The Biot-Savart operator and electrodynamics on subdomains of the three-sphere

We study steady-state magnetic fields in the geometric setting of positive curvature on subdomains of the three-dimensional sphere. By generalizing the Biot-Savart law to an integral operator BS acting on all vector fields, we show that electrodynamics in such a setting behaves rather similarly to Euclidean electrodynamics. For instance, for current J and magnetic field BS(J), we show that Maxwell's equations naturally hold. In all instances, the formulas we give are geometrically meaningful: they are preserved by orientation-preserving isometries of the three-sphere. This article describes several properties of BS: we show it is self-adjoint, bounded, and extends to a compact operator on a Hilbert space. For vector fields that act like currents, we prove the curl operator is a left inverse to BS; thus the Biot-Savart operator is important in the study of curl eigenvalues, with applications to energy-minimization problems in geometry and physics. We conclude with two examples, which indicate our bounds are typically within an order of magnitude of being sharp.Comment: 24 pages (was 28 pages) Revised to include a new introduction, a detailed example, and results about helicity; other changes for readabilit

Effectiveness of implementing a wake up and breathe program on sedation and delirium in the ICU

OBJECTIVES: Mechanically ventilated critically ill patients receive significant amounts of sedatives and analgesics that increase their risk of developing coma and delirium. We evaluated the impact of a "Wake-up and Breathe Protocol" at our local ICU on sedation and delirium. DESIGN: A pre/post implementation study design. SETTING: A 22-bed mixed surgical and medical ICU. PATIENTS: Seven hundred two consecutive mechanically ventilated ICU patients from June 2010 to January 2013. INTERVENTIONS: Implementation of daily paired spontaneous awakening trials (daily sedation vacation plus spontaneous breathing trials) as a quality improvement project. MEASUREMENTS AND MAIN RESULTS: After implementation of our program, there was an increase in the mean Richmond Agitation Sedation Scale scores on weekdays of 0.88 (p < 0.0001) and an increase in the mean Richmond Agitation Sedation Scale scores on weekends of 1.21 (p < 0.0001). After adjusting for age, race, gender, severity of illness, primary diagnosis, and ICU, the incidence and prevalence of delirium did not change post implementation of the protocol (incidence: 23% pre vs 19.6% post; p = 0.40; prevalence: 66.7% pre vs 55.3% post; p = 0.06). The combined prevalence of delirium/coma decreased from 90.8% pre protocol implementation to 85% postimplementation (odds ratio, 0.505; 95% CI, 0.299-0.853; p = 0.01). CONCLUSIONS: Implementing a "Wake Up and Breathe Program" resulted in reduced sedation among critically ill mechanically ventilated patients but did not change the incidence or prevalence of delirium

Jasmonic acid-dependent regulation of seed dormancy following maternal herbivory in Arabidopsis

Maternal experience of abiotic environmental factors such as temperature and light are well known to control seed dormancy in many plant species. Maternal biotic stress alters offspring defence phenotypes, but whether it also affects seed dormancy remains unexplored. We exposed Arabidopsis thaliana plants to herbivory and investigated plasticity in germination and defence phenotypes in their offspring, along with the roles of phytohormone signalling in regulating maternal effects. Maternal herbivory resulted in the accumulation of jasmonic acid-isoleucine and loss of dormancy in seeds of stressed plants. Dormancy was also reduced by engineering seed-specific accumulation of jasmonic acid in transgenic plants. Loss of dormancy was dependent on an intact jasmonate signalling pathway and was associated with increased gibberellin content and reduced abscisic acid sensitivity during germination. Altered dormancy was only observed in the first generation following herbivory, whereas defence priming was maintained for at least two generations. Herbivory generates a jasmonic acid-dependent reduction in seed dormancy, mediated by alteration of gibberellin and abscisic acid signalling. This is a direct maternal effect, operating independently from transgenerational herbivore resistance priming

Cubic and hexagonal InGaAsN dilute arsenides by unintentional homogeneous incorporation of As into InGaN

Arsenic alloying is observed for epitaxial layers nominally intended to be In0.75Ga0.25N. Voids form beneath their interfaces with GaAs substrates, acting as sources of Ga + As out-diffusion into the growing epilayers. As a result, heteroepitaxial single-phase quaternary InxGa1-xAsyN1-y, films are formed with x similar to 0.55 and 0.05 menor que y menor que 0,10. While an undoped epilayer retains the wurtzite structure, a Mn-doped sample showed randomly spaced dopant segregations, which, together with a slightly higher As concentration, led to a transformation from the hexagonal to the twinned cubic phase

Governors and directors: Competing models of corporate governance

Why do we use the term ‘corporate governance’ rather than ‘corporate direction’? Early British joint stock companies were normally managed by a single ‘governor’. The ‘court of governors’ or ‘board of directors’ emerged slowly as the ruling body for companies. By the nineteenth century, however, companies were typically run by directors while not-for-profit entities such as hospitals, schools and charitable bodies had governors. The nineteenth century saw steady refinement of the roles of company directors, often in response to corporate scandals, with a gradual change from the notion of the director as a ‘representative shareholder’ to the directors being seen collectively as ‘representatives of the shareholders’. Governors in not-for-profit entities, however, were regarded as having broader responsibilities. The term ‘governance’ itself suggests that corporate boards should be studied as ‘political’ entities rather than merely through economic lenses such as agency theory

Unsteady turbulence in tidal bores: Effects of bed roughness

A tidal bore is a wave propagating upstream as the tidal flow turns to rising. It forms during spring tide conditions when the flood tide is confined to a narrow funneled channel. To date, theoretical and numerical studies rely upon physical experiments to validate the developments, but the experimental data are limited mostly to visual observations and sometimes free-surface measurements. Herein turbulent velocity measurements were obtained in a large-size laboratory facility with a fine spatial and temporal resolution. The instantaneous velocity measurements showed rapid flow deceleration at all vertical elevations, and large fluctuations of all velocity components were recorded beneath the bore and secondary waves. A comparison between undular (nonbreaking) and breaking bores suggested some basic differences. In an undular bore, large velocity fluctuations were recorded beneath the first wave crest and the secondary waves showing a long-lasting effect after the bore passage. In a breaking bore, some large turbulent stresses were observed next to the shear zone in a region of high velocity gradients, while some transient flow recirculation was recorded next to the bed. The effects of bed roughness were tested further. The boundary friction contributed to some wave attenuation and dispersion, and the free-surface data showed some agreement with the wave dispersion theory for intermediate gravity waves. The instantaneous velocity data showed however a significant effect of the boundary roughness on the velocity field next to the boundary (z/d(o)< 0.2) for both undular and breaking bores. Overall the findings were consistent with field observations of tidal bores and highlighted the significant impact of undular (nonbreaking) bores on natural systems

Physical Modelling of the Flow Field in an Undular Tidal Bore

A tidal bore may form in a converging channel with a funnel shape when the tidal range exceeds 6-9 m. The advancing surge has a major impact on the estuarine ecosystem. Physical modelling of an undular bore has been conducted based upon a quasi-steady flow analogy. The experimental data highlight rapid flow redistributions between successive wave troughs and crests as well as large bottom shear stress variations. The results suggest a sediment transport process combining scour beneath wave troughs associated with upward matter dispersion between a trough and the following wave crest. The process is repeated at each trough and significant sediment transport takes place with deposition in upstream intertidal zones. The conceptual model is supported by field observations showing murky waters after the bore passage and long-lasting chaotic waves

Urinary levels of N-nitroso compounds in relation to risk of gastric cancer: Findings from the Shanghai cohort study

Background: N-Nitroso compounds are thought to play a significant role in the development of gastric cancer. Epidemiological data, however, are sparse in examining the associations between biomarkers of exposure to N-nitroso compounds and the risk of gastric cancer. Methods: A nested case-control study within a prospective cohort of 18,244 middle-aged and older men in Shanghai, China, was conducted to examine the association between urinary level of N-nitroso compounds and risk of gastric cancer. Information on demographics, usual dietary intake, and use of alcohol and tobacco was collected through in-person interviews at enrollment. Urinary levels of nitrate, nitrite, N-nitroso-2-methylthiazolidine-4-carboxylic acid (NMTCA), N-nitrosoproline (NPRO), N-nitrososarcosine (NSAR), N-nitrosothiazolidine-4-carboxylic acid (NTCA), as well as serum H. pylori antibodies were quantified in 191 gastric cancer cases and 569 individually matched controls. Logistic regression method was used to assess the association between urinary levels of N-nitroso compounds and risk of gastric cancer. Results: Compared with controls, gastric cancer patients had overall comparable levels of urinary nitrate, nitrite, and N-nitroso compounds. Among individuals seronegative for antibodies to H. pylori, elevated levels of urinary nitrate were associated with increased risk of gastric cancer. The multivariate-adjusted odds ratios for the second and third tertiles of nitrate were 3.27 (95% confidence interval = 0.76-14.04) and 4.82 (95% confidence interval = 1.05-22.17), respectively, compared with the lowest tertile (P for trend = 0.042). There was no statistically significant association between urinary levels of nitrite or N-nitroso compounds and risk of gastric cancer. Urinary NMTCA level was significantly associated with consumption of alcohol and preserved meat and fish food items. Conclusion: The present study demonstrates that exposure to nitrate, a precursor of N-nitroso compounds, may increase the risk of gastric cancer among individuals without a history of H. pylori infection

Turbulence measurements in positive surges and bores

A positive surge results from a sudden change in flow that increases the flow depth. New experiments were conducted in a large channel. Most positive surge tests were conducted with a horizontal bed slope, a constant flow rate and uncontrolled flow conditions. The only dependant variable was the downstream gate opening after closure. Detailed turbulence measurements were performed with high-temporal resolution using side-looking acoustic Doppler velocimetry. Two types of positive surge were observed: undular surge for Froude numbers less than 1.7, and weak (breaking) surges above. Instantaneous velocity measurements beneath advancing surges showed a marked effect of the surge passage on the velocity field. Streamwise velocities showed rapid flow deceleration at all vertical elevations. Large fluctuations of longitudinal and transverse velocities were recorded beneath the surges, including some unsteady flow recirculation beneath a weak surge front. Turbulent stresses were deduced from high-pass filtered data. The results showed large normal and tangential Reynolds stresses beneath the surges. A comparison between undular and weak surges suggested some major difference. In weak surge flows, the data showed rapid flow separation beneath the surge front. In undular surges, maximum Reynolds stresses were observed beneath and just before each wave crest behind the leading wave

Linkage studies in a Li-Fraumeni family with increased expression of p53 protein but no germline mutation in p53.

We report a family with the Li-Fraumeni syndrome (LFS) in whom we have been unable to detect a mutation in the coding sequence of the p53 gene. Analysis of linkage to three polymorphic markers within p53 enabled direct involvement of p53 to be excluded. This is the first example of a LFS family in whom exclusion of p53 has been possible. Four affected members of the family with sarcoma or premenopausal breast cancer showed increased expression of p53 protein in their normal tissues as detected by immunohistochemistry. It therefore appears that the LFS phenotype has been conferred by an aberrant gene, showing a dominant pattern of inheritance, which may be acting to compromise normal p53 function rather than by a mutation in p53 itself. In order to try to determine the chromosomal location of this putative gene, we have carried out studies of linkage to candidate loci. By these means we have excluded involvement of Rb1 and BRCA1 on chromosomes 13q and 17q respectively. The MDM2 oncogene on chromosome 12q was considered to be the prime candidate as MDM2 is amplified in sarcomas and the MDM2 product binds to p53. Furthermore, p53 mutation and amplification of MDM2 have been shown to be mutually exclusive events in tumour development. Linkage analysis to two polymorphic markers within MDM2 yielded a three-point LOD score of -5.4 at a recombination fraction theta equal to zero. Therefore MDM2 could be excluded. It is possible that the gene which is responsible for cancer susceptibility in this family, possibly via interaction with p53, will be important in the histogenesis of breast cancer in general. We are now carrying out further studies to locate and identify this gene