299 research outputs found
Does an Analysis of the Pulsatile Secretion Pattern of Adrenocorticotropin and Cortisol Predict the Result of Transsphenoidal Surgery in Cushing’s Disease.
The endocrinological, surgical, and histological findings of patients with ACTH-dependent Cushing's disease were correlated with the pulsatile secretion pattern of ACTH and cortisol and the outcome after transsphenoidal pituitary surgery. A total of 28 patients were studied. The preoperative pulsatile secretion of ACTH and cortisol was assessed by sampling blood at 20-min intervals over 24 h. The pulsatile pattern of secretion was analyzed by the Cluster program. In 21 patients, an ACTH-secreting pituitary adenoma was identified and resected. Of these patients, 18 underwent clinical remission, and their cortisol secretion was suppressed to a normal level by low dose dexamethasone. Histological examinations in the patients with persistent disease revealed normal pituitary in 6 cases, nodular hyperplasia in 1, and ACTH-secreting pituitary adenoma in 3 cases. Analysis of the pulsatile pattern of ACTH and cortisol secretion did not reveal significant differences in timing, frequency, and/or amplitude of ACTH and cortisol pulses in normalized patients and those with persistent disease after surgery. It is concluded that analysis of the secretory pattern is not a suitable method for predicting the outcome of ranssphenoidal surgery in patients with ACTH-dependent Cushing's disease
Influence of an Electrically Non-Conducting Heat Sink for Power Semiconductors on Radiated Interferences
Power semiconductors are used in a growing number of applications.
Furthermore, faster switching transients and therefore higher switching
frequencies can be realised. This leads to higher radiated interferences at
higher frequencies. In power electronic applications, often a cooling concept
for the semiconductors is required to comply with the allowed temperature
range. Typically, heat sinks are made of aluminium and their conductive
behaviour can cause EMC problems. Via capacitive coupling, voltage transients
are transferred from the power semiconductor to the heat sink, so that the
heat sink behaves as an antenna and radiated interferences occur.
Furthermore, a common mode current will appear if the heat sink is grounded.
In this paper, a promising approach to reduce radiated interferences from the
heat sink and solve the common mode issue by using an electrically isolating
ceramic heat sink is presented. The influence of an aluminium nitride ceramic
heat sink on cooling performance and EMC behaviour has been investigated. For
this purpose, two geometrical identically heat sinks made from aluminium and
aluminium nitride have been compared regarding thermal performance and
radiated interferences characterised by S-parameters.</p
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