Design and simulation of losses in Ge/SiGe terahertz quantum cascade laser waveguides.

The waveguide losses from a range of surface plasmon and double metal waveguides for Ge/Si1-xGex THz quantum cascade laser gain media are investigated at 4.79 THz (62.6 µm wavelength). Double metal waveguides demonstrate lower losses than surface plasmonic guiding with minimum losses for a 10 µm thick active gain region with silver metal of 21 cm-1 at 300 K reducing to 14.5 cm-1 at 10 K. Losses for silicon foundry compatible metals including Al and Cu are also provided for comparison and to provide a guide for gain requirements to enable lasers to be fabricated in commercial silicon foundries. To allow these losses to be calculated for a range of designs, the complex refractive index of a range of nominally undoped Si1-xGex with x = 0.7, 0.8 and 0.9 and doped Ge heterolayers were extracted from Fourier transform infrared spectroscopy measurements between 0.1 and 10 THz and from 300 K down to 10 K. The results demonstrate losses comparable to similar designs of GaAs/AlGaAs quantum cascade laser plasmon waveguides indicating that a gain threshold of 15.1 cm-1 and 23.8 cm-1 are required to produce a 4.79 THz Ge/SiGe THz laser at 10 K and 300 K, respectively, for 2 mm long double metal waveguide quantum cascade lasers with facet coatings.

Video-rate terahertz digital holographic imaging system.

Terahertz (THz) imaging has been demonstrated in numerous applications from medical to non-destructive evaluation (NDE), but current systems require expensive components, provide slow frame-rates and low resolutions. THz holography offers a potentially low-cost, high-performance alternative. Here we demonstrate the first full video-rate THz digital holography system at 2.52 THz (118.8 µm) using low-cost optical components. 2D digital reconstructions of samples are performed at frame-rates of 50 Hz - an order of magnitude higher than previous systems, whilst imaging of samples concealed in common packaging types demonstrates suitability for NDE applications. A lateral resolution of 250 µm was determined using a 1951 USAF target.

Choriocarcinoma complicated by splenic rupture: an unusual presentation.

A patient with choriocarcinoma presenting with acute abdominal pain due to splenic rupture from secondary deposits is reported. This rare case exhibited several other unusual features including coexisting bilateral ovarian teratomas and the absence of any evidence of a primary lesion. Several hemangiomata in the liver initially confused the clinic picture.

Plasma volume expansion with colloids increases blood-tissue albumin transport.

Extravasation of plasma proteins is increased after volume expansion with whole blood or plasma. To investigate the mechanisms responsible for this phenomenon, we measured extravascular accumulation of exogenous 131I-labeled bovine serum albumin in several tissues and organs of anesthetized rats. Plasma volume was increased acutely by infusion of isoncotic albumin or polyvinylpyrrolidone, with or without subsequent infusion of a 1:10 dilution of the colloid to induce blood-to-tissue fluid movement. Controls were given only a slow sustaining infusion of saline. The amounts of fluid and plasma protein lost from the circulation were followed simultaneously by two methods: 1) material balance in the whole animal, and 2) changes in 131I-labeled albumin uptake (VA) and water content (VW) in the individual tissues. Plasma volume expansion of 80-90% increased plasma protein extravasation in the whole rat by an average of 2.7-fold over a 30-min period. Of the protein extravasated, 42% entered the abdominal cavity. The rest was distributed in the interstitial compartment of various tissues and organs. Tracer albumin accumulation (averaged over 30 min) was increased 38-82% in skin and paw, 40-59% in skeletal muscles, 131% in hearts, and 167-230% in different parts of the intestine. Increased convective transport does not appear to be a major factor. There was little or no relation of albumin transport increase to the magnitude or direction of net fluid transfer. Coupling of albumin transport to volume flow was not greater than previously reported for saline infusion or venous congestion. Convective redistribution (convective transport without net fluid transfer, "volume recirculation") is estimated to increase albumin transport no more than 10% under the conditions of our experiments. The greater part of the increase is thus dissipative, i.e., attributable to increased diffusion or increased vesicular exchange. Control of dissipative transport of albumin may play an important role in regulating plasma volume.

Influence of saline infusion on blood-tissue albumin transport.

Anesthetized rats were infused with lactated Ringer solution (LR) at constant rate for 30 or 60 min; delivered volume loads ranged from 0.03 to 0.08 ml/g body wt. Controls were given only a sustaining infusion of saline at 0.002 ml.g-1.h-1. Only 7-14% of the LR remained in the plasma at the end of the infusion; 76-88% entered the interstitial compartment, and 7-17% was excreted. The amount of plasma protein lost from the circulation with the extravasated fluid was studied simultaneously by two methods: 1) material balance in the whole animal and 2) changes in 131I-labeled albumin uptake (VA) and water content (VW) in individual tissues. The extravasation of 0.03-0.06 ml fluid/g body wt (75-160% initial plasma volume) did not significantly increase plasma protein extravasation in the whole rat. Nearly all of the sampled tissues of LR-infused rats had higher VW than controls. Tissue VA tended to increase with VW, but the regression slopes (delta VA/delta VW), a measure of the tracer albumin concentration of capillary filtrate relative to plasma, were low; skin, 0.006; paw, 0.018; skeletal muscles, 0.007; heart, 0.057; jejunum, 0.095; ileum, 0.045; cecum, 0.026; and colon, 0.027. These ratios are consistent with the very small loss of total plasma protein observed and attest to high solvent-drag reflection coefficients (sigma approximately equal to 1 - delta VA/delta VW): greater than 0.98 in capillaries of skeletal muscles, skin, and paw and 0.91-0.97 in heart and intestine.