Monitoring Three-Dimensional Packings in Microgravity

We present results from experiments with granular packings in three dimensions in microgravity as realized on parabolic flights. Two different techniques are employed to monitor the inside of the packings during compaction: (1) X-ray radiography is used to measure in transmission the integrated fluctuations of particle positions. (2) Stress-birefringence in three dimensions is applied to visualize the stresses inside the packing. The particle motions below the transition into an arrested packing are found to produce a well agitated state. At the transition, the particles lose their energy quite rapidly and form a stress network. With both methods, non-arrested particles (rattlers) can be identified. In particular, it is found that rattlers inside the arrested packing can be excited to appreciable dynamics by the rest-accelerations (g-jitter) during a parabolic flight without destroying the packings. At low rates of compaction, a regime of slow granular cooling is identified. The slow cooling extends over several seconds, is described well by a linear law, and terminates in a rapid final collapse of dynamics before complete arrest of the packing.Comment: 8 pages, 8 figure

Bacterial mechanosensitive channels : progress towards an understanding of their roles in cell physiology

Open Access funded by Wellcome Trust Under a Creative Commons license Thanks to all members of the Aberdeen group, collaborators and friends whose discussions have spurred the development of the MS channel field. Special thanks to Doug Rees, Diane Newman and Rob Phillips for their support and hospitality at Caltech. Unique insights have been provided by members of the Newman and Phillips research groups, particularly, Caj Neubauer, Gargi Kulkarni and Megan Bergkessel, Heun Jin Lee and Maja Bialecka-Fornal. The author's research on MS channels is supported by a grant from The Wellcome Trust (WT092552MA) and the BBSRC (BB/H017917/1). The author is a Leverhulme Emeritus Fellow and this work was supported in part by a CEMI Visiting Faculty Fellowship from Caltech.Peer reviewedPublisher PD

Stability for Receding-horizon Stochastic Model Predictive Control

A stochastic model predictive control (SMPC) approach is presented for discrete-time linear systems with arbitrary time-invariant probabilistic uncertainties and additive Gaussian process noise. Closed-loop stability of the SMPC approach is established by appropriate selection of the cost function. Polynomial chaos is used for uncertainty propagation through system dynamics. The performance of the SMPC approach is demonstrated using the Van de Vusse reactions.Comment: American Control Conference (ACC) 201

MscS-like mechanosensitive channels in plants and microbes

The challenge of osmotic stress is something all living organisms must face as a result of environmental dynamics. Over the past three decades, innovative research and cooperation across disciplines have irrefutably established that cells utilize mechanically gated ion channels to release osmolytes and prevent cell lysis during hypoosmotic stress. Early electrophysiological analysis of the inner membrane of Escherichia coli identified the presence of three distinct mechanosensitive activities. The subsequent discoveries of the genes responsible for two of these activities, the mechanosensitive channels of large (MscL) and small (MscS) conductance, led to the identification of two diverse families of mechanosensitive channels. The latter of these two families, the MscS family, consists of members from bacteria, archaea, fungi, and plants. Genetic and electrophysiological analysis of these family members has provided insight into how organisms use mechanosensitive channels for osmotic regulation in response to changing environmental and developmental circumstances. Furthermore, determining the crystal structure of E. coli MscS and several homologues in several conformational states has contributed to our understanding of the gating mechanisms of these channels. Here we summarize our current knowledge of MscS homologues from all three domains of life and address their structure, proposed physiological functions, electrophysiological behaviors, and topological diversity

The statisticalanalysis of the fluvial inflow to the Baltic Sea in the years 1921-1970

W niniejszej analizie statystycznej wykorzystano dane zestawione przez Mikulskiego (1975) w ramach regionalnej współpracy hydrologicznej krajów bałtyckich (Międzynarodowy Program Hydrologiczny UNESCO) w projekcie pt. Bilans wodny Morza Bałtyckiego. Obliczenia przeprowadzono w Uniwersytecie Karola Marksa w Lipsku (NRD) w 1978 r. Podstawowe szeregi czasowe przedstawiają miesięczne wartości dopływu (m³ /s) 17 wybranych rzek reprezentujących dopływ do określonych regionów (akwenów) morza (regiony 1-7) (fig. 1, tab. 1). W dokonanej analizie regiony 6 i 7 zostały połączone w jeden region „przejściowy”. Sumy wartości dopływu do określonych regionów tworzą szereg czasowy „całego Bałtyku” (R1-7). Każdy szereg czasowy, składający się ze średnich miesięcznych wartości (m³ /s) okresu I 1921-XII 1970, ma liczebność N = 600 wyrazów. Celom porównawczym posłużą średnie miesięczne zawartości soli pomierzone przy duńskich latarniowcach Gedser Rev i Lappegrund oraz wartości opadów na posterunkach meteorologicznych

A mid-Holocene geochemical record of saline inflow to the Gotland Deep, Baltic Sea

The formation of Mn-enrichments in Gotland Deep sediments has been linked to the occurrence of periodic inflows of saline water from the North Sea. In turn these saline inflow events are very strongly linked to variation in North Atlantic atmospheric conditions. Here sedimentary Mn-concentrations in mid-Holocene sediments are measured with a 0.5 mm sampling resolution using scanning electron microscope techniques. As the sedimentation rate in core 20001-5 was estimated to be approximately 0.5–1 mm per year, examining the variation in Mn-enrichments may potentially provide an annual record of variation in saline inflow, and by extension, North Atlantic climate on interannual timescales. There are many processes that can affect Mn-cycling in the Gotland Deep. When considered together, these processes could potentially act to remove or significantly weaken the transmission of the primary saline inflow signal to the measured geochemical record, producing an effectively random Mn-record. Analysis of the Mn-record as a time series of discrete events revealed that the Mn-record was not consistent with a random distribution of events, and contains some long-term order. Spectral analysis of the Mn-record then indicates a significant periodicity in the Mn-record between 33 and 35.5 mm. This represents a discrete decadal periodicity in Mn-enrichment at 25–55 years that is consistent with the timing of previously reported Mn-enrichments in Gotland Deep sediments