Paschen\u27s Law for a Hollow Cathode Discharge

An expression for the breakdown voltage of a one‐dimensional hollow cathode discharge has been derived. The breakdown condition which corresponds to Paschen’s law contains, in addition to the first Townsend coefficient, and the secondary electron emission coefficient two parameters which characterize the reflecting action of the electric field and the lifetime of the electrons in the discharge. The breakdown voltage for a hollow cathode discharge in helium was calculated and compared to that of a glow discharge operating under similar conditions

Governance and Measures for the Prevention of Marine Debris

Marine microplastic pollution is increasingly seen as a transboundary problem that requires priority attention and represents a unique governance challenge, given the associated risks and ubiquity of microplastics in the marine environment. Various governance measures to reduce the use of microplastics and to prevent further pollution of the marine environment have been adopted or are under consideration by actors at different levels of governance. This chapter reviews these governance measures and we argue that the primary concern of regulators should be to prevent both primary and secondary microplastic leakage into the marine ecosystems. We proceed with the further assumption that most microplastic enters marine ecosystems from land-based sources, so policies designed to curtail this particular form of plastic pollution are given due emphasis in this chapter. The prevention of microplastic pollution in the oceans is inherently complex, and this chapter examines the governance framework on the global, regional, national, and subnational levels. Both international collaboration and complimentary governance by non-state actors are important in order to effectively prevent microplastic pollution entering the oceans. Evidence from the examples analyzed throughout the chapter confirms that a comprehensive, systems-level approach, including a combination of diverse prevention measures and the involvement of a wide range of actors, is necessary

Sheehan syndrome

WOS: 000397870700001PubMed ID: 28004764Sheehan syndrome or postpartum hypopituitarism is a condition characterized by hypopituitarism due to necrosis of the pituitary gland. The initial insult is caused by massive postpartum haemorrhage (PPH), leading to impaired blood supply to the pituitary gland, which has become enlarged during pregnancy. Small sella turcica size, vasospasms (caused by PPH) and/or thrombosis (associated with pregnancy or coagulation disorders) are predisposing factors; autoimmunity might be involved in the progressive worsening of pituitary functions. Symptoms are caused by a decrease or absence of one or more of the pituitary hormones, and vary, among others, from failure to lactate and nonspecific symptoms (such as fatigue) to severe adrenal crisis. In accordance with the location of hormone-secreting cells relative to the vasculature, the secretion of growth hormone and prolactin is most commonly affected, followed by follicle-stimulating hormone and luteinizing hormone; severe necrosis of the pituitary gland also affects the secretion of thyroid-stimulating hormone and adrenocorticotropic hormone. Symptoms usually become evident years after delivery, but can, in rare cases, develop acutely. The incidence of Sheehan syndrome depends, to a large extent, on the occurrence and management of PPH. Sheehan syndrome is an important cause of hypopituitarism in developing countries, but has become rare in developed countries. Diagnosis is based on clinical manifestations combined with a history of severe PPH; hormone levels and/or stimulation tests can confirm clinical suspicion. Hormone replacement therapy is the only available management option so far