with a vacuum Rabi-Splitting of 63 microeV.

Ultrafast time-domain spectroscopy based on high-speed asynchronous optical sampling.

High-speed asynchronous optical sampling (ASOPS) is a novel technique for ultrafast time-domain spectroscopy (TDS). It employs two mode-locked femtosecond oscillators operating at a fixed repetition frequency difference as sources of pump and probe pulses. We present a system where the 1 GHz pulse repetition frequencies of two Ti:sapphire oscillators are linked at an offset of Deltaf(R)=10 kHz. As a result, their relative time delay is repetitively ramped from zero to 1 ns within a scan time of 100 micros. Mechanical delay scanners common to conventional TDS systems are eliminated, thus systematic errors due to beam pointing instabilities and spot size variations are avoided when long time delays are scanned. Owing to the multikilohertz scan-rate, high-speed ASOPS permits data acquisition speeds impossible with conventional schemes. Within only 1 s of data acquisition time, a signal resolution of 6 x 10(-7) is achieved for optical pump-probe spectroscopy over a time-delay window of 1 ns. When applied to terahertz TDS, the same acquisition time yields high-resolution terahertz spectra with 37 dB signal-to-noise ratio under nitrogen purging of the spectrometer. Spectra with 57 dB are obtained within 2 min. A new approach to perform the offset lock between the two femtosecond oscillators in a master-slave configuration using a frequency shifter at the third harmonic of the pulse repetition frequency is employed. This approach permits an unprecedented time-delay resolution of better than 160 fs. High-speed ASOPS provides the functionality of an all-optical oscilloscope with a bandwidth in excess of 3000 GHz and with 1 GHz frequency resolution.

The role of AHA motifs in the activator function of tomato heat stress transcription factors HsfA1 and HsfA2.

Using reporter assays in tobacco protoplasts and yeast, we investigated the function of the acidic C-terminal activation domains of tomato heat stress transcription factors HsfA1 and HsfA2. Both transcription factors contain short, essential peptide motifs with a characteristic pattern of aromatic and large hydrophobic amino acid residues embedded in an acidic context (AHA motifs). The prototype is the AHA1 motif of HsfA2, which has the sequence DDIWEELL. Our mutational analysis supports the important role of the aromatic and large hydrophobic amino acid residues in the core positions of the AHA motifs. The pattern suggests the formation of an amphipathic, negatively charged helix as the putative contact region with components of the basal transcription complex. In support of this concept, proline or positively charged residues in or adjacent to the AHA motifs markedly reduce or abolish their activity. Both AHA motifs of HsfA1 and HsfA2 contribute to activator potential, and they can substitute for each other; however, there is evidence for sequence and positional specificity.

Quantitative investigation of hepatic genomic response to hormonal and pathophysiological stimuli by multivariate analysis of two-dimensional mRNA activity profiles.

We have applied techniques of multivariate analysis to the characterization and comparison of the effects of various pathophysiological and hormonal stimuli on the expression of the rat hepatic genome at a pretranslational level. In vitro translated products were resolved by two-dimensional gel electrophoresis. We analyzed 10 pathophysiological states brought about by variation in thyroidal status, starvation, administration of high carbohydrate diet, and the production of experimentally induced diabetes mellitus. Each state differed significantly from every other state in the two-dimensional electrophoretic profiles. The set consisting of the minimal number of products necessary for maintaining the distinctive patterns was identified. The analysis also defined those clusters of products that behaved in a coordinate fashion in response to the various stimuli. Lastly, the similarity and dissimilarity of hepatic mRNA activity profiles to each other could be geometrically represented in three-dimensional space. Our finding that the hepatic mRNA activity profile could distinguish reliably between closely related hormonal and pathophysiological stimuli indicates the specificity of hepatic genomic expression. A systematic analysis of such profiles may be useful as an overall index of the biologic response at the hepatocellular level.