A New Approach to the Cross-Neutralized Microelectrode Amplifier

A circuit is described that produces capacitance neutralization for double barreled microelectrodes. One adjustment compensates for mutual capacitance between electrodes, while the other two adjustments neutralize the capacitance to ground of each electrode.     

Bone marrow repopulation by human marrow stem cells after long-term expansion culture on a porcine endothelial cell line

In vitro exposure of murine hematopoietic stem cells (HSCs) to cell cycle-inducing cytokines has been shown to result in a defect in the ability of these cells to engraft. We used a porcine microvascular endothelial cell (PMVEC) line in conjunction with exogenous interleukin (IL)-3, IL-6, granulocyte-macrophage colony-stimulating factor (GM-CSF), and stem cell factor (SCF) to expand human HSCs that express the CD34 and Thy-1 antigens but lack lineage-associated markers (CD34+Thy-1+Lin- cells). Ex vivo expansion of hematopoietic cells was evaluated in comparison to stromal cell-free, cytokine-supplemented cultures. Cells expressing the CD34+Thy-1+Lin- phenotype were detectable in both culture systems for up to 3 weeks. These cells were reisolated from the cultures and their ability to engraft human fetal bones implanted into SCID mice (SCID-hu bone) was tested. HSCs expanded in PMVEC coculture were consistently capable of competitive marrow repopulation with multilineage (CD19+ B lymphoid, CD33+ myeloid, and CD34+ cells) progeny present 8 weeks postengraftment. In contrast, grafts composed of cells expanded in stroma-free cultures did not lead to multilineage SCID-hu bone repopulation. Proliferation analysis revealed that by 1 week of culture more than 80% of the cells in the PMVEC cocultures expressing the primitive CD34+CD38- phenotype had undergone cell division. Fewer than 1% of the cells that proliferated in the absence of stromal cells remained CD34+CD38-. These data suggest that the proliferation of HSCs in the presence of IL-3, IL-6, GM-CSF, and SCF without stromal cell support may result in impairment of engraftment capacity, which may be overcome by coculture with PMVECs.     

Conjunction of color and form without attention: Evidence from an orientation-contingent color aftereffect.

According to A. Treisman and G. Gelade's (see record 1980-04685-001) feature-integration theory, separable features such as color and shape exist in separate maps in preattentive vision and can be integrated only through the use of spatial attention. However, many perceptual aftereffects, which are also assumed to reflect the features available in preattentive vision, are sensitive to conjunctions of features. One possible resolution of these views holds that adaptation to conjunctions depends on spatial attention. Exp I tested this proposition by presenting 24 undergraduates with gratings varying in color and orientation. The resulting McCollough aftereffects were independent of whether the adaptation stimuli were presented inside or outside of the focus of spatial attention. Therefore, color and shape appear to be conjoined preattentively when perceptual aftereffects are used as the measure. These same stimuli, however, appeared to be separable in Exps II and III, which required 24 Ss to search for gratings of a specified color and orientation. These results show that different experimental procedures may be tapping into different stages of preattentive vision. (63 ref) (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Limit feeding of gravid Holstein heifers: effect on growth, manure nutrient excretion, and subsequent early lactation performance

A study was conducted to evaluate the effect of limit feeding on growth, feed efficiency, and manure excretion in Holstein heifers and subsequent milk production. Fifty-four gravid Holstein heifers were randomly assigned to replicate pens and fed 1 of 3 experimental diets for 111 d. Experimental diets included an ad libitum-fed control diet containing 11.3% crude protein (CP) and 2.46 Mcal/kg of metabolizable energy (ME). Two limit-fed diets of increased nutrient density were formulated to contain 12.7 and 14.2% CP and 2.55 and 2.68 Mcal/kg of ME, respectively. Feed intakes of limit-fed diets were limited to 90 and 80% of the control diet. Nutrient intake, growth, manure excretion, blood metabolites, behavior, and 150-d lactation performance were evaluated. Heifers fed 80 and 90% of the control diet consumed less dry matter (8.3 and 9.0 vs. 9.7 kg/d), but similar amounts of net energy for gain (9.5 and 9.4 vs. 9.4 Mcal/d) and CP (1.17, 1.15 vs. 1.10 kg/d) as compared with control diet-fed heifers. The weight gain and skeletal growth of heifers were not different, but heifers limit fed at 80 and 90% of the control had improved feed efficiency. Heifers limit fed at 80 and 90% of ad libitum intake excreted 0.86 and 0.36 kg/d less dry matter, respectively, as compared with control diet-fed heifers, but all heifers excreted similar amounts of N and P. Limit feeding did not affect calf birth weight, dystocia, or lactation performance. Limit feeding gravid heifers improved feed efficiency and reduced manure dry matter excretion without negative effects on lactation performance.     

An indirect implicit technique for modelling piezoelectric ceramics

The fatigue performance of piezoelectric ceramic components is governed by various factors such as the applied magnitude of electrical and mechanical loads and the number of loading cycles. This paper presents an indirect implicit modelling technique that improves the lifetime prediction for piezoelectric ceramics. The proposed technique has the ability to model hysteretic behaviour as well as complex cyclic degradation behaviour under a significant number of loading cycles. Experimental data of the piezoelectric ceramic, lead zirconate titanate (PZT), from different tests was used in the numerical example to justify the capability and applicability of the proposed technique in describing material cyclic behaviour as well as frequency dependent response without noticeable errors. Furthermore, since artificial neural networks are used as the implicit modelling technique, the proposed technique has the ability to predict multi-physical quantities, appearing in active piezoelectric ceramics, in a single model. Three numerical examples are presented and results show that the proposed technique provides good consistency when applied to different material behaviours.     

Cryogen spray cooling during Nd:YAG laser treatment of hemangiomas. A preliminary animal model study

BACKGROUND: Successful laser treatment of hemangiomas requires selective photothermal destruction of dilated cutaneous vessels without damaging the overlying epidermis. Delivering a short cryogen spurt, on the order of milliseconds, has been shown to result in localized cooling of the superficial skin structures during laser irradiation. OBJECTIVE: The purpose of this study was to examine the effectiveness of cryogen spray cooling (CSC) in protecting superficial tissue structures during continuous Nd:YAG laser irradiation of an in vivo model hemangioma. METHODS: The highly vascularized chicken comb was selected as the animal model for hemangiomas. The Nd:YAG laser irradiation ranged from 2.6 to 35.1 J/mm2. A feedback system utilizing infrared radiometry monitored the comb surface temperature and controlled delivery time of the cryogen spurt. When comb surface temperature during laser irradiation reached 36-42 degrees C, a 30-100 msec cryogen spurt was delivered. Animals were euthanized 1 hour to 21 days following each experiment. Gross and histologic analyses were performed. RESULTS: Nd:YAG laser irradiation resulted in deep (up to 6.1 mm) tissue photocoagulation, while CSC preserved the overlying epidermis and papillary dermis. CONCLUSION: The results demonstrate that CSC is effective in protecting the epidermis and papillary dermis, while achieving deep tissue photocoagulation during Nd:YAG laser irradiation. Further pilot studies in humans appear warranted.     

Selective cervical spine radiography in blunt trauma: methodology of the National Emergency X-Radiography Utilization Study (NEXUS)

BACKGROUND: The purpose of this study was to determine the correlation between progression and regression of myointimal hyperplasia (MH) and cytokine production in experimental vein grafts. Although the autologous vein is the best suitable bypass conduit for reconstruction of peripheral arteries, at the end of the first year thrombosis in the coronary and lower extremity circulation ranges from 20% to 50%. Many of these failures are caused by MH. METHODS: In 76 inbred Lewis rats, a 1 cm long segment of inferior vena cava was inserted at the level of the abdominal aorta. The segments of inferior vena cava were obtained from syngeneic Lewis rats. In 56 animals the arterial vein graft was explanted 3 days (n = 10), 7 days (n = 10), 4 weeks (n = 26), and 12 weeks (n = 10) after operation. In 20 animals the vein graft was explanted 4 weeks after being in the arterial system and reimplanted as iliac venovenous bypass in syngeneic Lewis rats. These grafts were explanted 2 weeks (n = 10) and 8 weeks (n = 10) later. Grafts were analyzed by light and electron microscopy, morphometric study, and histochemical analysis and were put in an organ culture to assess cytokine production. RESULTS: We observed MH formation in arterial vein grafts and MH regression in reimplanted vein grafts (p < 0.001). MH formation was correlated with production of platelet-derived growth factor, basic fibroblast growth factor, interleukin-1, and tumor necrosis factor-alpha. MH regression was correlated with transforming growth factor-beta 1 production. CONCLUSIONS: On the basis of the results of our study, we conclude that MH formation in experimental vein grafts depends on production of platelet-derived growth factor, basic fibroblast growth factor, interleukin-1, and tumor necrosis factor-alpha, and MH regression depends on transforming growth factor-beta 1 production. Cytokine therapy may represent a valuable new treatment to prevent vein bypass failures caused by MH.     

Expression of gonadotropin-releasing hormone (GnRH) gene in human uterine endometrial tissue

OBJECTIVE: To determine if adolescent mothers who request early removal of levonorgestrel implants differ from those who do not in ways that might predispose them to repeated conceptions and in their concerns about adverse effects. We hypothesized that adolescent mothers who request removal of levonorgestrel implants within 2 years of insertion have more risk factors for repeated pregnancy than those who do not. METHODS: We studied the prevalence of 21 characteristics associated with repeated adolescent pregnancy and 16 adverse effects of levonorgestrel implants in 181 postpartum, adolescent levonorgestrel implant recipients, 66 (36%) of whom had the levonorgestrel implants removed within 20 months of insertion (hereafter, removers). RESULTS: Removers (n = 66) had significantly more risk factors for repeated pregnancy and reported significantly more adverse effects than did those who continued to use levonorgestrel implants (hereafter, users) (n = 115). Concerns about adverse effects rose in tandem with risk factors for repeated pregnancy (r = 0.26; P = .001) and were the most important determinant of levonorgestrel implant removal (relative risk, 9.72; 95% confidence interval, 4.62-19.49). However, the number of risk factors for repeated pregnancy was also a significant, independent predictor of levonorgestrel implant removal (relative risk, 2.34; 95% confidence interval, 1.10-4.66). Following removal, contraceptive use was poor and conception occurred rapidly; 24 (37%) of the removers conceived again within 2 years of the index delivery. CONCLUSIONS: The study hypothesis was supported. Our findings that concerns about the adverse effects of levonorgestrel implants rise in tandem with risk factors for repeated pregnancy suggest that the efficacy of counseling before and after levonorgestrel implant insertion could be improved by addressing those aspects of the user's life that undermine the motivation to use contraception.     

Acid-Assisted Consolidation of Silver Alloys for Direct Fillings

Silver-rich metal powders cold-welded by consolidation have been investigated as possible direct dental filling material. The surface of the silver powder must undergo an acid treatment to remove existing contaminants and prevent formation of new surface contaminants during consolidation. This study was designed to investigate the effect of the acid treatment on the strength of the consolidated alloy, its reactivity with the surrounding tooth structure, and its reactions with certain cavity liners.This study investigated the effects of pH and concentration of fluoboric acid on the flexural strength of silver powder consolidated into rectangular beams in a partial 4 × 4 design. The study also assessed, by visible and scanning electron microscopy, what effect the acid-treated powders had on dentin that had been pre-coated with different cavity liners. Mean flexural strengths for beams consolidated using dental hand instruments were in the range (77.0 ± 9.28) MPa to (166.1 ± 17.6) MPa, where the quoted uncertainties are standard uncertainties (i.e., one standard deviation estimates). ANOVA indicated that fluoboric acid pH was highly significant (p < 0.0001) with lower pH values resulting in higher flexural strength. Concentration alone was not a significant factor for flexural strengths, but there was a significant interaction between concentration and pH (p < 0.0001). Microscopy revealed that the acid-treated silver powder demineralized approximately 2 μm of dentin when used with no liner. The use of copal or polyamide varnishes eliminated most of this demineralization, but the use of a dentin adhesive liner resulted in some dislodgment and breakdown of the adhesive film by the acid.The results of this study indicate that this silver powder when treated with dilute fluoboric acid at a pH of approximately 1.0 can result in a filling material with strength equivalent to currently used conventional amalgam. The demineralization of tooth structure appears to be minimal and can be eliminated with the use of cavity liners.