The fabrication of a new electrochemical cell where a thin layer of solution (6
nL) is confined between two closely-spaced parallel gold electrodes is described. By polarizing both electrodes at ...suitable potentials, the forced redox cycling ensures that steady-state conditions are attained almost instantaneously. Voltammetry with ferricyanide solutions demonstrated that the twin-electrode thin-layer cell (TETLC) may operate as a generator–collector device with collection efficiency values of 100%. Experimental results for voltammetry and chronoamperometry experiments agreed with predictions based on digital simulation. The increased sensitivity based on the forced redox cycling envisages future applications of the device, as the use of the TETLC as a pre-reactor at quiescent solutions for the determination of paracetamol in solutions containing ascorbic acid.
Gastroesophageal reflux disease (GERD) is a common medical problem in the United States. As a result, laparoscopic antireflux surgery is a common surgical procedure. At the authors' institution, the ...barium esophagram before and after antireflux surgery is a critical examination in patients with GERD. This article summarizes the authors' examination protocol and describes how the findings are integrated in the care of these patients.
A simple and reliable FIA-potentiometric system for rapid assays of chloride in certain food samples is described and evaluated. The system is constituted by an aquarium air pump to propel the ...carrier solution, a manually operated injector, a homemade dialysis flow cell, a solid-state chloride detector (Ag/AgCl), a reference electrode and a multimeter connected to a microcomputer for data acquisition. The dialysis unit enables direct analysis of liquid food samples without any other previous treatment. The principal novelties are the precision (R.S.D. of 1.2% for whole milk) and rapidity (90 determinations/h) of FIA measurements near and below the lower end of the linear (Nernstian) response region of the chloride ion-selective electrode (ISE), with an estimated detection limit (3
s) of 0.4
mg
L
−1 Cl
− in the sample injected in donor stream. Data of peak potential versus sample chloride concentration (donor stream) was accurately fitted with a quadratic polynomial over the range between 4 and 1000
mg
L
−1 (
r
2
=
0.9999) and used as a calibration curve. The method was applied to the determination of chloride in milk and in coconut water samples. The validation of the results was done by comparison with a NIST reference material (milk) or by capillary electrophoresis (coconut water). For all analysis, no significant difference at a 95% confidence level was observed.
Given its obvious prognostic implications, the correct interpretation of the significance of any residual mediastinal mass following Hodgkin's disease (HD) treatment keeps maintaining its paramount ...importance. In this respect, 18F-fluorodeoxyglucose positron emission tomography (PET) is proving very effective for both active disease detection and relapse prediction. Twenty-nine consecutive HD patients, in whom computed tomography (CT) scan performed after therapy completion had documented a residual mediatinal mass of at least 2 cm, prospectively entered the study and underwent PET within 1 week from CT scan. With a median follow-up of 28 months from PET execution, no relapse was recorded among the 17 patients presenting with a negative PET. On the contrary, 9 of the 12 patients presenting with a positive PET relapsed/progressed within one year from PET execution. PET's negative and positive predictive values at 1 year were 100% and 75%, respectively. A negative PET seems to possibly exclude relapse in HD patient with a residual mediastinal mass. On the contrary, a positive PET result indicates a significantly higher risk of relapse. However, due to possible false positive results, a closer follow-up for all and a pathologic study in few selected patients is warranted.
We identify an important set of key areas where an advanced observational Ultraviolet capability would have major impact on studies of cosmology and Galaxy formation in the young Universe. Most of ...these are associated with the Universe at z < 3-4. We address the issues associated with Dark matter evidence in the local Universe and the impact of the Warm-Hot Intergalactic Medium WHIM on the local Baryon count. The motivations to make ultraviolet (UV) studies of supernovae (SNe) are reviewed and discussed in the light of the results obtained so far by means of IUE and HST observations. It appears that UV studies of SNe can, and do lead to fundamental results not only for our understanding of the SN phenomenon, such as the kinematics and the metallicity of the ejecta, but also for exciting new findings in Cosmology, such as the tantalizing evidence for "dark energy" that seems to pervade the Universe and to dominate its energetics. The need for additional and more detailed UV observations is also considered and discussed. Finally we show the enormous importance of the UV for abundance evolution in the Intergalactic Medium (IGM), and the importance of the He II studies to identify re-ionization epochs, which can only be done in the UV.
Often overlooked and underfunded, ecological monitoring is an essential component of stream restoration work. It helps practitioners to identify successful restoration practices, detect ineffective ...ones, and adjust their adaptive-management activities to improve efficacy (Bernhardt and Palmer 2011). Monitoring, along with research and modeling, are the three legs of the scientific stool that support ecosystem restoration and management. Monitoring tells us what is happening, research tells us why and how it is happening, and modeling provides insights about what can happen under different management alternatives.
Specific and applicable monitoring strategies can vary with the type of stream corridor restoration project that
ABSTRACT
The association of continuous flow injection and spectrophotometry affords a simple, novel and rapid way of monitoring continuously the activity of naturally immobilized enzymes in their ...natural environment, thus eliminating cumbersome purification. The method was applied to determine the activity of polyphenol oxidase (PPO) enzymes naturally immobilized on coconut (Cocus nucifera, L.) fiber tissues. Maximum enzyme activity occurred at a temperature of 25C and at pH 6.0 using catechol as substrate. Thermal stability was assayed in a temperature range of 20 to 75C. The PPO exhibited excellent thermal stability, with only 50% loss in its activity at 75C after 4.3 min exposure. For catechol apparent Michaelis‐Menten constant (apparent Km), apparent Vmax and the apparent activation energy were 9.1 × 10−3 mol L−1, 0.20 abs min−1 and 10.5 kcal mol−1, respectively. The immobilized PPO showed high activity for o‐diphenols. The reactivity order was caffeic acid > pyrogallol > catechol. Complete inhibition of the enzyme was observed with 1 × 10−3 mol L−1 concentration of cyanide, thiourea, L‐cysteine, ascorbic acid, sodium sulfite, nitrates of cadmium, zinc and mercury, individually. Benzoic acid, 3‐hydroxy‐benzoic acid, 4‐acetamidephenol, sodium azide, resorcinol, L‐cystine and EDTA at equal concentrations inhibited PPO partially.
