Bose–Einstein condensation of exciton polaritons

Phase transitions to quantum condensed phases--such as Bose-Einstein condensation (BEC), superfluidity, and superconductivity--have long fascinated scientists, as they bring pure quantum effects to a macroscopic scale. BEC has, for example, famously been demonstrated in dilute atom gas of rubidium atoms at temperatures below 200 nanokelvin. Much effort has been devoted to finding a solid-state system in which BEC can take place. Promising candidate systems are semiconductor microcavities, in which photons are confined and strongly coupled to electronic excitations, leading to the creation of exciton polaritons. These bosonic quasi-particles are 10(9) times lighter than rubidium atoms, thus theoretically permitting BEC to occur at standard cryogenic temperatures. Here we detail a comprehensive set of experiments giving compelling evidence for BEC of polaritons. Above a critical density, we observe massive occupation of the ground state developing from a polariton gas at thermal equilibrium at 19 K, an increase of temporal coherence, and the build-up of long-range spatial coherence and linear polarization, all of which indicate the spontaneous onset of a macroscopic quantum phase.

Polariton parametric amplifier pump dynamics in the coherent regime

We studied the pump coherent dynamics in a II-VI microcavity parametric amplifier, using angle-resolved four-wave mixing. The polariton parametric amplification is found to result in a strong quenching and saturation of the pump coherence lifetime above the threshold. For the polariton scattering processes that remain below the amplification threshold, we find an angle-dependent collision broadening associated with the efficiency of the polariton scattering towards the excitonic reservoir.

Polarization control of the nonlinear emission of semiconductor microcavities

The degree of circular polarization ( Weierstrass p ) of the nonlinear emission in semiconductor microcavities is controlled by changing the exciton-cavity detuning. The polariton relaxation towards K approximately 0 cavitylike states is governed by final-state stimulated scattering. The helicity of the emission is selected due to the lifting of the degeneracy of the +/-1 spin levels at K approximately 0. At short times after a pulsed excitation Weierstrass p reaches very large values, either positive or negative, as a result of stimulated scattering to the spin level of lowest energy (+1/-1 spin for positive/negative detuning).

Primary mechanical stapled anastomosis in surgery for colorectal emergencies

From May 91 to March 99 a consecutive series of 100 acute obstructions or perforations of the left colon or rectum were treated by primary resection with mechanical anastomosis using a double or triple stapling technique without proximal colostomy. There were 8 postoperative deaths (8%) due to sepsis, acute respiratory distress syndrome, pulmonary embolism, stroke, and cachexy. Complications occurred in 29% of surviving patients. Clinical anastomotic leaks were observed in 7%, respiratory infection in 8%, wound infection in 8% and major cardiovascular problems in 4% of patients. The median hospital stay was 19 days. The morbidity and mortality of this series did not exceed the cumulative morbidity and mortality that can be expected after staged surgery. Compared with staged surgery, immediate resection and anastomosis using an entirely mechanical suture, thereby avoiding the problems of colostomy and reducing the length of hospital stay, has significant advantages for patients.

High-temperature ultrafast polariton parametric amplification in semiconductor microcavities

Cavity polaritons, the elementary optical excitations of semiconductor microcavities, may be understood as a superposition of excitons and cavity photons. Owing to their composite nature, these bosonic particles have a distinct optical response, at the same time very fast and highly nonlinear. Very efficient light amplification due to polariton-polariton parametric scattering has recently been reported in semiconductor microcavities at liquid-helium temperatures. Here we demonstrate polariton parametric amplification up to 120 K in GaAlAs-based microcavities and up to 220 K in CdTe-based microcavities. We show that the cut-off temperature for the amplification is ultimately determined by the binding energy of the exciton. A 5-micrometer-thick planar microcavity can amplify a weak light pulse more than 5,000 times. The effective gain coefficient of an equivalent homogeneous medium would be 107 cm-1. The subpicosecond duration and high efficiency of the amplification could be exploited for high-repetition all-optical microscopic switches and amplifiers. 105 polaritons occupy the same quantum state during the amplification, realizing a dynamical condensate of strongly interacting bosons which can be studied at high temperature.

Treatment of colon endoscopic perforations

We describe the treatment of 9 patients who underwent endoscopic perforation of the large bowel. All perforations occurred in patients with colonic diverticulosis or during polypectomy. The choice between conservative or surgical management essentially depends on clinical criteria. Conservative treatment, clinical observation, broad spectrum antibiotics and parenteral diet, is recommended for patient in good general condition and without any sign of peritoneal irritation. Free intraperitoneal gas on X-ray is not an indication for laparotomy. On the other hand, the development of peritonism or clinical deterioration under medical treatment requires a surgical management. Primary suture of the perforation can be performed if the colon was well cleansed for colonoscopy, if the perforation is small and if there is no suspicion of underlying carcinoma. In the other cases, resection including the perforation must be recommended.

Urethral involvement in female patients with bladder cancer. A study of 22 cystectomy specimens

The cystectomy specimens of 22 female patients with various types of bladder cancer were studied for evidence of urethral involvement. The bladder showed high-grade invasive transitional cell carcinoma in 18 patients, in 14 cases in association with flat carcinoma in situ (multifocal in 11 cases and unifocal in three). Three patients had multifocal carcinoma in situ of the bladder without evidence of invasion, and one patient had multifocal high-grade noninvasive papillary carcinoma. Urethral carcinoma in situ was observed in four of 14 patients (29%) with multifocal carcinoma in situ of the bladder, in three cases extending into the periurethral glands. This frequent concurrence of carcinoma in situ of the bladder with urethral and periurethral gland involvement, analogous to the carcinomatous involvement of the prostatic urethra and ducts in male patients, warrants caution in the intravesical therapy of female patients with superficial bladder cancer. The urethra showed invasive carcinoma in three of 18 patients (17%) with invasive bladder cancer (stromal invasion in two cases and vascular invasion in one). This finding reconfirms the use of routine urethrectomy in conjunction with cystectomy in female patients with invasive bladder cancer. An incidental finding was the presence of condylomatous changes in the urethra in five cases (23%).

[Deep cystic colitis. Apropos of a case simulating a neoplastic mass. Review of the literature]

Deep cystic colitis is a benign affection closely related to solitary ulcers of the rectum and inversed hamartomatous polyps. Symptoms lack specificity and its interest resides mainly in its possible confusion with a mucin secreting colloid carcinoma. Failure to recognize the lesion resulted in mutilating operations in several cases reported in the literature confirmed from clinical, radiologic and pathologic data, and the treatment of choice is local excision of the lesion.

[Myeloid leukemia with myelofibrosis (author's transl)]

Myelofibrosis is observed in 1/5 of the cases of C.M.L. It consists of reticulin fibers with few collagen and no osteosclerosis. It involves signs which usually indicate the extension of the myelosis to other organs and other types of cells: hepatosplenomegaly, erythroblastosis, thrombocytemia. Its prognosis is always bad. In one third of the cases, myelofibrosis develops early, and in two third it is late. Chimiotherapy is not responsible for it. These forms of C.M.L. with myelofibrosis appear as a special type of myeloproliferative disorder apart from the true C.M.L. and the true osteomyelofibrosis.