368 research outputs found
A uniform estimate for the density of rational points on quadrics
This paper is concerned with the density of rational points of bounded height
lying on a variety defined by an integral quadratic form Q. In the case of four
variables, we give an estimate that does not depend on the coefficients of Q.
For more variables, a similar estimate still holds with the restriction that we
only count points which do not lie on rational lines
Sup norms of newforms on with highly ramified central character
Recently, the problem of bounding the sup norms of -normalized cuspidal
automorphic newforms on in the level aspect has received
much attention. However at the moment strong upper bounds are only available if
the central character of is not too highly ramified. In this
paper, we establish a uniform upper bound in the level aspect for general
. If the level is a square, our result reduces to at least under the Ramanujan Conjecture. In
particular, when has conductor , this improves upon the previous best
known bound in this setup (due to
Saha [14]) and matches a lower bound due to Templier [18], thus our result is
essentially optimal in this case.Comment: Some computations in the non maximally ramified case in version 1
were erroneous. This version relies on the computations of Assing instead,
and contains some changes in the expositio
Critical evaluation of potentiometric redox titration in enology
Measurements of the zero current potential of a platinum electrode immersed in solutions of tanins or in wines of various origins, were performed during the additions of a solution of Ti(III), or of a solution of dichlorophenolindophenol (DCPIP), in order to obtain a global indication for the resistance to oxidation of some wines. The steady state intensityâpotential curves on a platinum electrode highlight the occurrence of mixed potentials between the oxidation of ethanol or catechin and the reduction of oxygen present at very low concentrations, as well as the irreversibility of the redox system Ti(IV)/Ti(III). The adsorption of various species on the platinum and the slowness of the oxidation reactions by DCPIP exclude use of potentiometric titration theory. The shape of the potentialâreagent volume curves depends on the nature of the solution and on the rate of reagent introduction. Generally, due to the slowness of the oxidation reactions with DCPIP it is impossible to find a linear relationship between the volume of titrant solution necessary to reach the inflexion point of the curves and the solution composition
Influence of electrical potential on the crystallization and adhesion of potassium hydrogen tartrate crystals
Interfacial interactions between a hydroalcoholic solution of potassium hydrogen tartrate (KHT) and a stainless steel surface are studied, when an electrical potential is applied to the metal substrate. The capacitive domain of the metalâsolution interface is determined by cyclic voltammetry. In order to study the influence of the potential on KHT nucleation and crystal adhesion, the solidâliquid interfacial energy is assessed from contact angle and capillary rise measurements. Experimentally, the contact angle between a NaF solution and a stainless steel vs. the potential has a parabolic behaviour. The metal topography has no apparent influence on physicochemical properties of the interface when ethanol is present in a KHT solution. The metal substrate promotes the formation of KHT crystals, which is improved by the application of an anodic potential. The adhesion of crystals becomes more effective when wires of 25 ÎŒm diameter are used in comparison with those of 250 ÎŒm
Improvement of the process for electrochemical impregnation of nickel hydroxide electrodes
Nickel hydroxide electrodes containing 11g/dsqm hydroxide, with capacities of 3.6 to 3.8 Ah/dsqm were prepared at 353 K by electrochemical impregnation. The reproducibility of the results is obtained by readjusting the pH before each preparation. The control of each electrode is done during two cycles of charge and discharge following the manufacture by a potential relaxation method
Silicate electrochemical measurements in seawater: chemical and analytical aspects towards a reagentless sensor
From the study of molybdenum oxidation in aqueous solutions we developed a semi-autonomous method to detect silicate in aqueous samples. Molybdenum oxidation was used to form molybdate in acidic media. The silicomolybdic complex formed with silicate is detectable by amperometry or cyclic voltammetry. The new electrochemical method is in good agreement with the method conventionally used for environmental water silicate analysis. In the second stage, a completely reagentless method was developed using molybdate and proton produced during molybdenum oxidation. Reproducibility tests show a precision of 2.6% for a concentration of 100 ÎŒmol Lâ1. This new method will be very suitable for the development of new autonomous silicate sensors easy to handle and without reagents. In this paper we present the analytical and chemical aspects necessary for a complete documentation of the method before the development of a new reagentless sensor
Electrochemical microsensors for cutaneous surface analysis: Application to the determination of pH and the antioxidant properties of stratum corneum
Potentiometry and cyclic voltammetry were proposed as simple, reliable and non invasive methods for the simultaneous determination of pH and antioxidant properties of skin. Experiments were performed with microelectrodes just deposited on skin surface without any gel or water added. pH was measured by means of the zero current potential of a tungsten W/WO3 sensor. A nerstian response was recorded in pH range 4 to 6 corresponding to the normal skin pH values. The global antioxidant capacity was deduced from the anodic charge passed during the plotting of cyclic voltammograms on platinum or gold microelectrodes. Comparing the half wave or peak potentials of these curves with those recorded for experiments performed in aqueous solution, the main hydrophilic antioxidants species were detected, i.e. ascorbic acid, uric acid and glutathione. This relatively easy-to-use analytical method made it possible to follow in real time the efficiency of topic treatment as well as to study the influence of oxidative stres
Electrochemical behaviour of N-acetyl-l-cysteine on gold electrodeâA tentative reaction mechanism
The electrochemical behaviour of N-acetyl-l-cysteine (NAC) has been investigated by linear and cyclic voltammetry on gold electrode at room temperature. The results showed two oxidation peaks under acid and neutral conditions and only one in basic medium. For each oxidation, as many electron was exchanged as proton. The influence of both the concentration and the potential scan rate on the peak currents highlighted a diffusion-controlled phenomenon for the first peak and an adsorption-limited reaction rate for the second one. The diffusion coefficient of NAC in solution and the surface concentration of the adsorbed species at pH 3 and 7 were close to 2 Ă 10â4 to 2 Ă 10â5 cm2 sâ1 and 6 Ă 10â9 to 6 Ă 10â10 mol cmâ2, respectively. Film transfer experiments resulted in an irreversible adsorption of NAC on gold electrode, and the formation of a self-assembled monolayer (SAM)
Les thérapies du Biofield, en complément de la médecine allopathique, permettent-elles une meilleure gestion des douleurs chroniques ?: travail de Bachelor
Ce travail de Bachelor prend en compte les mĂ©decines alternatives et complĂ©mentaires, plus particuliĂšrement certaines pratiques des thĂ©rapies Biofield, en complĂ©ment de la mĂ©decine allopathique. La pharmacologie est une des ressources de notre mĂ©decine occidentale. Cependant, les douleurs peuvent ĂȘtre gĂ©rĂ©es de diffĂ©rentes maniĂšres. Ce travail va permettre dâidentifier des ressources basĂ©es sur dâautres mĂ©decines. Pour accompagner ce travail, la science de lâĂȘtre-humain unitaire de Martha Rogers a contribuĂ© Ă avoir une vision centrĂ©e sur la personne et son environnement, qui vont permettre de mieux comprendre lâeffet de certaines pratiques. La finalitĂ© de ce travail est de valoriser ces mĂ©thodes en dĂ©montrant quâil est possible de les mettre en pratique dans les unitĂ©s de soins standards
Exploration of the global antioxidant capacity of the stratum corneum by cyclic voltammetry
Cyclic voltammetry is proposed as a new method for evaluating the antioxidant capacity of skin based on the reducing properties of low molecular weight antioxidants (LMWA). Experiments were performed simply by recording the anodic current at 0.9 V/SCE of a platinum microelectrode placed directly on the epidermis surface without any gel or water. This method ensured a direct, rapid (less than 1 min), reliable (accuracy 12%) and non-invasive measurement of the global antioxidant capacity of the stratum corneum with a high spatiotemporal resolution. At the same time, the pH of the skin surface was determined by recording the cathodic current at 0 V/SCE. Based on an exploratory study involving nine volunteer subjects, the evolution of the amperometric response of the microelectrode with time revealed a periodic modification of the redox properties
- âŠ