4 research outputs found
Droplet Conductivity Strongly Influences Bump and Crater Formation on Electrodes during Charge Transfer
Aqueous droplets
acquire charge when they contact electrodes in
high voltage electric fields, but the exact mechanism of charge transfer
is not understood. Recent work by Elton et al. revealed that electrodes
are physically pitted during charge transfer with aqueous droplets.
The pits are believed to result when a dielectric breakdown arc occurs
as a droplet approaches the electrode and the associated high current
density transiently locally melts the electrode, leaving distinct
crater-like deformations on the electrode surface. Here we show that
the droplet conductivity strongly modulates the pitting morphology
but has little effect on the amount of charge transferred. Electron
and atomic force microscopy shows that deionized water droplets yield
no observable deformations, but as the salt concentration in the droplet
increases above 10<sup>â3</sup> M, the deformations become
increasingly large. The observed intensity of the flash of light released
during the dielectric breakdown arc also increases with droplet conductivity.
Surprisingly, despite the large difference in pitting morphology and
corresponding arc intensity, droplets of any conductivity acquire
similar amounts of charge. These results suggest that the energy transferred
during dielectric breakdown is primarily responsible for electrode
pitting rather than the total amount of energy released during charge
transfer
Droplet Conductivity Strongly Influences Bump and Crater Formation on Electrodes during Charge Transfer
Aqueous droplets
acquire charge when they contact electrodes in
high voltage electric fields, but the exact mechanism of charge transfer
is not understood. Recent work by Elton et al. revealed that electrodes
are physically pitted during charge transfer with aqueous droplets.
The pits are believed to result when a dielectric breakdown arc occurs
as a droplet approaches the electrode and the associated high current
density transiently locally melts the electrode, leaving distinct
crater-like deformations on the electrode surface. Here we show that
the droplet conductivity strongly modulates the pitting morphology
but has little effect on the amount of charge transferred. Electron
and atomic force microscopy shows that deionized water droplets yield
no observable deformations, but as the salt concentration in the droplet
increases above 10<sup>â3</sup> M, the deformations become
increasingly large. The observed intensity of the flash of light released
during the dielectric breakdown arc also increases with droplet conductivity.
Surprisingly, despite the large difference in pitting morphology and
corresponding arc intensity, droplets of any conductivity acquire
similar amounts of charge. These results suggest that the energy transferred
during dielectric breakdown is primarily responsible for electrode
pitting rather than the total amount of energy released during charge
transfer
Candidoses invasives en rĂ©animation : donnĂ©es Ă©pidĂ©miologiques, Ă©laboration dâun score prĂ©dictif et mise au point de PCR pour le diagnostic
Patients in intensive care units (ICU) are at very high risk of invasive candidiasis associated with high mortality rate. Candida species are the third cause of septicemia. Clinical signs lack of specificity and blood cultures lack of sensitivity, and therefore the diagnosis remains a challenge. In order to improve the identification of patients with invasive candidiasis, predictive rules, biomarkers and PCR have been developed. The first part of this work describes the evolution over a ten years period in one ICU in Candida species distribution, susceptibility to antifungal drugs and consumption of antifungal agents. Changes in antifungal drug consumption were observed but they were not associated with significant changes in fungal ecology or with the emergence of resistant species. In a second part, we present a prospective, observational and bicentric study performed in 435 non-neutropenic patients in ICU. Several variables (risk factors of invasive candidiasis, Candida colonization, mannan antigen and anti-mannan antibodies) were analyzed and a predictive score of invasive candidiasis has been developed. Finally, the last part presents the development of Candida real-time PCR in blood, as well as the evaluation of a digital PCR.Les patients de rĂ©animation sont des patients Ă trĂšs haut risque de survenue de candidoses invasives associĂ©es Ă une importante mortalitĂ©. Les espĂšces du genre Candida sont retrouvĂ©es en troisiĂšme position des agents infectieux les plus frĂ©quemment isolĂ©s au cours des septicĂ©mies. Le diagnostic reste difficile en raison dâune clinique aspĂ©cifique et dâune sensibilitĂ© mĂ©diocre des hĂ©mocultures. Des scores prĂ©dictifs, des biomarqueurs ou encore des PCR ont Ă©tĂ© dĂ©veloppĂ©s de maniĂšre Ă amĂ©liorer le diagnostic et lâidentification des patients Ă risque. Dans ce travail, la premiĂšre partie prĂ©sente les donnĂ©es de lâĂ©volution de lâĂ©cologie fongique, des candidoses invasives, des prescriptions dâantifongiques et des sensibilitĂ©s aux antifongiques sur une pĂ©riode de dix ans dans un service de rĂ©animation. Au cours de cette pĂ©riode, les changements observĂ©s dans la prescription dâantifongiques nâont pas entrainĂ© de modifications significatives de lâĂ©cologie fongique ni dâapparition de rĂ©sistances. Dans une deuxiĂšme partie, nous prĂ©sentons les rĂ©sultats dâune Ă©tude prospective observationnelle bicentrique rĂ©alisĂ©e chez 435 patients non neutropĂ©niques de rĂ©animation. Lâanalyse de plusieurs variables (facteurs de risque de candidose invasive, colonisation Ă Candida sp., dosages dâantigĂšne mannane et dâanticorps anti-mannane) a permis lâĂ©laboration dâun score prĂ©dictif de survenue de candidose invasive. Finalement, la derniĂšre partie du travail prĂ©sente la mise au point de PCR Candida en temps rĂ©el dans le sang ainsi quâune Ă©valuation de la technologie de digital PCR
Measurement of Charge Transfer to Aqueous Droplets in High Voltage Electric Fields
The
electric charge acquired by aqueous droplets when they contact
an electrode is a crucial parameter in experimental and industrial
applications where electric fields are used to manipulate droplet
motion and coalescence. For unclear reasons, many investigators have
found that aqueous droplets acquire significantly more positive than
negative charge. Extant techniques for determining the droplet charge
typically rely on a hydrodynamic force balance that depends on accurate
characterization of the drag forces acting on the droplet. Here we
present an alternative methodology for measuring the droplet charge
via direct measurement of the electric current. As the droplet approaches
the electrode the current is observed to gradually increase, followed
by a large pulse when the droplet makes apparent contact. We interpret
the transient current signals as the superposition of the natural
response of an RLC circuit and an induced current described by the
ShockleyâRamo theory. Nonlinear regression of the observed
current to the theoretical model allows for the droplet charge to
be extracted, independent of any assumptions about the force balance
on the droplet. We demonstrate that regression of the current signal
yields charge values that are on average within 4% of charges measured
via a force balance. We use the chronocoulometric methodology to investigate
how the charge varies with the applied potential, and we demonstrate
that deionized water droplets contacting planar electrodes acquire
on average 69% more positive charge than negative charge