Open discussion

1982 ◽  
Vol 99 ◽  
pp. 605-613
Author(s):  
P. S. Conti
Keyword(s):  
Buenos Aires ◽  
Large Mass ◽  
List Type ◽  
Common Phenomenon ◽  
Open Discussion ◽  
The Stability ◽  
Ring Nebulae

Conti: One of the main conclusions of the Wolf-Rayet symposium in Buenos Aires was that Wolf-Rayet stars are evolutionary products of massive objects. Some questions:–Do hot helium-rich stars, that are not Wolf-Rayet stars, exist?–What about the stability of helium rich stars of large mass? We know a helium rich star of ∼40 MO. Has the stability something to do with the wind?–Ring nebulae and bubbles : this seems to be a much more common phenomenon than we thought of some years age.–What is the origin of the subtypes? This is important to find a possible matching of scenarios to subtypes.

scholarly journals The effect of flexural–torsional buckling on the stability of timber members: a case study

2021 ◽  
Vol 3 (6) ◽  
Author(s):  
Osama A. B. Hassan
Keyword(s):  
Axial Compression ◽  
Bending Moment ◽  
List Type ◽  
Torsional Buckling ◽  
Solution Methods ◽  
Simplified Solution ◽  
The Stability ◽  
Flexural Torsional Buckling ◽  
Building Engineering

Abstract This study investigates the stability of timber members subjected to simultaneously acting axial compression and bending moment, with possible risk for torsional and flexural–torsional buckling. This situation can occur in laterally supported members where one side of the member is braced but the other side is unbraced. In this case, the free side will buckle out of plane while the braced side will be prevented from torsional and flexural–torsional buckling. This problem can be evident for long members in timber-frame structures, which are subjected to high axial compression combined with bending moments in which the member is not sufficiently braced at both sides. This study is based on the design requirement stated in Eurocode 5. Solution methods discussed in this paper can be of interest within the framework of structural and building Engineering practices and education in which the stability of structural elements is investigated. Article Highlights This case study investigates some design situations where the timber member is not sufficiently braced. In this case, a stability problem associated with combined torsional buckling and flexural buckling can arise. The study shows that the torsional and/or flexural–torsional buckling of timber members can be important to control in order to fulfil the criteria of the stability of the member according to Eurocode 5 and help the structural engineer to achieve safer designs. The study investigates also a simplified solution to check the effect of flexural torsional buckling of laterally braced timber members.

scholarly journals Highly fluorescent CsPbBr3/TiO2 core/shell perovskite nanocrystals with excellent stability

2021 ◽  
Vol 3 (6) ◽  
Author(s):  
Haitao Chen ◽  
Renhua Li ◽  
Anqi Guo ◽  
Yu Xia
Keyword(s):  
Identical Particle ◽  
Core Shell ◽  
List Type ◽  
Easy Method ◽  
Time Resolved ◽  
Perovskite Nanocrystals ◽  
Promising Application ◽  
The Stability ◽  
Time Resolved Photoluminescence ◽  
Excellent Stability

AbstractThe poor stability of CsPbX3 (X = Cl, Br, I) perovskite nanocrystals is the most impediment to its application in the field of photoelectrics. In this work, monodisperse CsPbBr3/TiO2 nanocrystals are successfully prepared by coating titanium precursor on the surface of colloidal CsPbBr3 nanocrystals at room temperature. The CsPbBr3/TiO2 nanocomposites exhibit excellent stability, remaining the identical particle size (9.2 nm), crystal structures and optical properties. Time-resolved photoluminescence decay shows that the lifetime of CsPbBr3/TiO2 nanocrystals is about 4.04 ns and keeps great stability after lasting two months in the air. Results show that the coating of TiO2 on CsPbBr3 NCs greatly suppressed the anion exchange and photodegradation, which are the main reasons for dramatically improving their chemical stability and photostability. The results provide an effective method to solve the stability problem of perovskite nanostructures and are expected to have a promising application in optoelectronic fieldsArticle highlights 1. Prepared the all-inorganic CsPbBr3/TiO2 core/shell perovskite nanocrystals by an easy method. 2. Explored its essences of PL and lifetime of the synthesized CsPbBr3/TiO2 perovskite nanocrystals. 3. CsPbBr3/TiO2 nanocrystals show the great thermal stability after the post-annealing. 4. The CsPbBr3/TiO2 nanocrystals have a high PLQY and have a promising application in solar cells.

scholarly journals Study of Corrosion Resistance and Degradation Mechanisms in LiTiO2-Li2TiO3 Ceramic

Crystals ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 753
Author(s):  
Dmitriy Shlimas ◽  
Artem L. Kozlovskiy ◽  
Maxim Zdorovets
Keyword(s):  
Degradation Mechanism ◽  
Diffraction Method ◽  
Large Mass ◽  
Time Frame ◽  
X Ray Diffraction ◽  
Acidic Media ◽  
X Ray ◽  
Mass Losses ◽  
The Stability ◽  
Thermal Sintering

The interest in lithium-containing ceramics is due to their huge potential as blanket materials for thermonuclear reactors for the accumulation of tritium. However, an important factor in their use is the preservation of the stability of their strength and structural properties when under the influence of external factors that determine the time frame of their operation. This paper presents the results of a study that investigated the influence of the LiTiO2 phase on the increasing resistance to degradation and corrosion of Li2TiO3 ceramic when exposed to aggressive acidic media. Using the X-ray diffraction method, it was found that an increase in the concentration of LiClO4·3H2O during synthesis leads to the formation of a cubic LiTiO2 phase in the structure as a result of thermal sintering of the samples. During corrosion tests, it was found that the presence of the LiTiO2 phase leads to a decrease in the degradation rate in acidic media by 20–70%, depending on the concentration of the phase. At the same time, and in contrast to the samples of Li2TiO3 ceramics, for which the mechanisms of degradation during a long stay in aggressive media are accompanied by large mass losses, for the samples containing the LiTiO2 phase, the main degradation mechanism is pitting corrosion with the formation of pitting inclusions.

REVIEW ON THEORETICAL STUDIES OF SUPERHEAVY NUCLEI

2006 ◽  
Vol 15 (07) ◽  
pp. 1587-1599 ◽  
Author(s):  
ZHONGZHOU REN ◽  
DINGHAN CHEN ◽  
CHANG XU
Keyword(s):  
Ground State ◽  
Large Mass ◽  
Mass Region ◽  
Superheavy Nuclei ◽  
Theoretical Studies ◽  
Shape Coexistence ◽  
Good Test ◽  
Α Decay ◽  
The Stability ◽  
Theoretical Results

Superheavy elements have provided a good test of the validity of both nuclear structure models and nuclear decay models in a large mass region. We firstly review the recent progress on theoretical studies of superheavy nuclei. Emphasis is placed on the structure and decay of superheavy nuclei. Then theoretical results of odd-odd nuclei with Z = 109 - 115 are presented and discussed. It is clearly demonstrated that there is shape coexistence for the ground state of many superheavy nuclei from different models and many superheavy nuclei are deformed. In some cases superdeformation can become the ground state of superheavy nuclei and it is important for future studies of superheavy nuclei. This can lead to the existence of low-energy isomers in the superheavy region and it plays an important role for the stability of superheavy nuclei. As α-decay and spontaneous fission plays a crucial role for identifications of new elements, we also review some typical models of α-decay half-lives and spontaneous fissions half-lives. Some new views on superheavy nuclei are presented.

The Periodic Impact Responses of Human-Body in a Vehicle Traveling on the Rough Terrain

2002 ◽  
Author(s):  
Ke Yu ◽  
Albert C. J. Luo
Keyword(s):  
Linear Model ◽  
Human Body ◽  
Rotational Motion ◽  
Large Mass ◽  
Rough Terrain ◽  
Lumped Mass ◽  
The Stability ◽  
Vehicle Chassis ◽  
Specific Number ◽  
Impact Motion

The human-body in a vehicle traveling on the rough terrain is modeled through the lumped mass approach and its periodic impact motions and stability are investigated through a linear model of vehicle and passenger systems. The linear model assumes the motion response of vehicle is very small compared to passenger’s rotational motion since the vehicle chassis has a very large mass and moment of inertia. The period-1 impact motion for two impacts respectively on two walls for a specific number of periods is predicted analytically and numerically. The stability and bifurcation of such a period-1 impact motion are developed analytically. The phase planes of the periodic impact motions are illustrated for a better understanding of the human-body impacting motion in the vehicle.

scholarly journals Bars in Cusps

1996 ◽  
Vol 171 ◽  
pp. 357-357 ◽  
Author(s):  
Walter Dehnen
Keyword(s):  
Elliptical Galaxies ◽  
Distribution Functions ◽  
List Type ◽  
Type Number ◽  
Initial Model ◽  
Pattern Speed ◽  
Self Similar ◽  
The Stability ◽  
Inside Out ◽  
Insta Bility

In order to investigate the stability properties of galaxy models with central density cusps, TV-body simulations of oblate models with density ρ ∝ m–1 (m+a)–3 where m2=R2+[z/q]2 and distribution functions f(E, Lz) (computed as in Dehnen, 1995) have been performed with the following results. 1.An E7 model with identical amounts of stars of either sense of rotation was stable over 30 tdyn(r=a). This is interesting for the bending instability has been argued to set in at about this flattening and be responsible for the absence of flatter elliptical galaxies (Merritt & Sellwood, 1994).2.Rapidly rotating E≳E5 models quickly form weak bars inside the cusp, which are stronger for the more flattened, faster rotating initial configurations. The bars grow in a self similar fashion from inside out: the pattern speed decreases with increasing bar length and time. This process is initiated at the origin, where, because of finite AT, the actual density no longer follows the power law, and stops when the edge of the cusp is reached. A typical example is given in the figure showing the z-y-coordinates of particles with |z|<0.1a after ≃20tdyn(r=a) for an initially rapidly rotating E7-model. The bar has axis ratios of about 5:3:1, and extends almost to corotation. However, it has no sharp edge, but an inhomogenous density with a cusp steeper than the initial model. No sign of a buckling insta-bility has been observerd.

scholarly journals A New Search for Nebulae Surrounding Wolf-Rayet Stars

1982 ◽  
Vol 99 ◽  
pp. 463-468
Author(s):  
Joy N. Heckathorn ◽  
Frederick C. Bruhweiler ◽  
Theodore R. Gull
Keyword(s):  
Milky Way ◽  
Narrow Band ◽  
Interference Filter ◽  
Emission Lines ◽  
List Type ◽  
Type Number ◽  
Filamentary Structure ◽  
Line Survey ◽  
Ring Nebulae ◽  
Rayet Star

We have used the plate data from An Emission Line Survey of the Milky Way by Parker, Gull and Kirschner(1979) to make a new search for ring nebulae around Wolf-Rayet stars. The Survey consists of narrow-band interference filter direct imagery centered on the emission lines of Hα + [N II] at λ6570, [O III] at λ5007, and [S II] at λ6730. We have discovered at least five new ring nebulae. of the fifteen ring nebulae we were able to detect on the Survey, including our new discoveries, eleven were brighter in the [O III] bandpass than in the Hα + [N II] bandpass, and were filamentary in [O III]. All of the nebulosities we were able to detect were rated on the basis of three criteria: 1)Sharp, filamentary structure present in any or all bandpasses.2)Wolf-Rayet star centered in projected nebulosity, or, if off-center, the segment of the ring nearest the star proportionally brighter than the rest of the ring.3)Absence of any O stars within the nebulosity, or O star in off-centered position not adjacent to the brightest or sharpest portion of the ring.

Polly wants a Doha deal: what does the trade community think?

2011 ◽  
Vol 10 (4) ◽  
pp. 551-555 ◽  
Author(s):  
PATRICK MESSERLIN ◽  
ERIK VAN DER MAREL
Keyword(s):  
Latin America ◽  
International Institutions ◽  
Think Tanks ◽  
List Type ◽  
Type Number ◽  
Doha Round ◽  
Wide Range ◽  
The Usa ◽  
Open Discussion ◽  
Key Questions

After ten years of negotiations, the Doha ‘Round is on the verge of collapse. At this difficult juncture, it is interesting to get a sense of the mood and thinking of the trade community on three key questions1:1.How serious is the situation?2.What are the causes of the current stalemate?3.What are the best solution(s)Two recent fora give an opportunity to analyze the answers of 71 observers to these questions at a crucial time, namely the month preceding the collapse of expectations that Doha might be completed by the end of 2011 (from April 1 to May 2, 2011). The CUTS Trade Forum (2011) triggered by Jagdish Bhagwati's op.ed. ‘Polly Wants a Doha Deal’ offered an open discussion forum where the 57 self-selected respondents could make their remarks with no pre-established format. The VoxEU (2011) e-book ‘Why World Leaders Must Resist the False Promise of a Doha Delay’ gathered short chapters written by 14 authors chosen by the e-book editors and willing to contribute. The respondents (all of them with a long experience in trade matters) include academics (25), former and current negotiators (9), lawyers (4), journalists (3), business (3), national civil servants (2) and trade policy experts (25 in total, of whom six are working in international institutions and nine in think tanks). Participants came from all continents: Africa (1), Asia (6), Europe (23), North America (15), Latin America (6), with a few countries particularly well represented (11 from the USA, 4 from Canada, 3 from Australia). The 17 respondents based in Geneva represent a wide range of nationalities.

scholarly journals Performance Monitoring for Sensorimotor Confidence: A Visuomotor Tracking Study

2019 ◽  
Author(s):  
Shannon M. Locke ◽  
Pascal Mamassian ◽  
Michael S. Landy
Keyword(s):  
Task Difficulty ◽  
Performance Monitoring ◽  
Stimulus Presentation ◽  
Temporal Analysis ◽  
Tracking Performance ◽  
List Type ◽  
Visuomotor Tracking ◽  
Mouse Cursor ◽  
The Stability

AbstractTo best interact with the external world, humans are often required to consider the quality of their actions. Sometimes the environment furnishes rewards or punishments to signal action efficacy. However, when such feedback is absent or only partial, we must rely on internally generated signals to evaluate our performance (i.e., metacognition). Yet, very little is known about how humans form such judgements of sensorimotor confidence. Do they monitor their performance? Or do they rely on cues to sensorimotor uncertainty to infer how likely it is they performed well? We investigated motor metacognition in two visuomotor tracking experiments, where participants followed an unpredictably moving dot cloud with a mouse cursor as it followed a random trajectory. Their goal was to infer the underlying target generating the dots, track it for several seconds, and then report their confidence in their tracking as better or worse than their average. In Experiment 1, we manipulated task difficulty with two methods: varying the size of the dot cloud and varying the stability of the target’s velocity. In Experiment 2, the stimulus statistics were fixed and duration of the stimulus presentation was varied. We found similar levels of metacognitive sensitivity in all experiments, with the temporal analysis revealing a recency effect, where error later in the trial had a greater influence on the sensorimotor confidence. In sum, these results indicate humans predominantly monitor their tracking performance, albeit inefficiently, to judge sensorimotor confidence.HighlightsParticipants consciously reflected on their tracking performance with some accuracySensorimotor confidence was influenced by recent errorsExpectations of task difficulty did not play a large role in sensorimotor confidenceMetacognitive sensitivity of binary confidence judgements on continuous performance can be quantified with standard non-parametric techniques

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