Wideband infrared trap detector based upon doped silicon photocurrent devices.

We have designed, fabricated, and measured infrared trap detectors made from arsenic-doped silicon (Si:As) blocked impurity band (BIB) photodetectors. These trap detectors are composed of two detectors in a wedge geometry, with an entrance aperture diameter of either 1 or 3 mm. The detectors were calibrated for quantum efficiency against a pyroelectric reference detector using a Fourier transform spectral comparator system, and etalon effects and spatial uniformity of the traps were also quantified. Measurements of the traps at a temperature of 10 K show that nearly ideal external quantum efficiency (>90%) can be attained over much of the range from 4 to 24 µm, with significant responsivity from 2 to 30 µm. The traps exhibited maximum etalon oscillations of only 2%, which is about 10 times smaller amplitude than those of the single Si:As BIB detectors measured under similar conditions. Spatial nonuniformity across the entrance apertures of the traps was about 1%. The combination of high detectivity, wideband wavelength coverage, spectral flatness, and spatial uniformity make these trap detectors an excellent reference detector for spectrally resolved measurements and radiometric calibrations over the near- to far-infrared wavelength range.

Characterization of the optical properties of an infrared blocked impurity band detector.

Si:As blocked impurity band detectors have been partially deprocessed and measured by Fourier transform spectroscopy to determine their transmittance and reflectance at cryogenic temperatures over the wavelength range 2 µm to 40 µm. A method is presented by which the propagation constants can be extracted from an inversion of the transmittance and reflectance data. The effective propagation constants for the active layer from 2 µm to 20 µm were calculated as well as the absorption cross section of arsenic in silicon, which agrees well with previous results from the literature. The infrared absorptance of the full detector was determined, and the analytical method also provides an estimate of absorption in the active layer alone. Infrared absorptance of the active layer is compared to the quantum yield measured by photoelectric means on similar detectors. The optical methods outlined here, in conjunction with standard electronic measurements, could be used to predict the performance of such detectors from measurements of the blanket films from which they are to be fabricated.

Nanokelvin DC and AC Meissner-transition-edge temperature detectors.

Based upon a superconducting transition edge sensor (TES), the Meissner-TES is a relatively new type of high resolution cryogenic thermometer which employs the magnetic transition of a superconductor to measure temperature. We have improved the signal-to-noise for DC sensing by a factor of 30 compared to our prior effort and developed a new AC mode which uses an oscillating magnetic field and a lock-in technique with much lower magnetic noise than the DC mode. The thermometer was tuned in situ over a range of operating temperatures 10-50 times larger than the transition width of the superconductor, using an applied persistent magnetic field. The DC mode can have sensitivity better than 1 nK for 100 s averaging, and the AC mode has sensitivity better than 120 nK for very small applied magnetic fields near 14 nT and 100 s averaging. The Meissner-TES can be applied to high resolution temperature control, high sensitivity infrared sensing, optical power scale realization, and the study of temperature-dependent phase transitions.

High-gain cryogenic amplifier assembly employing a commercial CMOS operational amplifier.

We have developed a cryogenic amplifier for the measurement of small current signals (10 fA-100 nA) from cryogenic optical detectors. Typically operated with gain near 10(7) V/A, the amplifier performs well from DC to greater than 30 kHz and exhibits noise level near the Johnson limit. Care has been taken in the design and materials to control heat flow and temperatures throughout the entire detector-amplifier assembly. A simple one-board version of the amplifier assembly dissipates 8 mW to our detector cryostat cold stage, and a two-board version can dissipate as little as 17 µW to the detector cold stage. With current noise baseline of about 10 fA/(Hz)(1/2), the cryogenic amplifier is generally useful for cooled infrared detectors, and using blocked impurity band detectors operated at 10 K, the amplifier enables noise power levels of 2.5 fW/(Hz)(1/2) for detection of optical wavelengths near 10 µm.

A novel and inexpensive source of allophycocyanin for multicolor flow cytometry.

Allophycocyanin (APC) belongs to a family of phycobiliproteins that are well suited as fluorescent reagents for flow cytometric analysis, since they have a broad excitation spectrum, a large Stoke's shift and they fluoresce with a high quantum yield. The widespread use of APC has been limited by the availability of raw material and high cost of the purified phycobiliprotein. We have assessed the suitability of dry, powdered Spirulina platensis, available at health food stores, as an inexpensive source of APC. APC was extracted from Spirulina platensis by overnight treatment with lysozyme, followed by ammonium sulfate precipitation. APC was then separated from phycocyanin (the only other major phycobiliprotein in Spirulina) by elution of bound material from an hydroxylapatite column using an increasing continuous phosphate gradient. APC isolated in this manner retained its normal trimeric structure. The absorbance and fluorescence excitation and emission spectra of the purified phycobiliproteins were identical to those previously shown for C-PC and APC. APC can be stored concentrated at 4 degrees C, frozen at -70 degrees C, or as a saturated ammonium sulfate precipitate, with no subunit dissociation or change in spectral properties. Moreover, APC has been conjugated to monoclonal and polyclonal antibodies for use in multicolor FACS analysis, with the conjugated antibody activity remaining stable for at least 2 years. Thus, this procedure is a simple, cost-effective method for preparing reagents for multicolor immunofluorescence and flow cytometry.

Outcome analysis of the transglabellar/subcranial approach for lesions of the anterior cranial fossa: a comparison with the classic craniotomy approach.

The classic approach to anterior skull base lesions uses bifrontal craniotomies together with lateral rhinotomies. This approach requires frontal lobe retraction and is associated with postoperative anosmia and the development of frontal lobe encephalomalacia. The transglabellar/subcranial approach permits removal of anterior skull base lesions without frontal lobe retraction and avoids facial scars. No studies to date, however, have directly compared the two approaches in terms of patient morbidity. The present retrospective study compares the two approaches when used for the removal of anterior skull base lesions in terms of estimated blood loss, number of transfusions, number of days in the hospital and intensive care unit, and postoperative complications. Twenty patients with anterior skull base lesions were examined. The classic approach was used on 10, and the transglabellar/subcranial route was used on 10. When compared with the classic approach, the transglabellar/subcranial approach resulted in a lower estimated blood loss and subsequent transfusion rate, fewer days in the hospital and intensive care unit, and lower numbers and less severe types of complications. Furthermore, visualization of the tumors before resection with the transglabellar/subcranial approach allowed preservation of olfaction in virtually all of these patients. Although this study represents a small sample population, the results are sufficiently impressive to favor the transglabellar/subcranial approach for the removal of a variety of anterior skull base lesions.

Harvesting human hair cells.

The sensory hair cells of the inner ear are responsible for converting balance and hearing stimuli into electrical signals. Until recently, all previous studies of hair cell physiology had been performed on tissue obtained from non-mammals and rodents. In primates, hair cells are difficult to access, because they rest within the densest structure of the body, the otic capsule of the temporal bone. In this report, we describe a technique that we have used in physiological studies to harvest living human hair cells. We collected vestibular and cochlear tissue specimens from adult humans undergoing translabyrinthine and transotic surgical approaches for resection of lateral skull base tumors. Viable hair cells were identified and visualized with light microscopy. The ability to study normal hair cells from humans may further the study of normal and pathological human sensation, hair cell regeneration, and genetic causes of balance and hearing disorders.

Experimental measurements and noise analysis of a cryogenic radiometer.

A cryogenic radiometer device, intended for use as part of an electrical-substitution radiometer, was measured at low temperature. The device consists of a receiver cavity mechanically and thermally connected to a temperature-controlled stage through a thin-walled polyimide tube which serves as a weak thermal link. With the temperature difference between the receiver and the stage measured in millikelvin and the electrical power measured in picowatts, the measured responsivity was 4700 K/mW and the measured thermal time constant was 14 s at a stage temperature of 1.885 K. Noise analysis in terms of Noise Equivalent Power (NEP) was used to quantify the various fundamental and technical noise contributions, including phonon noise and Johnson-Nyquist noise. The noise analysis clarifies the path toward a cryogenic radiometer with a noise floor limited by fundamental phonon noise, where the magnitude of the phonon NEP is 6.5 fW/√Hz for the measured experimental parameters.

[Diagnostics and treatment of posterior cruciate ligament injuries]. / Diagnostik und Therapie von Verletzungen des hinteren Kreuzbandes.

Over the last few years, the posterior cruciate ligament (PCL) has taken over from the anterior cruciate ligament (ACL) as the new challenge in knee diagnosis and treatment. PCL injuries are much more frequent than previously thought. Despite increasing experience, we are often still confronted with an inappropriate and delayed diagnosis of this injury and its concomitant lesions. Additionally, the outcome of surgical treatment has not yet reached an acceptable rate of satisfaction. Therefore, the goal of this concept review is to give a comprehensive insight into injury mechanisms, diagnostics and treatment regimes based on our experience and data from the international literature. Furthermore, diagnostic problems with respect to clinical examination and imaging techniques are discussed. We also present a differential concept for the perioperative and conservative management of PCL deficient knees in order to adequately address concomitant injuries such as posterolateral rotatory instability and combined ACL injuries, with the aim of further improving results.

Rapid modulation of homing receptors (gp90MEL-14) induced by activators of protein kinase C. Receptor shedding due to accelerated proteolytic cleavage at the cell surface.

Lymphocyte entry into lymph nodes and Peyer's patches is initiated by the adhesion of the lymphocytes to specialized postcapillary high endothelial venules (HEV). The binding of lymphocytes to lymph node HEV is mediated by the cell surface receptor gp90MEL-14 (gp90). Previous work has shown that gp90 is down-regulated over a period of days after mitogenic or mixed lymphocyte reaction stimulation of T lymphocytes. In our study, it is shown that stimulation of lymphocytes with activators of protein kinase C (PKC), such as PMA or 1-oleoyl 2-acetyl-glycerol, results in the nearly complete loss of surface expression of gp90 within 1 h. Pretreatment of the cells with H-7 or staurosporine, PKC inhibitors, but not HA1004, a general protein kinase inhibitor, prevents the loss of gp90MEL-14. Within 15 min of stimulation of PKC, a novel form of gp90 can be immunoprecipitated from the supernatant of stimulated cells. Upon deglycosylation, this soluble gp90 polypeptide is shown to be 12 kDa smaller than the cell surface protein. Peptide mapping showed identical patterns for surface and soluble receptor, confirming that the soluble Ag is related to the cell membrane protein. Together, these experiments suggest that activation of PKC results in the proteolytic cleavage of gp90MEL-14, resulting in receptor shedding and the inability of the lymphocytes to adhere to HEV endothelium. Furthermore, because supernatant from unstimulated, normal lymphocytes also contains a small amount of the low Mr form of gp90, cell surface proteolysis may be part of the normal turnover of this receptor glycoprotein. These experiments suggest that PKC may play a role in the regulation of lymphocyte traffic to lymphoid tissues.

Down-regulation of homing receptors after T cell activation.

The specific pattern of lymphocyte localization and recirculation is important for the induction and expression of normal immune responses. In order to home to lymph nodes (LN), lymphocytes must first recognize and bind to specific high endothelial venules (HEV) in the LN. Binding to LN HEV is mediated by specific lymphocyte receptors, termed homing receptors, which are recognized by the mAb MEL-14. We examined the changes that occur in homing receptor expression after activation of murine T lymphocytes in vitro. Cells activated in MLC or by Con A undergo a 75% loss in their ability to recognize HEV, as demonstrated by a decrease in binding to HEV in vitro. Large, activated cells isolated from a primary MLC by elutriator centrifugation were completely unable to recognize HEV, whereas the small cells in the same culture continued to bind well. Flow cytometric analysis with MEL-14 showed that the activated fraction had lost expression of gp90MEL-14, the homing receptor Ag, whereas the inactivated cells remained MEL-14+. Concomitant with the loss of homing receptor expression, most of the activated cells became strongly peanut agglutinin (PNA)-positive, demonstrating a marked change in surface glycosylation. Thus, these MLC consist of two major populations of T cells--small, inactivated lymphocytes that are MEL-14+PNAlo and large, activated blast cells that are MEL-14-PNAhi. Purified MEL-14+ T cells activated by Con A gave rise to MEL-14- progeny, showing that gp90MEL-14 is lost from gp90MEL-14-positive precursors, rather than from the selective growth of MEL-14- cells. Furthermore, the loss of Ag expression on at least some activated cells is reversible in resting culture, with almost half of the cells reverting to MEL-14+ after the cessation of stimulation. These experiments show that activation of T cells results in down-regulation of surface homing receptors, resulting in their inability to recognize and bind to the endothelial surface of HEV. This suggests that the activation of T cells in vivo would result in a dramatic and physiologically significant change in their migration and localization properties which would be important during a normal immune response.

Ionic currents and electromotility in inner ear hair cells from humans.

The upright posture and rich vocalizations of primates place demands on their senses of balance and hearing that differ from those of other animals. There is a wealth of behavioral, psychophysical, and CNS measures characterizing these senses in primates, but no prior recordings from their inner ear sensory receptor cells. We harvested human hair cells from patients undergoing surgical removal of life-threatening brain stem tumors and measured their ionic currents and electromotile responses. The hair cells were either isolated or left in situ in their sensory epithelium and investigated using the tight-seal, whole cell technique. We recorded from both type I and type II vestibular hair cells under voltage clamp and found four voltage-dependent currents, each of which has been reported in hair cells of other animals. Cochlear outer hair cells demonstrated electromotility in response to voltage steps like that seen in rodent animal models. Our results reveal many qualitative similarities to hair cells obtained from other animals and justify continued investigations to explore quantitative differences that may be associated with normal or pathological human sensation.