Transition of wire-disturbed cylinder wake flow

The transition of the flow behind bluff bodies has been the main topic of research for many decades. Despite the efforts of many scientist and engineers, understanding of the transition mechanism of wake flows behind both streamlined and bluff bodies is still a challenge. The focus in this research is the modified flow regime in the wake of a circular cylinder. The modification is obtained by placing a very thin wire at a particular position in the cylinder wake. The occurring transitional flow is denoted as Mode-C, in comparison to Mode-A and Mode-B transition for the non-wired cylinder. The flow structures have been investigated both experimentally and numerically for different Reynolds numbers (Re=100-250) using flow visualizations based on tin-precipitation method, velocity measurements using Particle Image Velocimetry and numerical simulations based on Spectral Element method. In the laminar two-dimensional flow regime Re=100, it is observed, both numerically and experimentally, that the wake of the cylinder is taking different trajectories with respect to the wire position. A hypothesis is formulated about the reasons of the wake deflection using a Point Vortex Model. The hypothesis is supported with the assessment of vortex trajectories, strengths, lift and drag characteristics. It is concluded that the deflection of the wake is primarily caused by a modification of the vortex arrangement in the wake. This modified vortex arrangement is caused by different formation times of the upper and lower vortices, by different vortex strengths or by both. A three-dimensional transition of the wired cylinder flow is observed for Re>170. This transition is characterized by the so-called Mode-C instability. The analysis of the experimental results shows that this Mode-C instability consists of secondary vortices with a period-doubling character, ie. the secondary vortices alternate sign from one shedding cycle to the next. It is shown that a feedback mechanism of the streamwise vortices between the two consecutively shed upper von Karman vortices causes the period-doubling character of the wake. The analysis of Mode-C transition is further extended using the data from comprehensive PIV experiments. The three-dimensional wake structure and vortex dynamics are investigated with a particular focus on the energy distribution of the wake, vortex strengths and vortex trajectories. The secondary vortices are shown to be counter rotating vortex pairs with a spanwise wavelength of ¿Z/D=2.16. In the final stage of the research, experiments are performed to evaluate the wake behind a rotating cylinder, particularly focusing on the so-called Shedding Mode II regime. In literature only numerical proof is found for the existence of this Shedding Mode II for which a single vortex is shed with a much lower frequency compared to non-rotating case. Both flow visualization and PIV techniques are used to investigate this kind of flow. Shedding Mode II is experimentally detected for a Reynolds number of Re=100 in the same rotation rate regime as in the numerical studies

Effects of breeder age and pre-incubation storage of eggs on hatchability, time of hatch and relative organ weight of quail chicks at hatch

Two thousand four hundred quail (Coturnix coturnix japonica) hatching eggs were used to determine the effects of breeder age and pre-incubation storage time on egg traits, hatching traits and the growth of some selected organs in newly hatched chicks. Eggs from two non-commercial flocks (aged 10 vs. 40 weeks) of the same strain were incubated. Eggs were stored for 4 or 14 days prior to incubation. All eggs were set in an experimental setter and incubated under uniform conditions for approximately 19 days (448 h). Fresh egg weight, chick weight and percentage yolk weight were significantly higher in eggs obtained from breeders at 40 weeks of age than from those of 10 weeks of age, whereas percentage albumen weight was significantly higher in eggs obtained from 10 wk old breeders. There were significant storage period x hen age interactions for water loss in chicks, early embryonic death, late embryonic death, deaths during internal and external pipping, and hatchability of fertile eggs. From 405 h to 441 h of incubation, the percentage of hatched chicks was influenced by the storage period x breeder age interaction. The jejunum length of chicks from 40 wk old breeders was longer when eggs were stored for 4 days compared to 14 days. At hatch, chick liver weight as a percentage of live weight was higher when eggs obtained from 10 wk old breeders were stored for 4 days compared to 14 days. It was concluded that the effects of extended storage time on hatching traits were different for eggs laid by young compared to old breeders. Keywords: Hatchability; breeder age; egg storage; organ weights; quail South African Journal of Animal Sciences Vol. 35 (2) 2005: pp.135-14

Unusual structural tuning of magnetism in cuprate perovskites

Understanding the structural underpinnings of magnetism is of great fundamental and practical interest. Se_{1-x}Te_{x}CuO_{3} alloys are model systems for the study of this question, as composition-induced structural changes control their magnetic interactions. Our work reveals that this structural tuning is associated with the position of the supposedly dummy atoms Se and Te relative to the super-exchange (SE) Cu--O--Cu paths, and not with the SE angles as previously thought. We use density functional theory, tight-binding, and exact diagonalization methods to unveil the cause of this surprising effect and hint at new ways of engineering magnetic interactions in solids.Comment: 4 pages, with 4 postscript figures embedded. Uses REVTEX4 and graphicx macro

Encouraging users to improve password security and memorability

Security issues in text-based password authentication are rarely caused by technical issues, but rather by the limitations of human memory, and human perceptions together with their consequential responses. This study introduces a new user-friendly guideline approach to password creation, including persuasive messages that motivate and influence users to select more secure and memorable text passwords without overburdening their memory. From a broad understanding of human factors-caused security problems, we offer a reliable solution by encouraging users to create their own formula to compose passwords. A study has been conducted to evaluate the efficiency of the proposed password guidelines. Its results suggest that the password creation methods and persuasive message provided to users convinced them to create cryptographically strong and memorable passwords. Participants were divided into two groups in the study. The participants in the experimental group who were given several password creation methods along with a persuasive message created more secure and memorable passwords than the participants in the control group who were asked to comply with the usual strict password creation rules. The study also suggests that our password creation methods are much more efficient than strict password policy rules. The security and usability evaluation of the proposed password guideline showed that simple improvements such as adding persuasive text to the usual password guidelines consisting of several password restriction rules make significant changes to the strength and memorability of passwords. The proposed password guidelines are a low-cost solution to the problem of improving the security and usability of text-based passwords

Fungi in the atmospheric air of Çanakkale province in Turkey

No Abstrac

Effects of different hatcher temperatures on hatching traits of broiler embryos during the last five days of incubation

This study deals with the effects of different hatcher temperatures on hatching traits in modern commercial broiler eggs during the last five days of incubation. The hatching eggs were obtained from a 52-wk old (Ross 308) flock. All eggs were distributed randomly into one incubator and incubated for 17 d using uniform conditions (37.6 ± 0.5 °C and 58% relative humidity). At the start of 18th days of incubation, the eggs were randomly distributed to four experimental hatching cabinets. The temperatures were set in the cabinets at 36.1, 37.2, 38.3 and 39.4 °C from 17 d of incubation until hatch. Hatching time, hatchability, age of mortality and the incidence of embryo malpositions were recorded as percentage of fertile eggs. The highest mean embryonic heat production or eggshell surface temperature occurred in the hatching cabinets operated at 39.9 °C and lowest at 36.1 °C. Eggs incubated at 37.2 °C and 38.3 °C had a significantly higher hatchability than the other treatment groups. High embryo mortality at the late term stage of development was recorded at low (36.1 °C) and very high temperatures (39.9 °C). No significant difference in the incidence of malpositions was observed among the groups. These findings revealed that hatchability might be improved if incubation temperatures of 37.2 °C to 38.3 °C are used during last five days of incubation. The results indicate that the modern hatching broiler egg shows almost similar pattern as past generations for heat production and temperature in hatchers during the last five days of incubation. In other words, in spite of genetic improvements in the modern broilers, the incubation conditions and techniques remained largely unchanged. South African Journal of Animal Science Vol. 34(4) 2004: 211-21