The interrelation between temperature regimes and fish size in juvenile Atlantic cod (Gadus morhua): effects on growth and feed conversion efficiency

The present paper describes the growth properties of juvenile Atlantic cod (Gadus morhua) reared at 7, 10, 13 and 16 °C, and a group reared under “temperature steps” i.e. with temperature reduced successively from 16 to 13 and 10 °C. Growth rate and feed conversion efficiency of juvenile Atlantic cod were significantly influenced by the interaction of temperature and fish size. Overall growth was highest in the 13 °C and the T-step groups but for different reasons, as the fish at 13 °C had 10% higher overall feeding intake compared to the T-step group, whereas the T-step had 8% higher feeding efficiency. After termination of the laboratory study the fish were reared in sea pens at ambient conditions for 17 months. The groups performed differently when reared at ambient conditions in the sea as the T-step group was 11.6, 11.5, 5.3 and 7.5% larger than 7, 10, 13 and 16 °C, respectively in June 2005. Optimal temperature for growth and feed conversion efficiency decreased with size, indicating an ontogenetic reduction in optimum temperature for growth with increasing size. The results suggest an optimum temperature for growth of juvenile Atlantic cod in the size range 5–50 g dropping from 14.7 °C for 5–10 g juvenile to 12.4 °C for 40–50 g juvenile. Moreover, a broader parabolic regression curve between growth, feed conversion efficiency and temperature as size increases, indicate increased temperature tolerance with size. The study confirms that juvenile cod exhibits ontogenetic variation in temperature optimum, which might partly explain different spatial distribution of juvenile and adult cod in ocean waters. Our study also indicates a physiological mechanism that might be linked to cod migrations as cod may maximize their feeding efficiency by active thermoregulation

The effect of silicon content on the microstructure and creep behavior in die-cast magnesium AS alloys

The effect of increasing levels of silicon on the microstructure and creep properties of high-pressure die-cast Mg-Al-Si (AS) alloys has been investigated. The morphology of the Mg2Si phase in die-cast AS alloys was found to be a function of the silicon content. The Mg2Si particles in castings with up to 1.14 wt pct Si have a Chinese script morphology. For AS21 alloys with silicon contents greater than 1.4 wt pet Si (greater than the alpha-Mg2Si binary eutectic point), some Mg2Si particles have a coarse blocky shape. Increasing the silicon content above the eutectic level results in an increase in the number of coarse faceted Mg2Si particles in the microstructure. Creep rates at 100 hours were found to decrease with increasing silicon content in AS-type alloys. The decrease in creep rate was most dramatic for silicon contents up to 1.1 wt pct. Further additions of silicon of up to 2.64 wt pct also resulted in significant decreases in creep rate

A Comparative Study of Straight-Strip and Zigzag-Interleaved Anode Patterns for MPGD Readouts

International audienceDue to their simplicity and versatility of design, straight strip or rectangular pad anode structures are frequently used with micropattern gas detectors (MPGDs) to reconstruct high-precision space points for various tracking applications. The particle impact point is typically determined by interpolating the charge collected by several neighboring strips. However, to effectively extract the inherent positional information, the lateral spacing of the straight strips must be comparable to or preferably smaller than the full extent of the incident charge cloud. In contrast, highly interleaved anode patterns, such as zigzags, can adequately sample the incident charge with a pitch appreciably larger than the charge cloud. This has the considerable advantage of providing the same performance while requiring far fewer instrumented channels. Additionally, the geometric parameters defining such zigzag structures may be tuned to provide a near-uniform detector response along and perpendicular to the sensitive coordinate, without the need for so-called “pad response functions,” while simultaneously maintaining excellent position resolution. We have measured the position resolution of a variety of zigzag-shaped anode patterns optimized for various MPGDs, including gas electron multiplyer (GEM), Micromegas, and micro-resistive-well ( $\mu$ RWELL) and compared this performance with the same detectors equipped with straight strips of varying pitch. We report on the performance results of each readout structure, evaluated under identical conditions in a test beam

A Study of “Zigzag” Strip Readout for Micromegas Detectors

International audienceMicromegas detectors are now commonly used as tracking detectors for nuclear and particle physics experiments. The aim of this work was to optimize the segmentation of a Micromegas readout plane by performing a systematic study of overlapping patterns known as "zigzags". By improving the charge sharing between neighboring strips, the zigzag pattern allows one to maintain high spatial resolution even with relatively large values of strip-to-strip distance (pitch). This can decrease the number of channels and therefore substantially lower the cost and complexity of large detector systems such as those proposed for the future Electron Ion Collider (EIC). Using a laser ablation process we were able to successfully build four 10cm x 10cm Micromegas detectors with one hundred different zigzag patterns on a single readout plane. The detectors were tested in the test beam at Fermilab in March 2018 where the spatial resolution of each pattern was measured using the 120 GeV proton beam. Preliminary results show that spatial resolutions of ~90μm for a 0.8mm pitch can be achieved with a negligibly small fraction of single-pad clusters and would provide a substantial improvement for future tracking detectors

Design Studies of High-Resolution Readout Planes Using Zigzags With GEM Detectors

International audienceWe have developed highly interleaved zigzag-shaped electrodes for collecting charge on the readout plane of various micropattern gaseous detectors (MPGDs), including gas electron multiplier (GEM) and micromega detectors. An optimized zigzag pad (or strip) anode can greatly enhance charge sharing among neighboring pads compared to traditional straight strip or rectangular pad designs and as a result can deliver excellent position resolution with minimal channel count, while exhibiting a virtually uniform response across the detector. We have systematically studied the effects of varying the parameters that define the zigzag geometry using simulations and have measured several printed circuit boards (PCBs) comprising a range of zigzag designs. Recently, we have employed laser ablation to generate zigzag patterns with pad-to-pad gaps smaller than 1 mil (or 25 $\mu \text{m}$ ). Reducing the gap well below the 3-mil limit imposed by traditional chemical etching has allowed the production of zigzag electrodes with unprecedentedly small feature sizes. In turn, laser-etched zigzag PCBs were shown to exhibit markedly improved performance over earlier generation PCBs, with position resolutions below 50 $\mu \text{m}$ for a 2-mm pitch. This article will explore in detail the dependence of the position resolution on the structural parameters of a zigzag-shaped anode, specifically for the case of a quadruple GEM detector

Primary creep of die-cast magnesium-rare earth based alloys

The creep response of die-cast Mg-2.5RE-0.6Zn (wt pct) alloys with different rare earth (RE) mixtures has been investigated at 177 °C. The Nd-rich alloy displayed significantly lower primary creep than its La-rich counterpart. Microstructural analyses revealed the formation of additional Nd-containing precipitates on dislocations in the Nd-rich alloy during creep. The degree of supersaturation of RE solutes in the α-Mg matrix after die casting is suggested to be the key factor in influencing primary creep