Thyristor-Bypassed Sub-Module Power-Groups for Achieving High-Efficiency, DC Fault Tolerant Multilevel VSCs

Achieving DC fault tolerance in modular multilevel converters requires the use of a significant number of Sub-Modules (SMs) which are capable of generating a negative voltage. This results in an increase in the number of semiconductor devices in the current path, increasing converter conduction losses. This paper introduces a thyristor augmented multilevel structure called a Power-Group (PG), which replaces the stacks of SMs in modular converters. Each PG is formed out of a series stack of SMs with a parallel force-commutated thyristor branch, which is used during normal operation as a low loss bypass path in order to achieve significant reduction in overall losses. The PG also offers negative voltage capability and so can be used to construct high efficiency DC fault tolerant converters. Methods of achieving the turn-on and turn-off of the thyristors by using voltages generated by the parallel stack of SMs within each PG are presented, while keeping both the required size of the commutation inductor, and the thyristor turn-off losses low. Efficiency estimates indicate that this concept could result in converter topologies with power-losses as low as 0.3% rated power, whilst retaining high quality current waveforms and achieving tolerance to both AC and DC faults

Spuriously Elevated Serum IGF-1 in Adult Individuals with Delayed Puberty: A Diagnostic Pitfall

Serum insulin-like growth factor-1 (IGF-1) is a sensitive marker of growth hormone (GH) activity. The levels of IGF-1 vary widely, peaking during puberty and declining with advancing age. During adolescence, serum IGF-1 levels tend to correlate better with pubertal stage rather than chronological age. Here we discuss two cases of delayed puberty, both in their 20s, who presented with high serum IGF-1 but no clinical or biochemical evidence of hypersomatotropism as confirmed by appropriate GH response to an oral glucose challenge. Both individuals achieved full pubertal status with testosterone replacement therapy and their serum IGF-1 levels settled into normal age-specific range. We suggest that in chronologically adult individuals with delayed puberty, serum IGF-1 should not be interpreted on the basis of age-specific normal values but rather on their pubertal status. Furthermore, in the absence of another cause of elevated IGF-1, the expectation is that IGF-1 levels will decline towards age-normative ranges following androgen replacement therapy

Strategies for detecting biological molecules on Titan

Saturn’s moon Titan has all the ingredients needed to produce “life as we know it”. When exposed to liquid water, organic molecules analogous to those found on Titan produce a range of biomolecules such as amino acids. Titan thus provides a natural laboratory for studying the products of prebiotic chemistry. In this work, we examine the ideal locales to search for evidence of, or progression towards, life on Titan. We determine that the best sites to identify biological molecules are deposits of impact melt on the floors of large, fresh impact craters, specifically Sinlap, Selk, and Menrva craters. We find that it is not possible to identify biomolecules on Titan through remote sensing, but rather through in-situ measurements capable of identifying a wide range of biological molecules. Given the non-uniformity of impact melt exposures on the floor of a weathered impact crater, the ideal lander would be capable of precision targeting. This would allow it to identify the locations of fresh impact melt deposits, and/or sites where the melt deposits have been exposed through erosion or mass wasting. Determining the extent of prebiotic chemistry within these melt deposits would help us to understand how life could originate on a world very different from Earth

Thyristor/Diode-Bypassed Sub-Module Power-Groups for Improved Efficiency in Modular Multilevel Converters

The half-bridge Modular Multilevel Converter (MMC) is a Voltage Source Converter (VSC) with high effi- ciency, controllability and modularity. The topology is weak to DC side faults unless bipolar sub-modules are used, but this results in decreased efficiency. Power-Groups (PGs), a thyristor augmented multilevel structure, have been proposed as a way to reduce the power-loss increase arising from achieving DC- fault-tolerance. This paper investigates whether the PG concept can also achieve significant efficiency improvements in VSCs that are not required to be DC fault tolerant. A Single Sub-Module Voltage (SSMV) method of controlling the turn-on/turn-off of the thyristor assembly within each PG structure is presented and the differences with the previously detailed Dual Sub-Module Voltage (DSMV) technique are described. Two thyristor-based PG structures for use in non-DC-fault-tolerant MMCs are proposed, one using SSMV and the other using DSMV. A comparison is made considering the required semiconductor device count, the impact on thyristor snubber design, and the overall power- losses achieved. A further, simplified, variant using a diode bypassed PG structure is presented which results in power- loss reductions during rectifier mode only. Results show that power-loss reductions of ∼ 20-25% can be achieved by using the proposed PG structures to augment a half-bridge MMC

Patient-reported outcomes of parenteral somatostatin analogue injections in 195 patients with acromegaly.

This work is licensed under a Creative Commons Attribution 3.0 Unported LicenseBACKGROUND: Long-acting somatostatin analogues delivered parenterally are the most widely used medical treatment in acromegaly. This patient-reported outcomes survey was designed to assess the impact of chronic injections on subjects with acromegaly. METHODS: The survey was conducted in nine pituitary centres in Germany, UK and The Netherlands. The questionnaire was developed by endocrinologists and covered aspects of acromegaly symptoms, injection-related manifestations, emotional and daily life impact, treatment satisfaction and unmet medical needs. RESULTS: In total, 195 patients participated, of which 112 (57%) were on octreotide (Sandostatin LAR) and 83 (43%) on lanreotide (Somatuline Depot). The majority (>70%) of patients reported acromegaly symptoms despite treatment. A total of 52% of patients reported that their symptoms worsen towards the end of the dosing interval. Administration site pain lasting up to a week following injection was the most frequently reported injection-related symptom (70% of patients). Other injection site reactions included nodules (38%), swelling (28%), bruising (16%), scar tissue (8%) and inflammation (7%). Injection burden was similar between octreotide and lanreotide. Only a minority of patients received injections at home (17%) and 5% were self-injecting. Over a third of patients indicated a feeling of loss of independence due to the injections, and 16% reported repeated work loss days. Despite the physical, emotional and daily life impact of injections, patients were satisfied with their treatment, yet reported that modifications that would offer major improvement over current care would be 'avoiding injections' and 'better symptom control'. CONCLUSION: Lifelong injections of long-acting somatostatin analogues have significant burden on the functioning, well-being and daily lives of patients with acromegaly.Chiasma, Inc. 60 Welles Ave, Newton, MA 02 459, USA

Harmful algal blooms and eutrophication : examining linkages from selected coastal regions of the United States

Author Posting. © Elsevier B.V., 2008. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Harmful Algae 8 (2008): 39-53, doi:10.1016/j.hal.2008.08.017.Coastal waters of the United States (U.S.) are subject to many of the major harmful algal bloom (HAB) poisoning syndromes and impacts. These include paralytic shellfish poisoning (PSP), neurotoxic shellfish poisoning (NSP), amnesic shellfish poisoning (ASP), ciguatera fish poisoning (CFP) and various other HAB phenomena such as fish kills, loss of submerged vegetation, shellfish mortalities, and widespread marine mammal mortalities. Here, the occurrences of selected HABs in a selected set of regions are described in terms of their relationship to eutrophication, illustrating a range of responses. Evidence suggestive of changes in the frequency, extent or magnitude of HABs in these areas is explored in the context of the nutrient sources underlying those blooms, both natural and anthropogenic. In some regions of the U.S., the linkages between HABs and eutrophication are clear and well documented, whereas in others, information is limited, thereby highlighting important areas for further research.Support was provided through the Woods Hole Center for Oceans and Human Health (to DMA), National Science Foundation (NSF) grants OCE-9808173 and OCE-0430724 (to DMA), OCE-0234587 (to WPC), OCE04-32479 (to MLP), OCE-0138544 (to RMK), OCE-9981617 (to PMG); National Institute of Environmental Health Sciences (NIEHS) grants P50ES012742-01 (to DMA) and P50ES012740 (to MLP); NOAA Grants NA96OP0099 (to DMA), NA16OP1450 (to VLT), NA96P00084 (to GAV and CAH), NA160C2936 and NA108H-C (to RMK), NA860P0493 and NA04NOS4780241 (to PMG), NA04NOS4780239-02 (to RMK), NA06NOS4780245 (to DWT). Support was also provided from the West Coast Center for Oceans and Human Health (to VLT and WPC), USEPA Grant CR826792-01-0 (to GAV and CAH), and the State of Florida Grant S7701617826 (to GAV and CAH)