455 research outputs found
Toward 'socially constructive' social constructions of leadership
In their introductory editorial essay for this special issue, David Grant and Gail Fairhurst have done us a great service by valiantly producing a "Sailing Guide" to the Social Construction of Leadership (Fairhurst & Grant, 2010). As with rounding the Capes, this is not a task for the faint of heart. A sailing guide is designed to provide vital knowledge about a particular sea or coast, providing us with charts, warnings about potential hazards and an indication where we might find safe havens in a storm. Their sailing guide does this to great effect as it skilfully "boxes the compass" by revealing all of the potential directions that one might set one‟s sail by if one was sufficiently foolhardy to embark on a cruise of the social construction of leadership
Combined observations of meteors by image-orthicon television camera and multi-station radar
Observations from multiple sites of a radar network and by television of 29 individual meteors from February 1969 through June 1970 are reported. Only 12 of the meteors did not appear to fragment over all the observed portion of their trajectories. From these 12, the relation for the radar magnitude to the panchromatic absolute magnitude was found in terms of velocity of the meteor. A very tentative fit to the data on the duration of long enduring echoes versus visual absolute magnitude is made. The exponential decay characteristics of the later parts of several of the light curves are pointed out as possible evidence of mutual coalescence of droplets into which the meteoroid has completely broken
Commissioning of Dedicated Furnace for Nb3Sn Coatings of 2.6 GHz Single Cell Cavities
We present the results of commissioning a dedicated furnace for Nb3Sn
coatings of 2.6 GHz single cell cavities. Nb3Sn is a desired coating due to its
high critical temperature and smaller surface resistance compared to bulk Nb.
Usage of Nb3Sn coated cavities will greatly reduce operating costs due to
decreased dependance on cryo cooling. Tin is deposited by use of a tin chloride
nucleation agent and tin vapor diffusion. Analysis of the resultant coating was
performed using SEM/EDS to verify successful formation of Nb3Sn. Witness
samples in line of sight of the source were used in order to understand the
coating efficacy.Comment: 21st Intl Conf Radio Frequency Superconductivity (SRF 2023
Demonstration of Niobium Tin in 218 MHz Low-beta Quarter Wave Accelerator Cavity
A 218 MHz quarter wave niobium cavity has been fabricated for the purpose of
demonstrating Nb3Sn technology on a low-beta accelerator cavity. Niobiumtin has
been established as a promising next generation SRF material, but development
has focused primarily in high-beta elliptical cell cavities. This material has
a significantly higher TC than niobium, allowing for design of higher frequency
quarter wave cavities (that are subsequently smaller) as well as for
significantly lowered cooling requirements (possibly leading to cryocooler
based designs). The fabrication, initial cold testing, and Nb3Sn coating are
discussed as well as test plans and details of future applications.Comment: 21st Intl Conf Radio Frequency Superconductivity (SRF 2023
PI Loop Resonance Control for Dark Photon Experiment at 2 K Using a 2.6 GHz SRF Cavity
Two 2.6 GHz SRF cavities are being used for a dark photon search at the
vertical test stand (VTS) in FNAL, for the second phase of the Dark SRF
experiment. During testing at 2 K the cavities experience frequency detuning
caused by microphonics and slow frequency drifts. The experiment requires that
the two cavities have the same frequency within the cavity's bandwidth. These
two cavities are equipped with frequency tuners consisting of three piezo
actuators. The piezo actuators are used for fine-fast frequency tuning. A
proportional-integral (PI) loop utilizing the three piezos on the emitter was
used to stabilize the cavity frequency and match the receiver cavity frequency.
The results from this implementation will be discussed. The integration time
was also calculated via simulation.Comment: 21st International Conference on Radio-Frequency Superconductivity
(SRF 2023
Preservation of the High Quality Factor and Accelerating Gradient of Nb3Sn-coated Cavity During Pair Assembly
Two CEBAF 5-cell accelerator cavities have been coated with Nb3Sn film using
the vapor diffusion technique. One cavity was coated in the Jefferson Lab Nb3Sn
cavity coating system, and the other in the Fermilab Nb3Sn coating system. Both
cavities were measured at 4 K and 2 K in the vertical dewar test in each lab
and then assembled into a cavity pair at Jefferson Lab. Previous attempts to
assemble Nb3Sn cavities into a cavity pair degraded the superconducting
properties of Nb3Sn-coated cavities. This contribution discusses the efforts to
identify and mitigate the pair assembly challenges and will present the results
of the vertical tests before and after pair assembly. Notably, one of the
cavities reached the highest gradient above 80 mT in the vertical test after
the pair assembly.Comment: 21st Intl Conf Radio Frequency Superconductivity (SRF 2023
Testing of the 2.6 GHz SRF Cavity Tuner for the Dark Photon Experiment at 2 K
At FNAL two single cell 2.6 GHz SRF cavities are being used to search for
dark photons, the experiment can be conducted at 2 K or in a dilution
refrigerator. Precise frequency tuning is required for these two cavities so
they can be matched in frequency. A cooling capacity constraint on the dilution
refrigerator only allows piezo actuators to be part of the design of the 2.6
GHz cavity tuner. The tuner is equipped with three encapsulated piezos that
deliver long and short-range frequency tuning. Modifications were implemented
on the first tuner design due to the low forces on the piezos caused by the
cavity. Three brass rods with Belleville washers were added to the design to
increase the overall force on the piezos. The testing results at 2 K are
presented with the original design tuner and with the modification.Comment: 21st International Conference on Radio-Frequency Superconductivity
(SRF 2023
Impact of abiotic factors and husbandry on saprolegniosis in salmonid farms
Oomycetes of the genus Saprolegnia are widespread in freshwater environment and are among the main path-
ogens causing economic losses in salmonid aquaculture.
Infections by mycotic agents in fish farming are generally considered to result from chronic stress and poor fish
condition associated with water quality problems, adverse environmental conditions, frequent/rough/incorrect
handling, concurrent infections, physiological changes associated with reproduction and immunocompromised
animals.
To identify risk factors for Saprolegnia infections in trout and Atlantic salmon farming, longitudinal studies
were carried out in different Italian, Spanish, and Scottish fish farms. Prevalence of saprolegniosis and fish
mortality were monitored over time and statistically analysed with respect to husbandry and environmental
factors.
Overall, statistical results by production cycle (trout vs salmon farming) and by country indicate that the
prevalence of Saprolegnia may be influenced by peculiarities of the culture system and farming environment.
Nevertheless, a specific set of parameters, including lower water temperature, and handling procedures increased
Saprolegnia prevalence in all the considered farms. Particularly, in trout farms Saprolegnia infections represented
an important contribution to mortality, and prevalence was influenced by water temperature and pH, and by fish
density within the tanks. Similarly, temperature and water quality were the main factors influencing the prev-
alence of Saprolegnia in Atlantic salmon farms. Moreover, molecular analyses confirmed the role of S. parasitica as
the main pathogenic oomycete in trout and salmon farming in the considered countries. The identification of risk
factors for introduction and increase of Saprolegnia infection in fish farms will allow the correct design of bio-
security and pathogen control strategie
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