Wafer-scale epitaxial modulation of quantum dot density.

Precise control of the properties of semiconductor quantum dots (QDs) is vital for creating novel devices for quantum photonics and advanced opto-electronics. Suitable low QD-densities for single QD devices and experiments are challenging to control during epitaxy and are typically found only in limited regions of the wafer. Here, we demonstrate how conventional molecular beam epitaxy (MBE) can be used to modulate the density of optically active QDs in one- and two- dimensional patterns, while still retaining excellent quality. We find that material thickness gradients during layer-by-layer growth result in surface roughness modulations across the whole wafer. Growth on such templates strongly influences the QD nucleation probability. We obtain density modulations between 1 and 10 QDs/µm2 and periods ranging from several millimeters down to at least a few hundred microns. This method is universal and expected to be applicable to a wide variety of different semiconductor material systems. We apply the method to enable growth of ultra-low noise QDs across an entire 3-inch semiconductor wafer.

Neovascularisation of the testes by experimental omentotesticulopexy.

With the currently used surgical procedures, surgical correction of extreme forms of high undescended testes is associated with an atrophy rate of 10% to 30%. In this experimental study in two groups of Sprague-Dawley rats of pubescent age, we examined whether fixation (pexy) of an omental flap on the testis (omentotesticulopexy = OMTX) permits preservation of the viability of the parenchyma. A left-sided OMTX was performed in group 1 with the animals under general anaesthesia. An omental flap was prepared. The tunica albuginea of the testis planned for OMTX was pierced with a needle (26 x 23 G) within an area with a diameter of 1 cm; a puncture distance of 2 mm was used. The omental flap was then fixed using absorbable monofilament 6-0 interrupted sutures. Six weeks later the spermatic vessel was transected at this site. The right testis was left untouched throughout the procedure; it remained in situ. In group 2 only the spermatic vessel on the left side was severed. The right testis was not manipulated and remained in situ. After a total of 10 weeks both testes were removed from all rats and fixed in formalin. Standardised haematoxylin and eosin staining was performed and histological sections were obtained. The size of the testicles, Leydig-cell count, viability, and calcified areas within the tissue were determined for all testicles. Student's t-test was used for statistical evaluation. The study showed that OMTX leads to neovascularisation in the area of fixation and that viability can be preserved within this area.

Appendicitis in children with a ventriculoperitoneal shunt.

The presentation of an acute abdomen in children with a ventriculoperitoneal shunt requires skillful diagnostic workup. Apart from complications caused by the shunt, primary abdominal pathological conditions must be taken into consideration, particularly in the older child. A series of 6 children with a ventriculoperitoneal shunt had to be treated surgically for appendicitis. Their medical records were analyzed retrospectively. Despite difficulties with the initial diagnosis, the time from admission to final diagnosis and operation was relatively short. An accurate history, careful evaluation of the clinical signs and, above all, ultrasound of the abdomen were helpful in decision making. During the operation the shunts were left in place. Only 1 patient developed a cerebrospinal fluid pseudocyst in the early postoperative period, which made a conversion into a ventriculoatrial shunt necessary. No ascending infection occurred, even when the abdominal tip of the shunt came in close contact with the focus of inflammation. An acute abdomen due to shunt infection should be managed conservatively and by removal of the shunt from the abdomen, thus avoiding an unnecessary laparotomy. On the other hand, a primary intraabdominal disease requires surgical treatment, during which the shunt system can be left in place.