Generation of optical frequency combs by Q-switching integrated multi-section semiconductor lasers.

In this work we perform a theoretical and simulation analysis of the behavior of an integrated four section distributed Bragg reflector semiconductor laser under optical injection and Q-switching operation. An electro-absorption modulator is introduced into the laser cavity to control the total losses and perform Q-switching. The simulations are done using a rate equation model. Q-switching operation produces very short and high power pulses. This, together with the use of optical injection, allows obtaining flat and broad optical frequency combs with up to 2100 optical lines within 10 dB (642 lines within 3 dB) at a repetition frequency of 100 MHz. The high chirp of the pulses is responsible for the broad spectra of these combs in comparison with gain switched combs, and the device structure allows fabrication in commercial foundries using standard building blocks.

Surgical treatment of retrorectal tumors: a plea for a laparoscopic approach.

INTRODUCTION: Retrorectal tumors (RRTs) are rare and often surgically excised due to the risk of malignant degeneration and compressive or obstructive symptoms. The approach for excision has traditionally been based on tumor location and performed using either a transabdominal or perineal approach depending on the position of the tumor. The advent of minimally invasive surgery, however, has challenged this paradigm. Here, we determined the applicability and potential advantages of a laparoscopic transabdominal approach in a series of 23 patients with RRTs. MATERIAL AND METHODS: We included 23 patients presenting with RRTs treated at the Surgical Gastrointestinal Unit at Hospital de Sant Pau that were registered prospectively since 1998. The preoperative evaluation consisted of colonoscopy, CT scan and/or MRI, mechanical bowel lavage, and antibiotic therapy. Signed consent was obtained from all patients for a laparoscopic transabdominal approach unless the tumor was easily accessible via a perineal approach. In case of recurrence, a transanal endoscopic microsurgery (TEM) approach was considered. Surgical details, immediate morbidity, and short- and long-term outcomes were recorded. RESULTS: Of the 23 RRT cases evaluated, 16 patients underwent a laparoscopic transabdominal approach and 6 underwent a perineal approach. No patients required conversion to open surgery. In the laparoscopic transabdominal group, the mean operating time was 158 min, the average postoperative hospital stay was 5 days, and postoperative morbidity was 18%. Three patients had recurrent RRTs, two of the three underwent surgical reintervention. The third patient was radiologically stable and close follow-up was decided. CONCLUSION: Our results show that laparoscopic transabdominal excision of RRT is a safe and effective technique, offering the potential advantages of less invasive access and reduced morbidity. This approach challenges the traditional paradigm of excision of these infrequent tumors based solely on tumor location and offers a viable alternative for the treatment of these infrequent tumors.

Viral envelope glycoprotein processing by proprotein convertases.

The proprotein convertases (PCs) are a family of nine mammalian enzymes that play key roles in the maintenance of cell homeostasis by activating or inactivating proteins via limited proteolysis under temporal and spatial control. A wide range of pathogens, including major human pathogenic viruses can hijack cellular PCs for their own purposes. In particular, productive infection with many enveloped viruses critically depends on the processing of their fusion-active viral envelope glycoproteins by cellular PCs. Based on their crucial role in virus-host interaction, PCs can be important determinants for viral pathogenesis and represent promising targets of therapeutic antiviral intervention. In the present review we will cover basic aspects and recent developments of PC-mediated maturation of viral envelope glycoproteins of selected medically important viruses. The molecular mechanisms underlying the recognition of PCs by viral glycoproteins will be described, including recent findings demonstrating differential PC-recognition of viral and cellular substrates. We will further discuss a possible scenario how viruses during co-evolution with their hosts adapted their glycoproteins to modulate the activity of cellular PCs for their own benefit and discuss the consequences for virus-host interaction and pathogenesis. Particular attention will be given to past and current efforts to evaluate cellular PCs as targets for antiviral therapeutic intervention, with emphasis on emerging highly pathogenic viruses for which no efficacious drugs or vaccines are currently available.