Diurnal and spatial variation of xylem dielectric constant in Norway Spruce (Picea abies [L.] Karst.) as related to microclimate, xylem sap flow, and xylem chemistry

Spatial and temporal variations in vegetation dielectric properties strongly influence the microwave backscatter characteristics of forested landscapes. This paper examines the relationship between xylem tissue dielectric constant, xylem sap flux density, and xylem sap chemical composition as measured in the stems of two Norway Spruce (Picea abies [L.] Karst.) trees in the Fichtelgebirge region of Northern Bavaria, Germany. Dielectric constant and xylem sap flux were monitored continuously from June through October 1995, at several heights along the tree trunks. At the end of the measurement series, each tree was harvested, and its xylem sap extracted and analyzed to determine the concentrations of amino acids and cations. Results show that the sap flux density was correlated with vapor pressure deficit (VPD) at all heights in the stem. In contrast, the xylem tissue dielectric constant is influenced by VPD but can exhibit a significant temporal lag relative to changes in VPD. This lag varies with position along the tree trunk. The temporal variability of the dielectric constant is compared with both trees at several positions along the tree trunks. Results of xylem sap chemical analysis are presented. We show that spatial and temporal variability in the xylem tissue dielectric constant is influenced not only by water content, but by variations in xylem sap chemistry as well. This has important implications for microwave remote sensing of forested landscapes, as useful information may be acquired regarding stand physiology and water relations and where variations in dielectric properties within individual trees and across geographic areas can be significant error sources for forest inventory mapping.     

Progress in the development of polymer cholesteric liquid crystal flakes for display applications

Polymer cholesteric liquid crystal (PCLC) flake technology is being developed as an alternative display technology for flexible, reflective particle displays. The motion of PCLC flakes suspended in a host fluid can be controlled with an electric field, creating a way to electrically control the flakes' ability to brightly reflect light that is circularly polarized. The PCLC flake/host fluid dispersion has been successfully microencapsulated both in a polymer matrix and in gelatin micro-capsules. Microencapsulation will not only expand the applications scope of the technology, but also may aid in addressing some potential problem areas that are inherent to many forms of particle display technology. A second important development in PCLC flake technology involves the manufacture of shaped flakes based on soft lithography techniques. The size and shape of a flake impact its reorientation, and uniformly shaped flakes respond in a similar manner. The unique reflective properties of PCLC flakes also provide possible applications in areas such as optics and photonics, switchable ‘smart windows’ or conformal coatings, and information displays such as ‘electronic paper.’     

Pigeon perception and discrimination of rapidly changing texture stimuli

The perception and discrimination of rapidly changing texture stimuli by pigeons was examined in a target localization task. Five experienced pigeons were rewarded for finding and pecking at a randomly placed odd target block of small repeated elements embedded in a larger rectangular array of contrasting distractor elements. On dynamic color test trials, the color of the target, distractor, or both of these regions changed at rates of 100, 250, 500, or 1000 ms per frame. The number of colors appearing within such trials also varied. Pigeons performed well above chance in all test conditions, with target-associated changes producing the best discrimination. The results suggest: (a) global relational information can exclusively guide target localization behavior, (b) pigeons can perceptually group and segregate colored textured differences quite rapidly (< or = 100 ms), and (c) pigeons may possess automatic search control processes that can be captured by stimulus-driven changes in the display.     

Dantrolene inhibition of sarcoplasmic reticulum Ca2+ release by direct and specific action at skeletal muscle ryanodine receptors

The skeletal muscle relaxant dantrolene inhibits the release of Ca2+ from the sarcoplasmic reticulum during excitation-contraction coupling and suppresses the uncontrolled Ca2+ release that underlies the skeletal muscle pharmacogenetic disorder malignant hyperthermia; however, the molecular mechanism by which dantrolene selectively affects skeletal muscle Ca2+ regulation remains to be defined. Here we provide evidence of a high-affinity, monophasic inhibition by dantrolene of ryanodine receptor Ca2+ channel function in isolated sarcoplasmic reticulum vesicles prepared from malignant hyperthermia-susceptible and normal pig skeletal muscle. In media simulating resting myoplasm, dantrolene increased the half-time for 45Ca2+ release from both malignant hyperthermia and normal vesicles approximately 3.5-fold and inhibited sarcoplasmic reticulum vesicle [3H]ryanodine binding (Ki approximately 150 nM for both malignant hyperthermia and normal). Inhibition of vesicle [3H]ryanodine binding by dantrolene was associated with a decrease in the extent of activation by both calmodulin and Ca2+. Dantrolene also inhibited [3H]ryanodine binding to purified skeletal muscle ryanodine receptor protein reconstituted into liposomes. In contrast, cardiac sarcoplasmic reticulum vesicle 45Ca2+ release and [3H]ryanodine binding were unaffected by dantrolene. Together, these results demonstrate selective effects of dantrolene on skeletal muscle ryanodine receptors that are consistent with the actions of dantrolene in vivo and suggest a mechanism of action in which dantrolene may act directly at the skeletal muscle ryanodine receptor complex to limit its activation by calmodulin and Ca2+. The potential implications of these results for understanding how dantrolene and malignant hyperthermia mutations may affect the voltage-dependent activation of Ca2+ release in intact skeletal muscle are discussed.     

Anatomical suitability of abdominal aortic aneurysms for endovascular repair

BACKGROUND: Aortic aneurysm anatomy is crucial when considering patients for endovascular repair. The aim of this study was to determine the proportion of patients with aortic aneurysm suitable for endovascular repair with three different graft-stent systems. METHODS: Spiral computed tomographic angiography was used to assess the anatomy of 154 abdominal aortic aneurysms. Measurements were made of aneurysm neck length and diameter, renal artery to aortic bifurcation length, common iliac artery diameter and length, and external iliac artery diameter. Aneurysms were assessed for anatomical suitability for currently available aortoaortic, aortobi-iliac and aortouni-iliac devices. RESULTS: Six patients (4 per cent) had a distal aortic neck suitable for implantation of a straight aortic graft. Fifteen patients (10 per cent) had arterial anatomy suitable for implantation of a bifurcated graft and 85 (55 per cent) patients were suitable for endovascular repair with an aortouni-iliac graft. The primary reasons for unsuitability were: proximal neck length less than 1.5 cm (44 patients), proximal neck diameter greater than 3.0 cm (12), and angulation of the proximal neck (three). A further ten patients were considered unsuitable for an aortouni-iliac graft because of bilateral common iliac artery aneurysms (four), tortuous iliac arteries (four) and narrow external iliac arteries (two). CONCLUSION: The aortouni-iliac device has the widest applicability of the currently available endovascular systems but open repair remains the only option for a large proportion of patients.     

Prognostic significance of cathepsin-D in patients with breast cancer

The expression of the protease cathepsin-D has been evaluated using an immunohistochemical technique with a polyclonal antibody in paraffin-embedded tissue from 359 patients treated between the years 1975-1981 for Stage I and II breast cancer. One hundred and twenty seven patients (35%) have strongly positive, granular staining, 138 (38%) are intermediately stained in the cytoplasm, and in 94 (26%) no staining is observed. There is a strong positive association between expression of cathepsin-D and the presence of tumour in axillary lymph nodes (P < 0.006). Expression of the protease is associated with significantly poorer survival of patients in univariate analysis (P = 0.025); however, this is not independent of other tumour variables.     

Clinical pharmacokinetics of mycophenolate mofetil

The pharmacokinetics of the immunosuppressant mycophenolate mofetil have been investigated in healthy volunteers and mainly in recipients of renal allografts. Following oral administration, mycophenolate mofetil was rapidly and completely absorbed, and underwent extensive presystemic de-esterification. Systemic plasma clearance of intravenous mycophenolate mofetil was around 10 L/min in healthy individuals, and plasma mycophenolate mofetil concentrations fell below the quantitation limit (0.4 mg/L) within 10 minutes of the cessation of infusion. Similar plasma mycophenolate mofetil concentrations were seen after intravenous administration in patients with severe renal or hepatic impairment, implying that the de-esterification process had not been substantially affected. Mycophenolic acid, the active immunosuppressant species, is glucuronidated to a stable phenolic glucuronide (MPAG) which is not pharmacologically active. Over 90% of the administered dose is eventually excreted in the urine, mostly as MPAG. The magnitude of the MPAG renal clearance indicates that active tubular secretion of MPAG must occur. At clinically relevant concentrations, mycophenolic acid and MPAG are about 97% and 82% bound to albumin, respectively. MPAG at high (but clinically realisable) concentrations reduced the plasma binding of mycophenolic acid. The mean maximum plasma mycophenolic acid concentration (Cmax) after a mycophenolate mofetil 1 g dose in healthy individuals was around 25 mg/L, occurred at 0.8 hours postdose, decayed with a mean apparent half-life (t1/2) of around 16 hours, and generated a mean total area under the plasma concentration-time curve (AUC infinity) of around 64 mg.h/L. Intra- and interindividual coefficients of variation for the AUC infinity of the drug were estimated to be 25% and 10%, respectively. Intravenous and oral administration of mycophenolate mofetil showed statistically equivalent MPA AUC infinity values in healthy individuals. Compared with mycophenolic acid, MPAG showed a roughly similar Cmax about 1 hour after mycophenolic acid Cmax, with a similar t1/2 and an AUC infinity about 5-fold larger than that for mycophenolic acid. Secondary mycophenolic acid peaks represent a significant enterohepatic cycling process. Since MPAG was the sole material excreted in bile, entrohepatic cycling must involve colonic bacterial deconjugation of MPAG. An oral cholestyramine interaction study showed that the mean contribution of entrohepatic cycling to the AUC infinity of mycophenolic acid was around 40% with a range of 10 to 60%. The pharmacokinetics of patients with renal transplants (after 3 months or more) compared with those of healthy individuals were similar after oral mycophenolate mofetil. Immediately post-transplant, the mean Cmax and AUC infinity of mycophenolic acid were 30 to 50% of those in the 3-month post-transplant patients. These parameters rose slowly over the 3-month interval. Slow metabolic changes, rather than poor absorption, seem responsible for this nonstationarity, since intravenous and oral administration of mycophenolate mofetil in the immediate post-transplant period generated comparable MPA AUC infinity values. Renal impairment had no major effect on the pharmacokinetic of mycophenolic acid after single doses of mycophenolate mofetil, but there was a progressive decrease in MPAG clearance as glomerular filtration rate (GFR) declined. Compared to individuals with a normal GFR, patients with severe renal impairment (GFR 1.5 L/h/1.73m2) showed 3-to 6-fold higher MPAG AUC values. In rental transplant recipients during acute renal impairment in the early post-transplant period, the plasma MPA concentrations were comparable to those in patients without renal failure, whereas plasma MPAG concentrations were 2- to 3-fold higher. Haemodialysis had no major effect on plasma mycophenolic acid or MPAG. Dosage adjustments appear to not be necessary either in renal impairment or during dialysis. (ABSTRACT TRUN     

Effective shelf-life of prepared sodium hypochlorite solution

Although the tissue solvent and bactericidal properties of sodium hypochlorite are well known, the effective shelf-life of prepared sodium hypochlorite solutions is not known. The stability of sodium hypochlorite is adversely affected by exposure to high temperature, light, air, and the presence of organic and inorganic contaminants. The purpose of this study was to investigate the variables of storage conditions and time on the tissue-dissolving capacity of three different concentrations of sodium hypochlorite. Fresh frozen human umbilical cord was used as the tissue sample for this experiment. Tissue samples were dissolved at time intervals ranging from 1 day to 10 wk in 5.25%, 2.62%, and 1.0% solutions of sodium hypochlorite. The tissue-dissolving ability of 5.25% sodium hypochlorite remains stable for at least 10 wk. The tissue-dissolving ability of 2.62% and 1.0% sodium hypochlorite remains relatively stable for 1 wk after mixing, then exhibits a significant decrease in tissue-dissolving ability at 2 wk and beyond.