Firehose and Mirror Instabilities in a Collisionless Shearing Plasma

Hybrid-kinetic numerical simulations of firehose and mirror instabilities in a collisionless plasma are performed in which pressure anisotropy is driven as the magnetic field is changed by a persistent linear shear $S$. For a decreasing field, it is found that mostly oblique firehose fluctuations grow at ion Larmor scales and saturate with energies $\sim$$S^{1/2}$; the pressure anisotropy is pinned at the stability threshold by particle scattering off microscale fluctuations. In contrast, nonlinear mirror fluctuations are large compared to the ion Larmor scale and grow secularly in time; marginality is maintained by an increasing population of resonant particles trapped in magnetic mirrors. After one shear time, saturated order-unity magnetic mirrors are formed and particles scatter off their sharp edges. Both instabilities drive sub-ion-Larmor--scale fluctuations, which appear to be kinetic-Alfv\'{e}n-wave turbulence. Our results impact theories of momentum and heat transport in astrophysical and space plasmas, in which the stretching of a magnetic field by shear is a generic process.Comment: 5 pages, 8 figures, accepted for publication in Physical Review Letter

Fabrication and optimisation of a fused filament 3D-printed microfluidic platform

A 3D-printed microfluidic device was designed and manufactured using a low cost ($2000) consumer grade fusion deposition modelling (FDM) 3D printer. FDM printers are not typically used, or are capable, of producing the fine detailed structures required for microfluidic fabrication. However, in this work, the optical transparency of the device was improved through manufacture optimisation to such a point that optical colorimetric assays can be performed in a 50 µl device. A colorimetric enzymatic cascade assay was optimised using glucose oxidase and horseradish peroxidase for the oxidative coupling of aminoantipyrine and chromotropic acid to produce a blue quinoneimine dye with a broad absorbance peaking at 590 nm for the quantification of glucose in solution. For comparison the assay was run in standard 96 well plates with a commercial plate reader. The results show the accurate and reproducible quantification of 0–10 mM glucose solution using a 3D-printed microfluidic optical device with performance comparable to that of a plate reader assay

Just luck: an experimental study of risk taking and fairness

Choices involving risk significantly affect the distribution of income and wealth in society. This paper reports the results of the first experiment, to our knowledge, to study fairness views about risk-taking, specifically whether such views are based chiefly on ex ante opportunities or on ex post outcomes. We find that, even though many participants focus exclusively on ex ante opportunities, most favor some redistribution ex post. Many participants also make a distinction between ex post inequalities that reflect differences in luck and ex post inequalities that reflect differences in choices. These findings apply to both stakeholders and impartial spectators.fairness; justice; risk

Mechano-transduction: from molecules to tissues.

External forces play complex roles in cell organization, fate, and homeostasis. Changes in these forces, or how cells respond to them, can result in abnormal embryonic development and diseases in adults. How cells sense and respond to these mechanical stimuli requires an understanding of the biophysical principles that underlie changes in protein conformation and result in alterations in the organization and function of cells and tissues. Here, we discuss mechano-transduction as it applies to protein conformation, cellular organization, and multi-cell (tissue) function

Just Luck: An Experimental Study of Risk Taking and Fairness.

Choices involving risk significantly aect the distribution of income and wealth in society, but there is probably no more contentious question of justice than how to allocate the gains and losses that inevitably result from risky choices. This paper reports the results from the first experiment, to our knowledge, to study fairness views about risk-taking, where the main aim is to examine whether people's fairness considerations mainly focus on ex ante opportunities or ex post outcomes. The experiment was a two stage dictator game where the distribution phase was preceded by a risk-taking phase. Our analysis provides four main findings. First, we show that even though many participants focus exclusively on ex ante opportunities, the majority favors some redistribution ex post. Second, we find that, among the participants who redistribute ex post, a substantial share make a distinction between ex post inequalities that reflect differences in luck and ex post inequalities that reflect differences in choices. Third, we show that the appeal of the ex ante view is independent of how costly it is to avoid exposure to risk. Fourth, we find that the choices of stakeholders and impartial spectators reflect the same set of fairness considerations.Risk-taking; fairness; luck; equal opportunities.

Rotation of Coulomb crystals in a magnetized inductively coupled complex plasma

Under suitable conditions, micron-sized dust particles introduced into inductively coupled argon plasma form a stable microscopic crystal lattice, known as a Coulomb (or plasma) crystal. In the experiment described, an external axial magnetic field was applied to various configurations of Coulomb crystal, including small crystal lattices consisting of one to several particles, and large crystal lattices with many hundreds of particles. The crystals were observed to rotate collectively under the influence of the magnetic field. This paper describes the experimental procedures and the preliminary results of this investigation

Coordination and Sustainability of River Observing Activities in the Arctic

To understand and respond to changes in the world’s northern regions, we need a coordinated system of long-term Arctic observations. River networks naturally integrate across landscapes and link the terrestrial and ocean domains. Changes in river discharge reflect changes in the terrestrial water balance, whereas changes in water chemistry are linked to changes in biogeochemical processes and water flow paths. Sustained measurements of river water discharge and water chemistry are therefore essential components of an Arctic observing network. As we strive to establish and sustain long-term observations in the Arctic, these two measurements must be coupled. Although river discharge and chemistry measurements are already coupled to some extent within national boundaries, this is not done in a consistent and coordinated fashion across the pan-Arctic domain. As a consequence, data quality and availability vary widely among regions. International coordination of river discharge and chemistry measurements in the Arctic would be greatly facilitated by formal commitments to maintain a set of core sites and associated measurements that are mutually agreed upon among pan-Arctic nations. Involvement of the agencies currently operating river discharge gauges around the Arctic and establishment of an overarching coordination entity to implement shared protocols, track data quality, and manage data streams would be essential in this endeavor. Focused studies addressing scale-dependent relationships between watershed characteristics and water chemistry, in-stream processes, and estuarine and coastal dynamics are also needed to support interpretation and application of Arctic river observing data as they relate to land and ocean change

River Discharge

In 2014, combined discharge from the eight largest Arctic rivers (2,487 km3) was 10% greater than average discharge for the period 1980-1989. Values for 2013 (2,282 km3) and 2012 (2,240 km3) were 1% greater than and 1% less than the 1980-1989 average, respectively. For the first seven months of 2015, the combined discharge for the six largest Eurasian Arctic rivers shows that peak discharge was 10% greater and five days earlier than the 1980-1989 average for those months

Fetal injury associated with cesarean delivery.

Journal ArticleOBJECTIVE: To describe the incidence and type of fetal injury identified in women undergoing cesarean delivery. METHODS: Between January 1, 1999, and December 31, 2000, a prospective cohort study of all cesarean deliveries was conducted at 13 university centers. Information regarding maternal and infant outcomes was abstracted directly from hospital charts. RESULTS: A total of 37,110 cesarean deliveries were included in the registry, and 418 (1.1%) had an identified fetal injury. The most common injury was skin laceration (n = 272, 0.7%). Other injuries included cephalohematoma (n = 88), clavicular fracture (n = 11), brachial plexus (n = 9), skull fracture (n = 6), and facial nerve palsy (n = 11). Among primary cesarean deliveries, deliveries with a failed forceps or vacuum attempt had the highest rate of injuries (6.9%). In women with a prior cesarean delivery, the highest rate of injury also occurred in the unsuccessful trial of forceps or vacuum (1.7%), and the lowest rate occurred in the elective repeat cesarean group (0.5%). The type of uterine incision was associated with fetal injury, 3.4% "T" or "J" incision, 1.4% for vertical incision, and 1.1% for a low transverse (P = .003), as was a skin incision-to-delivery time of 3 minutes or less. Fetal injury did not vary in frequency with the type of skin incision, preterm delivery, maternal body mass index, or infant birth weight greater than 4,000 g. CONCLUSION: Fetal injuries complicate 1.1% of cesarean deliveries. The frequency of fetal injury at cesarean delivery varies with the indication for surgery as well as with the duration of the skin incision-to-delivery interval and the type of uterine incision. LEVEL OF EVIDENCE: II-3